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Microwave Photonic Links

Microwave Photonic Links

Components and Circuits

Christian Rumelhard

Catherine Algani Anne-Laure Billabert

First published 2011 in Great Britain and the United States by ISTE Ltd and John Wiley amp Sons Inc Adapted and updated from Composants et circuits pour liaisons photoniques en micro-ondes published 2010 in France by Hermes ScienceLavoisier copy LAVOISIER 2010

Apart from any fair dealing for the purposes of research or private study or criticism or review as permitted under the Copyright Designs and Patents Act 1988 this publication may only be reproduced stored or transmitted in any form or by any means with the prior permission in writing of the publishers or in the case of reprographic reproduction in accordance with the terms and licenses issued by the CLA Enquiries concerning reproduction outside these terms should be sent to the publishers at the undermentioned address

ISTE Ltd John Wiley amp Sons Inc 27-37 St Georgersquos Road 111 River Street London SW19 4EU Hoboken NJ 07030 UK USA

wwwistecouk wwwwileycom

copy ISTE Ltd 2011 The rights of Christian Rumelhard Catherine Algani Anne-Laure Billabert to be identified as the authors of this work have been asserted by them in accordance with the Copyright Designs and Patents Act 1988

____________________________________________________________________________________ Library of Congress Cataloging-in-Publication Data

Rumelhard Christian Microwave photonic links components and circuits Christian Rumelhard Catherine Algani Anne-Laure Billabert p cm Includes bibliographical references and index ISBN 978-1-84821-226-8 1 Optical communications--Equipment and supplies 2 Microwave communication systems--Equipment and supplies 3 Telecommunication--Switching systems I Algani Catherine II Billabert Anne-Laure III Title TK510359R86 2011 6213813--dc22

2010046517

British Library Cataloguing-in-Publication Data A CIP record for this book is available from the British Library ISBN 978-1-84821-226-8 Printed and bound in Great Britain by CPI Antony Rowe Chippenham and Eastbourne

Table of Contents

Preface xiii

Abbrevation Glossary xvii

Chapter 1 General Points 1

11 Microwave photonic links 1 12 Link description 4 13 Signal to transmit 5

131 Microwave signal 5 132 Microwave carrier for a digital signal 5 133 UWB signal 6 134 Optical carrier 6 135 Summary 6

14 Limitations of microwave photonic links 7 141 Limitations due to the materials constituting the different elements 7 142 Noise sources in microwave photonic links 8 143 Nonlinearities 13

15 The components and characteristics of microwave photonic links 13

Chapter 2 Generation and Modulation of Light 15

21 Laser 15 211 General points 15 212 Semiconductor laser structure and optical gain in the active zone 17 213 Operation of a Fabry-Perot laser 19

vi Microwave Photonic Links

214 Optical confinement factor and rate equations 21 215 Static mode of laser operation (or CW mode of operation) 24 216 Dynamic mode of laser operation RF small signal response 26 217 RIN laser noise 28 218 Increase in 1f of RIN and superposition of a small signal and noise 31 219 Different laser configurations 32 2110 CAD laser models 41 2111 Laser measurements and temperature stabilization 47

22 Electro-optic modulator EOM 49 221 General physical principles 50 222 Pockels or linear electro-optical effect 50 223 Mach-Zehnder electro-optic modulator 53 224 Single-Drive MZM one driving electrode 55 225 Dual-drive MZM two driving electrodes 69 226 Real Mach-Zehnder modulator characteristics and performances 71 227 Mach-Zehnder modulator technology 73

23 Electro-absorption modulator EAM 75 231 Electro-absorption effect 75 232 FKE 80 233 Stark effect 80 234 Quantum well structures 82 235 MEA operation 82 236 Characteristics of an EAM 85 237 EML EAM integrated to a DFB laser 86 238 EAM electrical modeling for ultra-fast signal simulation 87

Chapter 3 Optical Fibers and Amplifiers 93 31 Optical fibers 93

311 General 93 312 Material attenuation 96 313 Material refraction index and dispersion 98 314 Total reflection numerical aperture transmitted maximum frequency 100 315 Step-index fiber 105 316 Graded index fiber 107 317 Single-mode fiber 110 318 Plastic optical fibers 114

Table of Contents vii

32 Optical amplifiers 118 321 Semiconductor optical amplifiers SOA 119 322 EDFAs 120

33 Appendix modal analysis of propagation in a fiber 122 331 Maxwell equations 122 332 Maxwell equations in a cylindrical fiber 123 333 Continuity and characteristic equation conditions 127 334 Research of different propagation modes 128 335 Approximation of linearly polarized modes 132

Chapter 4 Photodetectors 137 41 Photodetector definition 137 42 Photodiodes 138

421 Presentation 138 422 Light absorption in a semiconductor 139 423 p-i-n photodiode 142 424 Metal-semiconductor-metal or MSM photodiode 145 425 Equivalent circuits for p-i-n and MSM photodiodes 147 426 Nonlinearities 147 427 UTC photodiodes 149 428 Charge compensation 150 429 Partially depleted absorption zone 151 4210 Lateral lighting 152 4211 Lateral lighting progressive wave structure 153 4212 Lateral lighting periodic structures 156 4213 Resonant optical cavity photodetector 157 4214 Diluted waveguides and evanescent mode coupling 160 4215 Summary 161

43 Phototransistors 163 431 Bipolar or field-effect phototransistors 163 432 GaAlAsGaAs and InGaPGaAs phototransistors 165 433 InPInGaAs phototransistors 167 434 SiSiGe phototransistors 172 435 Resonant optical cavities for phototransistors 176 436 Phototransistor simulations and models 176 437 Influence of the base load impedance 180 438 Summary 183

44 Appendix 184 441 Lattice matched layers pseudomorphic layer metamorphic layer 184 442 Velocity overshoot effect 186 443 Heterojunction bipolar phototransistor 188

viii Microwave Photonic Links

Chapter 5 Performance of Microwave Photonic Links 193

51 Microwave photonic links diagrams and definitions 193 511 Direct modulation link diagram and definitions 193 512 External modulation link diagram and definitions 197 513 Simplified link diagram and first gain computation 198

52 Optomicrowave S-parameters and gains of each photonic link component 201

521 Introduction 201 522 Optomicrowave laser S-parameters and optomicrowave gain 202 523 Optomicrowave optical fiber S-parameters and optomicrowave gain 203 524 Photodiode optomicrowave S-parameters and gain 204 525 Localized component external modulator optomicrowave S-parameters and gain 205 526 Distributed component external modulator optomicrowave S-parameters and gain 207 527 Summary of all S-parameters and optomicrowave gain 209

53 Microwave photonic links optomicrowave S-parameters and gains 210

531 Direct modulation microwave photonic link S-parameters 210 532 Direct modulation microwave photonic link gains 211 533 Localized external modulator microwave photonic link S-parameters 212 534 Localized external modulator microwave photonic link gains 213 535 Distributed external modulator microwave photonic link S-parameters 213 536 Distributed external modulator microwave photonic link gains 214 537 Link gain computation generalization 215

54 Comparison of different link gains 218 541 Direct modulation link gain computation 218 542 Localized external modulator link gain computation 219 543 Distributed external modulator link gain computations 220

55 Direct modulation microwave photonic link optomicrowave noise figures 221

551 Link noise figure diagram and computation method 221 552 Laser noise figure 223 553 Optical fiber noise figure 223 554 Photodiode noise figure 224

Table of Contents ix

555 Direct modulation link noise figure 224 556 Matching effect at the input of a direct modulation link 225 557 Generalization of a link noise figure computation 226

56 External modulation microwave photonic link optomicrowave noise figure 227

561 Equivalent diagram and steps recall 227 562 Localized external modulator noise figure 227 563 Distributed external modulator noise figure 228 564 New evaluation of photodetector noise figure 230 565 Localized external modulator microwave photonic link noise figure 231 566 Matched input localized external modulator microwave photonic link noise figure 231 567 Distributed external modulator microwave photonic link noise figure 232

57 Comparisons of different link noise figures 232 571 Evaluation of direct modulation link noise figure 232 572 Evaluation of localized external modulator link noise figure 234 573 Evaluation of matched input localized external modulator link noise figure 235 574 Evaluation of distributed external modulator link noise figures 236 575 Output noise power 237 576 Some effectively measured noise figure values 239

58 Microwave photonic link nonlinearity distortion phenomena 241

581 Single microwave signal nonlinearity 241 582 Several input microwave signals nonlinearity 242 583 Wideband input signal nonlinearity 244 584 Nonlinearity combination of microwave photonic link components 245

59 Microwave photonic link interference-free dynamic range 246 591 Single input signal microwave photonic link interference-free dynamic range 246 592 Several-input signal microwave photonic link interference-free dynamic range 247 593 Some effectively measured interference-free dynamic range values 249

510 Appendix 250 5101 Relation between parameters S Z Y and ABCD 250 5102 Equation choice for the computation of microwave photonic link optomicrowave noise figure 251

x Microwave Photonic Links

5103 Calculation of a two-input signal microwave photonic link interference-free dynamic range 261

Chapter 6 Complement to Microwave Photonic Link Performances 267

61 Microwave signal attenuation during double sideband modulation 267

611 Double sideband modulation recall 267 612 Recall of single-mode optical fiber propagation characteristics 268 613 Optical fiber double sideband modulated signal propagation 270 614 Double sideband-modulated signal photodetection at the optical fiber output 271

62 Modulator structures for optical carrier or high and low sideband removal 273

621 Optical modulation recall 273 622 Single sideband or carrier suppression optical modulators 274 623 Carrier suppression and single sideband optical modulator 277

63 Degradation of a microwave signal spectral purity by an optical link 280

631 Phenomenon description 280 632 Some definitions concerning the noise around a microwave carrier 281 633 Amplitude and phase noise in an optical link 282 634 Phase noise computation of a microwave signal transmitted by an optical link 284 635 Amplitude noise computation of a microwave signal transmitted by an optical link 286

Chapter 7 Electronic Amplifiers in Microwave Photonic Links 289

71 Electronic amplifiers in optical links 289 72 Amplifiers in the optical link emitter 289

721 Different roles of electronic amplifiers on optical emitter 289 722 Emission modulator or laser input amplifiers 290

73 Receiver amplifiers at the photodetector output 293 731 General points 293 732 Transimpedance amplifiers 294 733 Distributed amplifiers 296

Table of Contents xi

734 Combination of transimpedance and distributed amplifiers 298 735 Narrowband amplifiers 298 736 Preamplifier after a phototransistor 299 737 Other circuits after a phototransistor 299

74 Appendix analog and microwave amplifiers 300 741 General points 300 742 Analog amplifiers 300 743 Microwave amplifier expression of transistor reflection coefficients 304 744 Microwave amplifiers gain expressions 306 745 Unilateralized transistor model two-port network matching computation 307 746 Non-unilateralized transistor general case of a transistor with S12 0 312 747 Low noise amplifier 313 748 General models of low signal microwave amplifiers 315

Chapter 8 Simulation and Measurement of Microwave Photonic Links 321

81 State of the art and context 321 811 Objective 321 812 Choice of simulation software 321 813 Different ADS simulation techniques 322

82 Microwave optical link models 324 821 Two-port network approach 324 822 Electro-optic transducer the laser 325 823 Transmission guiding the optical fiber 329 824 The optoelectric transducer the photodiode 334

83 Nonlinearity effects in the link 337 831 Nonlinearity sources 337 832 1 dB compression point and first-order dynamic of the link 338 833 Third-order intermodulation and third-order interference-free dynamic range of the link 339

84 Link noise modeling 340 841 Noise in the laser 340 842 The optical fiber 342 843 Noise in the photodiode 342 844 Direct modulation link noise figure 343 845 Noise power at the receiver 344

xii Microwave Photonic Links

85 Other types of modulation of signals transmitted on an optical fiber 348

851 Ultra-wideband signal modulation 348 852 External modulation 353 853 Generation of microwave signal by frequency beating 358

86 Conclusion 361 87 Appendix 362

871 MB-OOK modulation 362 872 OFDM modulation 363

Bibliography 367

Index 393

Preface

Two important areas of applications of microwave photonic links are electromagnetic sensors and radio-over-fiber (RoF) applications

Electromagnetic sensor microwave systems of the future will principally use active phased-array antennas The development will be determined by reliability requirements resistance to interference and total emission flexibility of the beamforming networks This type of antenna would therefore be used in a diverse range of applications eg radar communication and countermeasures To satisfy this multifunctional approach it will be necessary to distribute these antennas all over the surface area of strategic platforms (planes drones boats etc) While on the ground the multistatic mode of operation will force multiple antennas to be deported from their processing unit

This will require links with very low loss and noise enabling remote-control antennas and the distribution and processing of very wide bandwidth microwave signals (typically 1-20 GHz 40 GHz will be seen in the future)

Currently the maturity and performance notably in terms of spectral purity and opto-electronic component linearity are such that it is possible to consider both optical distribution and processing of these electrical signals Thus the optical transmission of microwaves offers as well as propagation of broad frequency bands advantages regarding weight volume and flexibility characterized by a decrease in the weight of the wiring by 90 in comparison to coaxial cables and thus insensitivity to electromagnetic perturbation All of which will enable the introduction of new concepts in microwave systems based on optical architecture

xiv Microwave Photonic Links

Several sensor radar systems have been designed and produced in France the United States the UK and Italy and photonic technology for the distribution of microwave signals is already being used for ground airborne and aerospace applications

Fiber-optic distribution network technology is an emergence of this technology platform in reference to the design of opto-electronic links for the transmission of microwave and digital signals This optical wiring aims to replace coaxial wiring for onboard electronics interconnections Here the term transmission is taken in the sense that microwave transmissions on optical carriers are in-phase

These functions require the design of emitting and receiving opto-electronic modules the integration of both high thermal stability multiplexing demultiplexing functions and single-mode connectors either point to point or multipoints

Another area of reference is the optical control of the phase andor delay of microwave signals and their applications to electromagnetic sensor systems This occurs by the design of ultrafast opto-electronic multi-chip modules incorporating the optically-controlled switching the control synthesis of time delay systems and the multiwave laser sources

Amongst the most promising technologies is the synthesis of mono- and bidimensional time-delays for the single and multiple beamforming in receiver and emitter the ultraprecise (picoseconds) time synchronization of distributed electromagnetic sensors the time-delay control (precision in the order of picoseconds) of very wide bandwidth microwave signals to measure the arrival direction and the waveshape generation

Another important area involving all RoF applications is the extensive development of wireless networks using microwaves or ultra-wideband signals This is achieved by providing optical tunnels capable of reaching all areas of a company university etc or all the rooms of a house whilst benefiting from the very low loss associated with fiber optics

In their work titled ldquoMicrowave Photonic Linksrdquo C Rumelhard C Algani and A-L Billabert studied and developed models of the components and photonic functions in microwave applications thus laying the foundation for research into microwave photonic links in order to allow the

Preface xv

integration of these components in electromagnetic sensors systems The components and functions addressed range from optical sources (modulated semiconductor lasers or externally modulated continuous lasers) to photodetectors optical fibers and optical amplifiers

This work focuses upon optical components their transfer functionality and their modeling in terms of microwave components in order to create an electrical model of microwave photonic links In order to achieve this level of complexity a number of modeling approaches have been created by the authors to elucidate the influences of the constituent components of microwave photonic links

Because the advancement of opto-electronics photonics and microwaves is possible by the unification of modeling approaches there is no doubt that such works will be referenced by students but also by design engineers and architects of electromagnetic sensor systems who will incorporate this new technology into their designs

This is to the authorrsquos knowledge the first work addressing the description and modeling of microwave photonic link technology with an educational approach to physical phenomena and new approaches to modeling microwave photonic components

Jean Chazelas Scientific Director

Thales Aeronautics Division

Abbreviation Glossary

AC Alternating Current

ACPR Adjacent Channel Power Ratio

ADP Ammonium dihydrogen phosphate

ADS Advanced Design System

AlGaAs Aluminum gallium arsenide

AM Amplitude Modulation

AM-DD Amplitude Modulation ndash Direct Detection

ASE Amplified Spontaneous Emission

BER Bit Error Rate

BH Buried Heterostructure

BiCMOS Bipolar Complementary Metal Oxide Semiconductor

BILBAO Borne drsquoinfrastructures large bande avec accegraves optique (Wideband infrastructure base with optical access)

CAD Computer-aided design

CdS Cadmium sulfide

CEA-Leti Commissariat agrave lrsquoeacutenergie atomique (Atomic energy commission)

CMOS Complementary metal-oxide-semiconductor

CNAM Conservatoire national des arts et meacutetiers

CPW Coplanar waveguide

xviii Microwave Photonic Links

DBR Distributed Bragg reflector

DC Direct current

DD-MZM Dual drive-MZM

DFA Doped fiber amplifier

DFB Distributed feedback laser

DFT Discrete Fourier transform

EO Electricoptic

EAM Electro-absorption modulator

EDFA Erbium-doped fiber amplifier

EEL Edge emitting laser

EML Electro-absorption modulated laser

EMT Electromagnetic transverse

EOM Electro-optic modulator

ER Extinction ratio

ESYCOM Equipe systegravemes de communications et microsystegravemes (Communications and microsystems team)

ET Electric transverse

EVM Error vector magnitude

FCC Federal communications commission

FET Field-effect transistor

FKE Franz-Keldysh effect

FT RampD France Telecom Research amp Development

GaAs Galium arsenide

GaP Galium phosphide

Ge Germanium

GRINSCH Graded index separate confinement heterostructure

HB Harmonic balance

HBT Heterojunction bipolar transistor

Abbreviation Glossary xix

HEMT High electron mobility transistor

HFET Heterojunction field-effect transistor

HFSS High frequency simulation system

HPT Heterojunction bipolar phototransistor

IDFT Inverse discrete Fourier transform

IM-DD Intensity modulation-direct detection

IMEP Institut de microeacutelectronique eacutelectromagneacutetisme et optique (Institute of microelectronics electromagnetism and optics)

InAs Indium arsenide

InGaAs Indium gallium arsenide

InGaP Indium gallium phosphide

InP Indium phosphide

IR-UWB Impulse Radio ndash Ultra Wideband

KDP Potassium dihydrogen phosphate

LAHC Laboratoire drsquohyperfreacutequences et de caracteacuterisation (hyperfrequency and characterization laboratory)

LASER Light amplifier by stimulated emission of radiation

LF Low frequency

LiNbO3 Lithium niobate

LiTaO3 Lithium tantalate

MAG Maximum available gain

MASER Microwave amplifier by stimulated emission of radiation

MB-OFDM Multi-band ndash orthogonal frequency division modulation

MB-OOK Multi-band on off keying

MEMS Micro-electro-mechanical systems

MESFET Metal semiconductor field-effect transistor

MMIC Monolithic microwave integrated circuit

MODFET Modulation-doped field-effect transistor

MQW-EAM Multi-quantum well-EAM

xx Microwave Photonic Links

MSM Metal semiconductor metal

MZM Modulator Mach-Zehnder

NdYAG Neodymium-doped yttrium aluminum garnet

NF Noise factor Noise figure

nOI n order intermodulation

nOIP n order intercept point

NRA National Research Agency

OE Opticelectric

OEIC Optoelectronic integrated circuit

OEMMIC Optoelectronic millimeter-wave monolithic integrated circuit

OFDM Orthogonal frequency division modulation

PDFA Praseodymium-doped fiber amplifier

PDG Biased-dependent gain

PM Phase modulation

PMMA Poly(methyl methacrylate)

PRBS Pseudo-random bit sequence

PSK Phase-shift keying

QAM Quadrature amplitude modulation

QCSE Quantum confined stark effect

QW-EAM Quantum well-EAM

RCEPD Resonant cavity enhanced photodetectors

RFT Rapid Fourier transform

RIN Relative intensity noise

RoF Radio over fiber

SD-MZM Single drive ndashMZM

Si Silicon

SiGe Silicon-germanium

SiMOX Separation by implantation of oxygen

Abbreviation Glossary xxi

SiO2 Silicon dioxide

SOA Semiconductor optical amplifier

SOC System on a chip

SOI Substrate on insulator

TDFA Thulium-doped fiber amplifier

TEGFET Two-dimensional electron gas field-effect transistor

TW-MZM Travelling wave-MZM

UTC Uni-travelling carrier

UWB Ultra-wideband

VCSEL Vertical-cavity surface-emitting laser

VCSOA Vertical-cavity semiconductor optical amplifier

VMDP Velocity matched distributed photodetector

WDM Wavelength division multiplexing

YDFA Ytterbium-doped fiber amplifier

ZnS Zinc sulfide

Chapter 1

General Points

11 Microwave photonic links

All signals generated or observed due to human activity (measurement of different physical values remote control files sounds images etc) can be transformed into analog electrical signals These electrical signals can be processed or transmitted as they are but in most cases they are digitized beforehand Once digitized these signals have different forms regarding the digital coding or error-correcting algorithms used and protocols employed in the transmission systems To be processed or transmitted these analog or digital signals can use different mediums

If the transmission is performed via metallic lines or cables digital signals directly enter these lines or they modulate more or less complex subcarriers (ADSL Ethernet)

If transmission occurs with a radiowave a high-frequency carrier must be available Due to the congestion of the wireless spectrum carriers are now principally microwaves ie with frequencies of 1 to 100 GHz (GSM UMTS Wi-Fi Wimax etc) Wireless transmission can also be performed by very short pulses having a wide spectrum range including the microwave spectrum or these pulses can modulate a carrier in the millimeter wave spectrum This technique is known as ultra-wideband (UWB) [YAO 09]

If transmission is via fiber optics digital signals modulate one or several optical carriers (amplitude or soliton modulation) which are themselves

2 Microwave Photonic Links

transmitted over hundreds of kilometers on optical fibers This is the case for all passive optical networks (PON) and their different transmission protocols [LEC 97]

From these definitions the distinctive feature of microwave photonic links is to transmit a microwave signal analogically or for it be digitally modulated This microwave signal is transferred to an optical carrier which is guided with minimum loss by an optical fiber The microwave signal is then picked up by a photodetector at the end of the fiber

One of the first applications of microwave optical links was the distribution of the microwave carrier in radar or radio-astronomy systems comprising offset aerials or active phased-array antennas which benefited from the low weight and low volume of the fiber optics [COX 97 DEC 98]

Another important area comprises all radio over fiber (RoF) applications consisting of the extension of wireless networks using microwaves or UWB waves The optical tunnels produced are capable of reaching all rooms or buildings of a company university or diverse institutions or all the rooms of a house whilst benefiting from the very low loss associated with fiber optics [FRI 02]

Amongst the applications of RoF a promising domain is in the connection of internet transmission networks to the home These connections are increasingly popular with ever-increasing speeds (1 Gbs) due to fiber optics reaching households (fiber to the home or FTTH) whereby the house itself becomes a high-speed local network In this local network the signal distribution in each room is achieved by a 60 GHz millimeter-wave (wireless personal area network or WPAN) which stays confined in the room due to the extremely fast attenuation at this frequency All rooms are linked to each other by a network of passive fiber optics which extends the millimeter-wave UWB signal throughout the whole house (ultra broadband wireless home area network or UBB-WHAN) Examples of millimeter-wave over optical transmissions are presented in [CHU 07 KIM 04 WEI 08] and a demonstration of a UBB-WHAN with an up and down link is described in [HUC 08]

The length of a link ranges from 10 m to 1 km allowing several fiber types to be used (single mode or multimode silica or plastic) and several optical wavelengths ranging from 06 to 155 μm The light undergoes intensity modulation the signal is received via photodetection In just a few

General Points 3

years rates have risen from around 10 Mbs on carriers of a few gigahertz to rates of 1 or 10 Gbs on 60 GHz for microwave carriers

A microwave photonic link is constituted of three parts

ndash a coherent light source a laser that emits an optical carrier the intensity of which is directly modulated inside the laser or externally by an optical modulator In the case of external modulation the amplitude modulation is performed by a Mach-Zehnder or an electro-absorption modulator

ndash the modulated light is then transported by single or multi-mode optical fiber [GOM 08 KOO 08] made of silica or plastic [KOI 06] This part may include an optical amplification

ndash the modulated light is finally photodetected in a photodetector consisting of a photodiode or a phototransistor

After some deliberation regarding coherent and incoherent optical links [HAL 82] the solution finally adopted for these links was ldquointensity modulation (IM) direct detection (DD)rdquo As this is recalled in [COX 06] in this type of link the depth of optical modulation is sufficiently weak that we can initially use small signal or linear techniques for each aspect Because the signals applied to links or extracted from them are in microwaves the variables characterizing these systems are S-parameters gains and noise factors Also nonlinearities and hence intermodulation produced by each component on the signal introduced in the link must be considered The combination of these different characteristics leads to the notion of interference-free dynamic range (IFDR) This shall be evaluated regarding the properties of each element in the chapters concerning overall performances of such links

As a link includes electrical-to-optical optical-to-electrical and even optical-to-optical transducers each of the magnitudes in terms of S-parameters gains and noise factors should be presented in the form of optomicrowave magnitudes This aspect forces harmonization of notions from the optical optoelectronic and microwave disciplines This is described in Chapter 5

The term used initially to describe these links was ldquomicrowave optical linksrdquo However the techniques used have gradually distanced themselves from proper optical and optoelectronic techniques so that the more specific term ldquomicrowave photonic linksrdquo has been progressively used [SEE 02]

4 Microwave Photonic Links

12 Link description

Figures 11 and 12 represent a general diagram of an IM-DD microwave optical link

Figure 11 Diagram of directly modulated microwave optical link

Figure 11 represents a direct modulation link A laser emits a light of wavelength 08 or 13 or 155 μm this laser is modulated by a microwave signal (which is possibly itself modulated) through a driver circuit The modulated light enters an optical fiber coupled to a photodetector that detects the microwave modulation signal The optical modulation can have an amplitude frequency and phase However direct photodetection detects only the modulation in amplitude The detected microwave signal is then amplified by a low-noise amplifier

Figure 12 represents an external modulation link This time a light emitted from a laser is injected into a Mach-Zehnder or electro-absorption amplitude modulator In this case microwave modulation is also applied to the modulator through a driver circuit

After passing into an optical fiber the optical intensity modulation only is detected via a photodetector As in the previous diagram the detected microwave signal is amplified in a low-noise amplifier

Laser

Driver

Optical fiber Photodetector

Low noise amplifier

Microwave or UWB Microwave or UWB

λ = 155 or 13 or 08 μm

Amplitude modulation Direct detection

General Points 5

Figure 12 Diagram of externally modulated microwave optical link

13 Signal to transmit

131 Microwave signal

The first type of transmitted signal is a signal that constitutes a microwave frequency reference It can be used in offset aerial systems or active phased-array antenna After its reflection from a moving object the microwave signal emitted from an antenna can shift in frequency (Doppler modulation) and it is the spectral purity of the microwave that determines the minimum observed frequency shift and therefore the minimum relative speed of the moving object The spectral purity and degradation after transmission of the microwave by optical links must be watched closely to distinguish the frequency shift

132 Microwave carrier for a digital signal

If the microwave signal serves as a carrier for a digital signal this carrier is previously modulated All the modulation techniques normally used such as amplitude frequency phase OFDM and combined amplitude-phase modulation (QAM) or more complex techniques can be considered such as those used in GSM GPRS EDGE and UMTS for mobile telephones or such as Bluetooth Wi-Fi and Wimax for data transmission These modulations are generally carried out on single sideband (SSB) When microwave signal modulation is implemented in phase or frequency spectral purity is also of great importance

Laser

Amplifier or driver

Optical fiber

λ = 155 or 13 or 08 μm

Microwave or UWB

Optical modulator MZ or EA

Amplitude modulation

Photodetector

Low noise amplifier

Microwave or UWB

Direct detection

6 Microwave Photonic Links

133 UWB signal

Another signal category is available for transmission by fiber optics These signals are relevant to UWB techniques without carriers and with the spectrum in the microwave region or up-converted to a millimeter-wave carrier UWB wireless links are largely used over short distances The optical fibers are particularly indicated to enable extensions of such networks

134 Optical carrier

Microwave signals can carry analog information (frequency shift due to the Doppler effect) or they can be modulated by a digital signal or be constituted of UWB signals which are themselves digitally modulated All these microwave signals must be up-converted to an optical carrier This transfer exclusively occurs by intensity modulation One of the advantages of this modulation is that the microwave signal can be recovered in a simple photodetection unit permitting the elimination of possible frequency fluctuations of the optical carrier Loss of sensitivity resulting from direct detection does not occur if the optical wavelength allows us to insert an optical amplifier or if the link is very short Usually this modulation is double sideband (DSB) especially if the modulation occurs directly in the laser but for slightly longer links this type of modulation can lead to extinction phenomena A single sideband modulation can hence be considered but this modulation must be carried out by an external modulator

135 Summary

The complexity of microwave photonic links comes from the stacking of an optical carrier and microwave or UWB subcarrier The optical carrier is exclusively intensity modulated whereas the microwave subcarrier can be modulated following all known modulation types amplitude frequency phase or their combination including a frequency shift due to the Doppler effect All these modulations can be recovered via photodetection

The use of microwave optical links will increase as the transmitted signals will be numerous and emitted in parallel communications and the data rates will increase accordingly Thus telecommunication optical

Microwave Photonic Links

Microwave Photonic Links

Components and Circuits

Christian Rumelhard

Catherine Algani Anne-Laure Billabert

First published 2011 in Great Britain and the United States by ISTE Ltd and John Wiley amp Sons Inc Adapted and updated from Composants et circuits pour liaisons photoniques en micro-ondes published 2010 in France by Hermes ScienceLavoisier copy LAVOISIER 2010

Apart from any fair dealing for the purposes of research or private study or criticism or review as permitted under the Copyright Designs and Patents Act 1988 this publication may only be reproduced stored or transmitted in any form or by any means with the prior permission in writing of the publishers or in the case of reprographic reproduction in accordance with the terms and licenses issued by the CLA Enquiries concerning reproduction outside these terms should be sent to the publishers at the undermentioned address

ISTE Ltd John Wiley amp Sons Inc 27-37 St Georgersquos Road 111 River Street London SW19 4EU Hoboken NJ 07030 UK USA

wwwistecouk wwwwileycom

copy ISTE Ltd 2011 The rights of Christian Rumelhard Catherine Algani Anne-Laure Billabert to be identified as the authors of this work have been asserted by them in accordance with the Copyright Designs and Patents Act 1988

____________________________________________________________________________________ Library of Congress Cataloging-in-Publication Data

Rumelhard Christian Microwave photonic links components and circuits Christian Rumelhard Catherine Algani Anne-Laure Billabert p cm Includes bibliographical references and index ISBN 978-1-84821-226-8 1 Optical communications--Equipment and supplies 2 Microwave communication systems--Equipment and supplies 3 Telecommunication--Switching systems I Algani Catherine II Billabert Anne-Laure III Title TK510359R86 2011 6213813--dc22

2010046517

British Library Cataloguing-in-Publication Data A CIP record for this book is available from the British Library ISBN 978-1-84821-226-8 Printed and bound in Great Britain by CPI Antony Rowe Chippenham and Eastbourne

Table of Contents

Preface xiii

Abbrevation Glossary xvii

Chapter 1 General Points 1

11 Microwave photonic links 1 12 Link description 4 13 Signal to transmit 5

131 Microwave signal 5 132 Microwave carrier for a digital signal 5 133 UWB signal 6 134 Optical carrier 6 135 Summary 6

14 Limitations of microwave photonic links 7 141 Limitations due to the materials constituting the different elements 7 142 Noise sources in microwave photonic links 8 143 Nonlinearities 13

15 The components and characteristics of microwave photonic links 13

Chapter 2 Generation and Modulation of Light 15

21 Laser 15 211 General points 15 212 Semiconductor laser structure and optical gain in the active zone 17 213 Operation of a Fabry-Perot laser 19

vi Microwave Photonic Links

214 Optical confinement factor and rate equations 21 215 Static mode of laser operation (or CW mode of operation) 24 216 Dynamic mode of laser operation RF small signal response 26 217 RIN laser noise 28 218 Increase in 1f of RIN and superposition of a small signal and noise 31 219 Different laser configurations 32 2110 CAD laser models 41 2111 Laser measurements and temperature stabilization 47

22 Electro-optic modulator EOM 49 221 General physical principles 50 222 Pockels or linear electro-optical effect 50 223 Mach-Zehnder electro-optic modulator 53 224 Single-Drive MZM one driving electrode 55 225 Dual-drive MZM two driving electrodes 69 226 Real Mach-Zehnder modulator characteristics and performances 71 227 Mach-Zehnder modulator technology 73

23 Electro-absorption modulator EAM 75 231 Electro-absorption effect 75 232 FKE 80 233 Stark effect 80 234 Quantum well structures 82 235 MEA operation 82 236 Characteristics of an EAM 85 237 EML EAM integrated to a DFB laser 86 238 EAM electrical modeling for ultra-fast signal simulation 87

Chapter 3 Optical Fibers and Amplifiers 93 31 Optical fibers 93

311 General 93 312 Material attenuation 96 313 Material refraction index and dispersion 98 314 Total reflection numerical aperture transmitted maximum frequency 100 315 Step-index fiber 105 316 Graded index fiber 107 317 Single-mode fiber 110 318 Plastic optical fibers 114

Table of Contents vii

32 Optical amplifiers 118 321 Semiconductor optical amplifiers SOA 119 322 EDFAs 120

33 Appendix modal analysis of propagation in a fiber 122 331 Maxwell equations 122 332 Maxwell equations in a cylindrical fiber 123 333 Continuity and characteristic equation conditions 127 334 Research of different propagation modes 128 335 Approximation of linearly polarized modes 132

Chapter 4 Photodetectors 137 41 Photodetector definition 137 42 Photodiodes 138

421 Presentation 138 422 Light absorption in a semiconductor 139 423 p-i-n photodiode 142 424 Metal-semiconductor-metal or MSM photodiode 145 425 Equivalent circuits for p-i-n and MSM photodiodes 147 426 Nonlinearities 147 427 UTC photodiodes 149 428 Charge compensation 150 429 Partially depleted absorption zone 151 4210 Lateral lighting 152 4211 Lateral lighting progressive wave structure 153 4212 Lateral lighting periodic structures 156 4213 Resonant optical cavity photodetector 157 4214 Diluted waveguides and evanescent mode coupling 160 4215 Summary 161

43 Phototransistors 163 431 Bipolar or field-effect phototransistors 163 432 GaAlAsGaAs and InGaPGaAs phototransistors 165 433 InPInGaAs phototransistors 167 434 SiSiGe phototransistors 172 435 Resonant optical cavities for phototransistors 176 436 Phototransistor simulations and models 176 437 Influence of the base load impedance 180 438 Summary 183

44 Appendix 184 441 Lattice matched layers pseudomorphic layer metamorphic layer 184 442 Velocity overshoot effect 186 443 Heterojunction bipolar phototransistor 188

viii Microwave Photonic Links

Chapter 5 Performance of Microwave Photonic Links 193

51 Microwave photonic links diagrams and definitions 193 511 Direct modulation link diagram and definitions 193 512 External modulation link diagram and definitions 197 513 Simplified link diagram and first gain computation 198

52 Optomicrowave S-parameters and gains of each photonic link component 201

521 Introduction 201 522 Optomicrowave laser S-parameters and optomicrowave gain 202 523 Optomicrowave optical fiber S-parameters and optomicrowave gain 203 524 Photodiode optomicrowave S-parameters and gain 204 525 Localized component external modulator optomicrowave S-parameters and gain 205 526 Distributed component external modulator optomicrowave S-parameters and gain 207 527 Summary of all S-parameters and optomicrowave gain 209

53 Microwave photonic links optomicrowave S-parameters and gains 210

531 Direct modulation microwave photonic link S-parameters 210 532 Direct modulation microwave photonic link gains 211 533 Localized external modulator microwave photonic link S-parameters 212 534 Localized external modulator microwave photonic link gains 213 535 Distributed external modulator microwave photonic link S-parameters 213 536 Distributed external modulator microwave photonic link gains 214 537 Link gain computation generalization 215

54 Comparison of different link gains 218 541 Direct modulation link gain computation 218 542 Localized external modulator link gain computation 219 543 Distributed external modulator link gain computations 220

55 Direct modulation microwave photonic link optomicrowave noise figures 221

551 Link noise figure diagram and computation method 221 552 Laser noise figure 223 553 Optical fiber noise figure 223 554 Photodiode noise figure 224

Table of Contents ix

555 Direct modulation link noise figure 224 556 Matching effect at the input of a direct modulation link 225 557 Generalization of a link noise figure computation 226

56 External modulation microwave photonic link optomicrowave noise figure 227

561 Equivalent diagram and steps recall 227 562 Localized external modulator noise figure 227 563 Distributed external modulator noise figure 228 564 New evaluation of photodetector noise figure 230 565 Localized external modulator microwave photonic link noise figure 231 566 Matched input localized external modulator microwave photonic link noise figure 231 567 Distributed external modulator microwave photonic link noise figure 232

57 Comparisons of different link noise figures 232 571 Evaluation of direct modulation link noise figure 232 572 Evaluation of localized external modulator link noise figure 234 573 Evaluation of matched input localized external modulator link noise figure 235 574 Evaluation of distributed external modulator link noise figures 236 575 Output noise power 237 576 Some effectively measured noise figure values 239

58 Microwave photonic link nonlinearity distortion phenomena 241

581 Single microwave signal nonlinearity 241 582 Several input microwave signals nonlinearity 242 583 Wideband input signal nonlinearity 244 584 Nonlinearity combination of microwave photonic link components 245

59 Microwave photonic link interference-free dynamic range 246 591 Single input signal microwave photonic link interference-free dynamic range 246 592 Several-input signal microwave photonic link interference-free dynamic range 247 593 Some effectively measured interference-free dynamic range values 249

510 Appendix 250 5101 Relation between parameters S Z Y and ABCD 250 5102 Equation choice for the computation of microwave photonic link optomicrowave noise figure 251

x Microwave Photonic Links

5103 Calculation of a two-input signal microwave photonic link interference-free dynamic range 261

Chapter 6 Complement to Microwave Photonic Link Performances 267

61 Microwave signal attenuation during double sideband modulation 267

611 Double sideband modulation recall 267 612 Recall of single-mode optical fiber propagation characteristics 268 613 Optical fiber double sideband modulated signal propagation 270 614 Double sideband-modulated signal photodetection at the optical fiber output 271

62 Modulator structures for optical carrier or high and low sideband removal 273

621 Optical modulation recall 273 622 Single sideband or carrier suppression optical modulators 274 623 Carrier suppression and single sideband optical modulator 277

63 Degradation of a microwave signal spectral purity by an optical link 280

631 Phenomenon description 280 632 Some definitions concerning the noise around a microwave carrier 281 633 Amplitude and phase noise in an optical link 282 634 Phase noise computation of a microwave signal transmitted by an optical link 284 635 Amplitude noise computation of a microwave signal transmitted by an optical link 286

Chapter 7 Electronic Amplifiers in Microwave Photonic Links 289

71 Electronic amplifiers in optical links 289 72 Amplifiers in the optical link emitter 289

721 Different roles of electronic amplifiers on optical emitter 289 722 Emission modulator or laser input amplifiers 290

73 Receiver amplifiers at the photodetector output 293 731 General points 293 732 Transimpedance amplifiers 294 733 Distributed amplifiers 296

Table of Contents xi

734 Combination of transimpedance and distributed amplifiers 298 735 Narrowband amplifiers 298 736 Preamplifier after a phototransistor 299 737 Other circuits after a phototransistor 299

74 Appendix analog and microwave amplifiers 300 741 General points 300 742 Analog amplifiers 300 743 Microwave amplifier expression of transistor reflection coefficients 304 744 Microwave amplifiers gain expressions 306 745 Unilateralized transistor model two-port network matching computation 307 746 Non-unilateralized transistor general case of a transistor with S12 0 312 747 Low noise amplifier 313 748 General models of low signal microwave amplifiers 315

Chapter 8 Simulation and Measurement of Microwave Photonic Links 321

81 State of the art and context 321 811 Objective 321 812 Choice of simulation software 321 813 Different ADS simulation techniques 322

82 Microwave optical link models 324 821 Two-port network approach 324 822 Electro-optic transducer the laser 325 823 Transmission guiding the optical fiber 329 824 The optoelectric transducer the photodiode 334

83 Nonlinearity effects in the link 337 831 Nonlinearity sources 337 832 1 dB compression point and first-order dynamic of the link 338 833 Third-order intermodulation and third-order interference-free dynamic range of the link 339

84 Link noise modeling 340 841 Noise in the laser 340 842 The optical fiber 342 843 Noise in the photodiode 342 844 Direct modulation link noise figure 343 845 Noise power at the receiver 344

xii Microwave Photonic Links

85 Other types of modulation of signals transmitted on an optical fiber 348

851 Ultra-wideband signal modulation 348 852 External modulation 353 853 Generation of microwave signal by frequency beating 358

86 Conclusion 361 87 Appendix 362

871 MB-OOK modulation 362 872 OFDM modulation 363

Bibliography 367

Index 393

Preface

Two important areas of applications of microwave photonic links are electromagnetic sensors and radio-over-fiber (RoF) applications

Electromagnetic sensor microwave systems of the future will principally use active phased-array antennas The development will be determined by reliability requirements resistance to interference and total emission flexibility of the beamforming networks This type of antenna would therefore be used in a diverse range of applications eg radar communication and countermeasures To satisfy this multifunctional approach it will be necessary to distribute these antennas all over the surface area of strategic platforms (planes drones boats etc) While on the ground the multistatic mode of operation will force multiple antennas to be deported from their processing unit

This will require links with very low loss and noise enabling remote-control antennas and the distribution and processing of very wide bandwidth microwave signals (typically 1-20 GHz 40 GHz will be seen in the future)

Currently the maturity and performance notably in terms of spectral purity and opto-electronic component linearity are such that it is possible to consider both optical distribution and processing of these electrical signals Thus the optical transmission of microwaves offers as well as propagation of broad frequency bands advantages regarding weight volume and flexibility characterized by a decrease in the weight of the wiring by 90 in comparison to coaxial cables and thus insensitivity to electromagnetic perturbation All of which will enable the introduction of new concepts in microwave systems based on optical architecture

xiv Microwave Photonic Links

Several sensor radar systems have been designed and produced in France the United States the UK and Italy and photonic technology for the distribution of microwave signals is already being used for ground airborne and aerospace applications

Fiber-optic distribution network technology is an emergence of this technology platform in reference to the design of opto-electronic links for the transmission of microwave and digital signals This optical wiring aims to replace coaxial wiring for onboard electronics interconnections Here the term transmission is taken in the sense that microwave transmissions on optical carriers are in-phase

These functions require the design of emitting and receiving opto-electronic modules the integration of both high thermal stability multiplexing demultiplexing functions and single-mode connectors either point to point or multipoints

Another area of reference is the optical control of the phase andor delay of microwave signals and their applications to electromagnetic sensor systems This occurs by the design of ultrafast opto-electronic multi-chip modules incorporating the optically-controlled switching the control synthesis of time delay systems and the multiwave laser sources

Amongst the most promising technologies is the synthesis of mono- and bidimensional time-delays for the single and multiple beamforming in receiver and emitter the ultraprecise (picoseconds) time synchronization of distributed electromagnetic sensors the time-delay control (precision in the order of picoseconds) of very wide bandwidth microwave signals to measure the arrival direction and the waveshape generation

Another important area involving all RoF applications is the extensive development of wireless networks using microwaves or ultra-wideband signals This is achieved by providing optical tunnels capable of reaching all areas of a company university etc or all the rooms of a house whilst benefiting from the very low loss associated with fiber optics

In their work titled ldquoMicrowave Photonic Linksrdquo C Rumelhard C Algani and A-L Billabert studied and developed models of the components and photonic functions in microwave applications thus laying the foundation for research into microwave photonic links in order to allow the

Preface xv

integration of these components in electromagnetic sensors systems The components and functions addressed range from optical sources (modulated semiconductor lasers or externally modulated continuous lasers) to photodetectors optical fibers and optical amplifiers

This work focuses upon optical components their transfer functionality and their modeling in terms of microwave components in order to create an electrical model of microwave photonic links In order to achieve this level of complexity a number of modeling approaches have been created by the authors to elucidate the influences of the constituent components of microwave photonic links

Because the advancement of opto-electronics photonics and microwaves is possible by the unification of modeling approaches there is no doubt that such works will be referenced by students but also by design engineers and architects of electromagnetic sensor systems who will incorporate this new technology into their designs

This is to the authorrsquos knowledge the first work addressing the description and modeling of microwave photonic link technology with an educational approach to physical phenomena and new approaches to modeling microwave photonic components

Jean Chazelas Scientific Director

Thales Aeronautics Division

Abbreviation Glossary

AC Alternating Current

ACPR Adjacent Channel Power Ratio

ADP Ammonium dihydrogen phosphate

ADS Advanced Design System

AlGaAs Aluminum gallium arsenide

AM Amplitude Modulation

AM-DD Amplitude Modulation ndash Direct Detection

ASE Amplified Spontaneous Emission

BER Bit Error Rate

BH Buried Heterostructure

BiCMOS Bipolar Complementary Metal Oxide Semiconductor

BILBAO Borne drsquoinfrastructures large bande avec accegraves optique (Wideband infrastructure base with optical access)

CAD Computer-aided design

CdS Cadmium sulfide

CEA-Leti Commissariat agrave lrsquoeacutenergie atomique (Atomic energy commission)

CMOS Complementary metal-oxide-semiconductor

CNAM Conservatoire national des arts et meacutetiers

CPW Coplanar waveguide

xviii Microwave Photonic Links

DBR Distributed Bragg reflector

DC Direct current

DD-MZM Dual drive-MZM

DFA Doped fiber amplifier

DFB Distributed feedback laser

DFT Discrete Fourier transform

EO Electricoptic

EAM Electro-absorption modulator

EDFA Erbium-doped fiber amplifier

EEL Edge emitting laser

EML Electro-absorption modulated laser

EMT Electromagnetic transverse

EOM Electro-optic modulator

ER Extinction ratio

ESYCOM Equipe systegravemes de communications et microsystegravemes (Communications and microsystems team)

ET Electric transverse

EVM Error vector magnitude

FCC Federal communications commission

FET Field-effect transistor

FKE Franz-Keldysh effect

FT RampD France Telecom Research amp Development

GaAs Galium arsenide

GaP Galium phosphide

Ge Germanium

GRINSCH Graded index separate confinement heterostructure

HB Harmonic balance

HBT Heterojunction bipolar transistor

Abbreviation Glossary xix

HEMT High electron mobility transistor

HFET Heterojunction field-effect transistor

HFSS High frequency simulation system

HPT Heterojunction bipolar phototransistor

IDFT Inverse discrete Fourier transform

IM-DD Intensity modulation-direct detection

IMEP Institut de microeacutelectronique eacutelectromagneacutetisme et optique (Institute of microelectronics electromagnetism and optics)

InAs Indium arsenide

InGaAs Indium gallium arsenide

InGaP Indium gallium phosphide

InP Indium phosphide

IR-UWB Impulse Radio ndash Ultra Wideband

KDP Potassium dihydrogen phosphate

LAHC Laboratoire drsquohyperfreacutequences et de caracteacuterisation (hyperfrequency and characterization laboratory)

LASER Light amplifier by stimulated emission of radiation

LF Low frequency

LiNbO3 Lithium niobate

LiTaO3 Lithium tantalate

MAG Maximum available gain

MASER Microwave amplifier by stimulated emission of radiation

MB-OFDM Multi-band ndash orthogonal frequency division modulation

MB-OOK Multi-band on off keying

MEMS Micro-electro-mechanical systems

MESFET Metal semiconductor field-effect transistor

MMIC Monolithic microwave integrated circuit

MODFET Modulation-doped field-effect transistor

MQW-EAM Multi-quantum well-EAM

xx Microwave Photonic Links

MSM Metal semiconductor metal

MZM Modulator Mach-Zehnder

NdYAG Neodymium-doped yttrium aluminum garnet

NF Noise factor Noise figure

nOI n order intermodulation

nOIP n order intercept point

NRA National Research Agency

OE Opticelectric

OEIC Optoelectronic integrated circuit

OEMMIC Optoelectronic millimeter-wave monolithic integrated circuit

OFDM Orthogonal frequency division modulation

PDFA Praseodymium-doped fiber amplifier

PDG Biased-dependent gain

PM Phase modulation

PMMA Poly(methyl methacrylate)

PRBS Pseudo-random bit sequence

PSK Phase-shift keying

QAM Quadrature amplitude modulation

QCSE Quantum confined stark effect

QW-EAM Quantum well-EAM

RCEPD Resonant cavity enhanced photodetectors

RFT Rapid Fourier transform

RIN Relative intensity noise

RoF Radio over fiber

SD-MZM Single drive ndashMZM

Si Silicon

SiGe Silicon-germanium

SiMOX Separation by implantation of oxygen

Abbreviation Glossary xxi

SiO2 Silicon dioxide

SOA Semiconductor optical amplifier

SOC System on a chip

SOI Substrate on insulator

TDFA Thulium-doped fiber amplifier

TEGFET Two-dimensional electron gas field-effect transistor

TW-MZM Travelling wave-MZM

UTC Uni-travelling carrier

UWB Ultra-wideband

VCSEL Vertical-cavity surface-emitting laser

VCSOA Vertical-cavity semiconductor optical amplifier

VMDP Velocity matched distributed photodetector

WDM Wavelength division multiplexing

YDFA Ytterbium-doped fiber amplifier

ZnS Zinc sulfide

Chapter 1

General Points

11 Microwave photonic links

All signals generated or observed due to human activity (measurement of different physical values remote control files sounds images etc) can be transformed into analog electrical signals These electrical signals can be processed or transmitted as they are but in most cases they are digitized beforehand Once digitized these signals have different forms regarding the digital coding or error-correcting algorithms used and protocols employed in the transmission systems To be processed or transmitted these analog or digital signals can use different mediums

If the transmission is performed via metallic lines or cables digital signals directly enter these lines or they modulate more or less complex subcarriers (ADSL Ethernet)

If transmission occurs with a radiowave a high-frequency carrier must be available Due to the congestion of the wireless spectrum carriers are now principally microwaves ie with frequencies of 1 to 100 GHz (GSM UMTS Wi-Fi Wimax etc) Wireless transmission can also be performed by very short pulses having a wide spectrum range including the microwave spectrum or these pulses can modulate a carrier in the millimeter wave spectrum This technique is known as ultra-wideband (UWB) [YAO 09]

If transmission is via fiber optics digital signals modulate one or several optical carriers (amplitude or soliton modulation) which are themselves

2 Microwave Photonic Links

transmitted over hundreds of kilometers on optical fibers This is the case for all passive optical networks (PON) and their different transmission protocols [LEC 97]

From these definitions the distinctive feature of microwave photonic links is to transmit a microwave signal analogically or for it be digitally modulated This microwave signal is transferred to an optical carrier which is guided with minimum loss by an optical fiber The microwave signal is then picked up by a photodetector at the end of the fiber

One of the first applications of microwave optical links was the distribution of the microwave carrier in radar or radio-astronomy systems comprising offset aerials or active phased-array antennas which benefited from the low weight and low volume of the fiber optics [COX 97 DEC 98]

Another important area comprises all radio over fiber (RoF) applications consisting of the extension of wireless networks using microwaves or UWB waves The optical tunnels produced are capable of reaching all rooms or buildings of a company university or diverse institutions or all the rooms of a house whilst benefiting from the very low loss associated with fiber optics [FRI 02]

Amongst the applications of RoF a promising domain is in the connection of internet transmission networks to the home These connections are increasingly popular with ever-increasing speeds (1 Gbs) due to fiber optics reaching households (fiber to the home or FTTH) whereby the house itself becomes a high-speed local network In this local network the signal distribution in each room is achieved by a 60 GHz millimeter-wave (wireless personal area network or WPAN) which stays confined in the room due to the extremely fast attenuation at this frequency All rooms are linked to each other by a network of passive fiber optics which extends the millimeter-wave UWB signal throughout the whole house (ultra broadband wireless home area network or UBB-WHAN) Examples of millimeter-wave over optical transmissions are presented in [CHU 07 KIM 04 WEI 08] and a demonstration of a UBB-WHAN with an up and down link is described in [HUC 08]

The length of a link ranges from 10 m to 1 km allowing several fiber types to be used (single mode or multimode silica or plastic) and several optical wavelengths ranging from 06 to 155 μm The light undergoes intensity modulation the signal is received via photodetection In just a few

General Points 3

years rates have risen from around 10 Mbs on carriers of a few gigahertz to rates of 1 or 10 Gbs on 60 GHz for microwave carriers

A microwave photonic link is constituted of three parts

ndash a coherent light source a laser that emits an optical carrier the intensity of which is directly modulated inside the laser or externally by an optical modulator In the case of external modulation the amplitude modulation is performed by a Mach-Zehnder or an electro-absorption modulator

ndash the modulated light is then transported by single or multi-mode optical fiber [GOM 08 KOO 08] made of silica or plastic [KOI 06] This part may include an optical amplification

ndash the modulated light is finally photodetected in a photodetector consisting of a photodiode or a phototransistor

After some deliberation regarding coherent and incoherent optical links [HAL 82] the solution finally adopted for these links was ldquointensity modulation (IM) direct detection (DD)rdquo As this is recalled in [COX 06] in this type of link the depth of optical modulation is sufficiently weak that we can initially use small signal or linear techniques for each aspect Because the signals applied to links or extracted from them are in microwaves the variables characterizing these systems are S-parameters gains and noise factors Also nonlinearities and hence intermodulation produced by each component on the signal introduced in the link must be considered The combination of these different characteristics leads to the notion of interference-free dynamic range (IFDR) This shall be evaluated regarding the properties of each element in the chapters concerning overall performances of such links

As a link includes electrical-to-optical optical-to-electrical and even optical-to-optical transducers each of the magnitudes in terms of S-parameters gains and noise factors should be presented in the form of optomicrowave magnitudes This aspect forces harmonization of notions from the optical optoelectronic and microwave disciplines This is described in Chapter 5

The term used initially to describe these links was ldquomicrowave optical linksrdquo However the techniques used have gradually distanced themselves from proper optical and optoelectronic techniques so that the more specific term ldquomicrowave photonic linksrdquo has been progressively used [SEE 02]

4 Microwave Photonic Links

12 Link description

Figures 11 and 12 represent a general diagram of an IM-DD microwave optical link

Figure 11 Diagram of directly modulated microwave optical link

Figure 11 represents a direct modulation link A laser emits a light of wavelength 08 or 13 or 155 μm this laser is modulated by a microwave signal (which is possibly itself modulated) through a driver circuit The modulated light enters an optical fiber coupled to a photodetector that detects the microwave modulation signal The optical modulation can have an amplitude frequency and phase However direct photodetection detects only the modulation in amplitude The detected microwave signal is then amplified by a low-noise amplifier

Figure 12 represents an external modulation link This time a light emitted from a laser is injected into a Mach-Zehnder or electro-absorption amplitude modulator In this case microwave modulation is also applied to the modulator through a driver circuit

After passing into an optical fiber the optical intensity modulation only is detected via a photodetector As in the previous diagram the detected microwave signal is amplified in a low-noise amplifier

Laser

Driver

Optical fiber Photodetector

Low noise amplifier

Microwave or UWB Microwave or UWB

λ = 155 or 13 or 08 μm

Amplitude modulation Direct detection

General Points 5

Figure 12 Diagram of externally modulated microwave optical link

13 Signal to transmit

131 Microwave signal

The first type of transmitted signal is a signal that constitutes a microwave frequency reference It can be used in offset aerial systems or active phased-array antenna After its reflection from a moving object the microwave signal emitted from an antenna can shift in frequency (Doppler modulation) and it is the spectral purity of the microwave that determines the minimum observed frequency shift and therefore the minimum relative speed of the moving object The spectral purity and degradation after transmission of the microwave by optical links must be watched closely to distinguish the frequency shift

132 Microwave carrier for a digital signal

If the microwave signal serves as a carrier for a digital signal this carrier is previously modulated All the modulation techniques normally used such as amplitude frequency phase OFDM and combined amplitude-phase modulation (QAM) or more complex techniques can be considered such as those used in GSM GPRS EDGE and UMTS for mobile telephones or such as Bluetooth Wi-Fi and Wimax for data transmission These modulations are generally carried out on single sideband (SSB) When microwave signal modulation is implemented in phase or frequency spectral purity is also of great importance

Laser

Amplifier or driver

Optical fiber

λ = 155 or 13 or 08 μm

Microwave or UWB

Optical modulator MZ or EA

Amplitude modulation

Photodetector

Low noise amplifier

Microwave or UWB

Direct detection

6 Microwave Photonic Links

133 UWB signal

Another signal category is available for transmission by fiber optics These signals are relevant to UWB techniques without carriers and with the spectrum in the microwave region or up-converted to a millimeter-wave carrier UWB wireless links are largely used over short distances The optical fibers are particularly indicated to enable extensions of such networks

134 Optical carrier

Microwave signals can carry analog information (frequency shift due to the Doppler effect) or they can be modulated by a digital signal or be constituted of UWB signals which are themselves digitally modulated All these microwave signals must be up-converted to an optical carrier This transfer exclusively occurs by intensity modulation One of the advantages of this modulation is that the microwave signal can be recovered in a simple photodetection unit permitting the elimination of possible frequency fluctuations of the optical carrier Loss of sensitivity resulting from direct detection does not occur if the optical wavelength allows us to insert an optical amplifier or if the link is very short Usually this modulation is double sideband (DSB) especially if the modulation occurs directly in the laser but for slightly longer links this type of modulation can lead to extinction phenomena A single sideband modulation can hence be considered but this modulation must be carried out by an external modulator

135 Summary

The complexity of microwave photonic links comes from the stacking of an optical carrier and microwave or UWB subcarrier The optical carrier is exclusively intensity modulated whereas the microwave subcarrier can be modulated following all known modulation types amplitude frequency phase or their combination including a frequency shift due to the Doppler effect All these modulations can be recovered via photodetection

The use of microwave optical links will increase as the transmitted signals will be numerous and emitted in parallel communications and the data rates will increase accordingly Thus telecommunication optical

Microwave Photonic Links

Components and Circuits

Christian Rumelhard

Catherine Algani Anne-Laure Billabert

First published 2011 in Great Britain and the United States by ISTE Ltd and John Wiley amp Sons Inc Adapted and updated from Composants et circuits pour liaisons photoniques en micro-ondes published 2010 in France by Hermes ScienceLavoisier copy LAVOISIER 2010

Apart from any fair dealing for the purposes of research or private study or criticism or review as permitted under the Copyright Designs and Patents Act 1988 this publication may only be reproduced stored or transmitted in any form or by any means with the prior permission in writing of the publishers or in the case of reprographic reproduction in accordance with the terms and licenses issued by the CLA Enquiries concerning reproduction outside these terms should be sent to the publishers at the undermentioned address

ISTE Ltd John Wiley amp Sons Inc 27-37 St Georgersquos Road 111 River Street London SW19 4EU Hoboken NJ 07030 UK USA

wwwistecouk wwwwileycom

copy ISTE Ltd 2011 The rights of Christian Rumelhard Catherine Algani Anne-Laure Billabert to be identified as the authors of this work have been asserted by them in accordance with the Copyright Designs and Patents Act 1988

____________________________________________________________________________________ Library of Congress Cataloging-in-Publication Data

Rumelhard Christian Microwave photonic links components and circuits Christian Rumelhard Catherine Algani Anne-Laure Billabert p cm Includes bibliographical references and index ISBN 978-1-84821-226-8 1 Optical communications--Equipment and supplies 2 Microwave communication systems--Equipment and supplies 3 Telecommunication--Switching systems I Algani Catherine II Billabert Anne-Laure III Title TK510359R86 2011 6213813--dc22

2010046517

British Library Cataloguing-in-Publication Data A CIP record for this book is available from the British Library ISBN 978-1-84821-226-8 Printed and bound in Great Britain by CPI Antony Rowe Chippenham and Eastbourne

Table of Contents

Preface xiii

Abbrevation Glossary xvii

Chapter 1 General Points 1

11 Microwave photonic links 1 12 Link description 4 13 Signal to transmit 5

131 Microwave signal 5 132 Microwave carrier for a digital signal 5 133 UWB signal 6 134 Optical carrier 6 135 Summary 6

14 Limitations of microwave photonic links 7 141 Limitations due to the materials constituting the different elements 7 142 Noise sources in microwave photonic links 8 143 Nonlinearities 13

15 The components and characteristics of microwave photonic links 13

Chapter 2 Generation and Modulation of Light 15

21 Laser 15 211 General points 15 212 Semiconductor laser structure and optical gain in the active zone 17 213 Operation of a Fabry-Perot laser 19

vi Microwave Photonic Links

214 Optical confinement factor and rate equations 21 215 Static mode of laser operation (or CW mode of operation) 24 216 Dynamic mode of laser operation RF small signal response 26 217 RIN laser noise 28 218 Increase in 1f of RIN and superposition of a small signal and noise 31 219 Different laser configurations 32 2110 CAD laser models 41 2111 Laser measurements and temperature stabilization 47

22 Electro-optic modulator EOM 49 221 General physical principles 50 222 Pockels or linear electro-optical effect 50 223 Mach-Zehnder electro-optic modulator 53 224 Single-Drive MZM one driving electrode 55 225 Dual-drive MZM two driving electrodes 69 226 Real Mach-Zehnder modulator characteristics and performances 71 227 Mach-Zehnder modulator technology 73

23 Electro-absorption modulator EAM 75 231 Electro-absorption effect 75 232 FKE 80 233 Stark effect 80 234 Quantum well structures 82 235 MEA operation 82 236 Characteristics of an EAM 85 237 EML EAM integrated to a DFB laser 86 238 EAM electrical modeling for ultra-fast signal simulation 87

Chapter 3 Optical Fibers and Amplifiers 93 31 Optical fibers 93

311 General 93 312 Material attenuation 96 313 Material refraction index and dispersion 98 314 Total reflection numerical aperture transmitted maximum frequency 100 315 Step-index fiber 105 316 Graded index fiber 107 317 Single-mode fiber 110 318 Plastic optical fibers 114

Table of Contents vii

32 Optical amplifiers 118 321 Semiconductor optical amplifiers SOA 119 322 EDFAs 120

33 Appendix modal analysis of propagation in a fiber 122 331 Maxwell equations 122 332 Maxwell equations in a cylindrical fiber 123 333 Continuity and characteristic equation conditions 127 334 Research of different propagation modes 128 335 Approximation of linearly polarized modes 132

Chapter 4 Photodetectors 137 41 Photodetector definition 137 42 Photodiodes 138

421 Presentation 138 422 Light absorption in a semiconductor 139 423 p-i-n photodiode 142 424 Metal-semiconductor-metal or MSM photodiode 145 425 Equivalent circuits for p-i-n and MSM photodiodes 147 426 Nonlinearities 147 427 UTC photodiodes 149 428 Charge compensation 150 429 Partially depleted absorption zone 151 4210 Lateral lighting 152 4211 Lateral lighting progressive wave structure 153 4212 Lateral lighting periodic structures 156 4213 Resonant optical cavity photodetector 157 4214 Diluted waveguides and evanescent mode coupling 160 4215 Summary 161

43 Phototransistors 163 431 Bipolar or field-effect phototransistors 163 432 GaAlAsGaAs and InGaPGaAs phototransistors 165 433 InPInGaAs phototransistors 167 434 SiSiGe phototransistors 172 435 Resonant optical cavities for phototransistors 176 436 Phototransistor simulations and models 176 437 Influence of the base load impedance 180 438 Summary 183

44 Appendix 184 441 Lattice matched layers pseudomorphic layer metamorphic layer 184 442 Velocity overshoot effect 186 443 Heterojunction bipolar phototransistor 188

viii Microwave Photonic Links

Chapter 5 Performance of Microwave Photonic Links 193

51 Microwave photonic links diagrams and definitions 193 511 Direct modulation link diagram and definitions 193 512 External modulation link diagram and definitions 197 513 Simplified link diagram and first gain computation 198

52 Optomicrowave S-parameters and gains of each photonic link component 201

521 Introduction 201 522 Optomicrowave laser S-parameters and optomicrowave gain 202 523 Optomicrowave optical fiber S-parameters and optomicrowave gain 203 524 Photodiode optomicrowave S-parameters and gain 204 525 Localized component external modulator optomicrowave S-parameters and gain 205 526 Distributed component external modulator optomicrowave S-parameters and gain 207 527 Summary of all S-parameters and optomicrowave gain 209

53 Microwave photonic links optomicrowave S-parameters and gains 210

531 Direct modulation microwave photonic link S-parameters 210 532 Direct modulation microwave photonic link gains 211 533 Localized external modulator microwave photonic link S-parameters 212 534 Localized external modulator microwave photonic link gains 213 535 Distributed external modulator microwave photonic link S-parameters 213 536 Distributed external modulator microwave photonic link gains 214 537 Link gain computation generalization 215

54 Comparison of different link gains 218 541 Direct modulation link gain computation 218 542 Localized external modulator link gain computation 219 543 Distributed external modulator link gain computations 220

55 Direct modulation microwave photonic link optomicrowave noise figures 221

551 Link noise figure diagram and computation method 221 552 Laser noise figure 223 553 Optical fiber noise figure 223 554 Photodiode noise figure 224

Table of Contents ix

555 Direct modulation link noise figure 224 556 Matching effect at the input of a direct modulation link 225 557 Generalization of a link noise figure computation 226

56 External modulation microwave photonic link optomicrowave noise figure 227

561 Equivalent diagram and steps recall 227 562 Localized external modulator noise figure 227 563 Distributed external modulator noise figure 228 564 New evaluation of photodetector noise figure 230 565 Localized external modulator microwave photonic link noise figure 231 566 Matched input localized external modulator microwave photonic link noise figure 231 567 Distributed external modulator microwave photonic link noise figure 232

57 Comparisons of different link noise figures 232 571 Evaluation of direct modulation link noise figure 232 572 Evaluation of localized external modulator link noise figure 234 573 Evaluation of matched input localized external modulator link noise figure 235 574 Evaluation of distributed external modulator link noise figures 236 575 Output noise power 237 576 Some effectively measured noise figure values 239

58 Microwave photonic link nonlinearity distortion phenomena 241

581 Single microwave signal nonlinearity 241 582 Several input microwave signals nonlinearity 242 583 Wideband input signal nonlinearity 244 584 Nonlinearity combination of microwave photonic link components 245

59 Microwave photonic link interference-free dynamic range 246 591 Single input signal microwave photonic link interference-free dynamic range 246 592 Several-input signal microwave photonic link interference-free dynamic range 247 593 Some effectively measured interference-free dynamic range values 249

510 Appendix 250 5101 Relation between parameters S Z Y and ABCD 250 5102 Equation choice for the computation of microwave photonic link optomicrowave noise figure 251

x Microwave Photonic Links

5103 Calculation of a two-input signal microwave photonic link interference-free dynamic range 261

Chapter 6 Complement to Microwave Photonic Link Performances 267

61 Microwave signal attenuation during double sideband modulation 267

611 Double sideband modulation recall 267 612 Recall of single-mode optical fiber propagation characteristics 268 613 Optical fiber double sideband modulated signal propagation 270 614 Double sideband-modulated signal photodetection at the optical fiber output 271

62 Modulator structures for optical carrier or high and low sideband removal 273

621 Optical modulation recall 273 622 Single sideband or carrier suppression optical modulators 274 623 Carrier suppression and single sideband optical modulator 277

63 Degradation of a microwave signal spectral purity by an optical link 280

631 Phenomenon description 280 632 Some definitions concerning the noise around a microwave carrier 281 633 Amplitude and phase noise in an optical link 282 634 Phase noise computation of a microwave signal transmitted by an optical link 284 635 Amplitude noise computation of a microwave signal transmitted by an optical link 286

Chapter 7 Electronic Amplifiers in Microwave Photonic Links 289

71 Electronic amplifiers in optical links 289 72 Amplifiers in the optical link emitter 289

721 Different roles of electronic amplifiers on optical emitter 289 722 Emission modulator or laser input amplifiers 290

73 Receiver amplifiers at the photodetector output 293 731 General points 293 732 Transimpedance amplifiers 294 733 Distributed amplifiers 296

Table of Contents xi

734 Combination of transimpedance and distributed amplifiers 298 735 Narrowband amplifiers 298 736 Preamplifier after a phototransistor 299 737 Other circuits after a phototransistor 299

74 Appendix analog and microwave amplifiers 300 741 General points 300 742 Analog amplifiers 300 743 Microwave amplifier expression of transistor reflection coefficients 304 744 Microwave amplifiers gain expressions 306 745 Unilateralized transistor model two-port network matching computation 307 746 Non-unilateralized transistor general case of a transistor with S12 0 312 747 Low noise amplifier 313 748 General models of low signal microwave amplifiers 315

Chapter 8 Simulation and Measurement of Microwave Photonic Links 321

81 State of the art and context 321 811 Objective 321 812 Choice of simulation software 321 813 Different ADS simulation techniques 322

82 Microwave optical link models 324 821 Two-port network approach 324 822 Electro-optic transducer the laser 325 823 Transmission guiding the optical fiber 329 824 The optoelectric transducer the photodiode 334

83 Nonlinearity effects in the link 337 831 Nonlinearity sources 337 832 1 dB compression point and first-order dynamic of the link 338 833 Third-order intermodulation and third-order interference-free dynamic range of the link 339

84 Link noise modeling 340 841 Noise in the laser 340 842 The optical fiber 342 843 Noise in the photodiode 342 844 Direct modulation link noise figure 343 845 Noise power at the receiver 344

xii Microwave Photonic Links

85 Other types of modulation of signals transmitted on an optical fiber 348

851 Ultra-wideband signal modulation 348 852 External modulation 353 853 Generation of microwave signal by frequency beating 358

86 Conclusion 361 87 Appendix 362

871 MB-OOK modulation 362 872 OFDM modulation 363

Bibliography 367

Index 393

Preface

Two important areas of applications of microwave photonic links are electromagnetic sensors and radio-over-fiber (RoF) applications

Electromagnetic sensor microwave systems of the future will principally use active phased-array antennas The development will be determined by reliability requirements resistance to interference and total emission flexibility of the beamforming networks This type of antenna would therefore be used in a diverse range of applications eg radar communication and countermeasures To satisfy this multifunctional approach it will be necessary to distribute these antennas all over the surface area of strategic platforms (planes drones boats etc) While on the ground the multistatic mode of operation will force multiple antennas to be deported from their processing unit

This will require links with very low loss and noise enabling remote-control antennas and the distribution and processing of very wide bandwidth microwave signals (typically 1-20 GHz 40 GHz will be seen in the future)

Currently the maturity and performance notably in terms of spectral purity and opto-electronic component linearity are such that it is possible to consider both optical distribution and processing of these electrical signals Thus the optical transmission of microwaves offers as well as propagation of broad frequency bands advantages regarding weight volume and flexibility characterized by a decrease in the weight of the wiring by 90 in comparison to coaxial cables and thus insensitivity to electromagnetic perturbation All of which will enable the introduction of new concepts in microwave systems based on optical architecture

xiv Microwave Photonic Links

Several sensor radar systems have been designed and produced in France the United States the UK and Italy and photonic technology for the distribution of microwave signals is already being used for ground airborne and aerospace applications

Fiber-optic distribution network technology is an emergence of this technology platform in reference to the design of opto-electronic links for the transmission of microwave and digital signals This optical wiring aims to replace coaxial wiring for onboard electronics interconnections Here the term transmission is taken in the sense that microwave transmissions on optical carriers are in-phase

These functions require the design of emitting and receiving opto-electronic modules the integration of both high thermal stability multiplexing demultiplexing functions and single-mode connectors either point to point or multipoints

Another area of reference is the optical control of the phase andor delay of microwave signals and their applications to electromagnetic sensor systems This occurs by the design of ultrafast opto-electronic multi-chip modules incorporating the optically-controlled switching the control synthesis of time delay systems and the multiwave laser sources

Amongst the most promising technologies is the synthesis of mono- and bidimensional time-delays for the single and multiple beamforming in receiver and emitter the ultraprecise (picoseconds) time synchronization of distributed electromagnetic sensors the time-delay control (precision in the order of picoseconds) of very wide bandwidth microwave signals to measure the arrival direction and the waveshape generation

Another important area involving all RoF applications is the extensive development of wireless networks using microwaves or ultra-wideband signals This is achieved by providing optical tunnels capable of reaching all areas of a company university etc or all the rooms of a house whilst benefiting from the very low loss associated with fiber optics

In their work titled ldquoMicrowave Photonic Linksrdquo C Rumelhard C Algani and A-L Billabert studied and developed models of the components and photonic functions in microwave applications thus laying the foundation for research into microwave photonic links in order to allow the

Preface xv

integration of these components in electromagnetic sensors systems The components and functions addressed range from optical sources (modulated semiconductor lasers or externally modulated continuous lasers) to photodetectors optical fibers and optical amplifiers

This work focuses upon optical components their transfer functionality and their modeling in terms of microwave components in order to create an electrical model of microwave photonic links In order to achieve this level of complexity a number of modeling approaches have been created by the authors to elucidate the influences of the constituent components of microwave photonic links

Because the advancement of opto-electronics photonics and microwaves is possible by the unification of modeling approaches there is no doubt that such works will be referenced by students but also by design engineers and architects of electromagnetic sensor systems who will incorporate this new technology into their designs

This is to the authorrsquos knowledge the first work addressing the description and modeling of microwave photonic link technology with an educational approach to physical phenomena and new approaches to modeling microwave photonic components

Jean Chazelas Scientific Director

Thales Aeronautics Division

Abbreviation Glossary

AC Alternating Current

ACPR Adjacent Channel Power Ratio

ADP Ammonium dihydrogen phosphate

ADS Advanced Design System

AlGaAs Aluminum gallium arsenide

AM Amplitude Modulation

AM-DD Amplitude Modulation ndash Direct Detection

ASE Amplified Spontaneous Emission

BER Bit Error Rate

BH Buried Heterostructure

BiCMOS Bipolar Complementary Metal Oxide Semiconductor

BILBAO Borne drsquoinfrastructures large bande avec accegraves optique (Wideband infrastructure base with optical access)

CAD Computer-aided design

CdS Cadmium sulfide

CEA-Leti Commissariat agrave lrsquoeacutenergie atomique (Atomic energy commission)

CMOS Complementary metal-oxide-semiconductor

CNAM Conservatoire national des arts et meacutetiers

CPW Coplanar waveguide

xviii Microwave Photonic Links

DBR Distributed Bragg reflector

DC Direct current

DD-MZM Dual drive-MZM

DFA Doped fiber amplifier

DFB Distributed feedback laser

DFT Discrete Fourier transform

EO Electricoptic

EAM Electro-absorption modulator

EDFA Erbium-doped fiber amplifier

EEL Edge emitting laser

EML Electro-absorption modulated laser

EMT Electromagnetic transverse

EOM Electro-optic modulator

ER Extinction ratio

ESYCOM Equipe systegravemes de communications et microsystegravemes (Communications and microsystems team)

ET Electric transverse

EVM Error vector magnitude

FCC Federal communications commission

FET Field-effect transistor

FKE Franz-Keldysh effect

FT RampD France Telecom Research amp Development

GaAs Galium arsenide

GaP Galium phosphide

Ge Germanium

GRINSCH Graded index separate confinement heterostructure

HB Harmonic balance

HBT Heterojunction bipolar transistor

Abbreviation Glossary xix

HEMT High electron mobility transistor

HFET Heterojunction field-effect transistor

HFSS High frequency simulation system

HPT Heterojunction bipolar phototransistor

IDFT Inverse discrete Fourier transform

IM-DD Intensity modulation-direct detection

IMEP Institut de microeacutelectronique eacutelectromagneacutetisme et optique (Institute of microelectronics electromagnetism and optics)

InAs Indium arsenide

InGaAs Indium gallium arsenide

InGaP Indium gallium phosphide

InP Indium phosphide

IR-UWB Impulse Radio ndash Ultra Wideband

KDP Potassium dihydrogen phosphate

LAHC Laboratoire drsquohyperfreacutequences et de caracteacuterisation (hyperfrequency and characterization laboratory)

LASER Light amplifier by stimulated emission of radiation

LF Low frequency

LiNbO3 Lithium niobate

LiTaO3 Lithium tantalate

MAG Maximum available gain

MASER Microwave amplifier by stimulated emission of radiation

MB-OFDM Multi-band ndash orthogonal frequency division modulation

MB-OOK Multi-band on off keying

MEMS Micro-electro-mechanical systems

MESFET Metal semiconductor field-effect transistor

MMIC Monolithic microwave integrated circuit

MODFET Modulation-doped field-effect transistor

MQW-EAM Multi-quantum well-EAM

xx Microwave Photonic Links

MSM Metal semiconductor metal

MZM Modulator Mach-Zehnder

NdYAG Neodymium-doped yttrium aluminum garnet

NF Noise factor Noise figure

nOI n order intermodulation

nOIP n order intercept point

NRA National Research Agency

OE Opticelectric

OEIC Optoelectronic integrated circuit

OEMMIC Optoelectronic millimeter-wave monolithic integrated circuit

OFDM Orthogonal frequency division modulation

PDFA Praseodymium-doped fiber amplifier

PDG Biased-dependent gain

PM Phase modulation

PMMA Poly(methyl methacrylate)

PRBS Pseudo-random bit sequence

PSK Phase-shift keying

QAM Quadrature amplitude modulation

QCSE Quantum confined stark effect

QW-EAM Quantum well-EAM

RCEPD Resonant cavity enhanced photodetectors

RFT Rapid Fourier transform

RIN Relative intensity noise

RoF Radio over fiber

SD-MZM Single drive ndashMZM

Si Silicon

SiGe Silicon-germanium

SiMOX Separation by implantation of oxygen

Abbreviation Glossary xxi

SiO2 Silicon dioxide

SOA Semiconductor optical amplifier

SOC System on a chip

SOI Substrate on insulator

TDFA Thulium-doped fiber amplifier

TEGFET Two-dimensional electron gas field-effect transistor

TW-MZM Travelling wave-MZM

UTC Uni-travelling carrier

UWB Ultra-wideband

VCSEL Vertical-cavity surface-emitting laser

VCSOA Vertical-cavity semiconductor optical amplifier

VMDP Velocity matched distributed photodetector

WDM Wavelength division multiplexing

YDFA Ytterbium-doped fiber amplifier

ZnS Zinc sulfide

Chapter 1

General Points

11 Microwave photonic links

All signals generated or observed due to human activity (measurement of different physical values remote control files sounds images etc) can be transformed into analog electrical signals These electrical signals can be processed or transmitted as they are but in most cases they are digitized beforehand Once digitized these signals have different forms regarding the digital coding or error-correcting algorithms used and protocols employed in the transmission systems To be processed or transmitted these analog or digital signals can use different mediums

If the transmission is performed via metallic lines or cables digital signals directly enter these lines or they modulate more or less complex subcarriers (ADSL Ethernet)

If transmission occurs with a radiowave a high-frequency carrier must be available Due to the congestion of the wireless spectrum carriers are now principally microwaves ie with frequencies of 1 to 100 GHz (GSM UMTS Wi-Fi Wimax etc) Wireless transmission can also be performed by very short pulses having a wide spectrum range including the microwave spectrum or these pulses can modulate a carrier in the millimeter wave spectrum This technique is known as ultra-wideband (UWB) [YAO 09]

If transmission is via fiber optics digital signals modulate one or several optical carriers (amplitude or soliton modulation) which are themselves

2 Microwave Photonic Links

transmitted over hundreds of kilometers on optical fibers This is the case for all passive optical networks (PON) and their different transmission protocols [LEC 97]

From these definitions the distinctive feature of microwave photonic links is to transmit a microwave signal analogically or for it be digitally modulated This microwave signal is transferred to an optical carrier which is guided with minimum loss by an optical fiber The microwave signal is then picked up by a photodetector at the end of the fiber

One of the first applications of microwave optical links was the distribution of the microwave carrier in radar or radio-astronomy systems comprising offset aerials or active phased-array antennas which benefited from the low weight and low volume of the fiber optics [COX 97 DEC 98]

Another important area comprises all radio over fiber (RoF) applications consisting of the extension of wireless networks using microwaves or UWB waves The optical tunnels produced are capable of reaching all rooms or buildings of a company university or diverse institutions or all the rooms of a house whilst benefiting from the very low loss associated with fiber optics [FRI 02]

Amongst the applications of RoF a promising domain is in the connection of internet transmission networks to the home These connections are increasingly popular with ever-increasing speeds (1 Gbs) due to fiber optics reaching households (fiber to the home or FTTH) whereby the house itself becomes a high-speed local network In this local network the signal distribution in each room is achieved by a 60 GHz millimeter-wave (wireless personal area network or WPAN) which stays confined in the room due to the extremely fast attenuation at this frequency All rooms are linked to each other by a network of passive fiber optics which extends the millimeter-wave UWB signal throughout the whole house (ultra broadband wireless home area network or UBB-WHAN) Examples of millimeter-wave over optical transmissions are presented in [CHU 07 KIM 04 WEI 08] and a demonstration of a UBB-WHAN with an up and down link is described in [HUC 08]

The length of a link ranges from 10 m to 1 km allowing several fiber types to be used (single mode or multimode silica or plastic) and several optical wavelengths ranging from 06 to 155 μm The light undergoes intensity modulation the signal is received via photodetection In just a few

General Points 3

years rates have risen from around 10 Mbs on carriers of a few gigahertz to rates of 1 or 10 Gbs on 60 GHz for microwave carriers

A microwave photonic link is constituted of three parts

ndash a coherent light source a laser that emits an optical carrier the intensity of which is directly modulated inside the laser or externally by an optical modulator In the case of external modulation the amplitude modulation is performed by a Mach-Zehnder or an electro-absorption modulator

ndash the modulated light is then transported by single or multi-mode optical fiber [GOM 08 KOO 08] made of silica or plastic [KOI 06] This part may include an optical amplification

ndash the modulated light is finally photodetected in a photodetector consisting of a photodiode or a phototransistor

After some deliberation regarding coherent and incoherent optical links [HAL 82] the solution finally adopted for these links was ldquointensity modulation (IM) direct detection (DD)rdquo As this is recalled in [COX 06] in this type of link the depth of optical modulation is sufficiently weak that we can initially use small signal or linear techniques for each aspect Because the signals applied to links or extracted from them are in microwaves the variables characterizing these systems are S-parameters gains and noise factors Also nonlinearities and hence intermodulation produced by each component on the signal introduced in the link must be considered The combination of these different characteristics leads to the notion of interference-free dynamic range (IFDR) This shall be evaluated regarding the properties of each element in the chapters concerning overall performances of such links

As a link includes electrical-to-optical optical-to-electrical and even optical-to-optical transducers each of the magnitudes in terms of S-parameters gains and noise factors should be presented in the form of optomicrowave magnitudes This aspect forces harmonization of notions from the optical optoelectronic and microwave disciplines This is described in Chapter 5

The term used initially to describe these links was ldquomicrowave optical linksrdquo However the techniques used have gradually distanced themselves from proper optical and optoelectronic techniques so that the more specific term ldquomicrowave photonic linksrdquo has been progressively used [SEE 02]

4 Microwave Photonic Links

12 Link description

Figures 11 and 12 represent a general diagram of an IM-DD microwave optical link

Figure 11 Diagram of directly modulated microwave optical link

Figure 11 represents a direct modulation link A laser emits a light of wavelength 08 or 13 or 155 μm this laser is modulated by a microwave signal (which is possibly itself modulated) through a driver circuit The modulated light enters an optical fiber coupled to a photodetector that detects the microwave modulation signal The optical modulation can have an amplitude frequency and phase However direct photodetection detects only the modulation in amplitude The detected microwave signal is then amplified by a low-noise amplifier

Figure 12 represents an external modulation link This time a light emitted from a laser is injected into a Mach-Zehnder or electro-absorption amplitude modulator In this case microwave modulation is also applied to the modulator through a driver circuit

After passing into an optical fiber the optical intensity modulation only is detected via a photodetector As in the previous diagram the detected microwave signal is amplified in a low-noise amplifier

Laser

Driver

Optical fiber Photodetector

Low noise amplifier

Microwave or UWB Microwave or UWB

λ = 155 or 13 or 08 μm

Amplitude modulation Direct detection

General Points 5

Figure 12 Diagram of externally modulated microwave optical link

13 Signal to transmit

131 Microwave signal

The first type of transmitted signal is a signal that constitutes a microwave frequency reference It can be used in offset aerial systems or active phased-array antenna After its reflection from a moving object the microwave signal emitted from an antenna can shift in frequency (Doppler modulation) and it is the spectral purity of the microwave that determines the minimum observed frequency shift and therefore the minimum relative speed of the moving object The spectral purity and degradation after transmission of the microwave by optical links must be watched closely to distinguish the frequency shift

132 Microwave carrier for a digital signal

If the microwave signal serves as a carrier for a digital signal this carrier is previously modulated All the modulation techniques normally used such as amplitude frequency phase OFDM and combined amplitude-phase modulation (QAM) or more complex techniques can be considered such as those used in GSM GPRS EDGE and UMTS for mobile telephones or such as Bluetooth Wi-Fi and Wimax for data transmission These modulations are generally carried out on single sideband (SSB) When microwave signal modulation is implemented in phase or frequency spectral purity is also of great importance

Laser

Amplifier or driver

Optical fiber

λ = 155 or 13 or 08 μm

Microwave or UWB

Optical modulator MZ or EA

Amplitude modulation

Photodetector

Low noise amplifier

Microwave or UWB

Direct detection

6 Microwave Photonic Links

133 UWB signal

Another signal category is available for transmission by fiber optics These signals are relevant to UWB techniques without carriers and with the spectrum in the microwave region or up-converted to a millimeter-wave carrier UWB wireless links are largely used over short distances The optical fibers are particularly indicated to enable extensions of such networks

134 Optical carrier

Microwave signals can carry analog information (frequency shift due to the Doppler effect) or they can be modulated by a digital signal or be constituted of UWB signals which are themselves digitally modulated All these microwave signals must be up-converted to an optical carrier This transfer exclusively occurs by intensity modulation One of the advantages of this modulation is that the microwave signal can be recovered in a simple photodetection unit permitting the elimination of possible frequency fluctuations of the optical carrier Loss of sensitivity resulting from direct detection does not occur if the optical wavelength allows us to insert an optical amplifier or if the link is very short Usually this modulation is double sideband (DSB) especially if the modulation occurs directly in the laser but for slightly longer links this type of modulation can lead to extinction phenomena A single sideband modulation can hence be considered but this modulation must be carried out by an external modulator

135 Summary

The complexity of microwave photonic links comes from the stacking of an optical carrier and microwave or UWB subcarrier The optical carrier is exclusively intensity modulated whereas the microwave subcarrier can be modulated following all known modulation types amplitude frequency phase or their combination including a frequency shift due to the Doppler effect All these modulations can be recovered via photodetection

The use of microwave optical links will increase as the transmitted signals will be numerous and emitted in parallel communications and the data rates will increase accordingly Thus telecommunication optical

First published 2011 in Great Britain and the United States by ISTE Ltd and John Wiley amp Sons Inc Adapted and updated from Composants et circuits pour liaisons photoniques en micro-ondes published 2010 in France by Hermes ScienceLavoisier copy LAVOISIER 2010

Apart from any fair dealing for the purposes of research or private study or criticism or review as permitted under the Copyright Designs and Patents Act 1988 this publication may only be reproduced stored or transmitted in any form or by any means with the prior permission in writing of the publishers or in the case of reprographic reproduction in accordance with the terms and licenses issued by the CLA Enquiries concerning reproduction outside these terms should be sent to the publishers at the undermentioned address

ISTE Ltd John Wiley amp Sons Inc 27-37 St Georgersquos Road 111 River Street London SW19 4EU Hoboken NJ 07030 UK USA

wwwistecouk wwwwileycom

copy ISTE Ltd 2011 The rights of Christian Rumelhard Catherine Algani Anne-Laure Billabert to be identified as the authors of this work have been asserted by them in accordance with the Copyright Designs and Patents Act 1988

____________________________________________________________________________________ Library of Congress Cataloging-in-Publication Data

Rumelhard Christian Microwave photonic links components and circuits Christian Rumelhard Catherine Algani Anne-Laure Billabert p cm Includes bibliographical references and index ISBN 978-1-84821-226-8 1 Optical communications--Equipment and supplies 2 Microwave communication systems--Equipment and supplies 3 Telecommunication--Switching systems I Algani Catherine II Billabert Anne-Laure III Title TK510359R86 2011 6213813--dc22

2010046517

British Library Cataloguing-in-Publication Data A CIP record for this book is available from the British Library ISBN 978-1-84821-226-8 Printed and bound in Great Britain by CPI Antony Rowe Chippenham and Eastbourne

Table of Contents

Preface xiii

Abbrevation Glossary xvii

Chapter 1 General Points 1

11 Microwave photonic links 1 12 Link description 4 13 Signal to transmit 5

131 Microwave signal 5 132 Microwave carrier for a digital signal 5 133 UWB signal 6 134 Optical carrier 6 135 Summary 6

14 Limitations of microwave photonic links 7 141 Limitations due to the materials constituting the different elements 7 142 Noise sources in microwave photonic links 8 143 Nonlinearities 13

15 The components and characteristics of microwave photonic links 13

Chapter 2 Generation and Modulation of Light 15

21 Laser 15 211 General points 15 212 Semiconductor laser structure and optical gain in the active zone 17 213 Operation of a Fabry-Perot laser 19

vi Microwave Photonic Links

214 Optical confinement factor and rate equations 21 215 Static mode of laser operation (or CW mode of operation) 24 216 Dynamic mode of laser operation RF small signal response 26 217 RIN laser noise 28 218 Increase in 1f of RIN and superposition of a small signal and noise 31 219 Different laser configurations 32 2110 CAD laser models 41 2111 Laser measurements and temperature stabilization 47

22 Electro-optic modulator EOM 49 221 General physical principles 50 222 Pockels or linear electro-optical effect 50 223 Mach-Zehnder electro-optic modulator 53 224 Single-Drive MZM one driving electrode 55 225 Dual-drive MZM two driving electrodes 69 226 Real Mach-Zehnder modulator characteristics and performances 71 227 Mach-Zehnder modulator technology 73

23 Electro-absorption modulator EAM 75 231 Electro-absorption effect 75 232 FKE 80 233 Stark effect 80 234 Quantum well structures 82 235 MEA operation 82 236 Characteristics of an EAM 85 237 EML EAM integrated to a DFB laser 86 238 EAM electrical modeling for ultra-fast signal simulation 87

Chapter 3 Optical Fibers and Amplifiers 93 31 Optical fibers 93

311 General 93 312 Material attenuation 96 313 Material refraction index and dispersion 98 314 Total reflection numerical aperture transmitted maximum frequency 100 315 Step-index fiber 105 316 Graded index fiber 107 317 Single-mode fiber 110 318 Plastic optical fibers 114

Table of Contents vii

32 Optical amplifiers 118 321 Semiconductor optical amplifiers SOA 119 322 EDFAs 120

33 Appendix modal analysis of propagation in a fiber 122 331 Maxwell equations 122 332 Maxwell equations in a cylindrical fiber 123 333 Continuity and characteristic equation conditions 127 334 Research of different propagation modes 128 335 Approximation of linearly polarized modes 132

Chapter 4 Photodetectors 137 41 Photodetector definition 137 42 Photodiodes 138

421 Presentation 138 422 Light absorption in a semiconductor 139 423 p-i-n photodiode 142 424 Metal-semiconductor-metal or MSM photodiode 145 425 Equivalent circuits for p-i-n and MSM photodiodes 147 426 Nonlinearities 147 427 UTC photodiodes 149 428 Charge compensation 150 429 Partially depleted absorption zone 151 4210 Lateral lighting 152 4211 Lateral lighting progressive wave structure 153 4212 Lateral lighting periodic structures 156 4213 Resonant optical cavity photodetector 157 4214 Diluted waveguides and evanescent mode coupling 160 4215 Summary 161

43 Phototransistors 163 431 Bipolar or field-effect phototransistors 163 432 GaAlAsGaAs and InGaPGaAs phototransistors 165 433 InPInGaAs phototransistors 167 434 SiSiGe phototransistors 172 435 Resonant optical cavities for phototransistors 176 436 Phototransistor simulations and models 176 437 Influence of the base load impedance 180 438 Summary 183

44 Appendix 184 441 Lattice matched layers pseudomorphic layer metamorphic layer 184 442 Velocity overshoot effect 186 443 Heterojunction bipolar phototransistor 188

viii Microwave Photonic Links

Chapter 5 Performance of Microwave Photonic Links 193

51 Microwave photonic links diagrams and definitions 193 511 Direct modulation link diagram and definitions 193 512 External modulation link diagram and definitions 197 513 Simplified link diagram and first gain computation 198

52 Optomicrowave S-parameters and gains of each photonic link component 201

521 Introduction 201 522 Optomicrowave laser S-parameters and optomicrowave gain 202 523 Optomicrowave optical fiber S-parameters and optomicrowave gain 203 524 Photodiode optomicrowave S-parameters and gain 204 525 Localized component external modulator optomicrowave S-parameters and gain 205 526 Distributed component external modulator optomicrowave S-parameters and gain 207 527 Summary of all S-parameters and optomicrowave gain 209

53 Microwave photonic links optomicrowave S-parameters and gains 210

531 Direct modulation microwave photonic link S-parameters 210 532 Direct modulation microwave photonic link gains 211 533 Localized external modulator microwave photonic link S-parameters 212 534 Localized external modulator microwave photonic link gains 213 535 Distributed external modulator microwave photonic link S-parameters 213 536 Distributed external modulator microwave photonic link gains 214 537 Link gain computation generalization 215

54 Comparison of different link gains 218 541 Direct modulation link gain computation 218 542 Localized external modulator link gain computation 219 543 Distributed external modulator link gain computations 220

55 Direct modulation microwave photonic link optomicrowave noise figures 221

551 Link noise figure diagram and computation method 221 552 Laser noise figure 223 553 Optical fiber noise figure 223 554 Photodiode noise figure 224

Table of Contents ix

555 Direct modulation link noise figure 224 556 Matching effect at the input of a direct modulation link 225 557 Generalization of a link noise figure computation 226

56 External modulation microwave photonic link optomicrowave noise figure 227

561 Equivalent diagram and steps recall 227 562 Localized external modulator noise figure 227 563 Distributed external modulator noise figure 228 564 New evaluation of photodetector noise figure 230 565 Localized external modulator microwave photonic link noise figure 231 566 Matched input localized external modulator microwave photonic link noise figure 231 567 Distributed external modulator microwave photonic link noise figure 232

57 Comparisons of different link noise figures 232 571 Evaluation of direct modulation link noise figure 232 572 Evaluation of localized external modulator link noise figure 234 573 Evaluation of matched input localized external modulator link noise figure 235 574 Evaluation of distributed external modulator link noise figures 236 575 Output noise power 237 576 Some effectively measured noise figure values 239

58 Microwave photonic link nonlinearity distortion phenomena 241

581 Single microwave signal nonlinearity 241 582 Several input microwave signals nonlinearity 242 583 Wideband input signal nonlinearity 244 584 Nonlinearity combination of microwave photonic link components 245

59 Microwave photonic link interference-free dynamic range 246 591 Single input signal microwave photonic link interference-free dynamic range 246 592 Several-input signal microwave photonic link interference-free dynamic range 247 593 Some effectively measured interference-free dynamic range values 249

510 Appendix 250 5101 Relation between parameters S Z Y and ABCD 250 5102 Equation choice for the computation of microwave photonic link optomicrowave noise figure 251

x Microwave Photonic Links

5103 Calculation of a two-input signal microwave photonic link interference-free dynamic range 261

Chapter 6 Complement to Microwave Photonic Link Performances 267

61 Microwave signal attenuation during double sideband modulation 267

611 Double sideband modulation recall 267 612 Recall of single-mode optical fiber propagation characteristics 268 613 Optical fiber double sideband modulated signal propagation 270 614 Double sideband-modulated signal photodetection at the optical fiber output 271

62 Modulator structures for optical carrier or high and low sideband removal 273

621 Optical modulation recall 273 622 Single sideband or carrier suppression optical modulators 274 623 Carrier suppression and single sideband optical modulator 277

63 Degradation of a microwave signal spectral purity by an optical link 280

631 Phenomenon description 280 632 Some definitions concerning the noise around a microwave carrier 281 633 Amplitude and phase noise in an optical link 282 634 Phase noise computation of a microwave signal transmitted by an optical link 284 635 Amplitude noise computation of a microwave signal transmitted by an optical link 286

Chapter 7 Electronic Amplifiers in Microwave Photonic Links 289

71 Electronic amplifiers in optical links 289 72 Amplifiers in the optical link emitter 289

721 Different roles of electronic amplifiers on optical emitter 289 722 Emission modulator or laser input amplifiers 290

73 Receiver amplifiers at the photodetector output 293 731 General points 293 732 Transimpedance amplifiers 294 733 Distributed amplifiers 296

Table of Contents xi

734 Combination of transimpedance and distributed amplifiers 298 735 Narrowband amplifiers 298 736 Preamplifier after a phototransistor 299 737 Other circuits after a phototransistor 299

74 Appendix analog and microwave amplifiers 300 741 General points 300 742 Analog amplifiers 300 743 Microwave amplifier expression of transistor reflection coefficients 304 744 Microwave amplifiers gain expressions 306 745 Unilateralized transistor model two-port network matching computation 307 746 Non-unilateralized transistor general case of a transistor with S12 0 312 747 Low noise amplifier 313 748 General models of low signal microwave amplifiers 315

Chapter 8 Simulation and Measurement of Microwave Photonic Links 321

81 State of the art and context 321 811 Objective 321 812 Choice of simulation software 321 813 Different ADS simulation techniques 322

82 Microwave optical link models 324 821 Two-port network approach 324 822 Electro-optic transducer the laser 325 823 Transmission guiding the optical fiber 329 824 The optoelectric transducer the photodiode 334

83 Nonlinearity effects in the link 337 831 Nonlinearity sources 337 832 1 dB compression point and first-order dynamic of the link 338 833 Third-order intermodulation and third-order interference-free dynamic range of the link 339

84 Link noise modeling 340 841 Noise in the laser 340 842 The optical fiber 342 843 Noise in the photodiode 342 844 Direct modulation link noise figure 343 845 Noise power at the receiver 344

xii Microwave Photonic Links

85 Other types of modulation of signals transmitted on an optical fiber 348

851 Ultra-wideband signal modulation 348 852 External modulation 353 853 Generation of microwave signal by frequency beating 358

86 Conclusion 361 87 Appendix 362

871 MB-OOK modulation 362 872 OFDM modulation 363

Bibliography 367

Index 393

Preface

Two important areas of applications of microwave photonic links are electromagnetic sensors and radio-over-fiber (RoF) applications

Electromagnetic sensor microwave systems of the future will principally use active phased-array antennas The development will be determined by reliability requirements resistance to interference and total emission flexibility of the beamforming networks This type of antenna would therefore be used in a diverse range of applications eg radar communication and countermeasures To satisfy this multifunctional approach it will be necessary to distribute these antennas all over the surface area of strategic platforms (planes drones boats etc) While on the ground the multistatic mode of operation will force multiple antennas to be deported from their processing unit

This will require links with very low loss and noise enabling remote-control antennas and the distribution and processing of very wide bandwidth microwave signals (typically 1-20 GHz 40 GHz will be seen in the future)

Currently the maturity and performance notably in terms of spectral purity and opto-electronic component linearity are such that it is possible to consider both optical distribution and processing of these electrical signals Thus the optical transmission of microwaves offers as well as propagation of broad frequency bands advantages regarding weight volume and flexibility characterized by a decrease in the weight of the wiring by 90 in comparison to coaxial cables and thus insensitivity to electromagnetic perturbation All of which will enable the introduction of new concepts in microwave systems based on optical architecture

xiv Microwave Photonic Links

Several sensor radar systems have been designed and produced in France the United States the UK and Italy and photonic technology for the distribution of microwave signals is already being used for ground airborne and aerospace applications

Fiber-optic distribution network technology is an emergence of this technology platform in reference to the design of opto-electronic links for the transmission of microwave and digital signals This optical wiring aims to replace coaxial wiring for onboard electronics interconnections Here the term transmission is taken in the sense that microwave transmissions on optical carriers are in-phase

These functions require the design of emitting and receiving opto-electronic modules the integration of both high thermal stability multiplexing demultiplexing functions and single-mode connectors either point to point or multipoints

Another area of reference is the optical control of the phase andor delay of microwave signals and their applications to electromagnetic sensor systems This occurs by the design of ultrafast opto-electronic multi-chip modules incorporating the optically-controlled switching the control synthesis of time delay systems and the multiwave laser sources

Amongst the most promising technologies is the synthesis of mono- and bidimensional time-delays for the single and multiple beamforming in receiver and emitter the ultraprecise (picoseconds) time synchronization of distributed electromagnetic sensors the time-delay control (precision in the order of picoseconds) of very wide bandwidth microwave signals to measure the arrival direction and the waveshape generation

Another important area involving all RoF applications is the extensive development of wireless networks using microwaves or ultra-wideband signals This is achieved by providing optical tunnels capable of reaching all areas of a company university etc or all the rooms of a house whilst benefiting from the very low loss associated with fiber optics

In their work titled ldquoMicrowave Photonic Linksrdquo C Rumelhard C Algani and A-L Billabert studied and developed models of the components and photonic functions in microwave applications thus laying the foundation for research into microwave photonic links in order to allow the

Preface xv

integration of these components in electromagnetic sensors systems The components and functions addressed range from optical sources (modulated semiconductor lasers or externally modulated continuous lasers) to photodetectors optical fibers and optical amplifiers

This work focuses upon optical components their transfer functionality and their modeling in terms of microwave components in order to create an electrical model of microwave photonic links In order to achieve this level of complexity a number of modeling approaches have been created by the authors to elucidate the influences of the constituent components of microwave photonic links

Because the advancement of opto-electronics photonics and microwaves is possible by the unification of modeling approaches there is no doubt that such works will be referenced by students but also by design engineers and architects of electromagnetic sensor systems who will incorporate this new technology into their designs

This is to the authorrsquos knowledge the first work addressing the description and modeling of microwave photonic link technology with an educational approach to physical phenomena and new approaches to modeling microwave photonic components

Jean Chazelas Scientific Director

Thales Aeronautics Division

Abbreviation Glossary

AC Alternating Current

ACPR Adjacent Channel Power Ratio

ADP Ammonium dihydrogen phosphate

ADS Advanced Design System

AlGaAs Aluminum gallium arsenide

AM Amplitude Modulation

AM-DD Amplitude Modulation ndash Direct Detection

ASE Amplified Spontaneous Emission

BER Bit Error Rate

BH Buried Heterostructure

BiCMOS Bipolar Complementary Metal Oxide Semiconductor

BILBAO Borne drsquoinfrastructures large bande avec accegraves optique (Wideband infrastructure base with optical access)

CAD Computer-aided design

CdS Cadmium sulfide

CEA-Leti Commissariat agrave lrsquoeacutenergie atomique (Atomic energy commission)

CMOS Complementary metal-oxide-semiconductor

CNAM Conservatoire national des arts et meacutetiers

CPW Coplanar waveguide

xviii Microwave Photonic Links

DBR Distributed Bragg reflector

DC Direct current

DD-MZM Dual drive-MZM

DFA Doped fiber amplifier

DFB Distributed feedback laser

DFT Discrete Fourier transform

EO Electricoptic

EAM Electro-absorption modulator

EDFA Erbium-doped fiber amplifier

EEL Edge emitting laser

EML Electro-absorption modulated laser

EMT Electromagnetic transverse

EOM Electro-optic modulator

ER Extinction ratio

ESYCOM Equipe systegravemes de communications et microsystegravemes (Communications and microsystems team)

ET Electric transverse

EVM Error vector magnitude

FCC Federal communications commission

FET Field-effect transistor

FKE Franz-Keldysh effect

FT RampD France Telecom Research amp Development

GaAs Galium arsenide

GaP Galium phosphide

Ge Germanium

GRINSCH Graded index separate confinement heterostructure

HB Harmonic balance

HBT Heterojunction bipolar transistor

Abbreviation Glossary xix

HEMT High electron mobility transistor

HFET Heterojunction field-effect transistor

HFSS High frequency simulation system

HPT Heterojunction bipolar phototransistor

IDFT Inverse discrete Fourier transform

IM-DD Intensity modulation-direct detection

IMEP Institut de microeacutelectronique eacutelectromagneacutetisme et optique (Institute of microelectronics electromagnetism and optics)

InAs Indium arsenide

InGaAs Indium gallium arsenide

InGaP Indium gallium phosphide

InP Indium phosphide

IR-UWB Impulse Radio ndash Ultra Wideband

KDP Potassium dihydrogen phosphate

LAHC Laboratoire drsquohyperfreacutequences et de caracteacuterisation (hyperfrequency and characterization laboratory)

LASER Light amplifier by stimulated emission of radiation

LF Low frequency

LiNbO3 Lithium niobate

LiTaO3 Lithium tantalate

MAG Maximum available gain

MASER Microwave amplifier by stimulated emission of radiation

MB-OFDM Multi-band ndash orthogonal frequency division modulation

MB-OOK Multi-band on off keying

MEMS Micro-electro-mechanical systems

MESFET Metal semiconductor field-effect transistor

MMIC Monolithic microwave integrated circuit

MODFET Modulation-doped field-effect transistor

MQW-EAM Multi-quantum well-EAM

xx Microwave Photonic Links

MSM Metal semiconductor metal

MZM Modulator Mach-Zehnder

NdYAG Neodymium-doped yttrium aluminum garnet

NF Noise factor Noise figure

nOI n order intermodulation

nOIP n order intercept point

NRA National Research Agency

OE Opticelectric

OEIC Optoelectronic integrated circuit

OEMMIC Optoelectronic millimeter-wave monolithic integrated circuit

OFDM Orthogonal frequency division modulation

PDFA Praseodymium-doped fiber amplifier

PDG Biased-dependent gain

PM Phase modulation

PMMA Poly(methyl methacrylate)

PRBS Pseudo-random bit sequence

PSK Phase-shift keying

QAM Quadrature amplitude modulation

QCSE Quantum confined stark effect

QW-EAM Quantum well-EAM

RCEPD Resonant cavity enhanced photodetectors

RFT Rapid Fourier transform

RIN Relative intensity noise

RoF Radio over fiber

SD-MZM Single drive ndashMZM

Si Silicon

SiGe Silicon-germanium

SiMOX Separation by implantation of oxygen

Abbreviation Glossary xxi

SiO2 Silicon dioxide

SOA Semiconductor optical amplifier

SOC System on a chip

SOI Substrate on insulator

TDFA Thulium-doped fiber amplifier

TEGFET Two-dimensional electron gas field-effect transistor

TW-MZM Travelling wave-MZM

UTC Uni-travelling carrier

UWB Ultra-wideband

VCSEL Vertical-cavity surface-emitting laser

VCSOA Vertical-cavity semiconductor optical amplifier

VMDP Velocity matched distributed photodetector

WDM Wavelength division multiplexing

YDFA Ytterbium-doped fiber amplifier

ZnS Zinc sulfide

Chapter 1

General Points

11 Microwave photonic links

All signals generated or observed due to human activity (measurement of different physical values remote control files sounds images etc) can be transformed into analog electrical signals These electrical signals can be processed or transmitted as they are but in most cases they are digitized beforehand Once digitized these signals have different forms regarding the digital coding or error-correcting algorithms used and protocols employed in the transmission systems To be processed or transmitted these analog or digital signals can use different mediums

If the transmission is performed via metallic lines or cables digital signals directly enter these lines or they modulate more or less complex subcarriers (ADSL Ethernet)

If transmission occurs with a radiowave a high-frequency carrier must be available Due to the congestion of the wireless spectrum carriers are now principally microwaves ie with frequencies of 1 to 100 GHz (GSM UMTS Wi-Fi Wimax etc) Wireless transmission can also be performed by very short pulses having a wide spectrum range including the microwave spectrum or these pulses can modulate a carrier in the millimeter wave spectrum This technique is known as ultra-wideband (UWB) [YAO 09]

If transmission is via fiber optics digital signals modulate one or several optical carriers (amplitude or soliton modulation) which are themselves

2 Microwave Photonic Links

transmitted over hundreds of kilometers on optical fibers This is the case for all passive optical networks (PON) and their different transmission protocols [LEC 97]

From these definitions the distinctive feature of microwave photonic links is to transmit a microwave signal analogically or for it be digitally modulated This microwave signal is transferred to an optical carrier which is guided with minimum loss by an optical fiber The microwave signal is then picked up by a photodetector at the end of the fiber

One of the first applications of microwave optical links was the distribution of the microwave carrier in radar or radio-astronomy systems comprising offset aerials or active phased-array antennas which benefited from the low weight and low volume of the fiber optics [COX 97 DEC 98]

Another important area comprises all radio over fiber (RoF) applications consisting of the extension of wireless networks using microwaves or UWB waves The optical tunnels produced are capable of reaching all rooms or buildings of a company university or diverse institutions or all the rooms of a house whilst benefiting from the very low loss associated with fiber optics [FRI 02]

Amongst the applications of RoF a promising domain is in the connection of internet transmission networks to the home These connections are increasingly popular with ever-increasing speeds (1 Gbs) due to fiber optics reaching households (fiber to the home or FTTH) whereby the house itself becomes a high-speed local network In this local network the signal distribution in each room is achieved by a 60 GHz millimeter-wave (wireless personal area network or WPAN) which stays confined in the room due to the extremely fast attenuation at this frequency All rooms are linked to each other by a network of passive fiber optics which extends the millimeter-wave UWB signal throughout the whole house (ultra broadband wireless home area network or UBB-WHAN) Examples of millimeter-wave over optical transmissions are presented in [CHU 07 KIM 04 WEI 08] and a demonstration of a UBB-WHAN with an up and down link is described in [HUC 08]

The length of a link ranges from 10 m to 1 km allowing several fiber types to be used (single mode or multimode silica or plastic) and several optical wavelengths ranging from 06 to 155 μm The light undergoes intensity modulation the signal is received via photodetection In just a few

General Points 3

years rates have risen from around 10 Mbs on carriers of a few gigahertz to rates of 1 or 10 Gbs on 60 GHz for microwave carriers

A microwave photonic link is constituted of three parts

ndash a coherent light source a laser that emits an optical carrier the intensity of which is directly modulated inside the laser or externally by an optical modulator In the case of external modulation the amplitude modulation is performed by a Mach-Zehnder or an electro-absorption modulator

ndash the modulated light is then transported by single or multi-mode optical fiber [GOM 08 KOO 08] made of silica or plastic [KOI 06] This part may include an optical amplification

ndash the modulated light is finally photodetected in a photodetector consisting of a photodiode or a phototransistor

After some deliberation regarding coherent and incoherent optical links [HAL 82] the solution finally adopted for these links was ldquointensity modulation (IM) direct detection (DD)rdquo As this is recalled in [COX 06] in this type of link the depth of optical modulation is sufficiently weak that we can initially use small signal or linear techniques for each aspect Because the signals applied to links or extracted from them are in microwaves the variables characterizing these systems are S-parameters gains and noise factors Also nonlinearities and hence intermodulation produced by each component on the signal introduced in the link must be considered The combination of these different characteristics leads to the notion of interference-free dynamic range (IFDR) This shall be evaluated regarding the properties of each element in the chapters concerning overall performances of such links

As a link includes electrical-to-optical optical-to-electrical and even optical-to-optical transducers each of the magnitudes in terms of S-parameters gains and noise factors should be presented in the form of optomicrowave magnitudes This aspect forces harmonization of notions from the optical optoelectronic and microwave disciplines This is described in Chapter 5

The term used initially to describe these links was ldquomicrowave optical linksrdquo However the techniques used have gradually distanced themselves from proper optical and optoelectronic techniques so that the more specific term ldquomicrowave photonic linksrdquo has been progressively used [SEE 02]

4 Microwave Photonic Links

12 Link description

Figures 11 and 12 represent a general diagram of an IM-DD microwave optical link

Figure 11 Diagram of directly modulated microwave optical link

Figure 11 represents a direct modulation link A laser emits a light of wavelength 08 or 13 or 155 μm this laser is modulated by a microwave signal (which is possibly itself modulated) through a driver circuit The modulated light enters an optical fiber coupled to a photodetector that detects the microwave modulation signal The optical modulation can have an amplitude frequency and phase However direct photodetection detects only the modulation in amplitude The detected microwave signal is then amplified by a low-noise amplifier

Figure 12 represents an external modulation link This time a light emitted from a laser is injected into a Mach-Zehnder or electro-absorption amplitude modulator In this case microwave modulation is also applied to the modulator through a driver circuit

After passing into an optical fiber the optical intensity modulation only is detected via a photodetector As in the previous diagram the detected microwave signal is amplified in a low-noise amplifier

Laser

Driver

Optical fiber Photodetector

Low noise amplifier

Microwave or UWB Microwave or UWB

λ = 155 or 13 or 08 μm

Amplitude modulation Direct detection

General Points 5

Figure 12 Diagram of externally modulated microwave optical link

13 Signal to transmit

131 Microwave signal

The first type of transmitted signal is a signal that constitutes a microwave frequency reference It can be used in offset aerial systems or active phased-array antenna After its reflection from a moving object the microwave signal emitted from an antenna can shift in frequency (Doppler modulation) and it is the spectral purity of the microwave that determines the minimum observed frequency shift and therefore the minimum relative speed of the moving object The spectral purity and degradation after transmission of the microwave by optical links must be watched closely to distinguish the frequency shift

132 Microwave carrier for a digital signal

If the microwave signal serves as a carrier for a digital signal this carrier is previously modulated All the modulation techniques normally used such as amplitude frequency phase OFDM and combined amplitude-phase modulation (QAM) or more complex techniques can be considered such as those used in GSM GPRS EDGE and UMTS for mobile telephones or such as Bluetooth Wi-Fi and Wimax for data transmission These modulations are generally carried out on single sideband (SSB) When microwave signal modulation is implemented in phase or frequency spectral purity is also of great importance

Laser

Amplifier or driver

Optical fiber

λ = 155 or 13 or 08 μm

Microwave or UWB

Optical modulator MZ or EA

Amplitude modulation

Photodetector

Low noise amplifier

Microwave or UWB

Direct detection

6 Microwave Photonic Links

133 UWB signal

Another signal category is available for transmission by fiber optics These signals are relevant to UWB techniques without carriers and with the spectrum in the microwave region or up-converted to a millimeter-wave carrier UWB wireless links are largely used over short distances The optical fibers are particularly indicated to enable extensions of such networks

134 Optical carrier

Microwave signals can carry analog information (frequency shift due to the Doppler effect) or they can be modulated by a digital signal or be constituted of UWB signals which are themselves digitally modulated All these microwave signals must be up-converted to an optical carrier This transfer exclusively occurs by intensity modulation One of the advantages of this modulation is that the microwave signal can be recovered in a simple photodetection unit permitting the elimination of possible frequency fluctuations of the optical carrier Loss of sensitivity resulting from direct detection does not occur if the optical wavelength allows us to insert an optical amplifier or if the link is very short Usually this modulation is double sideband (DSB) especially if the modulation occurs directly in the laser but for slightly longer links this type of modulation can lead to extinction phenomena A single sideband modulation can hence be considered but this modulation must be carried out by an external modulator

135 Summary

The complexity of microwave photonic links comes from the stacking of an optical carrier and microwave or UWB subcarrier The optical carrier is exclusively intensity modulated whereas the microwave subcarrier can be modulated following all known modulation types amplitude frequency phase or their combination including a frequency shift due to the Doppler effect All these modulations can be recovered via photodetection

The use of microwave optical links will increase as the transmitted signals will be numerous and emitted in parallel communications and the data rates will increase accordingly Thus telecommunication optical

Table of Contents

Preface xiii

Abbrevation Glossary xvii

Chapter 1 General Points 1

11 Microwave photonic links 1 12 Link description 4 13 Signal to transmit 5

131 Microwave signal 5 132 Microwave carrier for a digital signal 5 133 UWB signal 6 134 Optical carrier 6 135 Summary 6

14 Limitations of microwave photonic links 7 141 Limitations due to the materials constituting the different elements 7 142 Noise sources in microwave photonic links 8 143 Nonlinearities 13

15 The components and characteristics of microwave photonic links 13

Chapter 2 Generation and Modulation of Light 15

21 Laser 15 211 General points 15 212 Semiconductor laser structure and optical gain in the active zone 17 213 Operation of a Fabry-Perot laser 19

vi Microwave Photonic Links

214 Optical confinement factor and rate equations 21 215 Static mode of laser operation (or CW mode of operation) 24 216 Dynamic mode of laser operation RF small signal response 26 217 RIN laser noise 28 218 Increase in 1f of RIN and superposition of a small signal and noise 31 219 Different laser configurations 32 2110 CAD laser models 41 2111 Laser measurements and temperature stabilization 47

22 Electro-optic modulator EOM 49 221 General physical principles 50 222 Pockels or linear electro-optical effect 50 223 Mach-Zehnder electro-optic modulator 53 224 Single-Drive MZM one driving electrode 55 225 Dual-drive MZM two driving electrodes 69 226 Real Mach-Zehnder modulator characteristics and performances 71 227 Mach-Zehnder modulator technology 73

23 Electro-absorption modulator EAM 75 231 Electro-absorption effect 75 232 FKE 80 233 Stark effect 80 234 Quantum well structures 82 235 MEA operation 82 236 Characteristics of an EAM 85 237 EML EAM integrated to a DFB laser 86 238 EAM electrical modeling for ultra-fast signal simulation 87

Chapter 3 Optical Fibers and Amplifiers 93 31 Optical fibers 93

311 General 93 312 Material attenuation 96 313 Material refraction index and dispersion 98 314 Total reflection numerical aperture transmitted maximum frequency 100 315 Step-index fiber 105 316 Graded index fiber 107 317 Single-mode fiber 110 318 Plastic optical fibers 114

Table of Contents vii

32 Optical amplifiers 118 321 Semiconductor optical amplifiers SOA 119 322 EDFAs 120

33 Appendix modal analysis of propagation in a fiber 122 331 Maxwell equations 122 332 Maxwell equations in a cylindrical fiber 123 333 Continuity and characteristic equation conditions 127 334 Research of different propagation modes 128 335 Approximation of linearly polarized modes 132

Chapter 4 Photodetectors 137 41 Photodetector definition 137 42 Photodiodes 138

421 Presentation 138 422 Light absorption in a semiconductor 139 423 p-i-n photodiode 142 424 Metal-semiconductor-metal or MSM photodiode 145 425 Equivalent circuits for p-i-n and MSM photodiodes 147 426 Nonlinearities 147 427 UTC photodiodes 149 428 Charge compensation 150 429 Partially depleted absorption zone 151 4210 Lateral lighting 152 4211 Lateral lighting progressive wave structure 153 4212 Lateral lighting periodic structures 156 4213 Resonant optical cavity photodetector 157 4214 Diluted waveguides and evanescent mode coupling 160 4215 Summary 161

43 Phototransistors 163 431 Bipolar or field-effect phototransistors 163 432 GaAlAsGaAs and InGaPGaAs phototransistors 165 433 InPInGaAs phototransistors 167 434 SiSiGe phototransistors 172 435 Resonant optical cavities for phototransistors 176 436 Phototransistor simulations and models 176 437 Influence of the base load impedance 180 438 Summary 183

44 Appendix 184 441 Lattice matched layers pseudomorphic layer metamorphic layer 184 442 Velocity overshoot effect 186 443 Heterojunction bipolar phototransistor 188

viii Microwave Photonic Links

Chapter 5 Performance of Microwave Photonic Links 193

51 Microwave photonic links diagrams and definitions 193 511 Direct modulation link diagram and definitions 193 512 External modulation link diagram and definitions 197 513 Simplified link diagram and first gain computation 198

52 Optomicrowave S-parameters and gains of each photonic link component 201

521 Introduction 201 522 Optomicrowave laser S-parameters and optomicrowave gain 202 523 Optomicrowave optical fiber S-parameters and optomicrowave gain 203 524 Photodiode optomicrowave S-parameters and gain 204 525 Localized component external modulator optomicrowave S-parameters and gain 205 526 Distributed component external modulator optomicrowave S-parameters and gain 207 527 Summary of all S-parameters and optomicrowave gain 209

53 Microwave photonic links optomicrowave S-parameters and gains 210

531 Direct modulation microwave photonic link S-parameters 210 532 Direct modulation microwave photonic link gains 211 533 Localized external modulator microwave photonic link S-parameters 212 534 Localized external modulator microwave photonic link gains 213 535 Distributed external modulator microwave photonic link S-parameters 213 536 Distributed external modulator microwave photonic link gains 214 537 Link gain computation generalization 215

54 Comparison of different link gains 218 541 Direct modulation link gain computation 218 542 Localized external modulator link gain computation 219 543 Distributed external modulator link gain computations 220

55 Direct modulation microwave photonic link optomicrowave noise figures 221

551 Link noise figure diagram and computation method 221 552 Laser noise figure 223 553 Optical fiber noise figure 223 554 Photodiode noise figure 224

Table of Contents ix

555 Direct modulation link noise figure 224 556 Matching effect at the input of a direct modulation link 225 557 Generalization of a link noise figure computation 226

56 External modulation microwave photonic link optomicrowave noise figure 227

561 Equivalent diagram and steps recall 227 562 Localized external modulator noise figure 227 563 Distributed external modulator noise figure 228 564 New evaluation of photodetector noise figure 230 565 Localized external modulator microwave photonic link noise figure 231 566 Matched input localized external modulator microwave photonic link noise figure 231 567 Distributed external modulator microwave photonic link noise figure 232

57 Comparisons of different link noise figures 232 571 Evaluation of direct modulation link noise figure 232 572 Evaluation of localized external modulator link noise figure 234 573 Evaluation of matched input localized external modulator link noise figure 235 574 Evaluation of distributed external modulator link noise figures 236 575 Output noise power 237 576 Some effectively measured noise figure values 239

58 Microwave photonic link nonlinearity distortion phenomena 241

581 Single microwave signal nonlinearity 241 582 Several input microwave signals nonlinearity 242 583 Wideband input signal nonlinearity 244 584 Nonlinearity combination of microwave photonic link components 245

59 Microwave photonic link interference-free dynamic range 246 591 Single input signal microwave photonic link interference-free dynamic range 246 592 Several-input signal microwave photonic link interference-free dynamic range 247 593 Some effectively measured interference-free dynamic range values 249

510 Appendix 250 5101 Relation between parameters S Z Y and ABCD 250 5102 Equation choice for the computation of microwave photonic link optomicrowave noise figure 251

x Microwave Photonic Links

5103 Calculation of a two-input signal microwave photonic link interference-free dynamic range 261

Chapter 6 Complement to Microwave Photonic Link Performances 267

61 Microwave signal attenuation during double sideband modulation 267

611 Double sideband modulation recall 267 612 Recall of single-mode optical fiber propagation characteristics 268 613 Optical fiber double sideband modulated signal propagation 270 614 Double sideband-modulated signal photodetection at the optical fiber output 271

62 Modulator structures for optical carrier or high and low sideband removal 273

621 Optical modulation recall 273 622 Single sideband or carrier suppression optical modulators 274 623 Carrier suppression and single sideband optical modulator 277

63 Degradation of a microwave signal spectral purity by an optical link 280

631 Phenomenon description 280 632 Some definitions concerning the noise around a microwave carrier 281 633 Amplitude and phase noise in an optical link 282 634 Phase noise computation of a microwave signal transmitted by an optical link 284 635 Amplitude noise computation of a microwave signal transmitted by an optical link 286

Chapter 7 Electronic Amplifiers in Microwave Photonic Links 289

71 Electronic amplifiers in optical links 289 72 Amplifiers in the optical link emitter 289

721 Different roles of electronic amplifiers on optical emitter 289 722 Emission modulator or laser input amplifiers 290

73 Receiver amplifiers at the photodetector output 293 731 General points 293 732 Transimpedance amplifiers 294 733 Distributed amplifiers 296

Table of Contents xi

734 Combination of transimpedance and distributed amplifiers 298 735 Narrowband amplifiers 298 736 Preamplifier after a phototransistor 299 737 Other circuits after a phototransistor 299

74 Appendix analog and microwave amplifiers 300 741 General points 300 742 Analog amplifiers 300 743 Microwave amplifier expression of transistor reflection coefficients 304 744 Microwave amplifiers gain expressions 306 745 Unilateralized transistor model two-port network matching computation 307 746 Non-unilateralized transistor general case of a transistor with S12 0 312 747 Low noise amplifier 313 748 General models of low signal microwave amplifiers 315

Chapter 8 Simulation and Measurement of Microwave Photonic Links 321

81 State of the art and context 321 811 Objective 321 812 Choice of simulation software 321 813 Different ADS simulation techniques 322

82 Microwave optical link models 324 821 Two-port network approach 324 822 Electro-optic transducer the laser 325 823 Transmission guiding the optical fiber 329 824 The optoelectric transducer the photodiode 334

83 Nonlinearity effects in the link 337 831 Nonlinearity sources 337 832 1 dB compression point and first-order dynamic of the link 338 833 Third-order intermodulation and third-order interference-free dynamic range of the link 339

84 Link noise modeling 340 841 Noise in the laser 340 842 The optical fiber 342 843 Noise in the photodiode 342 844 Direct modulation link noise figure 343 845 Noise power at the receiver 344

xii Microwave Photonic Links

85 Other types of modulation of signals transmitted on an optical fiber 348

851 Ultra-wideband signal modulation 348 852 External modulation 353 853 Generation of microwave signal by frequency beating 358

86 Conclusion 361 87 Appendix 362

871 MB-OOK modulation 362 872 OFDM modulation 363

Bibliography 367

Index 393

Preface

Two important areas of applications of microwave photonic links are electromagnetic sensors and radio-over-fiber (RoF) applications

Electromagnetic sensor microwave systems of the future will principally use active phased-array antennas The development will be determined by reliability requirements resistance to interference and total emission flexibility of the beamforming networks This type of antenna would therefore be used in a diverse range of applications eg radar communication and countermeasures To satisfy this multifunctional approach it will be necessary to distribute these antennas all over the surface area of strategic platforms (planes drones boats etc) While on the ground the multistatic mode of operation will force multiple antennas to be deported from their processing unit

This will require links with very low loss and noise enabling remote-control antennas and the distribution and processing of very wide bandwidth microwave signals (typically 1-20 GHz 40 GHz will be seen in the future)

Currently the maturity and performance notably in terms of spectral purity and opto-electronic component linearity are such that it is possible to consider both optical distribution and processing of these electrical signals Thus the optical transmission of microwaves offers as well as propagation of broad frequency bands advantages regarding weight volume and flexibility characterized by a decrease in the weight of the wiring by 90 in comparison to coaxial cables and thus insensitivity to electromagnetic perturbation All of which will enable the introduction of new concepts in microwave systems based on optical architecture

xiv Microwave Photonic Links

Several sensor radar systems have been designed and produced in France the United States the UK and Italy and photonic technology for the distribution of microwave signals is already being used for ground airborne and aerospace applications

Fiber-optic distribution network technology is an emergence of this technology platform in reference to the design of opto-electronic links for the transmission of microwave and digital signals This optical wiring aims to replace coaxial wiring for onboard electronics interconnections Here the term transmission is taken in the sense that microwave transmissions on optical carriers are in-phase

These functions require the design of emitting and receiving opto-electronic modules the integration of both high thermal stability multiplexing demultiplexing functions and single-mode connectors either point to point or multipoints

Another area of reference is the optical control of the phase andor delay of microwave signals and their applications to electromagnetic sensor systems This occurs by the design of ultrafast opto-electronic multi-chip modules incorporating the optically-controlled switching the control synthesis of time delay systems and the multiwave laser sources

Amongst the most promising technologies is the synthesis of mono- and bidimensional time-delays for the single and multiple beamforming in receiver and emitter the ultraprecise (picoseconds) time synchronization of distributed electromagnetic sensors the time-delay control (precision in the order of picoseconds) of very wide bandwidth microwave signals to measure the arrival direction and the waveshape generation

Another important area involving all RoF applications is the extensive development of wireless networks using microwaves or ultra-wideband signals This is achieved by providing optical tunnels capable of reaching all areas of a company university etc or all the rooms of a house whilst benefiting from the very low loss associated with fiber optics

In their work titled ldquoMicrowave Photonic Linksrdquo C Rumelhard C Algani and A-L Billabert studied and developed models of the components and photonic functions in microwave applications thus laying the foundation for research into microwave photonic links in order to allow the

Preface xv

integration of these components in electromagnetic sensors systems The components and functions addressed range from optical sources (modulated semiconductor lasers or externally modulated continuous lasers) to photodetectors optical fibers and optical amplifiers

This work focuses upon optical components their transfer functionality and their modeling in terms of microwave components in order to create an electrical model of microwave photonic links In order to achieve this level of complexity a number of modeling approaches have been created by the authors to elucidate the influences of the constituent components of microwave photonic links

Because the advancement of opto-electronics photonics and microwaves is possible by the unification of modeling approaches there is no doubt that such works will be referenced by students but also by design engineers and architects of electromagnetic sensor systems who will incorporate this new technology into their designs

This is to the authorrsquos knowledge the first work addressing the description and modeling of microwave photonic link technology with an educational approach to physical phenomena and new approaches to modeling microwave photonic components

Jean Chazelas Scientific Director

Thales Aeronautics Division

Abbreviation Glossary

AC Alternating Current

ACPR Adjacent Channel Power Ratio

ADP Ammonium dihydrogen phosphate

ADS Advanced Design System

AlGaAs Aluminum gallium arsenide

AM Amplitude Modulation

AM-DD Amplitude Modulation ndash Direct Detection

ASE Amplified Spontaneous Emission

BER Bit Error Rate

BH Buried Heterostructure

BiCMOS Bipolar Complementary Metal Oxide Semiconductor

BILBAO Borne drsquoinfrastructures large bande avec accegraves optique (Wideband infrastructure base with optical access)

CAD Computer-aided design

CdS Cadmium sulfide

CEA-Leti Commissariat agrave lrsquoeacutenergie atomique (Atomic energy commission)

CMOS Complementary metal-oxide-semiconductor

CNAM Conservatoire national des arts et meacutetiers

CPW Coplanar waveguide

xviii Microwave Photonic Links

DBR Distributed Bragg reflector

DC Direct current

DD-MZM Dual drive-MZM

DFA Doped fiber amplifier

DFB Distributed feedback laser

DFT Discrete Fourier transform

EO Electricoptic

EAM Electro-absorption modulator

EDFA Erbium-doped fiber amplifier

EEL Edge emitting laser

EML Electro-absorption modulated laser

EMT Electromagnetic transverse

EOM Electro-optic modulator

ER Extinction ratio

ESYCOM Equipe systegravemes de communications et microsystegravemes (Communications and microsystems team)

ET Electric transverse

EVM Error vector magnitude

FCC Federal communications commission

FET Field-effect transistor

FKE Franz-Keldysh effect

FT RampD France Telecom Research amp Development

GaAs Galium arsenide

GaP Galium phosphide

Ge Germanium

GRINSCH Graded index separate confinement heterostructure

HB Harmonic balance

HBT Heterojunction bipolar transistor

Abbreviation Glossary xix

HEMT High electron mobility transistor

HFET Heterojunction field-effect transistor

HFSS High frequency simulation system

HPT Heterojunction bipolar phototransistor

IDFT Inverse discrete Fourier transform

IM-DD Intensity modulation-direct detection

IMEP Institut de microeacutelectronique eacutelectromagneacutetisme et optique (Institute of microelectronics electromagnetism and optics)

InAs Indium arsenide

InGaAs Indium gallium arsenide

InGaP Indium gallium phosphide

InP Indium phosphide

IR-UWB Impulse Radio ndash Ultra Wideband

KDP Potassium dihydrogen phosphate

LAHC Laboratoire drsquohyperfreacutequences et de caracteacuterisation (hyperfrequency and characterization laboratory)

LASER Light amplifier by stimulated emission of radiation

LF Low frequency

LiNbO3 Lithium niobate

LiTaO3 Lithium tantalate

MAG Maximum available gain

MASER Microwave amplifier by stimulated emission of radiation

MB-OFDM Multi-band ndash orthogonal frequency division modulation

MB-OOK Multi-band on off keying

MEMS Micro-electro-mechanical systems

MESFET Metal semiconductor field-effect transistor

MMIC Monolithic microwave integrated circuit

MODFET Modulation-doped field-effect transistor

MQW-EAM Multi-quantum well-EAM

xx Microwave Photonic Links

MSM Metal semiconductor metal

MZM Modulator Mach-Zehnder

NdYAG Neodymium-doped yttrium aluminum garnet

NF Noise factor Noise figure

nOI n order intermodulation

nOIP n order intercept point

NRA National Research Agency

OE Opticelectric

OEIC Optoelectronic integrated circuit

OEMMIC Optoelectronic millimeter-wave monolithic integrated circuit

OFDM Orthogonal frequency division modulation

PDFA Praseodymium-doped fiber amplifier

PDG Biased-dependent gain

PM Phase modulation

PMMA Poly(methyl methacrylate)

PRBS Pseudo-random bit sequence

PSK Phase-shift keying

QAM Quadrature amplitude modulation

QCSE Quantum confined stark effect

QW-EAM Quantum well-EAM

RCEPD Resonant cavity enhanced photodetectors

RFT Rapid Fourier transform

RIN Relative intensity noise

RoF Radio over fiber

SD-MZM Single drive ndashMZM

Si Silicon

SiGe Silicon-germanium

SiMOX Separation by implantation of oxygen

Abbreviation Glossary xxi

SiO2 Silicon dioxide

SOA Semiconductor optical amplifier

SOC System on a chip

SOI Substrate on insulator

TDFA Thulium-doped fiber amplifier

TEGFET Two-dimensional electron gas field-effect transistor

TW-MZM Travelling wave-MZM

UTC Uni-travelling carrier

UWB Ultra-wideband

VCSEL Vertical-cavity surface-emitting laser

VCSOA Vertical-cavity semiconductor optical amplifier

VMDP Velocity matched distributed photodetector

WDM Wavelength division multiplexing

YDFA Ytterbium-doped fiber amplifier

ZnS Zinc sulfide

Chapter 1

General Points

11 Microwave photonic links

All signals generated or observed due to human activity (measurement of different physical values remote control files sounds images etc) can be transformed into analog electrical signals These electrical signals can be processed or transmitted as they are but in most cases they are digitized beforehand Once digitized these signals have different forms regarding the digital coding or error-correcting algorithms used and protocols employed in the transmission systems To be processed or transmitted these analog or digital signals can use different mediums

If the transmission is performed via metallic lines or cables digital signals directly enter these lines or they modulate more or less complex subcarriers (ADSL Ethernet)

If transmission occurs with a radiowave a high-frequency carrier must be available Due to the congestion of the wireless spectrum carriers are now principally microwaves ie with frequencies of 1 to 100 GHz (GSM UMTS Wi-Fi Wimax etc) Wireless transmission can also be performed by very short pulses having a wide spectrum range including the microwave spectrum or these pulses can modulate a carrier in the millimeter wave spectrum This technique is known as ultra-wideband (UWB) [YAO 09]

If transmission is via fiber optics digital signals modulate one or several optical carriers (amplitude or soliton modulation) which are themselves

2 Microwave Photonic Links

transmitted over hundreds of kilometers on optical fibers This is the case for all passive optical networks (PON) and their different transmission protocols [LEC 97]

From these definitions the distinctive feature of microwave photonic links is to transmit a microwave signal analogically or for it be digitally modulated This microwave signal is transferred to an optical carrier which is guided with minimum loss by an optical fiber The microwave signal is then picked up by a photodetector at the end of the fiber

One of the first applications of microwave optical links was the distribution of the microwave carrier in radar or radio-astronomy systems comprising offset aerials or active phased-array antennas which benefited from the low weight and low volume of the fiber optics [COX 97 DEC 98]

Another important area comprises all radio over fiber (RoF) applications consisting of the extension of wireless networks using microwaves or UWB waves The optical tunnels produced are capable of reaching all rooms or buildings of a company university or diverse institutions or all the rooms of a house whilst benefiting from the very low loss associated with fiber optics [FRI 02]

Amongst the applications of RoF a promising domain is in the connection of internet transmission networks to the home These connections are increasingly popular with ever-increasing speeds (1 Gbs) due to fiber optics reaching households (fiber to the home or FTTH) whereby the house itself becomes a high-speed local network In this local network the signal distribution in each room is achieved by a 60 GHz millimeter-wave (wireless personal area network or WPAN) which stays confined in the room due to the extremely fast attenuation at this frequency All rooms are linked to each other by a network of passive fiber optics which extends the millimeter-wave UWB signal throughout the whole house (ultra broadband wireless home area network or UBB-WHAN) Examples of millimeter-wave over optical transmissions are presented in [CHU 07 KIM 04 WEI 08] and a demonstration of a UBB-WHAN with an up and down link is described in [HUC 08]

The length of a link ranges from 10 m to 1 km allowing several fiber types to be used (single mode or multimode silica or plastic) and several optical wavelengths ranging from 06 to 155 μm The light undergoes intensity modulation the signal is received via photodetection In just a few

General Points 3

years rates have risen from around 10 Mbs on carriers of a few gigahertz to rates of 1 or 10 Gbs on 60 GHz for microwave carriers

A microwave photonic link is constituted of three parts

ndash a coherent light source a laser that emits an optical carrier the intensity of which is directly modulated inside the laser or externally by an optical modulator In the case of external modulation the amplitude modulation is performed by a Mach-Zehnder or an electro-absorption modulator

ndash the modulated light is then transported by single or multi-mode optical fiber [GOM 08 KOO 08] made of silica or plastic [KOI 06] This part may include an optical amplification

ndash the modulated light is finally photodetected in a photodetector consisting of a photodiode or a phototransistor

After some deliberation regarding coherent and incoherent optical links [HAL 82] the solution finally adopted for these links was ldquointensity modulation (IM) direct detection (DD)rdquo As this is recalled in [COX 06] in this type of link the depth of optical modulation is sufficiently weak that we can initially use small signal or linear techniques for each aspect Because the signals applied to links or extracted from them are in microwaves the variables characterizing these systems are S-parameters gains and noise factors Also nonlinearities and hence intermodulation produced by each component on the signal introduced in the link must be considered The combination of these different characteristics leads to the notion of interference-free dynamic range (IFDR) This shall be evaluated regarding the properties of each element in the chapters concerning overall performances of such links

As a link includes electrical-to-optical optical-to-electrical and even optical-to-optical transducers each of the magnitudes in terms of S-parameters gains and noise factors should be presented in the form of optomicrowave magnitudes This aspect forces harmonization of notions from the optical optoelectronic and microwave disciplines This is described in Chapter 5

The term used initially to describe these links was ldquomicrowave optical linksrdquo However the techniques used have gradually distanced themselves from proper optical and optoelectronic techniques so that the more specific term ldquomicrowave photonic linksrdquo has been progressively used [SEE 02]

4 Microwave Photonic Links

12 Link description

Figures 11 and 12 represent a general diagram of an IM-DD microwave optical link

Figure 11 Diagram of directly modulated microwave optical link

Figure 11 represents a direct modulation link A laser emits a light of wavelength 08 or 13 or 155 μm this laser is modulated by a microwave signal (which is possibly itself modulated) through a driver circuit The modulated light enters an optical fiber coupled to a photodetector that detects the microwave modulation signal The optical modulation can have an amplitude frequency and phase However direct photodetection detects only the modulation in amplitude The detected microwave signal is then amplified by a low-noise amplifier

Figure 12 represents an external modulation link This time a light emitted from a laser is injected into a Mach-Zehnder or electro-absorption amplitude modulator In this case microwave modulation is also applied to the modulator through a driver circuit

After passing into an optical fiber the optical intensity modulation only is detected via a photodetector As in the previous diagram the detected microwave signal is amplified in a low-noise amplifier

Laser

Driver

Optical fiber Photodetector

Low noise amplifier

Microwave or UWB Microwave or UWB

λ = 155 or 13 or 08 μm

Amplitude modulation Direct detection

General Points 5

Figure 12 Diagram of externally modulated microwave optical link

13 Signal to transmit

131 Microwave signal

The first type of transmitted signal is a signal that constitutes a microwave frequency reference It can be used in offset aerial systems or active phased-array antenna After its reflection from a moving object the microwave signal emitted from an antenna can shift in frequency (Doppler modulation) and it is the spectral purity of the microwave that determines the minimum observed frequency shift and therefore the minimum relative speed of the moving object The spectral purity and degradation after transmission of the microwave by optical links must be watched closely to distinguish the frequency shift

132 Microwave carrier for a digital signal

If the microwave signal serves as a carrier for a digital signal this carrier is previously modulated All the modulation techniques normally used such as amplitude frequency phase OFDM and combined amplitude-phase modulation (QAM) or more complex techniques can be considered such as those used in GSM GPRS EDGE and UMTS for mobile telephones or such as Bluetooth Wi-Fi and Wimax for data transmission These modulations are generally carried out on single sideband (SSB) When microwave signal modulation is implemented in phase or frequency spectral purity is also of great importance

Laser

Amplifier or driver

Optical fiber

λ = 155 or 13 or 08 μm

Microwave or UWB

Optical modulator MZ or EA

Amplitude modulation

Photodetector

Low noise amplifier

Microwave or UWB

Direct detection

6 Microwave Photonic Links

133 UWB signal

Another signal category is available for transmission by fiber optics These signals are relevant to UWB techniques without carriers and with the spectrum in the microwave region or up-converted to a millimeter-wave carrier UWB wireless links are largely used over short distances The optical fibers are particularly indicated to enable extensions of such networks

134 Optical carrier

Microwave signals can carry analog information (frequency shift due to the Doppler effect) or they can be modulated by a digital signal or be constituted of UWB signals which are themselves digitally modulated All these microwave signals must be up-converted to an optical carrier This transfer exclusively occurs by intensity modulation One of the advantages of this modulation is that the microwave signal can be recovered in a simple photodetection unit permitting the elimination of possible frequency fluctuations of the optical carrier Loss of sensitivity resulting from direct detection does not occur if the optical wavelength allows us to insert an optical amplifier or if the link is very short Usually this modulation is double sideband (DSB) especially if the modulation occurs directly in the laser but for slightly longer links this type of modulation can lead to extinction phenomena A single sideband modulation can hence be considered but this modulation must be carried out by an external modulator

135 Summary

The complexity of microwave photonic links comes from the stacking of an optical carrier and microwave or UWB subcarrier The optical carrier is exclusively intensity modulated whereas the microwave subcarrier can be modulated following all known modulation types amplitude frequency phase or their combination including a frequency shift due to the Doppler effect All these modulations can be recovered via photodetection

The use of microwave optical links will increase as the transmitted signals will be numerous and emitted in parallel communications and the data rates will increase accordingly Thus telecommunication optical

vi Microwave Photonic Links

214 Optical confinement factor and rate equations 21 215 Static mode of laser operation (or CW mode of operation) 24 216 Dynamic mode of laser operation RF small signal response 26 217 RIN laser noise 28 218 Increase in 1f of RIN and superposition of a small signal and noise 31 219 Different laser configurations 32 2110 CAD laser models 41 2111 Laser measurements and temperature stabilization 47

22 Electro-optic modulator EOM 49 221 General physical principles 50 222 Pockels or linear electro-optical effect 50 223 Mach-Zehnder electro-optic modulator 53 224 Single-Drive MZM one driving electrode 55 225 Dual-drive MZM two driving electrodes 69 226 Real Mach-Zehnder modulator characteristics and performances 71 227 Mach-Zehnder modulator technology 73

23 Electro-absorption modulator EAM 75 231 Electro-absorption effect 75 232 FKE 80 233 Stark effect 80 234 Quantum well structures 82 235 MEA operation 82 236 Characteristics of an EAM 85 237 EML EAM integrated to a DFB laser 86 238 EAM electrical modeling for ultra-fast signal simulation 87

Chapter 3 Optical Fibers and Amplifiers 93 31 Optical fibers 93

311 General 93 312 Material attenuation 96 313 Material refraction index and dispersion 98 314 Total reflection numerical aperture transmitted maximum frequency 100 315 Step-index fiber 105 316 Graded index fiber 107 317 Single-mode fiber 110 318 Plastic optical fibers 114

Table of Contents vii

32 Optical amplifiers 118 321 Semiconductor optical amplifiers SOA 119 322 EDFAs 120

33 Appendix modal analysis of propagation in a fiber 122 331 Maxwell equations 122 332 Maxwell equations in a cylindrical fiber 123 333 Continuity and characteristic equation conditions 127 334 Research of different propagation modes 128 335 Approximation of linearly polarized modes 132

Chapter 4 Photodetectors 137 41 Photodetector definition 137 42 Photodiodes 138

421 Presentation 138 422 Light absorption in a semiconductor 139 423 p-i-n photodiode 142 424 Metal-semiconductor-metal or MSM photodiode 145 425 Equivalent circuits for p-i-n and MSM photodiodes 147 426 Nonlinearities 147 427 UTC photodiodes 149 428 Charge compensation 150 429 Partially depleted absorption zone 151 4210 Lateral lighting 152 4211 Lateral lighting progressive wave structure 153 4212 Lateral lighting periodic structures 156 4213 Resonant optical cavity photodetector 157 4214 Diluted waveguides and evanescent mode coupling 160 4215 Summary 161

43 Phototransistors 163 431 Bipolar or field-effect phototransistors 163 432 GaAlAsGaAs and InGaPGaAs phototransistors 165 433 InPInGaAs phototransistors 167 434 SiSiGe phototransistors 172 435 Resonant optical cavities for phototransistors 176 436 Phototransistor simulations and models 176 437 Influence of the base load impedance 180 438 Summary 183

44 Appendix 184 441 Lattice matched layers pseudomorphic layer metamorphic layer 184 442 Velocity overshoot effect 186 443 Heterojunction bipolar phototransistor 188

viii Microwave Photonic Links

Chapter 5 Performance of Microwave Photonic Links 193

51 Microwave photonic links diagrams and definitions 193 511 Direct modulation link diagram and definitions 193 512 External modulation link diagram and definitions 197 513 Simplified link diagram and first gain computation 198

52 Optomicrowave S-parameters and gains of each photonic link component 201

521 Introduction 201 522 Optomicrowave laser S-parameters and optomicrowave gain 202 523 Optomicrowave optical fiber S-parameters and optomicrowave gain 203 524 Photodiode optomicrowave S-parameters and gain 204 525 Localized component external modulator optomicrowave S-parameters and gain 205 526 Distributed component external modulator optomicrowave S-parameters and gain 207 527 Summary of all S-parameters and optomicrowave gain 209

53 Microwave photonic links optomicrowave S-parameters and gains 210

531 Direct modulation microwave photonic link S-parameters 210 532 Direct modulation microwave photonic link gains 211 533 Localized external modulator microwave photonic link S-parameters 212 534 Localized external modulator microwave photonic link gains 213 535 Distributed external modulator microwave photonic link S-parameters 213 536 Distributed external modulator microwave photonic link gains 214 537 Link gain computation generalization 215

54 Comparison of different link gains 218 541 Direct modulation link gain computation 218 542 Localized external modulator link gain computation 219 543 Distributed external modulator link gain computations 220

55 Direct modulation microwave photonic link optomicrowave noise figures 221

551 Link noise figure diagram and computation method 221 552 Laser noise figure 223 553 Optical fiber noise figure 223 554 Photodiode noise figure 224

Table of Contents ix

555 Direct modulation link noise figure 224 556 Matching effect at the input of a direct modulation link 225 557 Generalization of a link noise figure computation 226

56 External modulation microwave photonic link optomicrowave noise figure 227

561 Equivalent diagram and steps recall 227 562 Localized external modulator noise figure 227 563 Distributed external modulator noise figure 228 564 New evaluation of photodetector noise figure 230 565 Localized external modulator microwave photonic link noise figure 231 566 Matched input localized external modulator microwave photonic link noise figure 231 567 Distributed external modulator microwave photonic link noise figure 232

57 Comparisons of different link noise figures 232 571 Evaluation of direct modulation link noise figure 232 572 Evaluation of localized external modulator link noise figure 234 573 Evaluation of matched input localized external modulator link noise figure 235 574 Evaluation of distributed external modulator link noise figures 236 575 Output noise power 237 576 Some effectively measured noise figure values 239

58 Microwave photonic link nonlinearity distortion phenomena 241

581 Single microwave signal nonlinearity 241 582 Several input microwave signals nonlinearity 242 583 Wideband input signal nonlinearity 244 584 Nonlinearity combination of microwave photonic link components 245

59 Microwave photonic link interference-free dynamic range 246 591 Single input signal microwave photonic link interference-free dynamic range 246 592 Several-input signal microwave photonic link interference-free dynamic range 247 593 Some effectively measured interference-free dynamic range values 249

510 Appendix 250 5101 Relation between parameters S Z Y and ABCD 250 5102 Equation choice for the computation of microwave photonic link optomicrowave noise figure 251

x Microwave Photonic Links

5103 Calculation of a two-input signal microwave photonic link interference-free dynamic range 261

Chapter 6 Complement to Microwave Photonic Link Performances 267

61 Microwave signal attenuation during double sideband modulation 267

611 Double sideband modulation recall 267 612 Recall of single-mode optical fiber propagation characteristics 268 613 Optical fiber double sideband modulated signal propagation 270 614 Double sideband-modulated signal photodetection at the optical fiber output 271

62 Modulator structures for optical carrier or high and low sideband removal 273

621 Optical modulation recall 273 622 Single sideband or carrier suppression optical modulators 274 623 Carrier suppression and single sideband optical modulator 277

63 Degradation of a microwave signal spectral purity by an optical link 280

631 Phenomenon description 280 632 Some definitions concerning the noise around a microwave carrier 281 633 Amplitude and phase noise in an optical link 282 634 Phase noise computation of a microwave signal transmitted by an optical link 284 635 Amplitude noise computation of a microwave signal transmitted by an optical link 286

Chapter 7 Electronic Amplifiers in Microwave Photonic Links 289

71 Electronic amplifiers in optical links 289 72 Amplifiers in the optical link emitter 289

721 Different roles of electronic amplifiers on optical emitter 289 722 Emission modulator or laser input amplifiers 290

73 Receiver amplifiers at the photodetector output 293 731 General points 293 732 Transimpedance amplifiers 294 733 Distributed amplifiers 296

Table of Contents xi

734 Combination of transimpedance and distributed amplifiers 298 735 Narrowband amplifiers 298 736 Preamplifier after a phototransistor 299 737 Other circuits after a phototransistor 299

74 Appendix analog and microwave amplifiers 300 741 General points 300 742 Analog amplifiers 300 743 Microwave amplifier expression of transistor reflection coefficients 304 744 Microwave amplifiers gain expressions 306 745 Unilateralized transistor model two-port network matching computation 307 746 Non-unilateralized transistor general case of a transistor with S12 0 312 747 Low noise amplifier 313 748 General models of low signal microwave amplifiers 315

Chapter 8 Simulation and Measurement of Microwave Photonic Links 321

81 State of the art and context 321 811 Objective 321 812 Choice of simulation software 321 813 Different ADS simulation techniques 322

82 Microwave optical link models 324 821 Two-port network approach 324 822 Electro-optic transducer the laser 325 823 Transmission guiding the optical fiber 329 824 The optoelectric transducer the photodiode 334

83 Nonlinearity effects in the link 337 831 Nonlinearity sources 337 832 1 dB compression point and first-order dynamic of the link 338 833 Third-order intermodulation and third-order interference-free dynamic range of the link 339

84 Link noise modeling 340 841 Noise in the laser 340 842 The optical fiber 342 843 Noise in the photodiode 342 844 Direct modulation link noise figure 343 845 Noise power at the receiver 344

xii Microwave Photonic Links

85 Other types of modulation of signals transmitted on an optical fiber 348

851 Ultra-wideband signal modulation 348 852 External modulation 353 853 Generation of microwave signal by frequency beating 358

86 Conclusion 361 87 Appendix 362

871 MB-OOK modulation 362 872 OFDM modulation 363

Bibliography 367

Index 393

Preface

Two important areas of applications of microwave photonic links are electromagnetic sensors and radio-over-fiber (RoF) applications

Electromagnetic sensor microwave systems of the future will principally use active phased-array antennas The development will be determined by reliability requirements resistance to interference and total emission flexibility of the beamforming networks This type of antenna would therefore be used in a diverse range of applications eg radar communication and countermeasures To satisfy this multifunctional approach it will be necessary to distribute these antennas all over the surface area of strategic platforms (planes drones boats etc) While on the ground the multistatic mode of operation will force multiple antennas to be deported from their processing unit

This will require links with very low loss and noise enabling remote-control antennas and the distribution and processing of very wide bandwidth microwave signals (typically 1-20 GHz 40 GHz will be seen in the future)

Currently the maturity and performance notably in terms of spectral purity and opto-electronic component linearity are such that it is possible to consider both optical distribution and processing of these electrical signals Thus the optical transmission of microwaves offers as well as propagation of broad frequency bands advantages regarding weight volume and flexibility characterized by a decrease in the weight of the wiring by 90 in comparison to coaxial cables and thus insensitivity to electromagnetic perturbation All of which will enable the introduction of new concepts in microwave systems based on optical architecture

xiv Microwave Photonic Links

Several sensor radar systems have been designed and produced in France the United States the UK and Italy and photonic technology for the distribution of microwave signals is already being used for ground airborne and aerospace applications

Fiber-optic distribution network technology is an emergence of this technology platform in reference to the design of opto-electronic links for the transmission of microwave and digital signals This optical wiring aims to replace coaxial wiring for onboard electronics interconnections Here the term transmission is taken in the sense that microwave transmissions on optical carriers are in-phase

These functions require the design of emitting and receiving opto-electronic modules the integration of both high thermal stability multiplexing demultiplexing functions and single-mode connectors either point to point or multipoints

Another area of reference is the optical control of the phase andor delay of microwave signals and their applications to electromagnetic sensor systems This occurs by the design of ultrafast opto-electronic multi-chip modules incorporating the optically-controlled switching the control synthesis of time delay systems and the multiwave laser sources

Amongst the most promising technologies is the synthesis of mono- and bidimensional time-delays for the single and multiple beamforming in receiver and emitter the ultraprecise (picoseconds) time synchronization of distributed electromagnetic sensors the time-delay control (precision in the order of picoseconds) of very wide bandwidth microwave signals to measure the arrival direction and the waveshape generation

Another important area involving all RoF applications is the extensive development of wireless networks using microwaves or ultra-wideband signals This is achieved by providing optical tunnels capable of reaching all areas of a company university etc or all the rooms of a house whilst benefiting from the very low loss associated with fiber optics

In their work titled ldquoMicrowave Photonic Linksrdquo C Rumelhard C Algani and A-L Billabert studied and developed models of the components and photonic functions in microwave applications thus laying the foundation for research into microwave photonic links in order to allow the

Preface xv

integration of these components in electromagnetic sensors systems The components and functions addressed range from optical sources (modulated semiconductor lasers or externally modulated continuous lasers) to photodetectors optical fibers and optical amplifiers

This work focuses upon optical components their transfer functionality and their modeling in terms of microwave components in order to create an electrical model of microwave photonic links In order to achieve this level of complexity a number of modeling approaches have been created by the authors to elucidate the influences of the constituent components of microwave photonic links

Because the advancement of opto-electronics photonics and microwaves is possible by the unification of modeling approaches there is no doubt that such works will be referenced by students but also by design engineers and architects of electromagnetic sensor systems who will incorporate this new technology into their designs

This is to the authorrsquos knowledge the first work addressing the description and modeling of microwave photonic link technology with an educational approach to physical phenomena and new approaches to modeling microwave photonic components

Jean Chazelas Scientific Director

Thales Aeronautics Division

Abbreviation Glossary

AC Alternating Current

ACPR Adjacent Channel Power Ratio

ADP Ammonium dihydrogen phosphate

ADS Advanced Design System

AlGaAs Aluminum gallium arsenide

AM Amplitude Modulation

AM-DD Amplitude Modulation ndash Direct Detection

ASE Amplified Spontaneous Emission

BER Bit Error Rate

BH Buried Heterostructure

BiCMOS Bipolar Complementary Metal Oxide Semiconductor

BILBAO Borne drsquoinfrastructures large bande avec accegraves optique (Wideband infrastructure base with optical access)

CAD Computer-aided design

CdS Cadmium sulfide

CEA-Leti Commissariat agrave lrsquoeacutenergie atomique (Atomic energy commission)

CMOS Complementary metal-oxide-semiconductor

CNAM Conservatoire national des arts et meacutetiers

CPW Coplanar waveguide

xviii Microwave Photonic Links

DBR Distributed Bragg reflector

DC Direct current

DD-MZM Dual drive-MZM

DFA Doped fiber amplifier

DFB Distributed feedback laser

DFT Discrete Fourier transform

EO Electricoptic

EAM Electro-absorption modulator

EDFA Erbium-doped fiber amplifier

EEL Edge emitting laser

EML Electro-absorption modulated laser

EMT Electromagnetic transverse

EOM Electro-optic modulator

ER Extinction ratio

ESYCOM Equipe systegravemes de communications et microsystegravemes (Communications and microsystems team)

ET Electric transverse

EVM Error vector magnitude

FCC Federal communications commission

FET Field-effect transistor

FKE Franz-Keldysh effect

FT RampD France Telecom Research amp Development

GaAs Galium arsenide

GaP Galium phosphide

Ge Germanium

GRINSCH Graded index separate confinement heterostructure

HB Harmonic balance

HBT Heterojunction bipolar transistor

Abbreviation Glossary xix

HEMT High electron mobility transistor

HFET Heterojunction field-effect transistor

HFSS High frequency simulation system

HPT Heterojunction bipolar phototransistor

IDFT Inverse discrete Fourier transform

IM-DD Intensity modulation-direct detection

IMEP Institut de microeacutelectronique eacutelectromagneacutetisme et optique (Institute of microelectronics electromagnetism and optics)

InAs Indium arsenide

InGaAs Indium gallium arsenide

InGaP Indium gallium phosphide

InP Indium phosphide

IR-UWB Impulse Radio ndash Ultra Wideband

KDP Potassium dihydrogen phosphate

LAHC Laboratoire drsquohyperfreacutequences et de caracteacuterisation (hyperfrequency and characterization laboratory)

LASER Light amplifier by stimulated emission of radiation

LF Low frequency

LiNbO3 Lithium niobate

LiTaO3 Lithium tantalate

MAG Maximum available gain

MASER Microwave amplifier by stimulated emission of radiation

MB-OFDM Multi-band ndash orthogonal frequency division modulation

MB-OOK Multi-band on off keying

MEMS Micro-electro-mechanical systems

MESFET Metal semiconductor field-effect transistor

MMIC Monolithic microwave integrated circuit

MODFET Modulation-doped field-effect transistor

MQW-EAM Multi-quantum well-EAM

xx Microwave Photonic Links

MSM Metal semiconductor metal

MZM Modulator Mach-Zehnder

NdYAG Neodymium-doped yttrium aluminum garnet

NF Noise factor Noise figure

nOI n order intermodulation

nOIP n order intercept point

NRA National Research Agency

OE Opticelectric

OEIC Optoelectronic integrated circuit

OEMMIC Optoelectronic millimeter-wave monolithic integrated circuit

OFDM Orthogonal frequency division modulation

PDFA Praseodymium-doped fiber amplifier

PDG Biased-dependent gain

PM Phase modulation

PMMA Poly(methyl methacrylate)

PRBS Pseudo-random bit sequence

PSK Phase-shift keying

QAM Quadrature amplitude modulation

QCSE Quantum confined stark effect

QW-EAM Quantum well-EAM

RCEPD Resonant cavity enhanced photodetectors

RFT Rapid Fourier transform

RIN Relative intensity noise

RoF Radio over fiber

SD-MZM Single drive ndashMZM

Si Silicon

SiGe Silicon-germanium

SiMOX Separation by implantation of oxygen

Abbreviation Glossary xxi

SiO2 Silicon dioxide

SOA Semiconductor optical amplifier

SOC System on a chip

SOI Substrate on insulator

TDFA Thulium-doped fiber amplifier

TEGFET Two-dimensional electron gas field-effect transistor

TW-MZM Travelling wave-MZM

UTC Uni-travelling carrier

UWB Ultra-wideband

VCSEL Vertical-cavity surface-emitting laser

VCSOA Vertical-cavity semiconductor optical amplifier

VMDP Velocity matched distributed photodetector

WDM Wavelength division multiplexing

YDFA Ytterbium-doped fiber amplifier

ZnS Zinc sulfide

Chapter 1

General Points

11 Microwave photonic links

All signals generated or observed due to human activity (measurement of different physical values remote control files sounds images etc) can be transformed into analog electrical signals These electrical signals can be processed or transmitted as they are but in most cases they are digitized beforehand Once digitized these signals have different forms regarding the digital coding or error-correcting algorithms used and protocols employed in the transmission systems To be processed or transmitted these analog or digital signals can use different mediums

If the transmission is performed via metallic lines or cables digital signals directly enter these lines or they modulate more or less complex subcarriers (ADSL Ethernet)

If transmission occurs with a radiowave a high-frequency carrier must be available Due to the congestion of the wireless spectrum carriers are now principally microwaves ie with frequencies of 1 to 100 GHz (GSM UMTS Wi-Fi Wimax etc) Wireless transmission can also be performed by very short pulses having a wide spectrum range including the microwave spectrum or these pulses can modulate a carrier in the millimeter wave spectrum This technique is known as ultra-wideband (UWB) [YAO 09]

If transmission is via fiber optics digital signals modulate one or several optical carriers (amplitude or soliton modulation) which are themselves

2 Microwave Photonic Links

transmitted over hundreds of kilometers on optical fibers This is the case for all passive optical networks (PON) and their different transmission protocols [LEC 97]

From these definitions the distinctive feature of microwave photonic links is to transmit a microwave signal analogically or for it be digitally modulated This microwave signal is transferred to an optical carrier which is guided with minimum loss by an optical fiber The microwave signal is then picked up by a photodetector at the end of the fiber

One of the first applications of microwave optical links was the distribution of the microwave carrier in radar or radio-astronomy systems comprising offset aerials or active phased-array antennas which benefited from the low weight and low volume of the fiber optics [COX 97 DEC 98]

Another important area comprises all radio over fiber (RoF) applications consisting of the extension of wireless networks using microwaves or UWB waves The optical tunnels produced are capable of reaching all rooms or buildings of a company university or diverse institutions or all the rooms of a house whilst benefiting from the very low loss associated with fiber optics [FRI 02]

Amongst the applications of RoF a promising domain is in the connection of internet transmission networks to the home These connections are increasingly popular with ever-increasing speeds (1 Gbs) due to fiber optics reaching households (fiber to the home or FTTH) whereby the house itself becomes a high-speed local network In this local network the signal distribution in each room is achieved by a 60 GHz millimeter-wave (wireless personal area network or WPAN) which stays confined in the room due to the extremely fast attenuation at this frequency All rooms are linked to each other by a network of passive fiber optics which extends the millimeter-wave UWB signal throughout the whole house (ultra broadband wireless home area network or UBB-WHAN) Examples of millimeter-wave over optical transmissions are presented in [CHU 07 KIM 04 WEI 08] and a demonstration of a UBB-WHAN with an up and down link is described in [HUC 08]

The length of a link ranges from 10 m to 1 km allowing several fiber types to be used (single mode or multimode silica or plastic) and several optical wavelengths ranging from 06 to 155 μm The light undergoes intensity modulation the signal is received via photodetection In just a few

General Points 3

years rates have risen from around 10 Mbs on carriers of a few gigahertz to rates of 1 or 10 Gbs on 60 GHz for microwave carriers

A microwave photonic link is constituted of three parts

ndash a coherent light source a laser that emits an optical carrier the intensity of which is directly modulated inside the laser or externally by an optical modulator In the case of external modulation the amplitude modulation is performed by a Mach-Zehnder or an electro-absorption modulator

ndash the modulated light is then transported by single or multi-mode optical fiber [GOM 08 KOO 08] made of silica or plastic [KOI 06] This part may include an optical amplification

ndash the modulated light is finally photodetected in a photodetector consisting of a photodiode or a phototransistor

After some deliberation regarding coherent and incoherent optical links [HAL 82] the solution finally adopted for these links was ldquointensity modulation (IM) direct detection (DD)rdquo As this is recalled in [COX 06] in this type of link the depth of optical modulation is sufficiently weak that we can initially use small signal or linear techniques for each aspect Because the signals applied to links or extracted from them are in microwaves the variables characterizing these systems are S-parameters gains and noise factors Also nonlinearities and hence intermodulation produced by each component on the signal introduced in the link must be considered The combination of these different characteristics leads to the notion of interference-free dynamic range (IFDR) This shall be evaluated regarding the properties of each element in the chapters concerning overall performances of such links

As a link includes electrical-to-optical optical-to-electrical and even optical-to-optical transducers each of the magnitudes in terms of S-parameters gains and noise factors should be presented in the form of optomicrowave magnitudes This aspect forces harmonization of notions from the optical optoelectronic and microwave disciplines This is described in Chapter 5

The term used initially to describe these links was ldquomicrowave optical linksrdquo However the techniques used have gradually distanced themselves from proper optical and optoelectronic techniques so that the more specific term ldquomicrowave photonic linksrdquo has been progressively used [SEE 02]

4 Microwave Photonic Links

12 Link description

Figures 11 and 12 represent a general diagram of an IM-DD microwave optical link

Figure 11 Diagram of directly modulated microwave optical link

Figure 11 represents a direct modulation link A laser emits a light of wavelength 08 or 13 or 155 μm this laser is modulated by a microwave signal (which is possibly itself modulated) through a driver circuit The modulated light enters an optical fiber coupled to a photodetector that detects the microwave modulation signal The optical modulation can have an amplitude frequency and phase However direct photodetection detects only the modulation in amplitude The detected microwave signal is then amplified by a low-noise amplifier

Figure 12 represents an external modulation link This time a light emitted from a laser is injected into a Mach-Zehnder or electro-absorption amplitude modulator In this case microwave modulation is also applied to the modulator through a driver circuit

After passing into an optical fiber the optical intensity modulation only is detected via a photodetector As in the previous diagram the detected microwave signal is amplified in a low-noise amplifier

Laser

Driver

Optical fiber Photodetector

Low noise amplifier

Microwave or UWB Microwave or UWB

λ = 155 or 13 or 08 μm

Amplitude modulation Direct detection

General Points 5

Figure 12 Diagram of externally modulated microwave optical link

13 Signal to transmit

131 Microwave signal

The first type of transmitted signal is a signal that constitutes a microwave frequency reference It can be used in offset aerial systems or active phased-array antenna After its reflection from a moving object the microwave signal emitted from an antenna can shift in frequency (Doppler modulation) and it is the spectral purity of the microwave that determines the minimum observed frequency shift and therefore the minimum relative speed of the moving object The spectral purity and degradation after transmission of the microwave by optical links must be watched closely to distinguish the frequency shift

132 Microwave carrier for a digital signal

If the microwave signal serves as a carrier for a digital signal this carrier is previously modulated All the modulation techniques normally used such as amplitude frequency phase OFDM and combined amplitude-phase modulation (QAM) or more complex techniques can be considered such as those used in GSM GPRS EDGE and UMTS for mobile telephones or such as Bluetooth Wi-Fi and Wimax for data transmission These modulations are generally carried out on single sideband (SSB) When microwave signal modulation is implemented in phase or frequency spectral purity is also of great importance

Laser

Amplifier or driver

Optical fiber

λ = 155 or 13 or 08 μm

Microwave or UWB

Optical modulator MZ or EA

Amplitude modulation

Photodetector

Low noise amplifier

Microwave or UWB

Direct detection

6 Microwave Photonic Links

133 UWB signal

Another signal category is available for transmission by fiber optics These signals are relevant to UWB techniques without carriers and with the spectrum in the microwave region or up-converted to a millimeter-wave carrier UWB wireless links are largely used over short distances The optical fibers are particularly indicated to enable extensions of such networks

134 Optical carrier

Microwave signals can carry analog information (frequency shift due to the Doppler effect) or they can be modulated by a digital signal or be constituted of UWB signals which are themselves digitally modulated All these microwave signals must be up-converted to an optical carrier This transfer exclusively occurs by intensity modulation One of the advantages of this modulation is that the microwave signal can be recovered in a simple photodetection unit permitting the elimination of possible frequency fluctuations of the optical carrier Loss of sensitivity resulting from direct detection does not occur if the optical wavelength allows us to insert an optical amplifier or if the link is very short Usually this modulation is double sideband (DSB) especially if the modulation occurs directly in the laser but for slightly longer links this type of modulation can lead to extinction phenomena A single sideband modulation can hence be considered but this modulation must be carried out by an external modulator

135 Summary

The complexity of microwave photonic links comes from the stacking of an optical carrier and microwave or UWB subcarrier The optical carrier is exclusively intensity modulated whereas the microwave subcarrier can be modulated following all known modulation types amplitude frequency phase or their combination including a frequency shift due to the Doppler effect All these modulations can be recovered via photodetection

The use of microwave optical links will increase as the transmitted signals will be numerous and emitted in parallel communications and the data rates will increase accordingly Thus telecommunication optical

Table of Contents vii

32 Optical amplifiers 118 321 Semiconductor optical amplifiers SOA 119 322 EDFAs 120

33 Appendix modal analysis of propagation in a fiber 122 331 Maxwell equations 122 332 Maxwell equations in a cylindrical fiber 123 333 Continuity and characteristic equation conditions 127 334 Research of different propagation modes 128 335 Approximation of linearly polarized modes 132

Chapter 4 Photodetectors 137 41 Photodetector definition 137 42 Photodiodes 138

421 Presentation 138 422 Light absorption in a semiconductor 139 423 p-i-n photodiode 142 424 Metal-semiconductor-metal or MSM photodiode 145 425 Equivalent circuits for p-i-n and MSM photodiodes 147 426 Nonlinearities 147 427 UTC photodiodes 149 428 Charge compensation 150 429 Partially depleted absorption zone 151 4210 Lateral lighting 152 4211 Lateral lighting progressive wave structure 153 4212 Lateral lighting periodic structures 156 4213 Resonant optical cavity photodetector 157 4214 Diluted waveguides and evanescent mode coupling 160 4215 Summary 161

43 Phototransistors 163 431 Bipolar or field-effect phototransistors 163 432 GaAlAsGaAs and InGaPGaAs phototransistors 165 433 InPInGaAs phototransistors 167 434 SiSiGe phototransistors 172 435 Resonant optical cavities for phototransistors 176 436 Phototransistor simulations and models 176 437 Influence of the base load impedance 180 438 Summary 183

44 Appendix 184 441 Lattice matched layers pseudomorphic layer metamorphic layer 184 442 Velocity overshoot effect 186 443 Heterojunction bipolar phototransistor 188

viii Microwave Photonic Links

Chapter 5 Performance of Microwave Photonic Links 193

51 Microwave photonic links diagrams and definitions 193 511 Direct modulation link diagram and definitions 193 512 External modulation link diagram and definitions 197 513 Simplified link diagram and first gain computation 198

52 Optomicrowave S-parameters and gains of each photonic link component 201

521 Introduction 201 522 Optomicrowave laser S-parameters and optomicrowave gain 202 523 Optomicrowave optical fiber S-parameters and optomicrowave gain 203 524 Photodiode optomicrowave S-parameters and gain 204 525 Localized component external modulator optomicrowave S-parameters and gain 205 526 Distributed component external modulator optomicrowave S-parameters and gain 207 527 Summary of all S-parameters and optomicrowave gain 209

53 Microwave photonic links optomicrowave S-parameters and gains 210

531 Direct modulation microwave photonic link S-parameters 210 532 Direct modulation microwave photonic link gains 211 533 Localized external modulator microwave photonic link S-parameters 212 534 Localized external modulator microwave photonic link gains 213 535 Distributed external modulator microwave photonic link S-parameters 213 536 Distributed external modulator microwave photonic link gains 214 537 Link gain computation generalization 215

54 Comparison of different link gains 218 541 Direct modulation link gain computation 218 542 Localized external modulator link gain computation 219 543 Distributed external modulator link gain computations 220

55 Direct modulation microwave photonic link optomicrowave noise figures 221

551 Link noise figure diagram and computation method 221 552 Laser noise figure 223 553 Optical fiber noise figure 223 554 Photodiode noise figure 224

Table of Contents ix

555 Direct modulation link noise figure 224 556 Matching effect at the input of a direct modulation link 225 557 Generalization of a link noise figure computation 226

56 External modulation microwave photonic link optomicrowave noise figure 227

561 Equivalent diagram and steps recall 227 562 Localized external modulator noise figure 227 563 Distributed external modulator noise figure 228 564 New evaluation of photodetector noise figure 230 565 Localized external modulator microwave photonic link noise figure 231 566 Matched input localized external modulator microwave photonic link noise figure 231 567 Distributed external modulator microwave photonic link noise figure 232

57 Comparisons of different link noise figures 232 571 Evaluation of direct modulation link noise figure 232 572 Evaluation of localized external modulator link noise figure 234 573 Evaluation of matched input localized external modulator link noise figure 235 574 Evaluation of distributed external modulator link noise figures 236 575 Output noise power 237 576 Some effectively measured noise figure values 239

58 Microwave photonic link nonlinearity distortion phenomena 241

581 Single microwave signal nonlinearity 241 582 Several input microwave signals nonlinearity 242 583 Wideband input signal nonlinearity 244 584 Nonlinearity combination of microwave photonic link components 245

59 Microwave photonic link interference-free dynamic range 246 591 Single input signal microwave photonic link interference-free dynamic range 246 592 Several-input signal microwave photonic link interference-free dynamic range 247 593 Some effectively measured interference-free dynamic range values 249

510 Appendix 250 5101 Relation between parameters S Z Y and ABCD 250 5102 Equation choice for the computation of microwave photonic link optomicrowave noise figure 251

x Microwave Photonic Links

5103 Calculation of a two-input signal microwave photonic link interference-free dynamic range 261

Chapter 6 Complement to Microwave Photonic Link Performances 267

61 Microwave signal attenuation during double sideband modulation 267

611 Double sideband modulation recall 267 612 Recall of single-mode optical fiber propagation characteristics 268 613 Optical fiber double sideband modulated signal propagation 270 614 Double sideband-modulated signal photodetection at the optical fiber output 271

62 Modulator structures for optical carrier or high and low sideband removal 273

621 Optical modulation recall 273 622 Single sideband or carrier suppression optical modulators 274 623 Carrier suppression and single sideband optical modulator 277

63 Degradation of a microwave signal spectral purity by an optical link 280

631 Phenomenon description 280 632 Some definitions concerning the noise around a microwave carrier 281 633 Amplitude and phase noise in an optical link 282 634 Phase noise computation of a microwave signal transmitted by an optical link 284 635 Amplitude noise computation of a microwave signal transmitted by an optical link 286

Chapter 7 Electronic Amplifiers in Microwave Photonic Links 289

71 Electronic amplifiers in optical links 289 72 Amplifiers in the optical link emitter 289

721 Different roles of electronic amplifiers on optical emitter 289 722 Emission modulator or laser input amplifiers 290

73 Receiver amplifiers at the photodetector output 293 731 General points 293 732 Transimpedance amplifiers 294 733 Distributed amplifiers 296

Table of Contents xi

734 Combination of transimpedance and distributed amplifiers 298 735 Narrowband amplifiers 298 736 Preamplifier after a phototransistor 299 737 Other circuits after a phototransistor 299

74 Appendix analog and microwave amplifiers 300 741 General points 300 742 Analog amplifiers 300 743 Microwave amplifier expression of transistor reflection coefficients 304 744 Microwave amplifiers gain expressions 306 745 Unilateralized transistor model two-port network matching computation 307 746 Non-unilateralized transistor general case of a transistor with S12 0 312 747 Low noise amplifier 313 748 General models of low signal microwave amplifiers 315

Chapter 8 Simulation and Measurement of Microwave Photonic Links 321

81 State of the art and context 321 811 Objective 321 812 Choice of simulation software 321 813 Different ADS simulation techniques 322

82 Microwave optical link models 324 821 Two-port network approach 324 822 Electro-optic transducer the laser 325 823 Transmission guiding the optical fiber 329 824 The optoelectric transducer the photodiode 334

83 Nonlinearity effects in the link 337 831 Nonlinearity sources 337 832 1 dB compression point and first-order dynamic of the link 338 833 Third-order intermodulation and third-order interference-free dynamic range of the link 339

84 Link noise modeling 340 841 Noise in the laser 340 842 The optical fiber 342 843 Noise in the photodiode 342 844 Direct modulation link noise figure 343 845 Noise power at the receiver 344

xii Microwave Photonic Links

85 Other types of modulation of signals transmitted on an optical fiber 348

851 Ultra-wideband signal modulation 348 852 External modulation 353 853 Generation of microwave signal by frequency beating 358

86 Conclusion 361 87 Appendix 362

871 MB-OOK modulation 362 872 OFDM modulation 363

Bibliography 367

Index 393

Preface

Two important areas of applications of microwave photonic links are electromagnetic sensors and radio-over-fiber (RoF) applications

Electromagnetic sensor microwave systems of the future will principally use active phased-array antennas The development will be determined by reliability requirements resistance to interference and total emission flexibility of the beamforming networks This type of antenna would therefore be used in a diverse range of applications eg radar communication and countermeasures To satisfy this multifunctional approach it will be necessary to distribute these antennas all over the surface area of strategic platforms (planes drones boats etc) While on the ground the multistatic mode of operation will force multiple antennas to be deported from their processing unit

This will require links with very low loss and noise enabling remote-control antennas and the distribution and processing of very wide bandwidth microwave signals (typically 1-20 GHz 40 GHz will be seen in the future)

Currently the maturity and performance notably in terms of spectral purity and opto-electronic component linearity are such that it is possible to consider both optical distribution and processing of these electrical signals Thus the optical transmission of microwaves offers as well as propagation of broad frequency bands advantages regarding weight volume and flexibility characterized by a decrease in the weight of the wiring by 90 in comparison to coaxial cables and thus insensitivity to electromagnetic perturbation All of which will enable the introduction of new concepts in microwave systems based on optical architecture

xiv Microwave Photonic Links

Several sensor radar systems have been designed and produced in France the United States the UK and Italy and photonic technology for the distribution of microwave signals is already being used for ground airborne and aerospace applications

Fiber-optic distribution network technology is an emergence of this technology platform in reference to the design of opto-electronic links for the transmission of microwave and digital signals This optical wiring aims to replace coaxial wiring for onboard electronics interconnections Here the term transmission is taken in the sense that microwave transmissions on optical carriers are in-phase

These functions require the design of emitting and receiving opto-electronic modules the integration of both high thermal stability multiplexing demultiplexing functions and single-mode connectors either point to point or multipoints

Another area of reference is the optical control of the phase andor delay of microwave signals and their applications to electromagnetic sensor systems This occurs by the design of ultrafast opto-electronic multi-chip modules incorporating the optically-controlled switching the control synthesis of time delay systems and the multiwave laser sources

Amongst the most promising technologies is the synthesis of mono- and bidimensional time-delays for the single and multiple beamforming in receiver and emitter the ultraprecise (picoseconds) time synchronization of distributed electromagnetic sensors the time-delay control (precision in the order of picoseconds) of very wide bandwidth microwave signals to measure the arrival direction and the waveshape generation

Another important area involving all RoF applications is the extensive development of wireless networks using microwaves or ultra-wideband signals This is achieved by providing optical tunnels capable of reaching all areas of a company university etc or all the rooms of a house whilst benefiting from the very low loss associated with fiber optics

In their work titled ldquoMicrowave Photonic Linksrdquo C Rumelhard C Algani and A-L Billabert studied and developed models of the components and photonic functions in microwave applications thus laying the foundation for research into microwave photonic links in order to allow the

Preface xv

integration of these components in electromagnetic sensors systems The components and functions addressed range from optical sources (modulated semiconductor lasers or externally modulated continuous lasers) to photodetectors optical fibers and optical amplifiers

This work focuses upon optical components their transfer functionality and their modeling in terms of microwave components in order to create an electrical model of microwave photonic links In order to achieve this level of complexity a number of modeling approaches have been created by the authors to elucidate the influences of the constituent components of microwave photonic links

Because the advancement of opto-electronics photonics and microwaves is possible by the unification of modeling approaches there is no doubt that such works will be referenced by students but also by design engineers and architects of electromagnetic sensor systems who will incorporate this new technology into their designs

This is to the authorrsquos knowledge the first work addressing the description and modeling of microwave photonic link technology with an educational approach to physical phenomena and new approaches to modeling microwave photonic components

Jean Chazelas Scientific Director

Thales Aeronautics Division

Abbreviation Glossary

AC Alternating Current

ACPR Adjacent Channel Power Ratio

ADP Ammonium dihydrogen phosphate

ADS Advanced Design System

AlGaAs Aluminum gallium arsenide

AM Amplitude Modulation

AM-DD Amplitude Modulation ndash Direct Detection

ASE Amplified Spontaneous Emission

BER Bit Error Rate

BH Buried Heterostructure

BiCMOS Bipolar Complementary Metal Oxide Semiconductor

BILBAO Borne drsquoinfrastructures large bande avec accegraves optique (Wideband infrastructure base with optical access)

CAD Computer-aided design

CdS Cadmium sulfide

CEA-Leti Commissariat agrave lrsquoeacutenergie atomique (Atomic energy commission)

CMOS Complementary metal-oxide-semiconductor

CNAM Conservatoire national des arts et meacutetiers

CPW Coplanar waveguide

xviii Microwave Photonic Links

DBR Distributed Bragg reflector

DC Direct current

DD-MZM Dual drive-MZM

DFA Doped fiber amplifier

DFB Distributed feedback laser

DFT Discrete Fourier transform

EO Electricoptic

EAM Electro-absorption modulator

EDFA Erbium-doped fiber amplifier

EEL Edge emitting laser

EML Electro-absorption modulated laser

EMT Electromagnetic transverse

EOM Electro-optic modulator

ER Extinction ratio

ESYCOM Equipe systegravemes de communications et microsystegravemes (Communications and microsystems team)

ET Electric transverse

EVM Error vector magnitude

FCC Federal communications commission

FET Field-effect transistor

FKE Franz-Keldysh effect

FT RampD France Telecom Research amp Development

GaAs Galium arsenide

GaP Galium phosphide

Ge Germanium

GRINSCH Graded index separate confinement heterostructure

HB Harmonic balance

HBT Heterojunction bipolar transistor

Abbreviation Glossary xix

HEMT High electron mobility transistor

HFET Heterojunction field-effect transistor

HFSS High frequency simulation system

HPT Heterojunction bipolar phototransistor

IDFT Inverse discrete Fourier transform

IM-DD Intensity modulation-direct detection

IMEP Institut de microeacutelectronique eacutelectromagneacutetisme et optique (Institute of microelectronics electromagnetism and optics)

InAs Indium arsenide

InGaAs Indium gallium arsenide

InGaP Indium gallium phosphide

InP Indium phosphide

IR-UWB Impulse Radio ndash Ultra Wideband

KDP Potassium dihydrogen phosphate

LAHC Laboratoire drsquohyperfreacutequences et de caracteacuterisation (hyperfrequency and characterization laboratory)

LASER Light amplifier by stimulated emission of radiation

LF Low frequency

LiNbO3 Lithium niobate

LiTaO3 Lithium tantalate

MAG Maximum available gain

MASER Microwave amplifier by stimulated emission of radiation

MB-OFDM Multi-band ndash orthogonal frequency division modulation

MB-OOK Multi-band on off keying

MEMS Micro-electro-mechanical systems

MESFET Metal semiconductor field-effect transistor

MMIC Monolithic microwave integrated circuit

MODFET Modulation-doped field-effect transistor

MQW-EAM Multi-quantum well-EAM

xx Microwave Photonic Links

MSM Metal semiconductor metal

MZM Modulator Mach-Zehnder

NdYAG Neodymium-doped yttrium aluminum garnet

NF Noise factor Noise figure

nOI n order intermodulation

nOIP n order intercept point

NRA National Research Agency

OE Opticelectric

OEIC Optoelectronic integrated circuit

OEMMIC Optoelectronic millimeter-wave monolithic integrated circuit

OFDM Orthogonal frequency division modulation

PDFA Praseodymium-doped fiber amplifier

PDG Biased-dependent gain

PM Phase modulation

PMMA Poly(methyl methacrylate)

PRBS Pseudo-random bit sequence

PSK Phase-shift keying

QAM Quadrature amplitude modulation

QCSE Quantum confined stark effect

QW-EAM Quantum well-EAM

RCEPD Resonant cavity enhanced photodetectors

RFT Rapid Fourier transform

RIN Relative intensity noise

RoF Radio over fiber

SD-MZM Single drive ndashMZM

Si Silicon

SiGe Silicon-germanium

SiMOX Separation by implantation of oxygen

Abbreviation Glossary xxi

SiO2 Silicon dioxide

SOA Semiconductor optical amplifier

SOC System on a chip

SOI Substrate on insulator

TDFA Thulium-doped fiber amplifier

TEGFET Two-dimensional electron gas field-effect transistor

TW-MZM Travelling wave-MZM

UTC Uni-travelling carrier

UWB Ultra-wideband

VCSEL Vertical-cavity surface-emitting laser

VCSOA Vertical-cavity semiconductor optical amplifier

VMDP Velocity matched distributed photodetector

WDM Wavelength division multiplexing

YDFA Ytterbium-doped fiber amplifier

ZnS Zinc sulfide

Chapter 1

General Points

11 Microwave photonic links

All signals generated or observed due to human activity (measurement of different physical values remote control files sounds images etc) can be transformed into analog electrical signals These electrical signals can be processed or transmitted as they are but in most cases they are digitized beforehand Once digitized these signals have different forms regarding the digital coding or error-correcting algorithms used and protocols employed in the transmission systems To be processed or transmitted these analog or digital signals can use different mediums

If the transmission is performed via metallic lines or cables digital signals directly enter these lines or they modulate more or less complex subcarriers (ADSL Ethernet)

If transmission occurs with a radiowave a high-frequency carrier must be available Due to the congestion of the wireless spectrum carriers are now principally microwaves ie with frequencies of 1 to 100 GHz (GSM UMTS Wi-Fi Wimax etc) Wireless transmission can also be performed by very short pulses having a wide spectrum range including the microwave spectrum or these pulses can modulate a carrier in the millimeter wave spectrum This technique is known as ultra-wideband (UWB) [YAO 09]

If transmission is via fiber optics digital signals modulate one or several optical carriers (amplitude or soliton modulation) which are themselves

2 Microwave Photonic Links

transmitted over hundreds of kilometers on optical fibers This is the case for all passive optical networks (PON) and their different transmission protocols [LEC 97]

From these definitions the distinctive feature of microwave photonic links is to transmit a microwave signal analogically or for it be digitally modulated This microwave signal is transferred to an optical carrier which is guided with minimum loss by an optical fiber The microwave signal is then picked up by a photodetector at the end of the fiber

One of the first applications of microwave optical links was the distribution of the microwave carrier in radar or radio-astronomy systems comprising offset aerials or active phased-array antennas which benefited from the low weight and low volume of the fiber optics [COX 97 DEC 98]

Another important area comprises all radio over fiber (RoF) applications consisting of the extension of wireless networks using microwaves or UWB waves The optical tunnels produced are capable of reaching all rooms or buildings of a company university or diverse institutions or all the rooms of a house whilst benefiting from the very low loss associated with fiber optics [FRI 02]

Amongst the applications of RoF a promising domain is in the connection of internet transmission networks to the home These connections are increasingly popular with ever-increasing speeds (1 Gbs) due to fiber optics reaching households (fiber to the home or FTTH) whereby the house itself becomes a high-speed local network In this local network the signal distribution in each room is achieved by a 60 GHz millimeter-wave (wireless personal area network or WPAN) which stays confined in the room due to the extremely fast attenuation at this frequency All rooms are linked to each other by a network of passive fiber optics which extends the millimeter-wave UWB signal throughout the whole house (ultra broadband wireless home area network or UBB-WHAN) Examples of millimeter-wave over optical transmissions are presented in [CHU 07 KIM 04 WEI 08] and a demonstration of a UBB-WHAN with an up and down link is described in [HUC 08]

The length of a link ranges from 10 m to 1 km allowing several fiber types to be used (single mode or multimode silica or plastic) and several optical wavelengths ranging from 06 to 155 μm The light undergoes intensity modulation the signal is received via photodetection In just a few

General Points 3

years rates have risen from around 10 Mbs on carriers of a few gigahertz to rates of 1 or 10 Gbs on 60 GHz for microwave carriers

A microwave photonic link is constituted of three parts

ndash a coherent light source a laser that emits an optical carrier the intensity of which is directly modulated inside the laser or externally by an optical modulator In the case of external modulation the amplitude modulation is performed by a Mach-Zehnder or an electro-absorption modulator

ndash the modulated light is then transported by single or multi-mode optical fiber [GOM 08 KOO 08] made of silica or plastic [KOI 06] This part may include an optical amplification

ndash the modulated light is finally photodetected in a photodetector consisting of a photodiode or a phototransistor

After some deliberation regarding coherent and incoherent optical links [HAL 82] the solution finally adopted for these links was ldquointensity modulation (IM) direct detection (DD)rdquo As this is recalled in [COX 06] in this type of link the depth of optical modulation is sufficiently weak that we can initially use small signal or linear techniques for each aspect Because the signals applied to links or extracted from them are in microwaves the variables characterizing these systems are S-parameters gains and noise factors Also nonlinearities and hence intermodulation produced by each component on the signal introduced in the link must be considered The combination of these different characteristics leads to the notion of interference-free dynamic range (IFDR) This shall be evaluated regarding the properties of each element in the chapters concerning overall performances of such links

As a link includes electrical-to-optical optical-to-electrical and even optical-to-optical transducers each of the magnitudes in terms of S-parameters gains and noise factors should be presented in the form of optomicrowave magnitudes This aspect forces harmonization of notions from the optical optoelectronic and microwave disciplines This is described in Chapter 5

The term used initially to describe these links was ldquomicrowave optical linksrdquo However the techniques used have gradually distanced themselves from proper optical and optoelectronic techniques so that the more specific term ldquomicrowave photonic linksrdquo has been progressively used [SEE 02]

4 Microwave Photonic Links

12 Link description

Figures 11 and 12 represent a general diagram of an IM-DD microwave optical link

Figure 11 Diagram of directly modulated microwave optical link

Figure 11 represents a direct modulation link A laser emits a light of wavelength 08 or 13 or 155 μm this laser is modulated by a microwave signal (which is possibly itself modulated) through a driver circuit The modulated light enters an optical fiber coupled to a photodetector that detects the microwave modulation signal The optical modulation can have an amplitude frequency and phase However direct photodetection detects only the modulation in amplitude The detected microwave signal is then amplified by a low-noise amplifier

Figure 12 represents an external modulation link This time a light emitted from a laser is injected into a Mach-Zehnder or electro-absorption amplitude modulator In this case microwave modulation is also applied to the modulator through a driver circuit

After passing into an optical fiber the optical intensity modulation only is detected via a photodetector As in the previous diagram the detected microwave signal is amplified in a low-noise amplifier

Laser

Driver

Optical fiber Photodetector

Low noise amplifier

Microwave or UWB Microwave or UWB

λ = 155 or 13 or 08 μm

Amplitude modulation Direct detection

General Points 5

Figure 12 Diagram of externally modulated microwave optical link

13 Signal to transmit

131 Microwave signal

The first type of transmitted signal is a signal that constitutes a microwave frequency reference It can be used in offset aerial systems or active phased-array antenna After its reflection from a moving object the microwave signal emitted from an antenna can shift in frequency (Doppler modulation) and it is the spectral purity of the microwave that determines the minimum observed frequency shift and therefore the minimum relative speed of the moving object The spectral purity and degradation after transmission of the microwave by optical links must be watched closely to distinguish the frequency shift

132 Microwave carrier for a digital signal

If the microwave signal serves as a carrier for a digital signal this carrier is previously modulated All the modulation techniques normally used such as amplitude frequency phase OFDM and combined amplitude-phase modulation (QAM) or more complex techniques can be considered such as those used in GSM GPRS EDGE and UMTS for mobile telephones or such as Bluetooth Wi-Fi and Wimax for data transmission These modulations are generally carried out on single sideband (SSB) When microwave signal modulation is implemented in phase or frequency spectral purity is also of great importance

Laser

Amplifier or driver

Optical fiber

λ = 155 or 13 or 08 μm

Microwave or UWB

Optical modulator MZ or EA

Amplitude modulation

Photodetector

Low noise amplifier

Microwave or UWB

Direct detection

6 Microwave Photonic Links

133 UWB signal

Another signal category is available for transmission by fiber optics These signals are relevant to UWB techniques without carriers and with the spectrum in the microwave region or up-converted to a millimeter-wave carrier UWB wireless links are largely used over short distances The optical fibers are particularly indicated to enable extensions of such networks

134 Optical carrier

Microwave signals can carry analog information (frequency shift due to the Doppler effect) or they can be modulated by a digital signal or be constituted of UWB signals which are themselves digitally modulated All these microwave signals must be up-converted to an optical carrier This transfer exclusively occurs by intensity modulation One of the advantages of this modulation is that the microwave signal can be recovered in a simple photodetection unit permitting the elimination of possible frequency fluctuations of the optical carrier Loss of sensitivity resulting from direct detection does not occur if the optical wavelength allows us to insert an optical amplifier or if the link is very short Usually this modulation is double sideband (DSB) especially if the modulation occurs directly in the laser but for slightly longer links this type of modulation can lead to extinction phenomena A single sideband modulation can hence be considered but this modulation must be carried out by an external modulator

135 Summary

The complexity of microwave photonic links comes from the stacking of an optical carrier and microwave or UWB subcarrier The optical carrier is exclusively intensity modulated whereas the microwave subcarrier can be modulated following all known modulation types amplitude frequency phase or their combination including a frequency shift due to the Doppler effect All these modulations can be recovered via photodetection

The use of microwave optical links will increase as the transmitted signals will be numerous and emitted in parallel communications and the data rates will increase accordingly Thus telecommunication optical

viii Microwave Photonic Links

Chapter 5 Performance of Microwave Photonic Links 193

51 Microwave photonic links diagrams and definitions 193 511 Direct modulation link diagram and definitions 193 512 External modulation link diagram and definitions 197 513 Simplified link diagram and first gain computation 198

52 Optomicrowave S-parameters and gains of each photonic link component 201

521 Introduction 201 522 Optomicrowave laser S-parameters and optomicrowave gain 202 523 Optomicrowave optical fiber S-parameters and optomicrowave gain 203 524 Photodiode optomicrowave S-parameters and gain 204 525 Localized component external modulator optomicrowave S-parameters and gain 205 526 Distributed component external modulator optomicrowave S-parameters and gain 207 527 Summary of all S-parameters and optomicrowave gain 209

53 Microwave photonic links optomicrowave S-parameters and gains 210

531 Direct modulation microwave photonic link S-parameters 210 532 Direct modulation microwave photonic link gains 211 533 Localized external modulator microwave photonic link S-parameters 212 534 Localized external modulator microwave photonic link gains 213 535 Distributed external modulator microwave photonic link S-parameters 213 536 Distributed external modulator microwave photonic link gains 214 537 Link gain computation generalization 215

54 Comparison of different link gains 218 541 Direct modulation link gain computation 218 542 Localized external modulator link gain computation 219 543 Distributed external modulator link gain computations 220

55 Direct modulation microwave photonic link optomicrowave noise figures 221

551 Link noise figure diagram and computation method 221 552 Laser noise figure 223 553 Optical fiber noise figure 223 554 Photodiode noise figure 224

Table of Contents ix

555 Direct modulation link noise figure 224 556 Matching effect at the input of a direct modulation link 225 557 Generalization of a link noise figure computation 226

56 External modulation microwave photonic link optomicrowave noise figure 227

561 Equivalent diagram and steps recall 227 562 Localized external modulator noise figure 227 563 Distributed external modulator noise figure 228 564 New evaluation of photodetector noise figure 230 565 Localized external modulator microwave photonic link noise figure 231 566 Matched input localized external modulator microwave photonic link noise figure 231 567 Distributed external modulator microwave photonic link noise figure 232

57 Comparisons of different link noise figures 232 571 Evaluation of direct modulation link noise figure 232 572 Evaluation of localized external modulator link noise figure 234 573 Evaluation of matched input localized external modulator link noise figure 235 574 Evaluation of distributed external modulator link noise figures 236 575 Output noise power 237 576 Some effectively measured noise figure values 239

58 Microwave photonic link nonlinearity distortion phenomena 241

581 Single microwave signal nonlinearity 241 582 Several input microwave signals nonlinearity 242 583 Wideband input signal nonlinearity 244 584 Nonlinearity combination of microwave photonic link components 245

59 Microwave photonic link interference-free dynamic range 246 591 Single input signal microwave photonic link interference-free dynamic range 246 592 Several-input signal microwave photonic link interference-free dynamic range 247 593 Some effectively measured interference-free dynamic range values 249

510 Appendix 250 5101 Relation between parameters S Z Y and ABCD 250 5102 Equation choice for the computation of microwave photonic link optomicrowave noise figure 251

x Microwave Photonic Links

5103 Calculation of a two-input signal microwave photonic link interference-free dynamic range 261

Chapter 6 Complement to Microwave Photonic Link Performances 267

61 Microwave signal attenuation during double sideband modulation 267

611 Double sideband modulation recall 267 612 Recall of single-mode optical fiber propagation characteristics 268 613 Optical fiber double sideband modulated signal propagation 270 614 Double sideband-modulated signal photodetection at the optical fiber output 271

62 Modulator structures for optical carrier or high and low sideband removal 273

621 Optical modulation recall 273 622 Single sideband or carrier suppression optical modulators 274 623 Carrier suppression and single sideband optical modulator 277

63 Degradation of a microwave signal spectral purity by an optical link 280

631 Phenomenon description 280 632 Some definitions concerning the noise around a microwave carrier 281 633 Amplitude and phase noise in an optical link 282 634 Phase noise computation of a microwave signal transmitted by an optical link 284 635 Amplitude noise computation of a microwave signal transmitted by an optical link 286

Chapter 7 Electronic Amplifiers in Microwave Photonic Links 289

71 Electronic amplifiers in optical links 289 72 Amplifiers in the optical link emitter 289

721 Different roles of electronic amplifiers on optical emitter 289 722 Emission modulator or laser input amplifiers 290

73 Receiver amplifiers at the photodetector output 293 731 General points 293 732 Transimpedance amplifiers 294 733 Distributed amplifiers 296

Table of Contents xi

734 Combination of transimpedance and distributed amplifiers 298 735 Narrowband amplifiers 298 736 Preamplifier after a phototransistor 299 737 Other circuits after a phototransistor 299

74 Appendix analog and microwave amplifiers 300 741 General points 300 742 Analog amplifiers 300 743 Microwave amplifier expression of transistor reflection coefficients 304 744 Microwave amplifiers gain expressions 306 745 Unilateralized transistor model two-port network matching computation 307 746 Non-unilateralized transistor general case of a transistor with S12 0 312 747 Low noise amplifier 313 748 General models of low signal microwave amplifiers 315

Chapter 8 Simulation and Measurement of Microwave Photonic Links 321

81 State of the art and context 321 811 Objective 321 812 Choice of simulation software 321 813 Different ADS simulation techniques 322

82 Microwave optical link models 324 821 Two-port network approach 324 822 Electro-optic transducer the laser 325 823 Transmission guiding the optical fiber 329 824 The optoelectric transducer the photodiode 334

83 Nonlinearity effects in the link 337 831 Nonlinearity sources 337 832 1 dB compression point and first-order dynamic of the link 338 833 Third-order intermodulation and third-order interference-free dynamic range of the link 339

84 Link noise modeling 340 841 Noise in the laser 340 842 The optical fiber 342 843 Noise in the photodiode 342 844 Direct modulation link noise figure 343 845 Noise power at the receiver 344

xii Microwave Photonic Links

85 Other types of modulation of signals transmitted on an optical fiber 348

851 Ultra-wideband signal modulation 348 852 External modulation 353 853 Generation of microwave signal by frequency beating 358

86 Conclusion 361 87 Appendix 362

871 MB-OOK modulation 362 872 OFDM modulation 363

Bibliography 367

Index 393

Preface

Two important areas of applications of microwave photonic links are electromagnetic sensors and radio-over-fiber (RoF) applications

Electromagnetic sensor microwave systems of the future will principally use active phased-array antennas The development will be determined by reliability requirements resistance to interference and total emission flexibility of the beamforming networks This type of antenna would therefore be used in a diverse range of applications eg radar communication and countermeasures To satisfy this multifunctional approach it will be necessary to distribute these antennas all over the surface area of strategic platforms (planes drones boats etc) While on the ground the multistatic mode of operation will force multiple antennas to be deported from their processing unit

This will require links with very low loss and noise enabling remote-control antennas and the distribution and processing of very wide bandwidth microwave signals (typically 1-20 GHz 40 GHz will be seen in the future)

Currently the maturity and performance notably in terms of spectral purity and opto-electronic component linearity are such that it is possible to consider both optical distribution and processing of these electrical signals Thus the optical transmission of microwaves offers as well as propagation of broad frequency bands advantages regarding weight volume and flexibility characterized by a decrease in the weight of the wiring by 90 in comparison to coaxial cables and thus insensitivity to electromagnetic perturbation All of which will enable the introduction of new concepts in microwave systems based on optical architecture

xiv Microwave Photonic Links

Several sensor radar systems have been designed and produced in France the United States the UK and Italy and photonic technology for the distribution of microwave signals is already being used for ground airborne and aerospace applications

Fiber-optic distribution network technology is an emergence of this technology platform in reference to the design of opto-electronic links for the transmission of microwave and digital signals This optical wiring aims to replace coaxial wiring for onboard electronics interconnections Here the term transmission is taken in the sense that microwave transmissions on optical carriers are in-phase

These functions require the design of emitting and receiving opto-electronic modules the integration of both high thermal stability multiplexing demultiplexing functions and single-mode connectors either point to point or multipoints

Another area of reference is the optical control of the phase andor delay of microwave signals and their applications to electromagnetic sensor systems This occurs by the design of ultrafast opto-electronic multi-chip modules incorporating the optically-controlled switching the control synthesis of time delay systems and the multiwave laser sources

Amongst the most promising technologies is the synthesis of mono- and bidimensional time-delays for the single and multiple beamforming in receiver and emitter the ultraprecise (picoseconds) time synchronization of distributed electromagnetic sensors the time-delay control (precision in the order of picoseconds) of very wide bandwidth microwave signals to measure the arrival direction and the waveshape generation

Another important area involving all RoF applications is the extensive development of wireless networks using microwaves or ultra-wideband signals This is achieved by providing optical tunnels capable of reaching all areas of a company university etc or all the rooms of a house whilst benefiting from the very low loss associated with fiber optics

In their work titled ldquoMicrowave Photonic Linksrdquo C Rumelhard C Algani and A-L Billabert studied and developed models of the components and photonic functions in microwave applications thus laying the foundation for research into microwave photonic links in order to allow the

Preface xv

integration of these components in electromagnetic sensors systems The components and functions addressed range from optical sources (modulated semiconductor lasers or externally modulated continuous lasers) to photodetectors optical fibers and optical amplifiers

This work focuses upon optical components their transfer functionality and their modeling in terms of microwave components in order to create an electrical model of microwave photonic links In order to achieve this level of complexity a number of modeling approaches have been created by the authors to elucidate the influences of the constituent components of microwave photonic links

Because the advancement of opto-electronics photonics and microwaves is possible by the unification of modeling approaches there is no doubt that such works will be referenced by students but also by design engineers and architects of electromagnetic sensor systems who will incorporate this new technology into their designs

This is to the authorrsquos knowledge the first work addressing the description and modeling of microwave photonic link technology with an educational approach to physical phenomena and new approaches to modeling microwave photonic components

Jean Chazelas Scientific Director

Thales Aeronautics Division

Abbreviation Glossary

AC Alternating Current

ACPR Adjacent Channel Power Ratio

ADP Ammonium dihydrogen phosphate

ADS Advanced Design System

AlGaAs Aluminum gallium arsenide

AM Amplitude Modulation

AM-DD Amplitude Modulation ndash Direct Detection

ASE Amplified Spontaneous Emission

BER Bit Error Rate

BH Buried Heterostructure

BiCMOS Bipolar Complementary Metal Oxide Semiconductor

BILBAO Borne drsquoinfrastructures large bande avec accegraves optique (Wideband infrastructure base with optical access)

CAD Computer-aided design

CdS Cadmium sulfide

CEA-Leti Commissariat agrave lrsquoeacutenergie atomique (Atomic energy commission)

CMOS Complementary metal-oxide-semiconductor

CNAM Conservatoire national des arts et meacutetiers

CPW Coplanar waveguide

xviii Microwave Photonic Links

DBR Distributed Bragg reflector

DC Direct current

DD-MZM Dual drive-MZM

DFA Doped fiber amplifier

DFB Distributed feedback laser

DFT Discrete Fourier transform

EO Electricoptic

EAM Electro-absorption modulator

EDFA Erbium-doped fiber amplifier

EEL Edge emitting laser

EML Electro-absorption modulated laser

EMT Electromagnetic transverse

EOM Electro-optic modulator

ER Extinction ratio

ESYCOM Equipe systegravemes de communications et microsystegravemes (Communications and microsystems team)

ET Electric transverse

EVM Error vector magnitude

FCC Federal communications commission

FET Field-effect transistor

FKE Franz-Keldysh effect

FT RampD France Telecom Research amp Development

GaAs Galium arsenide

GaP Galium phosphide

Ge Germanium

GRINSCH Graded index separate confinement heterostructure

HB Harmonic balance

HBT Heterojunction bipolar transistor

Abbreviation Glossary xix

HEMT High electron mobility transistor

HFET Heterojunction field-effect transistor

HFSS High frequency simulation system

HPT Heterojunction bipolar phototransistor

IDFT Inverse discrete Fourier transform

IM-DD Intensity modulation-direct detection

IMEP Institut de microeacutelectronique eacutelectromagneacutetisme et optique (Institute of microelectronics electromagnetism and optics)

InAs Indium arsenide

InGaAs Indium gallium arsenide

InGaP Indium gallium phosphide

InP Indium phosphide

IR-UWB Impulse Radio ndash Ultra Wideband

KDP Potassium dihydrogen phosphate

LAHC Laboratoire drsquohyperfreacutequences et de caracteacuterisation (hyperfrequency and characterization laboratory)

LASER Light amplifier by stimulated emission of radiation

LF Low frequency

LiNbO3 Lithium niobate

LiTaO3 Lithium tantalate

MAG Maximum available gain

MASER Microwave amplifier by stimulated emission of radiation

MB-OFDM Multi-band ndash orthogonal frequency division modulation

MB-OOK Multi-band on off keying

MEMS Micro-electro-mechanical systems

MESFET Metal semiconductor field-effect transistor

MMIC Monolithic microwave integrated circuit

MODFET Modulation-doped field-effect transistor

MQW-EAM Multi-quantum well-EAM

xx Microwave Photonic Links

MSM Metal semiconductor metal

MZM Modulator Mach-Zehnder

NdYAG Neodymium-doped yttrium aluminum garnet

NF Noise factor Noise figure

nOI n order intermodulation

nOIP n order intercept point

NRA National Research Agency

OE Opticelectric

OEIC Optoelectronic integrated circuit

OEMMIC Optoelectronic millimeter-wave monolithic integrated circuit

OFDM Orthogonal frequency division modulation

PDFA Praseodymium-doped fiber amplifier

PDG Biased-dependent gain

PM Phase modulation

PMMA Poly(methyl methacrylate)

PRBS Pseudo-random bit sequence

PSK Phase-shift keying

QAM Quadrature amplitude modulation

QCSE Quantum confined stark effect

QW-EAM Quantum well-EAM

RCEPD Resonant cavity enhanced photodetectors

RFT Rapid Fourier transform

RIN Relative intensity noise

RoF Radio over fiber

SD-MZM Single drive ndashMZM

Si Silicon

SiGe Silicon-germanium

SiMOX Separation by implantation of oxygen

Abbreviation Glossary xxi

SiO2 Silicon dioxide

SOA Semiconductor optical amplifier

SOC System on a chip

SOI Substrate on insulator

TDFA Thulium-doped fiber amplifier

TEGFET Two-dimensional electron gas field-effect transistor

TW-MZM Travelling wave-MZM

UTC Uni-travelling carrier

UWB Ultra-wideband

VCSEL Vertical-cavity surface-emitting laser

VCSOA Vertical-cavity semiconductor optical amplifier

VMDP Velocity matched distributed photodetector

WDM Wavelength division multiplexing

YDFA Ytterbium-doped fiber amplifier

ZnS Zinc sulfide

Chapter 1

General Points

11 Microwave photonic links

All signals generated or observed due to human activity (measurement of different physical values remote control files sounds images etc) can be transformed into analog electrical signals These electrical signals can be processed or transmitted as they are but in most cases they are digitized beforehand Once digitized these signals have different forms regarding the digital coding or error-correcting algorithms used and protocols employed in the transmission systems To be processed or transmitted these analog or digital signals can use different mediums

If the transmission is performed via metallic lines or cables digital signals directly enter these lines or they modulate more or less complex subcarriers (ADSL Ethernet)

If transmission occurs with a radiowave a high-frequency carrier must be available Due to the congestion of the wireless spectrum carriers are now principally microwaves ie with frequencies of 1 to 100 GHz (GSM UMTS Wi-Fi Wimax etc) Wireless transmission can also be performed by very short pulses having a wide spectrum range including the microwave spectrum or these pulses can modulate a carrier in the millimeter wave spectrum This technique is known as ultra-wideband (UWB) [YAO 09]

If transmission is via fiber optics digital signals modulate one or several optical carriers (amplitude or soliton modulation) which are themselves

2 Microwave Photonic Links

transmitted over hundreds of kilometers on optical fibers This is the case for all passive optical networks (PON) and their different transmission protocols [LEC 97]

From these definitions the distinctive feature of microwave photonic links is to transmit a microwave signal analogically or for it be digitally modulated This microwave signal is transferred to an optical carrier which is guided with minimum loss by an optical fiber The microwave signal is then picked up by a photodetector at the end of the fiber

One of the first applications of microwave optical links was the distribution of the microwave carrier in radar or radio-astronomy systems comprising offset aerials or active phased-array antennas which benefited from the low weight and low volume of the fiber optics [COX 97 DEC 98]

Another important area comprises all radio over fiber (RoF) applications consisting of the extension of wireless networks using microwaves or UWB waves The optical tunnels produced are capable of reaching all rooms or buildings of a company university or diverse institutions or all the rooms of a house whilst benefiting from the very low loss associated with fiber optics [FRI 02]

Amongst the applications of RoF a promising domain is in the connection of internet transmission networks to the home These connections are increasingly popular with ever-increasing speeds (1 Gbs) due to fiber optics reaching households (fiber to the home or FTTH) whereby the house itself becomes a high-speed local network In this local network the signal distribution in each room is achieved by a 60 GHz millimeter-wave (wireless personal area network or WPAN) which stays confined in the room due to the extremely fast attenuation at this frequency All rooms are linked to each other by a network of passive fiber optics which extends the millimeter-wave UWB signal throughout the whole house (ultra broadband wireless home area network or UBB-WHAN) Examples of millimeter-wave over optical transmissions are presented in [CHU 07 KIM 04 WEI 08] and a demonstration of a UBB-WHAN with an up and down link is described in [HUC 08]

The length of a link ranges from 10 m to 1 km allowing several fiber types to be used (single mode or multimode silica or plastic) and several optical wavelengths ranging from 06 to 155 μm The light undergoes intensity modulation the signal is received via photodetection In just a few

General Points 3

years rates have risen from around 10 Mbs on carriers of a few gigahertz to rates of 1 or 10 Gbs on 60 GHz for microwave carriers

A microwave photonic link is constituted of three parts

ndash a coherent light source a laser that emits an optical carrier the intensity of which is directly modulated inside the laser or externally by an optical modulator In the case of external modulation the amplitude modulation is performed by a Mach-Zehnder or an electro-absorption modulator

ndash the modulated light is then transported by single or multi-mode optical fiber [GOM 08 KOO 08] made of silica or plastic [KOI 06] This part may include an optical amplification

ndash the modulated light is finally photodetected in a photodetector consisting of a photodiode or a phototransistor

After some deliberation regarding coherent and incoherent optical links [HAL 82] the solution finally adopted for these links was ldquointensity modulation (IM) direct detection (DD)rdquo As this is recalled in [COX 06] in this type of link the depth of optical modulation is sufficiently weak that we can initially use small signal or linear techniques for each aspect Because the signals applied to links or extracted from them are in microwaves the variables characterizing these systems are S-parameters gains and noise factors Also nonlinearities and hence intermodulation produced by each component on the signal introduced in the link must be considered The combination of these different characteristics leads to the notion of interference-free dynamic range (IFDR) This shall be evaluated regarding the properties of each element in the chapters concerning overall performances of such links

As a link includes electrical-to-optical optical-to-electrical and even optical-to-optical transducers each of the magnitudes in terms of S-parameters gains and noise factors should be presented in the form of optomicrowave magnitudes This aspect forces harmonization of notions from the optical optoelectronic and microwave disciplines This is described in Chapter 5

The term used initially to describe these links was ldquomicrowave optical linksrdquo However the techniques used have gradually distanced themselves from proper optical and optoelectronic techniques so that the more specific term ldquomicrowave photonic linksrdquo has been progressively used [SEE 02]

4 Microwave Photonic Links

12 Link description

Figures 11 and 12 represent a general diagram of an IM-DD microwave optical link

Figure 11 Diagram of directly modulated microwave optical link

Figure 11 represents a direct modulation link A laser emits a light of wavelength 08 or 13 or 155 μm this laser is modulated by a microwave signal (which is possibly itself modulated) through a driver circuit The modulated light enters an optical fiber coupled to a photodetector that detects the microwave modulation signal The optical modulation can have an amplitude frequency and phase However direct photodetection detects only the modulation in amplitude The detected microwave signal is then amplified by a low-noise amplifier

Figure 12 represents an external modulation link This time a light emitted from a laser is injected into a Mach-Zehnder or electro-absorption amplitude modulator In this case microwave modulation is also applied to the modulator through a driver circuit

After passing into an optical fiber the optical intensity modulation only is detected via a photodetector As in the previous diagram the detected microwave signal is amplified in a low-noise amplifier

Laser

Driver

Optical fiber Photodetector

Low noise amplifier

Microwave or UWB Microwave or UWB

λ = 155 or 13 or 08 μm

Amplitude modulation Direct detection

General Points 5

Figure 12 Diagram of externally modulated microwave optical link

13 Signal to transmit

131 Microwave signal

The first type of transmitted signal is a signal that constitutes a microwave frequency reference It can be used in offset aerial systems or active phased-array antenna After its reflection from a moving object the microwave signal emitted from an antenna can shift in frequency (Doppler modulation) and it is the spectral purity of the microwave that determines the minimum observed frequency shift and therefore the minimum relative speed of the moving object The spectral purity and degradation after transmission of the microwave by optical links must be watched closely to distinguish the frequency shift

132 Microwave carrier for a digital signal

If the microwave signal serves as a carrier for a digital signal this carrier is previously modulated All the modulation techniques normally used such as amplitude frequency phase OFDM and combined amplitude-phase modulation (QAM) or more complex techniques can be considered such as those used in GSM GPRS EDGE and UMTS for mobile telephones or such as Bluetooth Wi-Fi and Wimax for data transmission These modulations are generally carried out on single sideband (SSB) When microwave signal modulation is implemented in phase or frequency spectral purity is also of great importance

Laser

Amplifier or driver

Optical fiber

λ = 155 or 13 or 08 μm

Microwave or UWB

Optical modulator MZ or EA

Amplitude modulation

Photodetector

Low noise amplifier

Microwave or UWB

Direct detection

6 Microwave Photonic Links

133 UWB signal

Another signal category is available for transmission by fiber optics These signals are relevant to UWB techniques without carriers and with the spectrum in the microwave region or up-converted to a millimeter-wave carrier UWB wireless links are largely used over short distances The optical fibers are particularly indicated to enable extensions of such networks

134 Optical carrier

Microwave signals can carry analog information (frequency shift due to the Doppler effect) or they can be modulated by a digital signal or be constituted of UWB signals which are themselves digitally modulated All these microwave signals must be up-converted to an optical carrier This transfer exclusively occurs by intensity modulation One of the advantages of this modulation is that the microwave signal can be recovered in a simple photodetection unit permitting the elimination of possible frequency fluctuations of the optical carrier Loss of sensitivity resulting from direct detection does not occur if the optical wavelength allows us to insert an optical amplifier or if the link is very short Usually this modulation is double sideband (DSB) especially if the modulation occurs directly in the laser but for slightly longer links this type of modulation can lead to extinction phenomena A single sideband modulation can hence be considered but this modulation must be carried out by an external modulator

135 Summary

The complexity of microwave photonic links comes from the stacking of an optical carrier and microwave or UWB subcarrier The optical carrier is exclusively intensity modulated whereas the microwave subcarrier can be modulated following all known modulation types amplitude frequency phase or their combination including a frequency shift due to the Doppler effect All these modulations can be recovered via photodetection

The use of microwave optical links will increase as the transmitted signals will be numerous and emitted in parallel communications and the data rates will increase accordingly Thus telecommunication optical

Table of Contents ix

555 Direct modulation link noise figure 224 556 Matching effect at the input of a direct modulation link 225 557 Generalization of a link noise figure computation 226

56 External modulation microwave photonic link optomicrowave noise figure 227

561 Equivalent diagram and steps recall 227 562 Localized external modulator noise figure 227 563 Distributed external modulator noise figure 228 564 New evaluation of photodetector noise figure 230 565 Localized external modulator microwave photonic link noise figure 231 566 Matched input localized external modulator microwave photonic link noise figure 231 567 Distributed external modulator microwave photonic link noise figure 232

57 Comparisons of different link noise figures 232 571 Evaluation of direct modulation link noise figure 232 572 Evaluation of localized external modulator link noise figure 234 573 Evaluation of matched input localized external modulator link noise figure 235 574 Evaluation of distributed external modulator link noise figures 236 575 Output noise power 237 576 Some effectively measured noise figure values 239

58 Microwave photonic link nonlinearity distortion phenomena 241

581 Single microwave signal nonlinearity 241 582 Several input microwave signals nonlinearity 242 583 Wideband input signal nonlinearity 244 584 Nonlinearity combination of microwave photonic link components 245

59 Microwave photonic link interference-free dynamic range 246 591 Single input signal microwave photonic link interference-free dynamic range 246 592 Several-input signal microwave photonic link interference-free dynamic range 247 593 Some effectively measured interference-free dynamic range values 249

510 Appendix 250 5101 Relation between parameters S Z Y and ABCD 250 5102 Equation choice for the computation of microwave photonic link optomicrowave noise figure 251

x Microwave Photonic Links

5103 Calculation of a two-input signal microwave photonic link interference-free dynamic range 261

Chapter 6 Complement to Microwave Photonic Link Performances 267

61 Microwave signal attenuation during double sideband modulation 267

611 Double sideband modulation recall 267 612 Recall of single-mode optical fiber propagation characteristics 268 613 Optical fiber double sideband modulated signal propagation 270 614 Double sideband-modulated signal photodetection at the optical fiber output 271

62 Modulator structures for optical carrier or high and low sideband removal 273

621 Optical modulation recall 273 622 Single sideband or carrier suppression optical modulators 274 623 Carrier suppression and single sideband optical modulator 277

63 Degradation of a microwave signal spectral purity by an optical link 280

631 Phenomenon description 280 632 Some definitions concerning the noise around a microwave carrier 281 633 Amplitude and phase noise in an optical link 282 634 Phase noise computation of a microwave signal transmitted by an optical link 284 635 Amplitude noise computation of a microwave signal transmitted by an optical link 286

Chapter 7 Electronic Amplifiers in Microwave Photonic Links 289

71 Electronic amplifiers in optical links 289 72 Amplifiers in the optical link emitter 289

721 Different roles of electronic amplifiers on optical emitter 289 722 Emission modulator or laser input amplifiers 290

73 Receiver amplifiers at the photodetector output 293 731 General points 293 732 Transimpedance amplifiers 294 733 Distributed amplifiers 296

Table of Contents xi

734 Combination of transimpedance and distributed amplifiers 298 735 Narrowband amplifiers 298 736 Preamplifier after a phototransistor 299 737 Other circuits after a phototransistor 299

74 Appendix analog and microwave amplifiers 300 741 General points 300 742 Analog amplifiers 300 743 Microwave amplifier expression of transistor reflection coefficients 304 744 Microwave amplifiers gain expressions 306 745 Unilateralized transistor model two-port network matching computation 307 746 Non-unilateralized transistor general case of a transistor with S12 0 312 747 Low noise amplifier 313 748 General models of low signal microwave amplifiers 315

Chapter 8 Simulation and Measurement of Microwave Photonic Links 321

81 State of the art and context 321 811 Objective 321 812 Choice of simulation software 321 813 Different ADS simulation techniques 322

82 Microwave optical link models 324 821 Two-port network approach 324 822 Electro-optic transducer the laser 325 823 Transmission guiding the optical fiber 329 824 The optoelectric transducer the photodiode 334

83 Nonlinearity effects in the link 337 831 Nonlinearity sources 337 832 1 dB compression point and first-order dynamic of the link 338 833 Third-order intermodulation and third-order interference-free dynamic range of the link 339

84 Link noise modeling 340 841 Noise in the laser 340 842 The optical fiber 342 843 Noise in the photodiode 342 844 Direct modulation link noise figure 343 845 Noise power at the receiver 344

xii Microwave Photonic Links

85 Other types of modulation of signals transmitted on an optical fiber 348

851 Ultra-wideband signal modulation 348 852 External modulation 353 853 Generation of microwave signal by frequency beating 358

86 Conclusion 361 87 Appendix 362

871 MB-OOK modulation 362 872 OFDM modulation 363

Bibliography 367

Index 393

Preface

Two important areas of applications of microwave photonic links are electromagnetic sensors and radio-over-fiber (RoF) applications

Electromagnetic sensor microwave systems of the future will principally use active phased-array antennas The development will be determined by reliability requirements resistance to interference and total emission flexibility of the beamforming networks This type of antenna would therefore be used in a diverse range of applications eg radar communication and countermeasures To satisfy this multifunctional approach it will be necessary to distribute these antennas all over the surface area of strategic platforms (planes drones boats etc) While on the ground the multistatic mode of operation will force multiple antennas to be deported from their processing unit

This will require links with very low loss and noise enabling remote-control antennas and the distribution and processing of very wide bandwidth microwave signals (typically 1-20 GHz 40 GHz will be seen in the future)

Currently the maturity and performance notably in terms of spectral purity and opto-electronic component linearity are such that it is possible to consider both optical distribution and processing of these electrical signals Thus the optical transmission of microwaves offers as well as propagation of broad frequency bands advantages regarding weight volume and flexibility characterized by a decrease in the weight of the wiring by 90 in comparison to coaxial cables and thus insensitivity to electromagnetic perturbation All of which will enable the introduction of new concepts in microwave systems based on optical architecture

xiv Microwave Photonic Links

Several sensor radar systems have been designed and produced in France the United States the UK and Italy and photonic technology for the distribution of microwave signals is already being used for ground airborne and aerospace applications

Fiber-optic distribution network technology is an emergence of this technology platform in reference to the design of opto-electronic links for the transmission of microwave and digital signals This optical wiring aims to replace coaxial wiring for onboard electronics interconnections Here the term transmission is taken in the sense that microwave transmissions on optical carriers are in-phase

These functions require the design of emitting and receiving opto-electronic modules the integration of both high thermal stability multiplexing demultiplexing functions and single-mode connectors either point to point or multipoints

Another area of reference is the optical control of the phase andor delay of microwave signals and their applications to electromagnetic sensor systems This occurs by the design of ultrafast opto-electronic multi-chip modules incorporating the optically-controlled switching the control synthesis of time delay systems and the multiwave laser sources

Amongst the most promising technologies is the synthesis of mono- and bidimensional time-delays for the single and multiple beamforming in receiver and emitter the ultraprecise (picoseconds) time synchronization of distributed electromagnetic sensors the time-delay control (precision in the order of picoseconds) of very wide bandwidth microwave signals to measure the arrival direction and the waveshape generation

Another important area involving all RoF applications is the extensive development of wireless networks using microwaves or ultra-wideband signals This is achieved by providing optical tunnels capable of reaching all areas of a company university etc or all the rooms of a house whilst benefiting from the very low loss associated with fiber optics

In their work titled ldquoMicrowave Photonic Linksrdquo C Rumelhard C Algani and A-L Billabert studied and developed models of the components and photonic functions in microwave applications thus laying the foundation for research into microwave photonic links in order to allow the

Preface xv

integration of these components in electromagnetic sensors systems The components and functions addressed range from optical sources (modulated semiconductor lasers or externally modulated continuous lasers) to photodetectors optical fibers and optical amplifiers

This work focuses upon optical components their transfer functionality and their modeling in terms of microwave components in order to create an electrical model of microwave photonic links In order to achieve this level of complexity a number of modeling approaches have been created by the authors to elucidate the influences of the constituent components of microwave photonic links

Because the advancement of opto-electronics photonics and microwaves is possible by the unification of modeling approaches there is no doubt that such works will be referenced by students but also by design engineers and architects of electromagnetic sensor systems who will incorporate this new technology into their designs

This is to the authorrsquos knowledge the first work addressing the description and modeling of microwave photonic link technology with an educational approach to physical phenomena and new approaches to modeling microwave photonic components

Jean Chazelas Scientific Director

Thales Aeronautics Division

Abbreviation Glossary

AC Alternating Current

ACPR Adjacent Channel Power Ratio

ADP Ammonium dihydrogen phosphate

ADS Advanced Design System

AlGaAs Aluminum gallium arsenide

AM Amplitude Modulation

AM-DD Amplitude Modulation ndash Direct Detection

ASE Amplified Spontaneous Emission

BER Bit Error Rate

BH Buried Heterostructure

BiCMOS Bipolar Complementary Metal Oxide Semiconductor

BILBAO Borne drsquoinfrastructures large bande avec accegraves optique (Wideband infrastructure base with optical access)

CAD Computer-aided design

CdS Cadmium sulfide

CEA-Leti Commissariat agrave lrsquoeacutenergie atomique (Atomic energy commission)

CMOS Complementary metal-oxide-semiconductor

CNAM Conservatoire national des arts et meacutetiers

CPW Coplanar waveguide

xviii Microwave Photonic Links

DBR Distributed Bragg reflector

DC Direct current

DD-MZM Dual drive-MZM

DFA Doped fiber amplifier

DFB Distributed feedback laser

DFT Discrete Fourier transform

EO Electricoptic

EAM Electro-absorption modulator

EDFA Erbium-doped fiber amplifier

EEL Edge emitting laser

EML Electro-absorption modulated laser

EMT Electromagnetic transverse

EOM Electro-optic modulator

ER Extinction ratio

ESYCOM Equipe systegravemes de communications et microsystegravemes (Communications and microsystems team)

ET Electric transverse

EVM Error vector magnitude

FCC Federal communications commission

FET Field-effect transistor

FKE Franz-Keldysh effect

FT RampD France Telecom Research amp Development

GaAs Galium arsenide

GaP Galium phosphide

Ge Germanium

GRINSCH Graded index separate confinement heterostructure

HB Harmonic balance

HBT Heterojunction bipolar transistor

Abbreviation Glossary xix

HEMT High electron mobility transistor

HFET Heterojunction field-effect transistor

HFSS High frequency simulation system

HPT Heterojunction bipolar phototransistor

IDFT Inverse discrete Fourier transform

IM-DD Intensity modulation-direct detection

IMEP Institut de microeacutelectronique eacutelectromagneacutetisme et optique (Institute of microelectronics electromagnetism and optics)

InAs Indium arsenide

InGaAs Indium gallium arsenide

InGaP Indium gallium phosphide

InP Indium phosphide

IR-UWB Impulse Radio ndash Ultra Wideband

KDP Potassium dihydrogen phosphate

LAHC Laboratoire drsquohyperfreacutequences et de caracteacuterisation (hyperfrequency and characterization laboratory)

LASER Light amplifier by stimulated emission of radiation

LF Low frequency

LiNbO3 Lithium niobate

LiTaO3 Lithium tantalate

MAG Maximum available gain

MASER Microwave amplifier by stimulated emission of radiation

MB-OFDM Multi-band ndash orthogonal frequency division modulation

MB-OOK Multi-band on off keying

MEMS Micro-electro-mechanical systems

MESFET Metal semiconductor field-effect transistor

MMIC Monolithic microwave integrated circuit

MODFET Modulation-doped field-effect transistor

MQW-EAM Multi-quantum well-EAM

xx Microwave Photonic Links

MSM Metal semiconductor metal

MZM Modulator Mach-Zehnder

NdYAG Neodymium-doped yttrium aluminum garnet

NF Noise factor Noise figure

nOI n order intermodulation

nOIP n order intercept point

NRA National Research Agency

OE Opticelectric

OEIC Optoelectronic integrated circuit

OEMMIC Optoelectronic millimeter-wave monolithic integrated circuit

OFDM Orthogonal frequency division modulation

PDFA Praseodymium-doped fiber amplifier

PDG Biased-dependent gain

PM Phase modulation

PMMA Poly(methyl methacrylate)

PRBS Pseudo-random bit sequence

PSK Phase-shift keying

QAM Quadrature amplitude modulation

QCSE Quantum confined stark effect

QW-EAM Quantum well-EAM

RCEPD Resonant cavity enhanced photodetectors

RFT Rapid Fourier transform

RIN Relative intensity noise

RoF Radio over fiber

SD-MZM Single drive ndashMZM

Si Silicon

SiGe Silicon-germanium

SiMOX Separation by implantation of oxygen

Abbreviation Glossary xxi

SiO2 Silicon dioxide

SOA Semiconductor optical amplifier

SOC System on a chip

SOI Substrate on insulator

TDFA Thulium-doped fiber amplifier

TEGFET Two-dimensional electron gas field-effect transistor

TW-MZM Travelling wave-MZM

UTC Uni-travelling carrier

UWB Ultra-wideband

VCSEL Vertical-cavity surface-emitting laser

VCSOA Vertical-cavity semiconductor optical amplifier

VMDP Velocity matched distributed photodetector

WDM Wavelength division multiplexing

YDFA Ytterbium-doped fiber amplifier

ZnS Zinc sulfide

Chapter 1

General Points

11 Microwave photonic links

All signals generated or observed due to human activity (measurement of different physical values remote control files sounds images etc) can be transformed into analog electrical signals These electrical signals can be processed or transmitted as they are but in most cases they are digitized beforehand Once digitized these signals have different forms regarding the digital coding or error-correcting algorithms used and protocols employed in the transmission systems To be processed or transmitted these analog or digital signals can use different mediums

If the transmission is performed via metallic lines or cables digital signals directly enter these lines or they modulate more or less complex subcarriers (ADSL Ethernet)

If transmission occurs with a radiowave a high-frequency carrier must be available Due to the congestion of the wireless spectrum carriers are now principally microwaves ie with frequencies of 1 to 100 GHz (GSM UMTS Wi-Fi Wimax etc) Wireless transmission can also be performed by very short pulses having a wide spectrum range including the microwave spectrum or these pulses can modulate a carrier in the millimeter wave spectrum This technique is known as ultra-wideband (UWB) [YAO 09]

If transmission is via fiber optics digital signals modulate one or several optical carriers (amplitude or soliton modulation) which are themselves

2 Microwave Photonic Links

transmitted over hundreds of kilometers on optical fibers This is the case for all passive optical networks (PON) and their different transmission protocols [LEC 97]

From these definitions the distinctive feature of microwave photonic links is to transmit a microwave signal analogically or for it be digitally modulated This microwave signal is transferred to an optical carrier which is guided with minimum loss by an optical fiber The microwave signal is then picked up by a photodetector at the end of the fiber

One of the first applications of microwave optical links was the distribution of the microwave carrier in radar or radio-astronomy systems comprising offset aerials or active phased-array antennas which benefited from the low weight and low volume of the fiber optics [COX 97 DEC 98]

Another important area comprises all radio over fiber (RoF) applications consisting of the extension of wireless networks using microwaves or UWB waves The optical tunnels produced are capable of reaching all rooms or buildings of a company university or diverse institutions or all the rooms of a house whilst benefiting from the very low loss associated with fiber optics [FRI 02]

Amongst the applications of RoF a promising domain is in the connection of internet transmission networks to the home These connections are increasingly popular with ever-increasing speeds (1 Gbs) due to fiber optics reaching households (fiber to the home or FTTH) whereby the house itself becomes a high-speed local network In this local network the signal distribution in each room is achieved by a 60 GHz millimeter-wave (wireless personal area network or WPAN) which stays confined in the room due to the extremely fast attenuation at this frequency All rooms are linked to each other by a network of passive fiber optics which extends the millimeter-wave UWB signal throughout the whole house (ultra broadband wireless home area network or UBB-WHAN) Examples of millimeter-wave over optical transmissions are presented in [CHU 07 KIM 04 WEI 08] and a demonstration of a UBB-WHAN with an up and down link is described in [HUC 08]

The length of a link ranges from 10 m to 1 km allowing several fiber types to be used (single mode or multimode silica or plastic) and several optical wavelengths ranging from 06 to 155 μm The light undergoes intensity modulation the signal is received via photodetection In just a few

General Points 3

years rates have risen from around 10 Mbs on carriers of a few gigahertz to rates of 1 or 10 Gbs on 60 GHz for microwave carriers

A microwave photonic link is constituted of three parts

ndash a coherent light source a laser that emits an optical carrier the intensity of which is directly modulated inside the laser or externally by an optical modulator In the case of external modulation the amplitude modulation is performed by a Mach-Zehnder or an electro-absorption modulator

ndash the modulated light is then transported by single or multi-mode optical fiber [GOM 08 KOO 08] made of silica or plastic [KOI 06] This part may include an optical amplification

ndash the modulated light is finally photodetected in a photodetector consisting of a photodiode or a phototransistor

After some deliberation regarding coherent and incoherent optical links [HAL 82] the solution finally adopted for these links was ldquointensity modulation (IM) direct detection (DD)rdquo As this is recalled in [COX 06] in this type of link the depth of optical modulation is sufficiently weak that we can initially use small signal or linear techniques for each aspect Because the signals applied to links or extracted from them are in microwaves the variables characterizing these systems are S-parameters gains and noise factors Also nonlinearities and hence intermodulation produced by each component on the signal introduced in the link must be considered The combination of these different characteristics leads to the notion of interference-free dynamic range (IFDR) This shall be evaluated regarding the properties of each element in the chapters concerning overall performances of such links

As a link includes electrical-to-optical optical-to-electrical and even optical-to-optical transducers each of the magnitudes in terms of S-parameters gains and noise factors should be presented in the form of optomicrowave magnitudes This aspect forces harmonization of notions from the optical optoelectronic and microwave disciplines This is described in Chapter 5

The term used initially to describe these links was ldquomicrowave optical linksrdquo However the techniques used have gradually distanced themselves from proper optical and optoelectronic techniques so that the more specific term ldquomicrowave photonic linksrdquo has been progressively used [SEE 02]

4 Microwave Photonic Links

12 Link description

Figures 11 and 12 represent a general diagram of an IM-DD microwave optical link

Figure 11 Diagram of directly modulated microwave optical link

Figure 11 represents a direct modulation link A laser emits a light of wavelength 08 or 13 or 155 μm this laser is modulated by a microwave signal (which is possibly itself modulated) through a driver circuit The modulated light enters an optical fiber coupled to a photodetector that detects the microwave modulation signal The optical modulation can have an amplitude frequency and phase However direct photodetection detects only the modulation in amplitude The detected microwave signal is then amplified by a low-noise amplifier

Figure 12 represents an external modulation link This time a light emitted from a laser is injected into a Mach-Zehnder or electro-absorption amplitude modulator In this case microwave modulation is also applied to the modulator through a driver circuit

After passing into an optical fiber the optical intensity modulation only is detected via a photodetector As in the previous diagram the detected microwave signal is amplified in a low-noise amplifier

Laser

Driver

Optical fiber Photodetector

Low noise amplifier

Microwave or UWB Microwave or UWB

λ = 155 or 13 or 08 μm

Amplitude modulation Direct detection

General Points 5

Figure 12 Diagram of externally modulated microwave optical link

13 Signal to transmit

131 Microwave signal

The first type of transmitted signal is a signal that constitutes a microwave frequency reference It can be used in offset aerial systems or active phased-array antenna After its reflection from a moving object the microwave signal emitted from an antenna can shift in frequency (Doppler modulation) and it is the spectral purity of the microwave that determines the minimum observed frequency shift and therefore the minimum relative speed of the moving object The spectral purity and degradation after transmission of the microwave by optical links must be watched closely to distinguish the frequency shift

132 Microwave carrier for a digital signal

If the microwave signal serves as a carrier for a digital signal this carrier is previously modulated All the modulation techniques normally used such as amplitude frequency phase OFDM and combined amplitude-phase modulation (QAM) or more complex techniques can be considered such as those used in GSM GPRS EDGE and UMTS for mobile telephones or such as Bluetooth Wi-Fi and Wimax for data transmission These modulations are generally carried out on single sideband (SSB) When microwave signal modulation is implemented in phase or frequency spectral purity is also of great importance

Laser

Amplifier or driver

Optical fiber

λ = 155 or 13 or 08 μm

Microwave or UWB

Optical modulator MZ or EA

Amplitude modulation

Photodetector

Low noise amplifier

Microwave or UWB

Direct detection

6 Microwave Photonic Links

133 UWB signal

Another signal category is available for transmission by fiber optics These signals are relevant to UWB techniques without carriers and with the spectrum in the microwave region or up-converted to a millimeter-wave carrier UWB wireless links are largely used over short distances The optical fibers are particularly indicated to enable extensions of such networks

134 Optical carrier

Microwave signals can carry analog information (frequency shift due to the Doppler effect) or they can be modulated by a digital signal or be constituted of UWB signals which are themselves digitally modulated All these microwave signals must be up-converted to an optical carrier This transfer exclusively occurs by intensity modulation One of the advantages of this modulation is that the microwave signal can be recovered in a simple photodetection unit permitting the elimination of possible frequency fluctuations of the optical carrier Loss of sensitivity resulting from direct detection does not occur if the optical wavelength allows us to insert an optical amplifier or if the link is very short Usually this modulation is double sideband (DSB) especially if the modulation occurs directly in the laser but for slightly longer links this type of modulation can lead to extinction phenomena A single sideband modulation can hence be considered but this modulation must be carried out by an external modulator

135 Summary

The complexity of microwave photonic links comes from the stacking of an optical carrier and microwave or UWB subcarrier The optical carrier is exclusively intensity modulated whereas the microwave subcarrier can be modulated following all known modulation types amplitude frequency phase or their combination including a frequency shift due to the Doppler effect All these modulations can be recovered via photodetection

The use of microwave optical links will increase as the transmitted signals will be numerous and emitted in parallel communications and the data rates will increase accordingly Thus telecommunication optical

x Microwave Photonic Links

5103 Calculation of a two-input signal microwave photonic link interference-free dynamic range 261

Chapter 6 Complement to Microwave Photonic Link Performances 267

61 Microwave signal attenuation during double sideband modulation 267

611 Double sideband modulation recall 267 612 Recall of single-mode optical fiber propagation characteristics 268 613 Optical fiber double sideband modulated signal propagation 270 614 Double sideband-modulated signal photodetection at the optical fiber output 271

62 Modulator structures for optical carrier or high and low sideband removal 273

621 Optical modulation recall 273 622 Single sideband or carrier suppression optical modulators 274 623 Carrier suppression and single sideband optical modulator 277

63 Degradation of a microwave signal spectral purity by an optical link 280

631 Phenomenon description 280 632 Some definitions concerning the noise around a microwave carrier 281 633 Amplitude and phase noise in an optical link 282 634 Phase noise computation of a microwave signal transmitted by an optical link 284 635 Amplitude noise computation of a microwave signal transmitted by an optical link 286

Chapter 7 Electronic Amplifiers in Microwave Photonic Links 289

71 Electronic amplifiers in optical links 289 72 Amplifiers in the optical link emitter 289

721 Different roles of electronic amplifiers on optical emitter 289 722 Emission modulator or laser input amplifiers 290

73 Receiver amplifiers at the photodetector output 293 731 General points 293 732 Transimpedance amplifiers 294 733 Distributed amplifiers 296

Table of Contents xi

734 Combination of transimpedance and distributed amplifiers 298 735 Narrowband amplifiers 298 736 Preamplifier after a phototransistor 299 737 Other circuits after a phototransistor 299

74 Appendix analog and microwave amplifiers 300 741 General points 300 742 Analog amplifiers 300 743 Microwave amplifier expression of transistor reflection coefficients 304 744 Microwave amplifiers gain expressions 306 745 Unilateralized transistor model two-port network matching computation 307 746 Non-unilateralized transistor general case of a transistor with S12 0 312 747 Low noise amplifier 313 748 General models of low signal microwave amplifiers 315

Chapter 8 Simulation and Measurement of Microwave Photonic Links 321

81 State of the art and context 321 811 Objective 321 812 Choice of simulation software 321 813 Different ADS simulation techniques 322

82 Microwave optical link models 324 821 Two-port network approach 324 822 Electro-optic transducer the laser 325 823 Transmission guiding the optical fiber 329 824 The optoelectric transducer the photodiode 334

83 Nonlinearity effects in the link 337 831 Nonlinearity sources 337 832 1 dB compression point and first-order dynamic of the link 338 833 Third-order intermodulation and third-order interference-free dynamic range of the link 339

84 Link noise modeling 340 841 Noise in the laser 340 842 The optical fiber 342 843 Noise in the photodiode 342 844 Direct modulation link noise figure 343 845 Noise power at the receiver 344

xii Microwave Photonic Links

85 Other types of modulation of signals transmitted on an optical fiber 348

851 Ultra-wideband signal modulation 348 852 External modulation 353 853 Generation of microwave signal by frequency beating 358

86 Conclusion 361 87 Appendix 362

871 MB-OOK modulation 362 872 OFDM modulation 363

Bibliography 367

Index 393

Preface

Two important areas of applications of microwave photonic links are electromagnetic sensors and radio-over-fiber (RoF) applications

Electromagnetic sensor microwave systems of the future will principally use active phased-array antennas The development will be determined by reliability requirements resistance to interference and total emission flexibility of the beamforming networks This type of antenna would therefore be used in a diverse range of applications eg radar communication and countermeasures To satisfy this multifunctional approach it will be necessary to distribute these antennas all over the surface area of strategic platforms (planes drones boats etc) While on the ground the multistatic mode of operation will force multiple antennas to be deported from their processing unit

This will require links with very low loss and noise enabling remote-control antennas and the distribution and processing of very wide bandwidth microwave signals (typically 1-20 GHz 40 GHz will be seen in the future)

Currently the maturity and performance notably in terms of spectral purity and opto-electronic component linearity are such that it is possible to consider both optical distribution and processing of these electrical signals Thus the optical transmission of microwaves offers as well as propagation of broad frequency bands advantages regarding weight volume and flexibility characterized by a decrease in the weight of the wiring by 90 in comparison to coaxial cables and thus insensitivity to electromagnetic perturbation All of which will enable the introduction of new concepts in microwave systems based on optical architecture

xiv Microwave Photonic Links

Several sensor radar systems have been designed and produced in France the United States the UK and Italy and photonic technology for the distribution of microwave signals is already being used for ground airborne and aerospace applications

Fiber-optic distribution network technology is an emergence of this technology platform in reference to the design of opto-electronic links for the transmission of microwave and digital signals This optical wiring aims to replace coaxial wiring for onboard electronics interconnections Here the term transmission is taken in the sense that microwave transmissions on optical carriers are in-phase

These functions require the design of emitting and receiving opto-electronic modules the integration of both high thermal stability multiplexing demultiplexing functions and single-mode connectors either point to point or multipoints

Another area of reference is the optical control of the phase andor delay of microwave signals and their applications to electromagnetic sensor systems This occurs by the design of ultrafast opto-electronic multi-chip modules incorporating the optically-controlled switching the control synthesis of time delay systems and the multiwave laser sources

Amongst the most promising technologies is the synthesis of mono- and bidimensional time-delays for the single and multiple beamforming in receiver and emitter the ultraprecise (picoseconds) time synchronization of distributed electromagnetic sensors the time-delay control (precision in the order of picoseconds) of very wide bandwidth microwave signals to measure the arrival direction and the waveshape generation

Another important area involving all RoF applications is the extensive development of wireless networks using microwaves or ultra-wideband signals This is achieved by providing optical tunnels capable of reaching all areas of a company university etc or all the rooms of a house whilst benefiting from the very low loss associated with fiber optics

In their work titled ldquoMicrowave Photonic Linksrdquo C Rumelhard C Algani and A-L Billabert studied and developed models of the components and photonic functions in microwave applications thus laying the foundation for research into microwave photonic links in order to allow the

Preface xv

integration of these components in electromagnetic sensors systems The components and functions addressed range from optical sources (modulated semiconductor lasers or externally modulated continuous lasers) to photodetectors optical fibers and optical amplifiers

This work focuses upon optical components their transfer functionality and their modeling in terms of microwave components in order to create an electrical model of microwave photonic links In order to achieve this level of complexity a number of modeling approaches have been created by the authors to elucidate the influences of the constituent components of microwave photonic links

Because the advancement of opto-electronics photonics and microwaves is possible by the unification of modeling approaches there is no doubt that such works will be referenced by students but also by design engineers and architects of electromagnetic sensor systems who will incorporate this new technology into their designs

This is to the authorrsquos knowledge the first work addressing the description and modeling of microwave photonic link technology with an educational approach to physical phenomena and new approaches to modeling microwave photonic components

Jean Chazelas Scientific Director

Thales Aeronautics Division

Abbreviation Glossary

AC Alternating Current

ACPR Adjacent Channel Power Ratio

ADP Ammonium dihydrogen phosphate

ADS Advanced Design System

AlGaAs Aluminum gallium arsenide

AM Amplitude Modulation

AM-DD Amplitude Modulation ndash Direct Detection

ASE Amplified Spontaneous Emission

BER Bit Error Rate

BH Buried Heterostructure

BiCMOS Bipolar Complementary Metal Oxide Semiconductor

BILBAO Borne drsquoinfrastructures large bande avec accegraves optique (Wideband infrastructure base with optical access)

CAD Computer-aided design

CdS Cadmium sulfide

CEA-Leti Commissariat agrave lrsquoeacutenergie atomique (Atomic energy commission)

CMOS Complementary metal-oxide-semiconductor

CNAM Conservatoire national des arts et meacutetiers

CPW Coplanar waveguide

xviii Microwave Photonic Links

DBR Distributed Bragg reflector

DC Direct current

DD-MZM Dual drive-MZM

DFA Doped fiber amplifier

DFB Distributed feedback laser

DFT Discrete Fourier transform

EO Electricoptic

EAM Electro-absorption modulator

EDFA Erbium-doped fiber amplifier

EEL Edge emitting laser

EML Electro-absorption modulated laser

EMT Electromagnetic transverse

EOM Electro-optic modulator

ER Extinction ratio

ESYCOM Equipe systegravemes de communications et microsystegravemes (Communications and microsystems team)

ET Electric transverse

EVM Error vector magnitude

FCC Federal communications commission

FET Field-effect transistor

FKE Franz-Keldysh effect

FT RampD France Telecom Research amp Development

GaAs Galium arsenide

GaP Galium phosphide

Ge Germanium

GRINSCH Graded index separate confinement heterostructure

HB Harmonic balance

HBT Heterojunction bipolar transistor

Abbreviation Glossary xix

HEMT High electron mobility transistor

HFET Heterojunction field-effect transistor

HFSS High frequency simulation system

HPT Heterojunction bipolar phototransistor

IDFT Inverse discrete Fourier transform

IM-DD Intensity modulation-direct detection

IMEP Institut de microeacutelectronique eacutelectromagneacutetisme et optique (Institute of microelectronics electromagnetism and optics)

InAs Indium arsenide

InGaAs Indium gallium arsenide

InGaP Indium gallium phosphide

InP Indium phosphide

IR-UWB Impulse Radio ndash Ultra Wideband

KDP Potassium dihydrogen phosphate

LAHC Laboratoire drsquohyperfreacutequences et de caracteacuterisation (hyperfrequency and characterization laboratory)

LASER Light amplifier by stimulated emission of radiation

LF Low frequency

LiNbO3 Lithium niobate

LiTaO3 Lithium tantalate

MAG Maximum available gain

MASER Microwave amplifier by stimulated emission of radiation

MB-OFDM Multi-band ndash orthogonal frequency division modulation

MB-OOK Multi-band on off keying

MEMS Micro-electro-mechanical systems

MESFET Metal semiconductor field-effect transistor

MMIC Monolithic microwave integrated circuit

MODFET Modulation-doped field-effect transistor

MQW-EAM Multi-quantum well-EAM

xx Microwave Photonic Links

MSM Metal semiconductor metal

MZM Modulator Mach-Zehnder

NdYAG Neodymium-doped yttrium aluminum garnet

NF Noise factor Noise figure

nOI n order intermodulation

nOIP n order intercept point

NRA National Research Agency

OE Opticelectric

OEIC Optoelectronic integrated circuit

OEMMIC Optoelectronic millimeter-wave monolithic integrated circuit

OFDM Orthogonal frequency division modulation

PDFA Praseodymium-doped fiber amplifier

PDG Biased-dependent gain

PM Phase modulation

PMMA Poly(methyl methacrylate)

PRBS Pseudo-random bit sequence

PSK Phase-shift keying

QAM Quadrature amplitude modulation

QCSE Quantum confined stark effect

QW-EAM Quantum well-EAM

RCEPD Resonant cavity enhanced photodetectors

RFT Rapid Fourier transform

RIN Relative intensity noise

RoF Radio over fiber

SD-MZM Single drive ndashMZM

Si Silicon

SiGe Silicon-germanium

SiMOX Separation by implantation of oxygen

Abbreviation Glossary xxi

SiO2 Silicon dioxide

SOA Semiconductor optical amplifier

SOC System on a chip

SOI Substrate on insulator

TDFA Thulium-doped fiber amplifier

TEGFET Two-dimensional electron gas field-effect transistor

TW-MZM Travelling wave-MZM

UTC Uni-travelling carrier

UWB Ultra-wideband

VCSEL Vertical-cavity surface-emitting laser

VCSOA Vertical-cavity semiconductor optical amplifier

VMDP Velocity matched distributed photodetector

WDM Wavelength division multiplexing

YDFA Ytterbium-doped fiber amplifier

ZnS Zinc sulfide

Chapter 1

General Points

11 Microwave photonic links

All signals generated or observed due to human activity (measurement of different physical values remote control files sounds images etc) can be transformed into analog electrical signals These electrical signals can be processed or transmitted as they are but in most cases they are digitized beforehand Once digitized these signals have different forms regarding the digital coding or error-correcting algorithms used and protocols employed in the transmission systems To be processed or transmitted these analog or digital signals can use different mediums

If the transmission is performed via metallic lines or cables digital signals directly enter these lines or they modulate more or less complex subcarriers (ADSL Ethernet)

If transmission occurs with a radiowave a high-frequency carrier must be available Due to the congestion of the wireless spectrum carriers are now principally microwaves ie with frequencies of 1 to 100 GHz (GSM UMTS Wi-Fi Wimax etc) Wireless transmission can also be performed by very short pulses having a wide spectrum range including the microwave spectrum or these pulses can modulate a carrier in the millimeter wave spectrum This technique is known as ultra-wideband (UWB) [YAO 09]

If transmission is via fiber optics digital signals modulate one or several optical carriers (amplitude or soliton modulation) which are themselves

2 Microwave Photonic Links

transmitted over hundreds of kilometers on optical fibers This is the case for all passive optical networks (PON) and their different transmission protocols [LEC 97]

From these definitions the distinctive feature of microwave photonic links is to transmit a microwave signal analogically or for it be digitally modulated This microwave signal is transferred to an optical carrier which is guided with minimum loss by an optical fiber The microwave signal is then picked up by a photodetector at the end of the fiber

One of the first applications of microwave optical links was the distribution of the microwave carrier in radar or radio-astronomy systems comprising offset aerials or active phased-array antennas which benefited from the low weight and low volume of the fiber optics [COX 97 DEC 98]

Another important area comprises all radio over fiber (RoF) applications consisting of the extension of wireless networks using microwaves or UWB waves The optical tunnels produced are capable of reaching all rooms or buildings of a company university or diverse institutions or all the rooms of a house whilst benefiting from the very low loss associated with fiber optics [FRI 02]

Amongst the applications of RoF a promising domain is in the connection of internet transmission networks to the home These connections are increasingly popular with ever-increasing speeds (1 Gbs) due to fiber optics reaching households (fiber to the home or FTTH) whereby the house itself becomes a high-speed local network In this local network the signal distribution in each room is achieved by a 60 GHz millimeter-wave (wireless personal area network or WPAN) which stays confined in the room due to the extremely fast attenuation at this frequency All rooms are linked to each other by a network of passive fiber optics which extends the millimeter-wave UWB signal throughout the whole house (ultra broadband wireless home area network or UBB-WHAN) Examples of millimeter-wave over optical transmissions are presented in [CHU 07 KIM 04 WEI 08] and a demonstration of a UBB-WHAN with an up and down link is described in [HUC 08]

The length of a link ranges from 10 m to 1 km allowing several fiber types to be used (single mode or multimode silica or plastic) and several optical wavelengths ranging from 06 to 155 μm The light undergoes intensity modulation the signal is received via photodetection In just a few

General Points 3

years rates have risen from around 10 Mbs on carriers of a few gigahertz to rates of 1 or 10 Gbs on 60 GHz for microwave carriers

A microwave photonic link is constituted of three parts

ndash a coherent light source a laser that emits an optical carrier the intensity of which is directly modulated inside the laser or externally by an optical modulator In the case of external modulation the amplitude modulation is performed by a Mach-Zehnder or an electro-absorption modulator

ndash the modulated light is then transported by single or multi-mode optical fiber [GOM 08 KOO 08] made of silica or plastic [KOI 06] This part may include an optical amplification

ndash the modulated light is finally photodetected in a photodetector consisting of a photodiode or a phototransistor

After some deliberation regarding coherent and incoherent optical links [HAL 82] the solution finally adopted for these links was ldquointensity modulation (IM) direct detection (DD)rdquo As this is recalled in [COX 06] in this type of link the depth of optical modulation is sufficiently weak that we can initially use small signal or linear techniques for each aspect Because the signals applied to links or extracted from them are in microwaves the variables characterizing these systems are S-parameters gains and noise factors Also nonlinearities and hence intermodulation produced by each component on the signal introduced in the link must be considered The combination of these different characteristics leads to the notion of interference-free dynamic range (IFDR) This shall be evaluated regarding the properties of each element in the chapters concerning overall performances of such links

As a link includes electrical-to-optical optical-to-electrical and even optical-to-optical transducers each of the magnitudes in terms of S-parameters gains and noise factors should be presented in the form of optomicrowave magnitudes This aspect forces harmonization of notions from the optical optoelectronic and microwave disciplines This is described in Chapter 5

The term used initially to describe these links was ldquomicrowave optical linksrdquo However the techniques used have gradually distanced themselves from proper optical and optoelectronic techniques so that the more specific term ldquomicrowave photonic linksrdquo has been progressively used [SEE 02]

4 Microwave Photonic Links

12 Link description

Figures 11 and 12 represent a general diagram of an IM-DD microwave optical link

Figure 11 Diagram of directly modulated microwave optical link

Figure 11 represents a direct modulation link A laser emits a light of wavelength 08 or 13 or 155 μm this laser is modulated by a microwave signal (which is possibly itself modulated) through a driver circuit The modulated light enters an optical fiber coupled to a photodetector that detects the microwave modulation signal The optical modulation can have an amplitude frequency and phase However direct photodetection detects only the modulation in amplitude The detected microwave signal is then amplified by a low-noise amplifier

Figure 12 represents an external modulation link This time a light emitted from a laser is injected into a Mach-Zehnder or electro-absorption amplitude modulator In this case microwave modulation is also applied to the modulator through a driver circuit

After passing into an optical fiber the optical intensity modulation only is detected via a photodetector As in the previous diagram the detected microwave signal is amplified in a low-noise amplifier

Laser

Driver

Optical fiber Photodetector

Low noise amplifier

Microwave or UWB Microwave or UWB

λ = 155 or 13 or 08 μm

Amplitude modulation Direct detection

General Points 5

Figure 12 Diagram of externally modulated microwave optical link

13 Signal to transmit

131 Microwave signal

The first type of transmitted signal is a signal that constitutes a microwave frequency reference It can be used in offset aerial systems or active phased-array antenna After its reflection from a moving object the microwave signal emitted from an antenna can shift in frequency (Doppler modulation) and it is the spectral purity of the microwave that determines the minimum observed frequency shift and therefore the minimum relative speed of the moving object The spectral purity and degradation after transmission of the microwave by optical links must be watched closely to distinguish the frequency shift

132 Microwave carrier for a digital signal

If the microwave signal serves as a carrier for a digital signal this carrier is previously modulated All the modulation techniques normally used such as amplitude frequency phase OFDM and combined amplitude-phase modulation (QAM) or more complex techniques can be considered such as those used in GSM GPRS EDGE and UMTS for mobile telephones or such as Bluetooth Wi-Fi and Wimax for data transmission These modulations are generally carried out on single sideband (SSB) When microwave signal modulation is implemented in phase or frequency spectral purity is also of great importance

Laser

Amplifier or driver

Optical fiber

λ = 155 or 13 or 08 μm

Microwave or UWB

Optical modulator MZ or EA

Amplitude modulation

Photodetector

Low noise amplifier

Microwave or UWB

Direct detection

6 Microwave Photonic Links

133 UWB signal

Another signal category is available for transmission by fiber optics These signals are relevant to UWB techniques without carriers and with the spectrum in the microwave region or up-converted to a millimeter-wave carrier UWB wireless links are largely used over short distances The optical fibers are particularly indicated to enable extensions of such networks

134 Optical carrier

Microwave signals can carry analog information (frequency shift due to the Doppler effect) or they can be modulated by a digital signal or be constituted of UWB signals which are themselves digitally modulated All these microwave signals must be up-converted to an optical carrier This transfer exclusively occurs by intensity modulation One of the advantages of this modulation is that the microwave signal can be recovered in a simple photodetection unit permitting the elimination of possible frequency fluctuations of the optical carrier Loss of sensitivity resulting from direct detection does not occur if the optical wavelength allows us to insert an optical amplifier or if the link is very short Usually this modulation is double sideband (DSB) especially if the modulation occurs directly in the laser but for slightly longer links this type of modulation can lead to extinction phenomena A single sideband modulation can hence be considered but this modulation must be carried out by an external modulator

135 Summary

The complexity of microwave photonic links comes from the stacking of an optical carrier and microwave or UWB subcarrier The optical carrier is exclusively intensity modulated whereas the microwave subcarrier can be modulated following all known modulation types amplitude frequency phase or their combination including a frequency shift due to the Doppler effect All these modulations can be recovered via photodetection

The use of microwave optical links will increase as the transmitted signals will be numerous and emitted in parallel communications and the data rates will increase accordingly Thus telecommunication optical

Table of Contents xi

734 Combination of transimpedance and distributed amplifiers 298 735 Narrowband amplifiers 298 736 Preamplifier after a phototransistor 299 737 Other circuits after a phototransistor 299

74 Appendix analog and microwave amplifiers 300 741 General points 300 742 Analog amplifiers 300 743 Microwave amplifier expression of transistor reflection coefficients 304 744 Microwave amplifiers gain expressions 306 745 Unilateralized transistor model two-port network matching computation 307 746 Non-unilateralized transistor general case of a transistor with S12 0 312 747 Low noise amplifier 313 748 General models of low signal microwave amplifiers 315

Chapter 8 Simulation and Measurement of Microwave Photonic Links 321

81 State of the art and context 321 811 Objective 321 812 Choice of simulation software 321 813 Different ADS simulation techniques 322

82 Microwave optical link models 324 821 Two-port network approach 324 822 Electro-optic transducer the laser 325 823 Transmission guiding the optical fiber 329 824 The optoelectric transducer the photodiode 334

83 Nonlinearity effects in the link 337 831 Nonlinearity sources 337 832 1 dB compression point and first-order dynamic of the link 338 833 Third-order intermodulation and third-order interference-free dynamic range of the link 339

84 Link noise modeling 340 841 Noise in the laser 340 842 The optical fiber 342 843 Noise in the photodiode 342 844 Direct modulation link noise figure 343 845 Noise power at the receiver 344

xii Microwave Photonic Links

85 Other types of modulation of signals transmitted on an optical fiber 348

851 Ultra-wideband signal modulation 348 852 External modulation 353 853 Generation of microwave signal by frequency beating 358

86 Conclusion 361 87 Appendix 362

871 MB-OOK modulation 362 872 OFDM modulation 363

Bibliography 367

Index 393

Preface

Two important areas of applications of microwave photonic links are electromagnetic sensors and radio-over-fiber (RoF) applications

Electromagnetic sensor microwave systems of the future will principally use active phased-array antennas The development will be determined by reliability requirements resistance to interference and total emission flexibility of the beamforming networks This type of antenna would therefore be used in a diverse range of applications eg radar communication and countermeasures To satisfy this multifunctional approach it will be necessary to distribute these antennas all over the surface area of strategic platforms (planes drones boats etc) While on the ground the multistatic mode of operation will force multiple antennas to be deported from their processing unit

This will require links with very low loss and noise enabling remote-control antennas and the distribution and processing of very wide bandwidth microwave signals (typically 1-20 GHz 40 GHz will be seen in the future)

Currently the maturity and performance notably in terms of spectral purity and opto-electronic component linearity are such that it is possible to consider both optical distribution and processing of these electrical signals Thus the optical transmission of microwaves offers as well as propagation of broad frequency bands advantages regarding weight volume and flexibility characterized by a decrease in the weight of the wiring by 90 in comparison to coaxial cables and thus insensitivity to electromagnetic perturbation All of which will enable the introduction of new concepts in microwave systems based on optical architecture

xiv Microwave Photonic Links

Several sensor radar systems have been designed and produced in France the United States the UK and Italy and photonic technology for the distribution of microwave signals is already being used for ground airborne and aerospace applications

Fiber-optic distribution network technology is an emergence of this technology platform in reference to the design of opto-electronic links for the transmission of microwave and digital signals This optical wiring aims to replace coaxial wiring for onboard electronics interconnections Here the term transmission is taken in the sense that microwave transmissions on optical carriers are in-phase

These functions require the design of emitting and receiving opto-electronic modules the integration of both high thermal stability multiplexing demultiplexing functions and single-mode connectors either point to point or multipoints

Another area of reference is the optical control of the phase andor delay of microwave signals and their applications to electromagnetic sensor systems This occurs by the design of ultrafast opto-electronic multi-chip modules incorporating the optically-controlled switching the control synthesis of time delay systems and the multiwave laser sources

Amongst the most promising technologies is the synthesis of mono- and bidimensional time-delays for the single and multiple beamforming in receiver and emitter the ultraprecise (picoseconds) time synchronization of distributed electromagnetic sensors the time-delay control (precision in the order of picoseconds) of very wide bandwidth microwave signals to measure the arrival direction and the waveshape generation

Another important area involving all RoF applications is the extensive development of wireless networks using microwaves or ultra-wideband signals This is achieved by providing optical tunnels capable of reaching all areas of a company university etc or all the rooms of a house whilst benefiting from the very low loss associated with fiber optics

In their work titled ldquoMicrowave Photonic Linksrdquo C Rumelhard C Algani and A-L Billabert studied and developed models of the components and photonic functions in microwave applications thus laying the foundation for research into microwave photonic links in order to allow the

Preface xv

integration of these components in electromagnetic sensors systems The components and functions addressed range from optical sources (modulated semiconductor lasers or externally modulated continuous lasers) to photodetectors optical fibers and optical amplifiers

This work focuses upon optical components their transfer functionality and their modeling in terms of microwave components in order to create an electrical model of microwave photonic links In order to achieve this level of complexity a number of modeling approaches have been created by the authors to elucidate the influences of the constituent components of microwave photonic links

Because the advancement of opto-electronics photonics and microwaves is possible by the unification of modeling approaches there is no doubt that such works will be referenced by students but also by design engineers and architects of electromagnetic sensor systems who will incorporate this new technology into their designs

This is to the authorrsquos knowledge the first work addressing the description and modeling of microwave photonic link technology with an educational approach to physical phenomena and new approaches to modeling microwave photonic components

Jean Chazelas Scientific Director

Thales Aeronautics Division

Abbreviation Glossary

AC Alternating Current

ACPR Adjacent Channel Power Ratio

ADP Ammonium dihydrogen phosphate

ADS Advanced Design System

AlGaAs Aluminum gallium arsenide

AM Amplitude Modulation

AM-DD Amplitude Modulation ndash Direct Detection

ASE Amplified Spontaneous Emission

BER Bit Error Rate

BH Buried Heterostructure

BiCMOS Bipolar Complementary Metal Oxide Semiconductor

BILBAO Borne drsquoinfrastructures large bande avec accegraves optique (Wideband infrastructure base with optical access)

CAD Computer-aided design

CdS Cadmium sulfide

CEA-Leti Commissariat agrave lrsquoeacutenergie atomique (Atomic energy commission)

CMOS Complementary metal-oxide-semiconductor

CNAM Conservatoire national des arts et meacutetiers

CPW Coplanar waveguide

xviii Microwave Photonic Links

DBR Distributed Bragg reflector

DC Direct current

DD-MZM Dual drive-MZM

DFA Doped fiber amplifier

DFB Distributed feedback laser

DFT Discrete Fourier transform

EO Electricoptic

EAM Electro-absorption modulator

EDFA Erbium-doped fiber amplifier

EEL Edge emitting laser

EML Electro-absorption modulated laser

EMT Electromagnetic transverse

EOM Electro-optic modulator

ER Extinction ratio

ESYCOM Equipe systegravemes de communications et microsystegravemes (Communications and microsystems team)

ET Electric transverse

EVM Error vector magnitude

FCC Federal communications commission

FET Field-effect transistor

FKE Franz-Keldysh effect

FT RampD France Telecom Research amp Development

GaAs Galium arsenide

GaP Galium phosphide

Ge Germanium

GRINSCH Graded index separate confinement heterostructure

HB Harmonic balance

HBT Heterojunction bipolar transistor

Abbreviation Glossary xix

HEMT High electron mobility transistor

HFET Heterojunction field-effect transistor

HFSS High frequency simulation system

HPT Heterojunction bipolar phototransistor

IDFT Inverse discrete Fourier transform

IM-DD Intensity modulation-direct detection

IMEP Institut de microeacutelectronique eacutelectromagneacutetisme et optique (Institute of microelectronics electromagnetism and optics)

InAs Indium arsenide

InGaAs Indium gallium arsenide

InGaP Indium gallium phosphide

InP Indium phosphide

IR-UWB Impulse Radio ndash Ultra Wideband

KDP Potassium dihydrogen phosphate

LAHC Laboratoire drsquohyperfreacutequences et de caracteacuterisation (hyperfrequency and characterization laboratory)

LASER Light amplifier by stimulated emission of radiation

LF Low frequency

LiNbO3 Lithium niobate

LiTaO3 Lithium tantalate

MAG Maximum available gain

MASER Microwave amplifier by stimulated emission of radiation

MB-OFDM Multi-band ndash orthogonal frequency division modulation

MB-OOK Multi-band on off keying

MEMS Micro-electro-mechanical systems

MESFET Metal semiconductor field-effect transistor

MMIC Monolithic microwave integrated circuit

MODFET Modulation-doped field-effect transistor

MQW-EAM Multi-quantum well-EAM

xx Microwave Photonic Links

MSM Metal semiconductor metal

MZM Modulator Mach-Zehnder

NdYAG Neodymium-doped yttrium aluminum garnet

NF Noise factor Noise figure

nOI n order intermodulation

nOIP n order intercept point

NRA National Research Agency

OE Opticelectric

OEIC Optoelectronic integrated circuit

OEMMIC Optoelectronic millimeter-wave monolithic integrated circuit

OFDM Orthogonal frequency division modulation

PDFA Praseodymium-doped fiber amplifier

PDG Biased-dependent gain

PM Phase modulation

PMMA Poly(methyl methacrylate)

PRBS Pseudo-random bit sequence

PSK Phase-shift keying

QAM Quadrature amplitude modulation

QCSE Quantum confined stark effect

QW-EAM Quantum well-EAM

RCEPD Resonant cavity enhanced photodetectors

RFT Rapid Fourier transform

RIN Relative intensity noise

RoF Radio over fiber

SD-MZM Single drive ndashMZM

Si Silicon

SiGe Silicon-germanium

SiMOX Separation by implantation of oxygen

Abbreviation Glossary xxi

SiO2 Silicon dioxide

SOA Semiconductor optical amplifier

SOC System on a chip

SOI Substrate on insulator

TDFA Thulium-doped fiber amplifier

TEGFET Two-dimensional electron gas field-effect transistor

TW-MZM Travelling wave-MZM

UTC Uni-travelling carrier

UWB Ultra-wideband

VCSEL Vertical-cavity surface-emitting laser

VCSOA Vertical-cavity semiconductor optical amplifier

VMDP Velocity matched distributed photodetector

WDM Wavelength division multiplexing

YDFA Ytterbium-doped fiber amplifier

ZnS Zinc sulfide

Chapter 1

General Points

11 Microwave photonic links

All signals generated or observed due to human activity (measurement of different physical values remote control files sounds images etc) can be transformed into analog electrical signals These electrical signals can be processed or transmitted as they are but in most cases they are digitized beforehand Once digitized these signals have different forms regarding the digital coding or error-correcting algorithms used and protocols employed in the transmission systems To be processed or transmitted these analog or digital signals can use different mediums

If the transmission is performed via metallic lines or cables digital signals directly enter these lines or they modulate more or less complex subcarriers (ADSL Ethernet)

If transmission occurs with a radiowave a high-frequency carrier must be available Due to the congestion of the wireless spectrum carriers are now principally microwaves ie with frequencies of 1 to 100 GHz (GSM UMTS Wi-Fi Wimax etc) Wireless transmission can also be performed by very short pulses having a wide spectrum range including the microwave spectrum or these pulses can modulate a carrier in the millimeter wave spectrum This technique is known as ultra-wideband (UWB) [YAO 09]

If transmission is via fiber optics digital signals modulate one or several optical carriers (amplitude or soliton modulation) which are themselves

2 Microwave Photonic Links

transmitted over hundreds of kilometers on optical fibers This is the case for all passive optical networks (PON) and their different transmission protocols [LEC 97]

From these definitions the distinctive feature of microwave photonic links is to transmit a microwave signal analogically or for it be digitally modulated This microwave signal is transferred to an optical carrier which is guided with minimum loss by an optical fiber The microwave signal is then picked up by a photodetector at the end of the fiber

One of the first applications of microwave optical links was the distribution of the microwave carrier in radar or radio-astronomy systems comprising offset aerials or active phased-array antennas which benefited from the low weight and low volume of the fiber optics [COX 97 DEC 98]

Another important area comprises all radio over fiber (RoF) applications consisting of the extension of wireless networks using microwaves or UWB waves The optical tunnels produced are capable of reaching all rooms or buildings of a company university or diverse institutions or all the rooms of a house whilst benefiting from the very low loss associated with fiber optics [FRI 02]

Amongst the applications of RoF a promising domain is in the connection of internet transmission networks to the home These connections are increasingly popular with ever-increasing speeds (1 Gbs) due to fiber optics reaching households (fiber to the home or FTTH) whereby the house itself becomes a high-speed local network In this local network the signal distribution in each room is achieved by a 60 GHz millimeter-wave (wireless personal area network or WPAN) which stays confined in the room due to the extremely fast attenuation at this frequency All rooms are linked to each other by a network of passive fiber optics which extends the millimeter-wave UWB signal throughout the whole house (ultra broadband wireless home area network or UBB-WHAN) Examples of millimeter-wave over optical transmissions are presented in [CHU 07 KIM 04 WEI 08] and a demonstration of a UBB-WHAN with an up and down link is described in [HUC 08]

The length of a link ranges from 10 m to 1 km allowing several fiber types to be used (single mode or multimode silica or plastic) and several optical wavelengths ranging from 06 to 155 μm The light undergoes intensity modulation the signal is received via photodetection In just a few

General Points 3

years rates have risen from around 10 Mbs on carriers of a few gigahertz to rates of 1 or 10 Gbs on 60 GHz for microwave carriers

A microwave photonic link is constituted of three parts

ndash a coherent light source a laser that emits an optical carrier the intensity of which is directly modulated inside the laser or externally by an optical modulator In the case of external modulation the amplitude modulation is performed by a Mach-Zehnder or an electro-absorption modulator

ndash the modulated light is then transported by single or multi-mode optical fiber [GOM 08 KOO 08] made of silica or plastic [KOI 06] This part may include an optical amplification

ndash the modulated light is finally photodetected in a photodetector consisting of a photodiode or a phototransistor

After some deliberation regarding coherent and incoherent optical links [HAL 82] the solution finally adopted for these links was ldquointensity modulation (IM) direct detection (DD)rdquo As this is recalled in [COX 06] in this type of link the depth of optical modulation is sufficiently weak that we can initially use small signal or linear techniques for each aspect Because the signals applied to links or extracted from them are in microwaves the variables characterizing these systems are S-parameters gains and noise factors Also nonlinearities and hence intermodulation produced by each component on the signal introduced in the link must be considered The combination of these different characteristics leads to the notion of interference-free dynamic range (IFDR) This shall be evaluated regarding the properties of each element in the chapters concerning overall performances of such links

As a link includes electrical-to-optical optical-to-electrical and even optical-to-optical transducers each of the magnitudes in terms of S-parameters gains and noise factors should be presented in the form of optomicrowave magnitudes This aspect forces harmonization of notions from the optical optoelectronic and microwave disciplines This is described in Chapter 5

The term used initially to describe these links was ldquomicrowave optical linksrdquo However the techniques used have gradually distanced themselves from proper optical and optoelectronic techniques so that the more specific term ldquomicrowave photonic linksrdquo has been progressively used [SEE 02]

4 Microwave Photonic Links

12 Link description

Figures 11 and 12 represent a general diagram of an IM-DD microwave optical link

Figure 11 Diagram of directly modulated microwave optical link

Figure 11 represents a direct modulation link A laser emits a light of wavelength 08 or 13 or 155 μm this laser is modulated by a microwave signal (which is possibly itself modulated) through a driver circuit The modulated light enters an optical fiber coupled to a photodetector that detects the microwave modulation signal The optical modulation can have an amplitude frequency and phase However direct photodetection detects only the modulation in amplitude The detected microwave signal is then amplified by a low-noise amplifier

Figure 12 represents an external modulation link This time a light emitted from a laser is injected into a Mach-Zehnder or electro-absorption amplitude modulator In this case microwave modulation is also applied to the modulator through a driver circuit

After passing into an optical fiber the optical intensity modulation only is detected via a photodetector As in the previous diagram the detected microwave signal is amplified in a low-noise amplifier

Laser

Driver

Optical fiber Photodetector

Low noise amplifier

Microwave or UWB Microwave or UWB

λ = 155 or 13 or 08 μm

Amplitude modulation Direct detection

General Points 5

Figure 12 Diagram of externally modulated microwave optical link

13 Signal to transmit

131 Microwave signal

The first type of transmitted signal is a signal that constitutes a microwave frequency reference It can be used in offset aerial systems or active phased-array antenna After its reflection from a moving object the microwave signal emitted from an antenna can shift in frequency (Doppler modulation) and it is the spectral purity of the microwave that determines the minimum observed frequency shift and therefore the minimum relative speed of the moving object The spectral purity and degradation after transmission of the microwave by optical links must be watched closely to distinguish the frequency shift

132 Microwave carrier for a digital signal

If the microwave signal serves as a carrier for a digital signal this carrier is previously modulated All the modulation techniques normally used such as amplitude frequency phase OFDM and combined amplitude-phase modulation (QAM) or more complex techniques can be considered such as those used in GSM GPRS EDGE and UMTS for mobile telephones or such as Bluetooth Wi-Fi and Wimax for data transmission These modulations are generally carried out on single sideband (SSB) When microwave signal modulation is implemented in phase or frequency spectral purity is also of great importance

Laser

Amplifier or driver

Optical fiber

λ = 155 or 13 or 08 μm

Microwave or UWB

Optical modulator MZ or EA

Amplitude modulation

Photodetector

Low noise amplifier

Microwave or UWB

Direct detection

6 Microwave Photonic Links

133 UWB signal

Another signal category is available for transmission by fiber optics These signals are relevant to UWB techniques without carriers and with the spectrum in the microwave region or up-converted to a millimeter-wave carrier UWB wireless links are largely used over short distances The optical fibers are particularly indicated to enable extensions of such networks

134 Optical carrier

Microwave signals can carry analog information (frequency shift due to the Doppler effect) or they can be modulated by a digital signal or be constituted of UWB signals which are themselves digitally modulated All these microwave signals must be up-converted to an optical carrier This transfer exclusively occurs by intensity modulation One of the advantages of this modulation is that the microwave signal can be recovered in a simple photodetection unit permitting the elimination of possible frequency fluctuations of the optical carrier Loss of sensitivity resulting from direct detection does not occur if the optical wavelength allows us to insert an optical amplifier or if the link is very short Usually this modulation is double sideband (DSB) especially if the modulation occurs directly in the laser but for slightly longer links this type of modulation can lead to extinction phenomena A single sideband modulation can hence be considered but this modulation must be carried out by an external modulator

135 Summary

The complexity of microwave photonic links comes from the stacking of an optical carrier and microwave or UWB subcarrier The optical carrier is exclusively intensity modulated whereas the microwave subcarrier can be modulated following all known modulation types amplitude frequency phase or their combination including a frequency shift due to the Doppler effect All these modulations can be recovered via photodetection

The use of microwave optical links will increase as the transmitted signals will be numerous and emitted in parallel communications and the data rates will increase accordingly Thus telecommunication optical

xii Microwave Photonic Links

85 Other types of modulation of signals transmitted on an optical fiber 348

851 Ultra-wideband signal modulation 348 852 External modulation 353 853 Generation of microwave signal by frequency beating 358

86 Conclusion 361 87 Appendix 362

871 MB-OOK modulation 362 872 OFDM modulation 363

Bibliography 367

Index 393

Preface

Two important areas of applications of microwave photonic links are electromagnetic sensors and radio-over-fiber (RoF) applications

Electromagnetic sensor microwave systems of the future will principally use active phased-array antennas The development will be determined by reliability requirements resistance to interference and total emission flexibility of the beamforming networks This type of antenna would therefore be used in a diverse range of applications eg radar communication and countermeasures To satisfy this multifunctional approach it will be necessary to distribute these antennas all over the surface area of strategic platforms (planes drones boats etc) While on the ground the multistatic mode of operation will force multiple antennas to be deported from their processing unit

This will require links with very low loss and noise enabling remote-control antennas and the distribution and processing of very wide bandwidth microwave signals (typically 1-20 GHz 40 GHz will be seen in the future)

Currently the maturity and performance notably in terms of spectral purity and opto-electronic component linearity are such that it is possible to consider both optical distribution and processing of these electrical signals Thus the optical transmission of microwaves offers as well as propagation of broad frequency bands advantages regarding weight volume and flexibility characterized by a decrease in the weight of the wiring by 90 in comparison to coaxial cables and thus insensitivity to electromagnetic perturbation All of which will enable the introduction of new concepts in microwave systems based on optical architecture

xiv Microwave Photonic Links

Several sensor radar systems have been designed and produced in France the United States the UK and Italy and photonic technology for the distribution of microwave signals is already being used for ground airborne and aerospace applications

Fiber-optic distribution network technology is an emergence of this technology platform in reference to the design of opto-electronic links for the transmission of microwave and digital signals This optical wiring aims to replace coaxial wiring for onboard electronics interconnections Here the term transmission is taken in the sense that microwave transmissions on optical carriers are in-phase

These functions require the design of emitting and receiving opto-electronic modules the integration of both high thermal stability multiplexing demultiplexing functions and single-mode connectors either point to point or multipoints

Another area of reference is the optical control of the phase andor delay of microwave signals and their applications to electromagnetic sensor systems This occurs by the design of ultrafast opto-electronic multi-chip modules incorporating the optically-controlled switching the control synthesis of time delay systems and the multiwave laser sources

Amongst the most promising technologies is the synthesis of mono- and bidimensional time-delays for the single and multiple beamforming in receiver and emitter the ultraprecise (picoseconds) time synchronization of distributed electromagnetic sensors the time-delay control (precision in the order of picoseconds) of very wide bandwidth microwave signals to measure the arrival direction and the waveshape generation

Another important area involving all RoF applications is the extensive development of wireless networks using microwaves or ultra-wideband signals This is achieved by providing optical tunnels capable of reaching all areas of a company university etc or all the rooms of a house whilst benefiting from the very low loss associated with fiber optics

In their work titled ldquoMicrowave Photonic Linksrdquo C Rumelhard C Algani and A-L Billabert studied and developed models of the components and photonic functions in microwave applications thus laying the foundation for research into microwave photonic links in order to allow the

Preface xv

integration of these components in electromagnetic sensors systems The components and functions addressed range from optical sources (modulated semiconductor lasers or externally modulated continuous lasers) to photodetectors optical fibers and optical amplifiers

This work focuses upon optical components their transfer functionality and their modeling in terms of microwave components in order to create an electrical model of microwave photonic links In order to achieve this level of complexity a number of modeling approaches have been created by the authors to elucidate the influences of the constituent components of microwave photonic links

Because the advancement of opto-electronics photonics and microwaves is possible by the unification of modeling approaches there is no doubt that such works will be referenced by students but also by design engineers and architects of electromagnetic sensor systems who will incorporate this new technology into their designs

This is to the authorrsquos knowledge the first work addressing the description and modeling of microwave photonic link technology with an educational approach to physical phenomena and new approaches to modeling microwave photonic components

Jean Chazelas Scientific Director

Thales Aeronautics Division

Abbreviation Glossary

AC Alternating Current

ACPR Adjacent Channel Power Ratio

ADP Ammonium dihydrogen phosphate

ADS Advanced Design System

AlGaAs Aluminum gallium arsenide

AM Amplitude Modulation

AM-DD Amplitude Modulation ndash Direct Detection

ASE Amplified Spontaneous Emission

BER Bit Error Rate

BH Buried Heterostructure

BiCMOS Bipolar Complementary Metal Oxide Semiconductor

BILBAO Borne drsquoinfrastructures large bande avec accegraves optique (Wideband infrastructure base with optical access)

CAD Computer-aided design

CdS Cadmium sulfide

CEA-Leti Commissariat agrave lrsquoeacutenergie atomique (Atomic energy commission)

CMOS Complementary metal-oxide-semiconductor

CNAM Conservatoire national des arts et meacutetiers

CPW Coplanar waveguide

xviii Microwave Photonic Links

DBR Distributed Bragg reflector

DC Direct current

DD-MZM Dual drive-MZM

DFA Doped fiber amplifier

DFB Distributed feedback laser

DFT Discrete Fourier transform

EO Electricoptic

EAM Electro-absorption modulator

EDFA Erbium-doped fiber amplifier

EEL Edge emitting laser

EML Electro-absorption modulated laser

EMT Electromagnetic transverse

EOM Electro-optic modulator

ER Extinction ratio

ESYCOM Equipe systegravemes de communications et microsystegravemes (Communications and microsystems team)

ET Electric transverse

EVM Error vector magnitude

FCC Federal communications commission

FET Field-effect transistor

FKE Franz-Keldysh effect

FT RampD France Telecom Research amp Development

GaAs Galium arsenide

GaP Galium phosphide

Ge Germanium

GRINSCH Graded index separate confinement heterostructure

HB Harmonic balance

HBT Heterojunction bipolar transistor

Abbreviation Glossary xix

HEMT High electron mobility transistor

HFET Heterojunction field-effect transistor

HFSS High frequency simulation system

HPT Heterojunction bipolar phototransistor

IDFT Inverse discrete Fourier transform

IM-DD Intensity modulation-direct detection

IMEP Institut de microeacutelectronique eacutelectromagneacutetisme et optique (Institute of microelectronics electromagnetism and optics)

InAs Indium arsenide

InGaAs Indium gallium arsenide

InGaP Indium gallium phosphide

InP Indium phosphide

IR-UWB Impulse Radio ndash Ultra Wideband

KDP Potassium dihydrogen phosphate

LAHC Laboratoire drsquohyperfreacutequences et de caracteacuterisation (hyperfrequency and characterization laboratory)

LASER Light amplifier by stimulated emission of radiation

LF Low frequency

LiNbO3 Lithium niobate

LiTaO3 Lithium tantalate

MAG Maximum available gain

MASER Microwave amplifier by stimulated emission of radiation

MB-OFDM Multi-band ndash orthogonal frequency division modulation

MB-OOK Multi-band on off keying

MEMS Micro-electro-mechanical systems

MESFET Metal semiconductor field-effect transistor

MMIC Monolithic microwave integrated circuit

MODFET Modulation-doped field-effect transistor

MQW-EAM Multi-quantum well-EAM

xx Microwave Photonic Links

MSM Metal semiconductor metal

MZM Modulator Mach-Zehnder

NdYAG Neodymium-doped yttrium aluminum garnet

NF Noise factor Noise figure

nOI n order intermodulation

nOIP n order intercept point

NRA National Research Agency

OE Opticelectric

OEIC Optoelectronic integrated circuit

OEMMIC Optoelectronic millimeter-wave monolithic integrated circuit

OFDM Orthogonal frequency division modulation

PDFA Praseodymium-doped fiber amplifier

PDG Biased-dependent gain

PM Phase modulation

PMMA Poly(methyl methacrylate)

PRBS Pseudo-random bit sequence

PSK Phase-shift keying

QAM Quadrature amplitude modulation

QCSE Quantum confined stark effect

QW-EAM Quantum well-EAM

RCEPD Resonant cavity enhanced photodetectors

RFT Rapid Fourier transform

RIN Relative intensity noise

RoF Radio over fiber

SD-MZM Single drive ndashMZM

Si Silicon

SiGe Silicon-germanium

SiMOX Separation by implantation of oxygen

Abbreviation Glossary xxi

SiO2 Silicon dioxide

SOA Semiconductor optical amplifier

SOC System on a chip

SOI Substrate on insulator

TDFA Thulium-doped fiber amplifier

TEGFET Two-dimensional electron gas field-effect transistor

TW-MZM Travelling wave-MZM

UTC Uni-travelling carrier

UWB Ultra-wideband

VCSEL Vertical-cavity surface-emitting laser

VCSOA Vertical-cavity semiconductor optical amplifier

VMDP Velocity matched distributed photodetector

WDM Wavelength division multiplexing

YDFA Ytterbium-doped fiber amplifier

ZnS Zinc sulfide

Chapter 1

General Points

11 Microwave photonic links

All signals generated or observed due to human activity (measurement of different physical values remote control files sounds images etc) can be transformed into analog electrical signals These electrical signals can be processed or transmitted as they are but in most cases they are digitized beforehand Once digitized these signals have different forms regarding the digital coding or error-correcting algorithms used and protocols employed in the transmission systems To be processed or transmitted these analog or digital signals can use different mediums

If the transmission is performed via metallic lines or cables digital signals directly enter these lines or they modulate more or less complex subcarriers (ADSL Ethernet)

If transmission occurs with a radiowave a high-frequency carrier must be available Due to the congestion of the wireless spectrum carriers are now principally microwaves ie with frequencies of 1 to 100 GHz (GSM UMTS Wi-Fi Wimax etc) Wireless transmission can also be performed by very short pulses having a wide spectrum range including the microwave spectrum or these pulses can modulate a carrier in the millimeter wave spectrum This technique is known as ultra-wideband (UWB) [YAO 09]

If transmission is via fiber optics digital signals modulate one or several optical carriers (amplitude or soliton modulation) which are themselves

2 Microwave Photonic Links

transmitted over hundreds of kilometers on optical fibers This is the case for all passive optical networks (PON) and their different transmission protocols [LEC 97]

From these definitions the distinctive feature of microwave photonic links is to transmit a microwave signal analogically or for it be digitally modulated This microwave signal is transferred to an optical carrier which is guided with minimum loss by an optical fiber The microwave signal is then picked up by a photodetector at the end of the fiber

One of the first applications of microwave optical links was the distribution of the microwave carrier in radar or radio-astronomy systems comprising offset aerials or active phased-array antennas which benefited from the low weight and low volume of the fiber optics [COX 97 DEC 98]

Another important area comprises all radio over fiber (RoF) applications consisting of the extension of wireless networks using microwaves or UWB waves The optical tunnels produced are capable of reaching all rooms or buildings of a company university or diverse institutions or all the rooms of a house whilst benefiting from the very low loss associated with fiber optics [FRI 02]

Amongst the applications of RoF a promising domain is in the connection of internet transmission networks to the home These connections are increasingly popular with ever-increasing speeds (1 Gbs) due to fiber optics reaching households (fiber to the home or FTTH) whereby the house itself becomes a high-speed local network In this local network the signal distribution in each room is achieved by a 60 GHz millimeter-wave (wireless personal area network or WPAN) which stays confined in the room due to the extremely fast attenuation at this frequency All rooms are linked to each other by a network of passive fiber optics which extends the millimeter-wave UWB signal throughout the whole house (ultra broadband wireless home area network or UBB-WHAN) Examples of millimeter-wave over optical transmissions are presented in [CHU 07 KIM 04 WEI 08] and a demonstration of a UBB-WHAN with an up and down link is described in [HUC 08]

The length of a link ranges from 10 m to 1 km allowing several fiber types to be used (single mode or multimode silica or plastic) and several optical wavelengths ranging from 06 to 155 μm The light undergoes intensity modulation the signal is received via photodetection In just a few

General Points 3

years rates have risen from around 10 Mbs on carriers of a few gigahertz to rates of 1 or 10 Gbs on 60 GHz for microwave carriers

A microwave photonic link is constituted of three parts

ndash a coherent light source a laser that emits an optical carrier the intensity of which is directly modulated inside the laser or externally by an optical modulator In the case of external modulation the amplitude modulation is performed by a Mach-Zehnder or an electro-absorption modulator

ndash the modulated light is then transported by single or multi-mode optical fiber [GOM 08 KOO 08] made of silica or plastic [KOI 06] This part may include an optical amplification

ndash the modulated light is finally photodetected in a photodetector consisting of a photodiode or a phototransistor

After some deliberation regarding coherent and incoherent optical links [HAL 82] the solution finally adopted for these links was ldquointensity modulation (IM) direct detection (DD)rdquo As this is recalled in [COX 06] in this type of link the depth of optical modulation is sufficiently weak that we can initially use small signal or linear techniques for each aspect Because the signals applied to links or extracted from them are in microwaves the variables characterizing these systems are S-parameters gains and noise factors Also nonlinearities and hence intermodulation produced by each component on the signal introduced in the link must be considered The combination of these different characteristics leads to the notion of interference-free dynamic range (IFDR) This shall be evaluated regarding the properties of each element in the chapters concerning overall performances of such links

As a link includes electrical-to-optical optical-to-electrical and even optical-to-optical transducers each of the magnitudes in terms of S-parameters gains and noise factors should be presented in the form of optomicrowave magnitudes This aspect forces harmonization of notions from the optical optoelectronic and microwave disciplines This is described in Chapter 5

The term used initially to describe these links was ldquomicrowave optical linksrdquo However the techniques used have gradually distanced themselves from proper optical and optoelectronic techniques so that the more specific term ldquomicrowave photonic linksrdquo has been progressively used [SEE 02]

4 Microwave Photonic Links

12 Link description

Figures 11 and 12 represent a general diagram of an IM-DD microwave optical link

Figure 11 Diagram of directly modulated microwave optical link

Figure 11 represents a direct modulation link A laser emits a light of wavelength 08 or 13 or 155 μm this laser is modulated by a microwave signal (which is possibly itself modulated) through a driver circuit The modulated light enters an optical fiber coupled to a photodetector that detects the microwave modulation signal The optical modulation can have an amplitude frequency and phase However direct photodetection detects only the modulation in amplitude The detected microwave signal is then amplified by a low-noise amplifier

Figure 12 represents an external modulation link This time a light emitted from a laser is injected into a Mach-Zehnder or electro-absorption amplitude modulator In this case microwave modulation is also applied to the modulator through a driver circuit

After passing into an optical fiber the optical intensity modulation only is detected via a photodetector As in the previous diagram the detected microwave signal is amplified in a low-noise amplifier

Laser

Driver

Optical fiber Photodetector

Low noise amplifier

Microwave or UWB Microwave or UWB

λ = 155 or 13 or 08 μm

Amplitude modulation Direct detection

General Points 5

Figure 12 Diagram of externally modulated microwave optical link

13 Signal to transmit

131 Microwave signal

The first type of transmitted signal is a signal that constitutes a microwave frequency reference It can be used in offset aerial systems or active phased-array antenna After its reflection from a moving object the microwave signal emitted from an antenna can shift in frequency (Doppler modulation) and it is the spectral purity of the microwave that determines the minimum observed frequency shift and therefore the minimum relative speed of the moving object The spectral purity and degradation after transmission of the microwave by optical links must be watched closely to distinguish the frequency shift

132 Microwave carrier for a digital signal

If the microwave signal serves as a carrier for a digital signal this carrier is previously modulated All the modulation techniques normally used such as amplitude frequency phase OFDM and combined amplitude-phase modulation (QAM) or more complex techniques can be considered such as those used in GSM GPRS EDGE and UMTS for mobile telephones or such as Bluetooth Wi-Fi and Wimax for data transmission These modulations are generally carried out on single sideband (SSB) When microwave signal modulation is implemented in phase or frequency spectral purity is also of great importance

Laser

Amplifier or driver

Optical fiber

λ = 155 or 13 or 08 μm

Microwave or UWB

Optical modulator MZ or EA

Amplitude modulation

Photodetector

Low noise amplifier

Microwave or UWB

Direct detection

6 Microwave Photonic Links

133 UWB signal

Another signal category is available for transmission by fiber optics These signals are relevant to UWB techniques without carriers and with the spectrum in the microwave region or up-converted to a millimeter-wave carrier UWB wireless links are largely used over short distances The optical fibers are particularly indicated to enable extensions of such networks

134 Optical carrier

Microwave signals can carry analog information (frequency shift due to the Doppler effect) or they can be modulated by a digital signal or be constituted of UWB signals which are themselves digitally modulated All these microwave signals must be up-converted to an optical carrier This transfer exclusively occurs by intensity modulation One of the advantages of this modulation is that the microwave signal can be recovered in a simple photodetection unit permitting the elimination of possible frequency fluctuations of the optical carrier Loss of sensitivity resulting from direct detection does not occur if the optical wavelength allows us to insert an optical amplifier or if the link is very short Usually this modulation is double sideband (DSB) especially if the modulation occurs directly in the laser but for slightly longer links this type of modulation can lead to extinction phenomena A single sideband modulation can hence be considered but this modulation must be carried out by an external modulator

135 Summary

The complexity of microwave photonic links comes from the stacking of an optical carrier and microwave or UWB subcarrier The optical carrier is exclusively intensity modulated whereas the microwave subcarrier can be modulated following all known modulation types amplitude frequency phase or their combination including a frequency shift due to the Doppler effect All these modulations can be recovered via photodetection

The use of microwave optical links will increase as the transmitted signals will be numerous and emitted in parallel communications and the data rates will increase accordingly Thus telecommunication optical

Preface

Two important areas of applications of microwave photonic links are electromagnetic sensors and radio-over-fiber (RoF) applications

Electromagnetic sensor microwave systems of the future will principally use active phased-array antennas The development will be determined by reliability requirements resistance to interference and total emission flexibility of the beamforming networks This type of antenna would therefore be used in a diverse range of applications eg radar communication and countermeasures To satisfy this multifunctional approach it will be necessary to distribute these antennas all over the surface area of strategic platforms (planes drones boats etc) While on the ground the multistatic mode of operation will force multiple antennas to be deported from their processing unit

This will require links with very low loss and noise enabling remote-control antennas and the distribution and processing of very wide bandwidth microwave signals (typically 1-20 GHz 40 GHz will be seen in the future)

Currently the maturity and performance notably in terms of spectral purity and opto-electronic component linearity are such that it is possible to consider both optical distribution and processing of these electrical signals Thus the optical transmission of microwaves offers as well as propagation of broad frequency bands advantages regarding weight volume and flexibility characterized by a decrease in the weight of the wiring by 90 in comparison to coaxial cables and thus insensitivity to electromagnetic perturbation All of which will enable the introduction of new concepts in microwave systems based on optical architecture

xiv Microwave Photonic Links

Several sensor radar systems have been designed and produced in France the United States the UK and Italy and photonic technology for the distribution of microwave signals is already being used for ground airborne and aerospace applications

Fiber-optic distribution network technology is an emergence of this technology platform in reference to the design of opto-electronic links for the transmission of microwave and digital signals This optical wiring aims to replace coaxial wiring for onboard electronics interconnections Here the term transmission is taken in the sense that microwave transmissions on optical carriers are in-phase

These functions require the design of emitting and receiving opto-electronic modules the integration of both high thermal stability multiplexing demultiplexing functions and single-mode connectors either point to point or multipoints

Another area of reference is the optical control of the phase andor delay of microwave signals and their applications to electromagnetic sensor systems This occurs by the design of ultrafast opto-electronic multi-chip modules incorporating the optically-controlled switching the control synthesis of time delay systems and the multiwave laser sources

Amongst the most promising technologies is the synthesis of mono- and bidimensional time-delays for the single and multiple beamforming in receiver and emitter the ultraprecise (picoseconds) time synchronization of distributed electromagnetic sensors the time-delay control (precision in the order of picoseconds) of very wide bandwidth microwave signals to measure the arrival direction and the waveshape generation

Another important area involving all RoF applications is the extensive development of wireless networks using microwaves or ultra-wideband signals This is achieved by providing optical tunnels capable of reaching all areas of a company university etc or all the rooms of a house whilst benefiting from the very low loss associated with fiber optics

In their work titled ldquoMicrowave Photonic Linksrdquo C Rumelhard C Algani and A-L Billabert studied and developed models of the components and photonic functions in microwave applications thus laying the foundation for research into microwave photonic links in order to allow the

Preface xv

integration of these components in electromagnetic sensors systems The components and functions addressed range from optical sources (modulated semiconductor lasers or externally modulated continuous lasers) to photodetectors optical fibers and optical amplifiers

This work focuses upon optical components their transfer functionality and their modeling in terms of microwave components in order to create an electrical model of microwave photonic links In order to achieve this level of complexity a number of modeling approaches have been created by the authors to elucidate the influences of the constituent components of microwave photonic links

Because the advancement of opto-electronics photonics and microwaves is possible by the unification of modeling approaches there is no doubt that such works will be referenced by students but also by design engineers and architects of electromagnetic sensor systems who will incorporate this new technology into their designs

This is to the authorrsquos knowledge the first work addressing the description and modeling of microwave photonic link technology with an educational approach to physical phenomena and new approaches to modeling microwave photonic components

Jean Chazelas Scientific Director

Thales Aeronautics Division

Abbreviation Glossary

AC Alternating Current

ACPR Adjacent Channel Power Ratio

ADP Ammonium dihydrogen phosphate

ADS Advanced Design System

AlGaAs Aluminum gallium arsenide

AM Amplitude Modulation

AM-DD Amplitude Modulation ndash Direct Detection

ASE Amplified Spontaneous Emission

BER Bit Error Rate

BH Buried Heterostructure

BiCMOS Bipolar Complementary Metal Oxide Semiconductor

BILBAO Borne drsquoinfrastructures large bande avec accegraves optique (Wideband infrastructure base with optical access)

CAD Computer-aided design

CdS Cadmium sulfide

CEA-Leti Commissariat agrave lrsquoeacutenergie atomique (Atomic energy commission)

CMOS Complementary metal-oxide-semiconductor

CNAM Conservatoire national des arts et meacutetiers

CPW Coplanar waveguide

xviii Microwave Photonic Links

DBR Distributed Bragg reflector

DC Direct current

DD-MZM Dual drive-MZM

DFA Doped fiber amplifier

DFB Distributed feedback laser

DFT Discrete Fourier transform

EO Electricoptic

EAM Electro-absorption modulator

EDFA Erbium-doped fiber amplifier

EEL Edge emitting laser

EML Electro-absorption modulated laser

EMT Electromagnetic transverse

EOM Electro-optic modulator

ER Extinction ratio

ESYCOM Equipe systegravemes de communications et microsystegravemes (Communications and microsystems team)

ET Electric transverse

EVM Error vector magnitude

FCC Federal communications commission

FET Field-effect transistor

FKE Franz-Keldysh effect

FT RampD France Telecom Research amp Development

GaAs Galium arsenide

GaP Galium phosphide

Ge Germanium

GRINSCH Graded index separate confinement heterostructure

HB Harmonic balance

HBT Heterojunction bipolar transistor

Abbreviation Glossary xix

HEMT High electron mobility transistor

HFET Heterojunction field-effect transistor

HFSS High frequency simulation system

HPT Heterojunction bipolar phototransistor

IDFT Inverse discrete Fourier transform

IM-DD Intensity modulation-direct detection

IMEP Institut de microeacutelectronique eacutelectromagneacutetisme et optique (Institute of microelectronics electromagnetism and optics)

InAs Indium arsenide

InGaAs Indium gallium arsenide

InGaP Indium gallium phosphide

InP Indium phosphide

IR-UWB Impulse Radio ndash Ultra Wideband

KDP Potassium dihydrogen phosphate

LAHC Laboratoire drsquohyperfreacutequences et de caracteacuterisation (hyperfrequency and characterization laboratory)

LASER Light amplifier by stimulated emission of radiation

LF Low frequency

LiNbO3 Lithium niobate

LiTaO3 Lithium tantalate

MAG Maximum available gain

MASER Microwave amplifier by stimulated emission of radiation

MB-OFDM Multi-band ndash orthogonal frequency division modulation

MB-OOK Multi-band on off keying

MEMS Micro-electro-mechanical systems

MESFET Metal semiconductor field-effect transistor

MMIC Monolithic microwave integrated circuit

MODFET Modulation-doped field-effect transistor

MQW-EAM Multi-quantum well-EAM

xx Microwave Photonic Links

MSM Metal semiconductor metal

MZM Modulator Mach-Zehnder

NdYAG Neodymium-doped yttrium aluminum garnet

NF Noise factor Noise figure

nOI n order intermodulation

nOIP n order intercept point

NRA National Research Agency

OE Opticelectric

OEIC Optoelectronic integrated circuit

OEMMIC Optoelectronic millimeter-wave monolithic integrated circuit

OFDM Orthogonal frequency division modulation

PDFA Praseodymium-doped fiber amplifier

PDG Biased-dependent gain

PM Phase modulation

PMMA Poly(methyl methacrylate)

PRBS Pseudo-random bit sequence

PSK Phase-shift keying

QAM Quadrature amplitude modulation

QCSE Quantum confined stark effect

QW-EAM Quantum well-EAM

RCEPD Resonant cavity enhanced photodetectors

RFT Rapid Fourier transform

RIN Relative intensity noise

RoF Radio over fiber

SD-MZM Single drive ndashMZM

Si Silicon

SiGe Silicon-germanium

SiMOX Separation by implantation of oxygen

Abbreviation Glossary xxi

SiO2 Silicon dioxide

SOA Semiconductor optical amplifier

SOC System on a chip

SOI Substrate on insulator

TDFA Thulium-doped fiber amplifier

TEGFET Two-dimensional electron gas field-effect transistor

TW-MZM Travelling wave-MZM

UTC Uni-travelling carrier

UWB Ultra-wideband

VCSEL Vertical-cavity surface-emitting laser

VCSOA Vertical-cavity semiconductor optical amplifier

VMDP Velocity matched distributed photodetector

WDM Wavelength division multiplexing

YDFA Ytterbium-doped fiber amplifier

ZnS Zinc sulfide

Chapter 1

General Points

11 Microwave photonic links

All signals generated or observed due to human activity (measurement of different physical values remote control files sounds images etc) can be transformed into analog electrical signals These electrical signals can be processed or transmitted as they are but in most cases they are digitized beforehand Once digitized these signals have different forms regarding the digital coding or error-correcting algorithms used and protocols employed in the transmission systems To be processed or transmitted these analog or digital signals can use different mediums

If the transmission is performed via metallic lines or cables digital signals directly enter these lines or they modulate more or less complex subcarriers (ADSL Ethernet)

If transmission occurs with a radiowave a high-frequency carrier must be available Due to the congestion of the wireless spectrum carriers are now principally microwaves ie with frequencies of 1 to 100 GHz (GSM UMTS Wi-Fi Wimax etc) Wireless transmission can also be performed by very short pulses having a wide spectrum range including the microwave spectrum or these pulses can modulate a carrier in the millimeter wave spectrum This technique is known as ultra-wideband (UWB) [YAO 09]

If transmission is via fiber optics digital signals modulate one or several optical carriers (amplitude or soliton modulation) which are themselves

2 Microwave Photonic Links

transmitted over hundreds of kilometers on optical fibers This is the case for all passive optical networks (PON) and their different transmission protocols [LEC 97]

From these definitions the distinctive feature of microwave photonic links is to transmit a microwave signal analogically or for it be digitally modulated This microwave signal is transferred to an optical carrier which is guided with minimum loss by an optical fiber The microwave signal is then picked up by a photodetector at the end of the fiber

One of the first applications of microwave optical links was the distribution of the microwave carrier in radar or radio-astronomy systems comprising offset aerials or active phased-array antennas which benefited from the low weight and low volume of the fiber optics [COX 97 DEC 98]

Another important area comprises all radio over fiber (RoF) applications consisting of the extension of wireless networks using microwaves or UWB waves The optical tunnels produced are capable of reaching all rooms or buildings of a company university or diverse institutions or all the rooms of a house whilst benefiting from the very low loss associated with fiber optics [FRI 02]

Amongst the applications of RoF a promising domain is in the connection of internet transmission networks to the home These connections are increasingly popular with ever-increasing speeds (1 Gbs) due to fiber optics reaching households (fiber to the home or FTTH) whereby the house itself becomes a high-speed local network In this local network the signal distribution in each room is achieved by a 60 GHz millimeter-wave (wireless personal area network or WPAN) which stays confined in the room due to the extremely fast attenuation at this frequency All rooms are linked to each other by a network of passive fiber optics which extends the millimeter-wave UWB signal throughout the whole house (ultra broadband wireless home area network or UBB-WHAN) Examples of millimeter-wave over optical transmissions are presented in [CHU 07 KIM 04 WEI 08] and a demonstration of a UBB-WHAN with an up and down link is described in [HUC 08]

The length of a link ranges from 10 m to 1 km allowing several fiber types to be used (single mode or multimode silica or plastic) and several optical wavelengths ranging from 06 to 155 μm The light undergoes intensity modulation the signal is received via photodetection In just a few

General Points 3

years rates have risen from around 10 Mbs on carriers of a few gigahertz to rates of 1 or 10 Gbs on 60 GHz for microwave carriers

A microwave photonic link is constituted of three parts

ndash a coherent light source a laser that emits an optical carrier the intensity of which is directly modulated inside the laser or externally by an optical modulator In the case of external modulation the amplitude modulation is performed by a Mach-Zehnder or an electro-absorption modulator

ndash the modulated light is then transported by single or multi-mode optical fiber [GOM 08 KOO 08] made of silica or plastic [KOI 06] This part may include an optical amplification

ndash the modulated light is finally photodetected in a photodetector consisting of a photodiode or a phototransistor

After some deliberation regarding coherent and incoherent optical links [HAL 82] the solution finally adopted for these links was ldquointensity modulation (IM) direct detection (DD)rdquo As this is recalled in [COX 06] in this type of link the depth of optical modulation is sufficiently weak that we can initially use small signal or linear techniques for each aspect Because the signals applied to links or extracted from them are in microwaves the variables characterizing these systems are S-parameters gains and noise factors Also nonlinearities and hence intermodulation produced by each component on the signal introduced in the link must be considered The combination of these different characteristics leads to the notion of interference-free dynamic range (IFDR) This shall be evaluated regarding the properties of each element in the chapters concerning overall performances of such links

As a link includes electrical-to-optical optical-to-electrical and even optical-to-optical transducers each of the magnitudes in terms of S-parameters gains and noise factors should be presented in the form of optomicrowave magnitudes This aspect forces harmonization of notions from the optical optoelectronic and microwave disciplines This is described in Chapter 5

The term used initially to describe these links was ldquomicrowave optical linksrdquo However the techniques used have gradually distanced themselves from proper optical and optoelectronic techniques so that the more specific term ldquomicrowave photonic linksrdquo has been progressively used [SEE 02]

4 Microwave Photonic Links

12 Link description

Figures 11 and 12 represent a general diagram of an IM-DD microwave optical link

Figure 11 Diagram of directly modulated microwave optical link

Figure 11 represents a direct modulation link A laser emits a light of wavelength 08 or 13 or 155 μm this laser is modulated by a microwave signal (which is possibly itself modulated) through a driver circuit The modulated light enters an optical fiber coupled to a photodetector that detects the microwave modulation signal The optical modulation can have an amplitude frequency and phase However direct photodetection detects only the modulation in amplitude The detected microwave signal is then amplified by a low-noise amplifier

Figure 12 represents an external modulation link This time a light emitted from a laser is injected into a Mach-Zehnder or electro-absorption amplitude modulator In this case microwave modulation is also applied to the modulator through a driver circuit

After passing into an optical fiber the optical intensity modulation only is detected via a photodetector As in the previous diagram the detected microwave signal is amplified in a low-noise amplifier

Laser

Driver

Optical fiber Photodetector

Low noise amplifier

Microwave or UWB Microwave or UWB

λ = 155 or 13 or 08 μm

Amplitude modulation Direct detection

General Points 5

Figure 12 Diagram of externally modulated microwave optical link

13 Signal to transmit

131 Microwave signal

The first type of transmitted signal is a signal that constitutes a microwave frequency reference It can be used in offset aerial systems or active phased-array antenna After its reflection from a moving object the microwave signal emitted from an antenna can shift in frequency (Doppler modulation) and it is the spectral purity of the microwave that determines the minimum observed frequency shift and therefore the minimum relative speed of the moving object The spectral purity and degradation after transmission of the microwave by optical links must be watched closely to distinguish the frequency shift

132 Microwave carrier for a digital signal

If the microwave signal serves as a carrier for a digital signal this carrier is previously modulated All the modulation techniques normally used such as amplitude frequency phase OFDM and combined amplitude-phase modulation (QAM) or more complex techniques can be considered such as those used in GSM GPRS EDGE and UMTS for mobile telephones or such as Bluetooth Wi-Fi and Wimax for data transmission These modulations are generally carried out on single sideband (SSB) When microwave signal modulation is implemented in phase or frequency spectral purity is also of great importance

Laser

Amplifier or driver

Optical fiber

λ = 155 or 13 or 08 μm

Microwave or UWB

Optical modulator MZ or EA

Amplitude modulation

Photodetector

Low noise amplifier

Microwave or UWB

Direct detection

6 Microwave Photonic Links

133 UWB signal

Another signal category is available for transmission by fiber optics These signals are relevant to UWB techniques without carriers and with the spectrum in the microwave region or up-converted to a millimeter-wave carrier UWB wireless links are largely used over short distances The optical fibers are particularly indicated to enable extensions of such networks

134 Optical carrier

Microwave signals can carry analog information (frequency shift due to the Doppler effect) or they can be modulated by a digital signal or be constituted of UWB signals which are themselves digitally modulated All these microwave signals must be up-converted to an optical carrier This transfer exclusively occurs by intensity modulation One of the advantages of this modulation is that the microwave signal can be recovered in a simple photodetection unit permitting the elimination of possible frequency fluctuations of the optical carrier Loss of sensitivity resulting from direct detection does not occur if the optical wavelength allows us to insert an optical amplifier or if the link is very short Usually this modulation is double sideband (DSB) especially if the modulation occurs directly in the laser but for slightly longer links this type of modulation can lead to extinction phenomena A single sideband modulation can hence be considered but this modulation must be carried out by an external modulator

135 Summary

The complexity of microwave photonic links comes from the stacking of an optical carrier and microwave or UWB subcarrier The optical carrier is exclusively intensity modulated whereas the microwave subcarrier can be modulated following all known modulation types amplitude frequency phase or their combination including a frequency shift due to the Doppler effect All these modulations can be recovered via photodetection

The use of microwave optical links will increase as the transmitted signals will be numerous and emitted in parallel communications and the data rates will increase accordingly Thus telecommunication optical

xiv Microwave Photonic Links

Several sensor radar systems have been designed and produced in France the United States the UK and Italy and photonic technology for the distribution of microwave signals is already being used for ground airborne and aerospace applications

Fiber-optic distribution network technology is an emergence of this technology platform in reference to the design of opto-electronic links for the transmission of microwave and digital signals This optical wiring aims to replace coaxial wiring for onboard electronics interconnections Here the term transmission is taken in the sense that microwave transmissions on optical carriers are in-phase

These functions require the design of emitting and receiving opto-electronic modules the integration of both high thermal stability multiplexing demultiplexing functions and single-mode connectors either point to point or multipoints

Another area of reference is the optical control of the phase andor delay of microwave signals and their applications to electromagnetic sensor systems This occurs by the design of ultrafast opto-electronic multi-chip modules incorporating the optically-controlled switching the control synthesis of time delay systems and the multiwave laser sources

Amongst the most promising technologies is the synthesis of mono- and bidimensional time-delays for the single and multiple beamforming in receiver and emitter the ultraprecise (picoseconds) time synchronization of distributed electromagnetic sensors the time-delay control (precision in the order of picoseconds) of very wide bandwidth microwave signals to measure the arrival direction and the waveshape generation

Another important area involving all RoF applications is the extensive development of wireless networks using microwaves or ultra-wideband signals This is achieved by providing optical tunnels capable of reaching all areas of a company university etc or all the rooms of a house whilst benefiting from the very low loss associated with fiber optics

In their work titled ldquoMicrowave Photonic Linksrdquo C Rumelhard C Algani and A-L Billabert studied and developed models of the components and photonic functions in microwave applications thus laying the foundation for research into microwave photonic links in order to allow the

Preface xv

integration of these components in electromagnetic sensors systems The components and functions addressed range from optical sources (modulated semiconductor lasers or externally modulated continuous lasers) to photodetectors optical fibers and optical amplifiers

This work focuses upon optical components their transfer functionality and their modeling in terms of microwave components in order to create an electrical model of microwave photonic links In order to achieve this level of complexity a number of modeling approaches have been created by the authors to elucidate the influences of the constituent components of microwave photonic links

Because the advancement of opto-electronics photonics and microwaves is possible by the unification of modeling approaches there is no doubt that such works will be referenced by students but also by design engineers and architects of electromagnetic sensor systems who will incorporate this new technology into their designs

This is to the authorrsquos knowledge the first work addressing the description and modeling of microwave photonic link technology with an educational approach to physical phenomena and new approaches to modeling microwave photonic components

Jean Chazelas Scientific Director

Thales Aeronautics Division

Abbreviation Glossary

AC Alternating Current

ACPR Adjacent Channel Power Ratio

ADP Ammonium dihydrogen phosphate

ADS Advanced Design System

AlGaAs Aluminum gallium arsenide

AM Amplitude Modulation

AM-DD Amplitude Modulation ndash Direct Detection

ASE Amplified Spontaneous Emission

BER Bit Error Rate

BH Buried Heterostructure

BiCMOS Bipolar Complementary Metal Oxide Semiconductor

BILBAO Borne drsquoinfrastructures large bande avec accegraves optique (Wideband infrastructure base with optical access)

CAD Computer-aided design

CdS Cadmium sulfide

CEA-Leti Commissariat agrave lrsquoeacutenergie atomique (Atomic energy commission)

CMOS Complementary metal-oxide-semiconductor

CNAM Conservatoire national des arts et meacutetiers

CPW Coplanar waveguide

xviii Microwave Photonic Links

DBR Distributed Bragg reflector

DC Direct current

DD-MZM Dual drive-MZM

DFA Doped fiber amplifier

DFB Distributed feedback laser

DFT Discrete Fourier transform

EO Electricoptic

EAM Electro-absorption modulator

EDFA Erbium-doped fiber amplifier

EEL Edge emitting laser

EML Electro-absorption modulated laser

EMT Electromagnetic transverse

EOM Electro-optic modulator

ER Extinction ratio

ESYCOM Equipe systegravemes de communications et microsystegravemes (Communications and microsystems team)

ET Electric transverse

EVM Error vector magnitude

FCC Federal communications commission

FET Field-effect transistor

FKE Franz-Keldysh effect

FT RampD France Telecom Research amp Development

GaAs Galium arsenide

GaP Galium phosphide

Ge Germanium

GRINSCH Graded index separate confinement heterostructure

HB Harmonic balance

HBT Heterojunction bipolar transistor

Abbreviation Glossary xix

HEMT High electron mobility transistor

HFET Heterojunction field-effect transistor

HFSS High frequency simulation system

HPT Heterojunction bipolar phototransistor

IDFT Inverse discrete Fourier transform

IM-DD Intensity modulation-direct detection

IMEP Institut de microeacutelectronique eacutelectromagneacutetisme et optique (Institute of microelectronics electromagnetism and optics)

InAs Indium arsenide

InGaAs Indium gallium arsenide

InGaP Indium gallium phosphide

InP Indium phosphide

IR-UWB Impulse Radio ndash Ultra Wideband

KDP Potassium dihydrogen phosphate

LAHC Laboratoire drsquohyperfreacutequences et de caracteacuterisation (hyperfrequency and characterization laboratory)

LASER Light amplifier by stimulated emission of radiation

LF Low frequency

LiNbO3 Lithium niobate

LiTaO3 Lithium tantalate

MAG Maximum available gain

MASER Microwave amplifier by stimulated emission of radiation

MB-OFDM Multi-band ndash orthogonal frequency division modulation

MB-OOK Multi-band on off keying

MEMS Micro-electro-mechanical systems

MESFET Metal semiconductor field-effect transistor

MMIC Monolithic microwave integrated circuit

MODFET Modulation-doped field-effect transistor

MQW-EAM Multi-quantum well-EAM

xx Microwave Photonic Links

MSM Metal semiconductor metal

MZM Modulator Mach-Zehnder

NdYAG Neodymium-doped yttrium aluminum garnet

NF Noise factor Noise figure

nOI n order intermodulation

nOIP n order intercept point

NRA National Research Agency

OE Opticelectric

OEIC Optoelectronic integrated circuit

OEMMIC Optoelectronic millimeter-wave monolithic integrated circuit

OFDM Orthogonal frequency division modulation

PDFA Praseodymium-doped fiber amplifier

PDG Biased-dependent gain

PM Phase modulation

PMMA Poly(methyl methacrylate)

PRBS Pseudo-random bit sequence

PSK Phase-shift keying

QAM Quadrature amplitude modulation

QCSE Quantum confined stark effect

QW-EAM Quantum well-EAM

RCEPD Resonant cavity enhanced photodetectors

RFT Rapid Fourier transform

RIN Relative intensity noise

RoF Radio over fiber

SD-MZM Single drive ndashMZM

Si Silicon

SiGe Silicon-germanium

SiMOX Separation by implantation of oxygen

Abbreviation Glossary xxi

SiO2 Silicon dioxide

SOA Semiconductor optical amplifier

SOC System on a chip

SOI Substrate on insulator

TDFA Thulium-doped fiber amplifier

TEGFET Two-dimensional electron gas field-effect transistor

TW-MZM Travelling wave-MZM

UTC Uni-travelling carrier

UWB Ultra-wideband

VCSEL Vertical-cavity surface-emitting laser

VCSOA Vertical-cavity semiconductor optical amplifier

VMDP Velocity matched distributed photodetector

WDM Wavelength division multiplexing

YDFA Ytterbium-doped fiber amplifier

ZnS Zinc sulfide

Chapter 1

General Points

11 Microwave photonic links

All signals generated or observed due to human activity (measurement of different physical values remote control files sounds images etc) can be transformed into analog electrical signals These electrical signals can be processed or transmitted as they are but in most cases they are digitized beforehand Once digitized these signals have different forms regarding the digital coding or error-correcting algorithms used and protocols employed in the transmission systems To be processed or transmitted these analog or digital signals can use different mediums

If the transmission is performed via metallic lines or cables digital signals directly enter these lines or they modulate more or less complex subcarriers (ADSL Ethernet)

If transmission occurs with a radiowave a high-frequency carrier must be available Due to the congestion of the wireless spectrum carriers are now principally microwaves ie with frequencies of 1 to 100 GHz (GSM UMTS Wi-Fi Wimax etc) Wireless transmission can also be performed by very short pulses having a wide spectrum range including the microwave spectrum or these pulses can modulate a carrier in the millimeter wave spectrum This technique is known as ultra-wideband (UWB) [YAO 09]

If transmission is via fiber optics digital signals modulate one or several optical carriers (amplitude or soliton modulation) which are themselves

2 Microwave Photonic Links

transmitted over hundreds of kilometers on optical fibers This is the case for all passive optical networks (PON) and their different transmission protocols [LEC 97]

From these definitions the distinctive feature of microwave photonic links is to transmit a microwave signal analogically or for it be digitally modulated This microwave signal is transferred to an optical carrier which is guided with minimum loss by an optical fiber The microwave signal is then picked up by a photodetector at the end of the fiber

One of the first applications of microwave optical links was the distribution of the microwave carrier in radar or radio-astronomy systems comprising offset aerials or active phased-array antennas which benefited from the low weight and low volume of the fiber optics [COX 97 DEC 98]

Another important area comprises all radio over fiber (RoF) applications consisting of the extension of wireless networks using microwaves or UWB waves The optical tunnels produced are capable of reaching all rooms or buildings of a company university or diverse institutions or all the rooms of a house whilst benefiting from the very low loss associated with fiber optics [FRI 02]

Amongst the applications of RoF a promising domain is in the connection of internet transmission networks to the home These connections are increasingly popular with ever-increasing speeds (1 Gbs) due to fiber optics reaching households (fiber to the home or FTTH) whereby the house itself becomes a high-speed local network In this local network the signal distribution in each room is achieved by a 60 GHz millimeter-wave (wireless personal area network or WPAN) which stays confined in the room due to the extremely fast attenuation at this frequency All rooms are linked to each other by a network of passive fiber optics which extends the millimeter-wave UWB signal throughout the whole house (ultra broadband wireless home area network or UBB-WHAN) Examples of millimeter-wave over optical transmissions are presented in [CHU 07 KIM 04 WEI 08] and a demonstration of a UBB-WHAN with an up and down link is described in [HUC 08]

The length of a link ranges from 10 m to 1 km allowing several fiber types to be used (single mode or multimode silica or plastic) and several optical wavelengths ranging from 06 to 155 μm The light undergoes intensity modulation the signal is received via photodetection In just a few

General Points 3

years rates have risen from around 10 Mbs on carriers of a few gigahertz to rates of 1 or 10 Gbs on 60 GHz for microwave carriers

A microwave photonic link is constituted of three parts

ndash a coherent light source a laser that emits an optical carrier the intensity of which is directly modulated inside the laser or externally by an optical modulator In the case of external modulation the amplitude modulation is performed by a Mach-Zehnder or an electro-absorption modulator

ndash the modulated light is then transported by single or multi-mode optical fiber [GOM 08 KOO 08] made of silica or plastic [KOI 06] This part may include an optical amplification

ndash the modulated light is finally photodetected in a photodetector consisting of a photodiode or a phototransistor

After some deliberation regarding coherent and incoherent optical links [HAL 82] the solution finally adopted for these links was ldquointensity modulation (IM) direct detection (DD)rdquo As this is recalled in [COX 06] in this type of link the depth of optical modulation is sufficiently weak that we can initially use small signal or linear techniques for each aspect Because the signals applied to links or extracted from them are in microwaves the variables characterizing these systems are S-parameters gains and noise factors Also nonlinearities and hence intermodulation produced by each component on the signal introduced in the link must be considered The combination of these different characteristics leads to the notion of interference-free dynamic range (IFDR) This shall be evaluated regarding the properties of each element in the chapters concerning overall performances of such links

As a link includes electrical-to-optical optical-to-electrical and even optical-to-optical transducers each of the magnitudes in terms of S-parameters gains and noise factors should be presented in the form of optomicrowave magnitudes This aspect forces harmonization of notions from the optical optoelectronic and microwave disciplines This is described in Chapter 5

The term used initially to describe these links was ldquomicrowave optical linksrdquo However the techniques used have gradually distanced themselves from proper optical and optoelectronic techniques so that the more specific term ldquomicrowave photonic linksrdquo has been progressively used [SEE 02]

4 Microwave Photonic Links

12 Link description

Figures 11 and 12 represent a general diagram of an IM-DD microwave optical link

Figure 11 Diagram of directly modulated microwave optical link

Figure 11 represents a direct modulation link A laser emits a light of wavelength 08 or 13 or 155 μm this laser is modulated by a microwave signal (which is possibly itself modulated) through a driver circuit The modulated light enters an optical fiber coupled to a photodetector that detects the microwave modulation signal The optical modulation can have an amplitude frequency and phase However direct photodetection detects only the modulation in amplitude The detected microwave signal is then amplified by a low-noise amplifier

Figure 12 represents an external modulation link This time a light emitted from a laser is injected into a Mach-Zehnder or electro-absorption amplitude modulator In this case microwave modulation is also applied to the modulator through a driver circuit

After passing into an optical fiber the optical intensity modulation only is detected via a photodetector As in the previous diagram the detected microwave signal is amplified in a low-noise amplifier

Laser

Driver

Optical fiber Photodetector

Low noise amplifier

Microwave or UWB Microwave or UWB

λ = 155 or 13 or 08 μm

Amplitude modulation Direct detection

General Points 5

Figure 12 Diagram of externally modulated microwave optical link

13 Signal to transmit

131 Microwave signal

The first type of transmitted signal is a signal that constitutes a microwave frequency reference It can be used in offset aerial systems or active phased-array antenna After its reflection from a moving object the microwave signal emitted from an antenna can shift in frequency (Doppler modulation) and it is the spectral purity of the microwave that determines the minimum observed frequency shift and therefore the minimum relative speed of the moving object The spectral purity and degradation after transmission of the microwave by optical links must be watched closely to distinguish the frequency shift

132 Microwave carrier for a digital signal

If the microwave signal serves as a carrier for a digital signal this carrier is previously modulated All the modulation techniques normally used such as amplitude frequency phase OFDM and combined amplitude-phase modulation (QAM) or more complex techniques can be considered such as those used in GSM GPRS EDGE and UMTS for mobile telephones or such as Bluetooth Wi-Fi and Wimax for data transmission These modulations are generally carried out on single sideband (SSB) When microwave signal modulation is implemented in phase or frequency spectral purity is also of great importance

Laser

Amplifier or driver

Optical fiber

λ = 155 or 13 or 08 μm

Microwave or UWB

Optical modulator MZ or EA

Amplitude modulation

Photodetector

Low noise amplifier

Microwave or UWB

Direct detection

6 Microwave Photonic Links

133 UWB signal

Another signal category is available for transmission by fiber optics These signals are relevant to UWB techniques without carriers and with the spectrum in the microwave region or up-converted to a millimeter-wave carrier UWB wireless links are largely used over short distances The optical fibers are particularly indicated to enable extensions of such networks

134 Optical carrier

Microwave signals can carry analog information (frequency shift due to the Doppler effect) or they can be modulated by a digital signal or be constituted of UWB signals which are themselves digitally modulated All these microwave signals must be up-converted to an optical carrier This transfer exclusively occurs by intensity modulation One of the advantages of this modulation is that the microwave signal can be recovered in a simple photodetection unit permitting the elimination of possible frequency fluctuations of the optical carrier Loss of sensitivity resulting from direct detection does not occur if the optical wavelength allows us to insert an optical amplifier or if the link is very short Usually this modulation is double sideband (DSB) especially if the modulation occurs directly in the laser but for slightly longer links this type of modulation can lead to extinction phenomena A single sideband modulation can hence be considered but this modulation must be carried out by an external modulator

135 Summary

The complexity of microwave photonic links comes from the stacking of an optical carrier and microwave or UWB subcarrier The optical carrier is exclusively intensity modulated whereas the microwave subcarrier can be modulated following all known modulation types amplitude frequency phase or their combination including a frequency shift due to the Doppler effect All these modulations can be recovered via photodetection

The use of microwave optical links will increase as the transmitted signals will be numerous and emitted in parallel communications and the data rates will increase accordingly Thus telecommunication optical

Preface xv

integration of these components in electromagnetic sensors systems The components and functions addressed range from optical sources (modulated semiconductor lasers or externally modulated continuous lasers) to photodetectors optical fibers and optical amplifiers

This work focuses upon optical components their transfer functionality and their modeling in terms of microwave components in order to create an electrical model of microwave photonic links In order to achieve this level of complexity a number of modeling approaches have been created by the authors to elucidate the influences of the constituent components of microwave photonic links

Because the advancement of opto-electronics photonics and microwaves is possible by the unification of modeling approaches there is no doubt that such works will be referenced by students but also by design engineers and architects of electromagnetic sensor systems who will incorporate this new technology into their designs

This is to the authorrsquos knowledge the first work addressing the description and modeling of microwave photonic link technology with an educational approach to physical phenomena and new approaches to modeling microwave photonic components

Jean Chazelas Scientific Director

Thales Aeronautics Division

Abbreviation Glossary

AC Alternating Current

ACPR Adjacent Channel Power Ratio

ADP Ammonium dihydrogen phosphate

ADS Advanced Design System

AlGaAs Aluminum gallium arsenide

AM Amplitude Modulation

AM-DD Amplitude Modulation ndash Direct Detection

ASE Amplified Spontaneous Emission

BER Bit Error Rate

BH Buried Heterostructure

BiCMOS Bipolar Complementary Metal Oxide Semiconductor

BILBAO Borne drsquoinfrastructures large bande avec accegraves optique (Wideband infrastructure base with optical access)

CAD Computer-aided design

CdS Cadmium sulfide

CEA-Leti Commissariat agrave lrsquoeacutenergie atomique (Atomic energy commission)

CMOS Complementary metal-oxide-semiconductor

CNAM Conservatoire national des arts et meacutetiers

CPW Coplanar waveguide

xviii Microwave Photonic Links

DBR Distributed Bragg reflector

DC Direct current

DD-MZM Dual drive-MZM

DFA Doped fiber amplifier

DFB Distributed feedback laser

DFT Discrete Fourier transform

EO Electricoptic

EAM Electro-absorption modulator

EDFA Erbium-doped fiber amplifier

EEL Edge emitting laser

EML Electro-absorption modulated laser

EMT Electromagnetic transverse

EOM Electro-optic modulator

ER Extinction ratio

ESYCOM Equipe systegravemes de communications et microsystegravemes (Communications and microsystems team)

ET Electric transverse

EVM Error vector magnitude

FCC Federal communications commission

FET Field-effect transistor

FKE Franz-Keldysh effect

FT RampD France Telecom Research amp Development

GaAs Galium arsenide

GaP Galium phosphide

Ge Germanium

GRINSCH Graded index separate confinement heterostructure

HB Harmonic balance

HBT Heterojunction bipolar transistor

Abbreviation Glossary xix

HEMT High electron mobility transistor

HFET Heterojunction field-effect transistor

HFSS High frequency simulation system

HPT Heterojunction bipolar phototransistor

IDFT Inverse discrete Fourier transform

IM-DD Intensity modulation-direct detection

IMEP Institut de microeacutelectronique eacutelectromagneacutetisme et optique (Institute of microelectronics electromagnetism and optics)

InAs Indium arsenide

InGaAs Indium gallium arsenide

InGaP Indium gallium phosphide

InP Indium phosphide

IR-UWB Impulse Radio ndash Ultra Wideband

KDP Potassium dihydrogen phosphate

LAHC Laboratoire drsquohyperfreacutequences et de caracteacuterisation (hyperfrequency and characterization laboratory)

LASER Light amplifier by stimulated emission of radiation

LF Low frequency

LiNbO3 Lithium niobate

LiTaO3 Lithium tantalate

MAG Maximum available gain

MASER Microwave amplifier by stimulated emission of radiation

MB-OFDM Multi-band ndash orthogonal frequency division modulation

MB-OOK Multi-band on off keying

MEMS Micro-electro-mechanical systems

MESFET Metal semiconductor field-effect transistor

MMIC Monolithic microwave integrated circuit

MODFET Modulation-doped field-effect transistor

MQW-EAM Multi-quantum well-EAM

xx Microwave Photonic Links

MSM Metal semiconductor metal

MZM Modulator Mach-Zehnder

NdYAG Neodymium-doped yttrium aluminum garnet

NF Noise factor Noise figure

nOI n order intermodulation

nOIP n order intercept point

NRA National Research Agency

OE Opticelectric

OEIC Optoelectronic integrated circuit

OEMMIC Optoelectronic millimeter-wave monolithic integrated circuit

OFDM Orthogonal frequency division modulation

PDFA Praseodymium-doped fiber amplifier

PDG Biased-dependent gain

PM Phase modulation

PMMA Poly(methyl methacrylate)

PRBS Pseudo-random bit sequence

PSK Phase-shift keying

QAM Quadrature amplitude modulation

QCSE Quantum confined stark effect

QW-EAM Quantum well-EAM

RCEPD Resonant cavity enhanced photodetectors

RFT Rapid Fourier transform

RIN Relative intensity noise

RoF Radio over fiber

SD-MZM Single drive ndashMZM

Si Silicon

SiGe Silicon-germanium

SiMOX Separation by implantation of oxygen

Abbreviation Glossary xxi

SiO2 Silicon dioxide

SOA Semiconductor optical amplifier

SOC System on a chip

SOI Substrate on insulator

TDFA Thulium-doped fiber amplifier

TEGFET Two-dimensional electron gas field-effect transistor

TW-MZM Travelling wave-MZM

UTC Uni-travelling carrier

UWB Ultra-wideband

VCSEL Vertical-cavity surface-emitting laser

VCSOA Vertical-cavity semiconductor optical amplifier

VMDP Velocity matched distributed photodetector

WDM Wavelength division multiplexing

YDFA Ytterbium-doped fiber amplifier

ZnS Zinc sulfide

Chapter 1

General Points

11 Microwave photonic links

All signals generated or observed due to human activity (measurement of different physical values remote control files sounds images etc) can be transformed into analog electrical signals These electrical signals can be processed or transmitted as they are but in most cases they are digitized beforehand Once digitized these signals have different forms regarding the digital coding or error-correcting algorithms used and protocols employed in the transmission systems To be processed or transmitted these analog or digital signals can use different mediums

If the transmission is performed via metallic lines or cables digital signals directly enter these lines or they modulate more or less complex subcarriers (ADSL Ethernet)

If transmission occurs with a radiowave a high-frequency carrier must be available Due to the congestion of the wireless spectrum carriers are now principally microwaves ie with frequencies of 1 to 100 GHz (GSM UMTS Wi-Fi Wimax etc) Wireless transmission can also be performed by very short pulses having a wide spectrum range including the microwave spectrum or these pulses can modulate a carrier in the millimeter wave spectrum This technique is known as ultra-wideband (UWB) [YAO 09]

If transmission is via fiber optics digital signals modulate one or several optical carriers (amplitude or soliton modulation) which are themselves

2 Microwave Photonic Links

transmitted over hundreds of kilometers on optical fibers This is the case for all passive optical networks (PON) and their different transmission protocols [LEC 97]

From these definitions the distinctive feature of microwave photonic links is to transmit a microwave signal analogically or for it be digitally modulated This microwave signal is transferred to an optical carrier which is guided with minimum loss by an optical fiber The microwave signal is then picked up by a photodetector at the end of the fiber

One of the first applications of microwave optical links was the distribution of the microwave carrier in radar or radio-astronomy systems comprising offset aerials or active phased-array antennas which benefited from the low weight and low volume of the fiber optics [COX 97 DEC 98]

Another important area comprises all radio over fiber (RoF) applications consisting of the extension of wireless networks using microwaves or UWB waves The optical tunnels produced are capable of reaching all rooms or buildings of a company university or diverse institutions or all the rooms of a house whilst benefiting from the very low loss associated with fiber optics [FRI 02]

Amongst the applications of RoF a promising domain is in the connection of internet transmission networks to the home These connections are increasingly popular with ever-increasing speeds (1 Gbs) due to fiber optics reaching households (fiber to the home or FTTH) whereby the house itself becomes a high-speed local network In this local network the signal distribution in each room is achieved by a 60 GHz millimeter-wave (wireless personal area network or WPAN) which stays confined in the room due to the extremely fast attenuation at this frequency All rooms are linked to each other by a network of passive fiber optics which extends the millimeter-wave UWB signal throughout the whole house (ultra broadband wireless home area network or UBB-WHAN) Examples of millimeter-wave over optical transmissions are presented in [CHU 07 KIM 04 WEI 08] and a demonstration of a UBB-WHAN with an up and down link is described in [HUC 08]

The length of a link ranges from 10 m to 1 km allowing several fiber types to be used (single mode or multimode silica or plastic) and several optical wavelengths ranging from 06 to 155 μm The light undergoes intensity modulation the signal is received via photodetection In just a few

General Points 3

years rates have risen from around 10 Mbs on carriers of a few gigahertz to rates of 1 or 10 Gbs on 60 GHz for microwave carriers

A microwave photonic link is constituted of three parts

ndash a coherent light source a laser that emits an optical carrier the intensity of which is directly modulated inside the laser or externally by an optical modulator In the case of external modulation the amplitude modulation is performed by a Mach-Zehnder or an electro-absorption modulator

ndash the modulated light is then transported by single or multi-mode optical fiber [GOM 08 KOO 08] made of silica or plastic [KOI 06] This part may include an optical amplification

ndash the modulated light is finally photodetected in a photodetector consisting of a photodiode or a phototransistor

After some deliberation regarding coherent and incoherent optical links [HAL 82] the solution finally adopted for these links was ldquointensity modulation (IM) direct detection (DD)rdquo As this is recalled in [COX 06] in this type of link the depth of optical modulation is sufficiently weak that we can initially use small signal or linear techniques for each aspect Because the signals applied to links or extracted from them are in microwaves the variables characterizing these systems are S-parameters gains and noise factors Also nonlinearities and hence intermodulation produced by each component on the signal introduced in the link must be considered The combination of these different characteristics leads to the notion of interference-free dynamic range (IFDR) This shall be evaluated regarding the properties of each element in the chapters concerning overall performances of such links

As a link includes electrical-to-optical optical-to-electrical and even optical-to-optical transducers each of the magnitudes in terms of S-parameters gains and noise factors should be presented in the form of optomicrowave magnitudes This aspect forces harmonization of notions from the optical optoelectronic and microwave disciplines This is described in Chapter 5

The term used initially to describe these links was ldquomicrowave optical linksrdquo However the techniques used have gradually distanced themselves from proper optical and optoelectronic techniques so that the more specific term ldquomicrowave photonic linksrdquo has been progressively used [SEE 02]

4 Microwave Photonic Links

12 Link description

Figures 11 and 12 represent a general diagram of an IM-DD microwave optical link

Figure 11 Diagram of directly modulated microwave optical link

Figure 11 represents a direct modulation link A laser emits a light of wavelength 08 or 13 or 155 μm this laser is modulated by a microwave signal (which is possibly itself modulated) through a driver circuit The modulated light enters an optical fiber coupled to a photodetector that detects the microwave modulation signal The optical modulation can have an amplitude frequency and phase However direct photodetection detects only the modulation in amplitude The detected microwave signal is then amplified by a low-noise amplifier

Figure 12 represents an external modulation link This time a light emitted from a laser is injected into a Mach-Zehnder or electro-absorption amplitude modulator In this case microwave modulation is also applied to the modulator through a driver circuit

After passing into an optical fiber the optical intensity modulation only is detected via a photodetector As in the previous diagram the detected microwave signal is amplified in a low-noise amplifier

Laser

Driver

Optical fiber Photodetector

Low noise amplifier

Microwave or UWB Microwave or UWB

λ = 155 or 13 or 08 μm

Amplitude modulation Direct detection

General Points 5

Figure 12 Diagram of externally modulated microwave optical link

13 Signal to transmit

131 Microwave signal

The first type of transmitted signal is a signal that constitutes a microwave frequency reference It can be used in offset aerial systems or active phased-array antenna After its reflection from a moving object the microwave signal emitted from an antenna can shift in frequency (Doppler modulation) and it is the spectral purity of the microwave that determines the minimum observed frequency shift and therefore the minimum relative speed of the moving object The spectral purity and degradation after transmission of the microwave by optical links must be watched closely to distinguish the frequency shift

132 Microwave carrier for a digital signal

If the microwave signal serves as a carrier for a digital signal this carrier is previously modulated All the modulation techniques normally used such as amplitude frequency phase OFDM and combined amplitude-phase modulation (QAM) or more complex techniques can be considered such as those used in GSM GPRS EDGE and UMTS for mobile telephones or such as Bluetooth Wi-Fi and Wimax for data transmission These modulations are generally carried out on single sideband (SSB) When microwave signal modulation is implemented in phase or frequency spectral purity is also of great importance

Laser

Amplifier or driver

Optical fiber

λ = 155 or 13 or 08 μm

Microwave or UWB

Optical modulator MZ or EA

Amplitude modulation

Photodetector

Low noise amplifier

Microwave or UWB

Direct detection

6 Microwave Photonic Links

133 UWB signal

Another signal category is available for transmission by fiber optics These signals are relevant to UWB techniques without carriers and with the spectrum in the microwave region or up-converted to a millimeter-wave carrier UWB wireless links are largely used over short distances The optical fibers are particularly indicated to enable extensions of such networks

134 Optical carrier

Microwave signals can carry analog information (frequency shift due to the Doppler effect) or they can be modulated by a digital signal or be constituted of UWB signals which are themselves digitally modulated All these microwave signals must be up-converted to an optical carrier This transfer exclusively occurs by intensity modulation One of the advantages of this modulation is that the microwave signal can be recovered in a simple photodetection unit permitting the elimination of possible frequency fluctuations of the optical carrier Loss of sensitivity resulting from direct detection does not occur if the optical wavelength allows us to insert an optical amplifier or if the link is very short Usually this modulation is double sideband (DSB) especially if the modulation occurs directly in the laser but for slightly longer links this type of modulation can lead to extinction phenomena A single sideband modulation can hence be considered but this modulation must be carried out by an external modulator

135 Summary

The complexity of microwave photonic links comes from the stacking of an optical carrier and microwave or UWB subcarrier The optical carrier is exclusively intensity modulated whereas the microwave subcarrier can be modulated following all known modulation types amplitude frequency phase or their combination including a frequency shift due to the Doppler effect All these modulations can be recovered via photodetection

The use of microwave optical links will increase as the transmitted signals will be numerous and emitted in parallel communications and the data rates will increase accordingly Thus telecommunication optical

Abbreviation Glossary

AC Alternating Current

ACPR Adjacent Channel Power Ratio

ADP Ammonium dihydrogen phosphate

ADS Advanced Design System

AlGaAs Aluminum gallium arsenide

AM Amplitude Modulation

AM-DD Amplitude Modulation ndash Direct Detection

ASE Amplified Spontaneous Emission

BER Bit Error Rate

BH Buried Heterostructure

BiCMOS Bipolar Complementary Metal Oxide Semiconductor

BILBAO Borne drsquoinfrastructures large bande avec accegraves optique (Wideband infrastructure base with optical access)

CAD Computer-aided design

CdS Cadmium sulfide

CEA-Leti Commissariat agrave lrsquoeacutenergie atomique (Atomic energy commission)

CMOS Complementary metal-oxide-semiconductor

CNAM Conservatoire national des arts et meacutetiers

CPW Coplanar waveguide

xviii Microwave Photonic Links

DBR Distributed Bragg reflector

DC Direct current

DD-MZM Dual drive-MZM

DFA Doped fiber amplifier

DFB Distributed feedback laser

DFT Discrete Fourier transform

EO Electricoptic

EAM Electro-absorption modulator

EDFA Erbium-doped fiber amplifier

EEL Edge emitting laser

EML Electro-absorption modulated laser

EMT Electromagnetic transverse

EOM Electro-optic modulator

ER Extinction ratio

ESYCOM Equipe systegravemes de communications et microsystegravemes (Communications and microsystems team)

ET Electric transverse

EVM Error vector magnitude

FCC Federal communications commission

FET Field-effect transistor

FKE Franz-Keldysh effect

FT RampD France Telecom Research amp Development

GaAs Galium arsenide

GaP Galium phosphide

Ge Germanium

GRINSCH Graded index separate confinement heterostructure

HB Harmonic balance

HBT Heterojunction bipolar transistor

Abbreviation Glossary xix

HEMT High electron mobility transistor

HFET Heterojunction field-effect transistor

HFSS High frequency simulation system

HPT Heterojunction bipolar phototransistor

IDFT Inverse discrete Fourier transform

IM-DD Intensity modulation-direct detection

IMEP Institut de microeacutelectronique eacutelectromagneacutetisme et optique (Institute of microelectronics electromagnetism and optics)

InAs Indium arsenide

InGaAs Indium gallium arsenide

InGaP Indium gallium phosphide

InP Indium phosphide

IR-UWB Impulse Radio ndash Ultra Wideband

KDP Potassium dihydrogen phosphate

LAHC Laboratoire drsquohyperfreacutequences et de caracteacuterisation (hyperfrequency and characterization laboratory)

LASER Light amplifier by stimulated emission of radiation

LF Low frequency

LiNbO3 Lithium niobate

LiTaO3 Lithium tantalate

MAG Maximum available gain

MASER Microwave amplifier by stimulated emission of radiation

MB-OFDM Multi-band ndash orthogonal frequency division modulation

MB-OOK Multi-band on off keying

MEMS Micro-electro-mechanical systems

MESFET Metal semiconductor field-effect transistor

MMIC Monolithic microwave integrated circuit

MODFET Modulation-doped field-effect transistor

MQW-EAM Multi-quantum well-EAM

xx Microwave Photonic Links

MSM Metal semiconductor metal

MZM Modulator Mach-Zehnder

NdYAG Neodymium-doped yttrium aluminum garnet

NF Noise factor Noise figure

nOI n order intermodulation

nOIP n order intercept point

NRA National Research Agency

OE Opticelectric

OEIC Optoelectronic integrated circuit

OEMMIC Optoelectronic millimeter-wave monolithic integrated circuit

OFDM Orthogonal frequency division modulation

PDFA Praseodymium-doped fiber amplifier

PDG Biased-dependent gain

PM Phase modulation

PMMA Poly(methyl methacrylate)

PRBS Pseudo-random bit sequence

PSK Phase-shift keying

QAM Quadrature amplitude modulation

QCSE Quantum confined stark effect

QW-EAM Quantum well-EAM

RCEPD Resonant cavity enhanced photodetectors

RFT Rapid Fourier transform

RIN Relative intensity noise

RoF Radio over fiber

SD-MZM Single drive ndashMZM

Si Silicon

SiGe Silicon-germanium

SiMOX Separation by implantation of oxygen

Abbreviation Glossary xxi

SiO2 Silicon dioxide

SOA Semiconductor optical amplifier

SOC System on a chip

SOI Substrate on insulator

TDFA Thulium-doped fiber amplifier

TEGFET Two-dimensional electron gas field-effect transistor

TW-MZM Travelling wave-MZM

UTC Uni-travelling carrier

UWB Ultra-wideband

VCSEL Vertical-cavity surface-emitting laser

VCSOA Vertical-cavity semiconductor optical amplifier

VMDP Velocity matched distributed photodetector

WDM Wavelength division multiplexing

YDFA Ytterbium-doped fiber amplifier

ZnS Zinc sulfide

Chapter 1

General Points

11 Microwave photonic links

All signals generated or observed due to human activity (measurement of different physical values remote control files sounds images etc) can be transformed into analog electrical signals These electrical signals can be processed or transmitted as they are but in most cases they are digitized beforehand Once digitized these signals have different forms regarding the digital coding or error-correcting algorithms used and protocols employed in the transmission systems To be processed or transmitted these analog or digital signals can use different mediums

If the transmission is performed via metallic lines or cables digital signals directly enter these lines or they modulate more or less complex subcarriers (ADSL Ethernet)

If transmission occurs with a radiowave a high-frequency carrier must be available Due to the congestion of the wireless spectrum carriers are now principally microwaves ie with frequencies of 1 to 100 GHz (GSM UMTS Wi-Fi Wimax etc) Wireless transmission can also be performed by very short pulses having a wide spectrum range including the microwave spectrum or these pulses can modulate a carrier in the millimeter wave spectrum This technique is known as ultra-wideband (UWB) [YAO 09]

If transmission is via fiber optics digital signals modulate one or several optical carriers (amplitude or soliton modulation) which are themselves

2 Microwave Photonic Links

transmitted over hundreds of kilometers on optical fibers This is the case for all passive optical networks (PON) and their different transmission protocols [LEC 97]

From these definitions the distinctive feature of microwave photonic links is to transmit a microwave signal analogically or for it be digitally modulated This microwave signal is transferred to an optical carrier which is guided with minimum loss by an optical fiber The microwave signal is then picked up by a photodetector at the end of the fiber

One of the first applications of microwave optical links was the distribution of the microwave carrier in radar or radio-astronomy systems comprising offset aerials or active phased-array antennas which benefited from the low weight and low volume of the fiber optics [COX 97 DEC 98]

Another important area comprises all radio over fiber (RoF) applications consisting of the extension of wireless networks using microwaves or UWB waves The optical tunnels produced are capable of reaching all rooms or buildings of a company university or diverse institutions or all the rooms of a house whilst benefiting from the very low loss associated with fiber optics [FRI 02]

Amongst the applications of RoF a promising domain is in the connection of internet transmission networks to the home These connections are increasingly popular with ever-increasing speeds (1 Gbs) due to fiber optics reaching households (fiber to the home or FTTH) whereby the house itself becomes a high-speed local network In this local network the signal distribution in each room is achieved by a 60 GHz millimeter-wave (wireless personal area network or WPAN) which stays confined in the room due to the extremely fast attenuation at this frequency All rooms are linked to each other by a network of passive fiber optics which extends the millimeter-wave UWB signal throughout the whole house (ultra broadband wireless home area network or UBB-WHAN) Examples of millimeter-wave over optical transmissions are presented in [CHU 07 KIM 04 WEI 08] and a demonstration of a UBB-WHAN with an up and down link is described in [HUC 08]

The length of a link ranges from 10 m to 1 km allowing several fiber types to be used (single mode or multimode silica or plastic) and several optical wavelengths ranging from 06 to 155 μm The light undergoes intensity modulation the signal is received via photodetection In just a few

General Points 3

years rates have risen from around 10 Mbs on carriers of a few gigahertz to rates of 1 or 10 Gbs on 60 GHz for microwave carriers

A microwave photonic link is constituted of three parts

ndash a coherent light source a laser that emits an optical carrier the intensity of which is directly modulated inside the laser or externally by an optical modulator In the case of external modulation the amplitude modulation is performed by a Mach-Zehnder or an electro-absorption modulator

ndash the modulated light is then transported by single or multi-mode optical fiber [GOM 08 KOO 08] made of silica or plastic [KOI 06] This part may include an optical amplification

ndash the modulated light is finally photodetected in a photodetector consisting of a photodiode or a phototransistor

After some deliberation regarding coherent and incoherent optical links [HAL 82] the solution finally adopted for these links was ldquointensity modulation (IM) direct detection (DD)rdquo As this is recalled in [COX 06] in this type of link the depth of optical modulation is sufficiently weak that we can initially use small signal or linear techniques for each aspect Because the signals applied to links or extracted from them are in microwaves the variables characterizing these systems are S-parameters gains and noise factors Also nonlinearities and hence intermodulation produced by each component on the signal introduced in the link must be considered The combination of these different characteristics leads to the notion of interference-free dynamic range (IFDR) This shall be evaluated regarding the properties of each element in the chapters concerning overall performances of such links

As a link includes electrical-to-optical optical-to-electrical and even optical-to-optical transducers each of the magnitudes in terms of S-parameters gains and noise factors should be presented in the form of optomicrowave magnitudes This aspect forces harmonization of notions from the optical optoelectronic and microwave disciplines This is described in Chapter 5

The term used initially to describe these links was ldquomicrowave optical linksrdquo However the techniques used have gradually distanced themselves from proper optical and optoelectronic techniques so that the more specific term ldquomicrowave photonic linksrdquo has been progressively used [SEE 02]

4 Microwave Photonic Links

12 Link description

Figures 11 and 12 represent a general diagram of an IM-DD microwave optical link

Figure 11 Diagram of directly modulated microwave optical link

Figure 11 represents a direct modulation link A laser emits a light of wavelength 08 or 13 or 155 μm this laser is modulated by a microwave signal (which is possibly itself modulated) through a driver circuit The modulated light enters an optical fiber coupled to a photodetector that detects the microwave modulation signal The optical modulation can have an amplitude frequency and phase However direct photodetection detects only the modulation in amplitude The detected microwave signal is then amplified by a low-noise amplifier

Figure 12 represents an external modulation link This time a light emitted from a laser is injected into a Mach-Zehnder or electro-absorption amplitude modulator In this case microwave modulation is also applied to the modulator through a driver circuit

After passing into an optical fiber the optical intensity modulation only is detected via a photodetector As in the previous diagram the detected microwave signal is amplified in a low-noise amplifier

Laser

Driver

Optical fiber Photodetector

Low noise amplifier

Microwave or UWB Microwave or UWB

λ = 155 or 13 or 08 μm

Amplitude modulation Direct detection

General Points 5

Figure 12 Diagram of externally modulated microwave optical link

13 Signal to transmit

131 Microwave signal

The first type of transmitted signal is a signal that constitutes a microwave frequency reference It can be used in offset aerial systems or active phased-array antenna After its reflection from a moving object the microwave signal emitted from an antenna can shift in frequency (Doppler modulation) and it is the spectral purity of the microwave that determines the minimum observed frequency shift and therefore the minimum relative speed of the moving object The spectral purity and degradation after transmission of the microwave by optical links must be watched closely to distinguish the frequency shift

132 Microwave carrier for a digital signal

If the microwave signal serves as a carrier for a digital signal this carrier is previously modulated All the modulation techniques normally used such as amplitude frequency phase OFDM and combined amplitude-phase modulation (QAM) or more complex techniques can be considered such as those used in GSM GPRS EDGE and UMTS for mobile telephones or such as Bluetooth Wi-Fi and Wimax for data transmission These modulations are generally carried out on single sideband (SSB) When microwave signal modulation is implemented in phase or frequency spectral purity is also of great importance

Laser

Amplifier or driver

Optical fiber

λ = 155 or 13 or 08 μm

Microwave or UWB

Optical modulator MZ or EA

Amplitude modulation

Photodetector

Low noise amplifier

Microwave or UWB

Direct detection

6 Microwave Photonic Links

133 UWB signal

Another signal category is available for transmission by fiber optics These signals are relevant to UWB techniques without carriers and with the spectrum in the microwave region or up-converted to a millimeter-wave carrier UWB wireless links are largely used over short distances The optical fibers are particularly indicated to enable extensions of such networks

134 Optical carrier

Microwave signals can carry analog information (frequency shift due to the Doppler effect) or they can be modulated by a digital signal or be constituted of UWB signals which are themselves digitally modulated All these microwave signals must be up-converted to an optical carrier This transfer exclusively occurs by intensity modulation One of the advantages of this modulation is that the microwave signal can be recovered in a simple photodetection unit permitting the elimination of possible frequency fluctuations of the optical carrier Loss of sensitivity resulting from direct detection does not occur if the optical wavelength allows us to insert an optical amplifier or if the link is very short Usually this modulation is double sideband (DSB) especially if the modulation occurs directly in the laser but for slightly longer links this type of modulation can lead to extinction phenomena A single sideband modulation can hence be considered but this modulation must be carried out by an external modulator

135 Summary

The complexity of microwave photonic links comes from the stacking of an optical carrier and microwave or UWB subcarrier The optical carrier is exclusively intensity modulated whereas the microwave subcarrier can be modulated following all known modulation types amplitude frequency phase or their combination including a frequency shift due to the Doppler effect All these modulations can be recovered via photodetection

The use of microwave optical links will increase as the transmitted signals will be numerous and emitted in parallel communications and the data rates will increase accordingly Thus telecommunication optical

xviii Microwave Photonic Links

DBR Distributed Bragg reflector

DC Direct current

DD-MZM Dual drive-MZM

DFA Doped fiber amplifier

DFB Distributed feedback laser

DFT Discrete Fourier transform

EO Electricoptic

EAM Electro-absorption modulator

EDFA Erbium-doped fiber amplifier

EEL Edge emitting laser

EML Electro-absorption modulated laser

EMT Electromagnetic transverse

EOM Electro-optic modulator

ER Extinction ratio

ESYCOM Equipe systegravemes de communications et microsystegravemes (Communications and microsystems team)

ET Electric transverse

EVM Error vector magnitude

FCC Federal communications commission

FET Field-effect transistor

FKE Franz-Keldysh effect

FT RampD France Telecom Research amp Development

GaAs Galium arsenide

GaP Galium phosphide

Ge Germanium

GRINSCH Graded index separate confinement heterostructure

HB Harmonic balance

HBT Heterojunction bipolar transistor

Abbreviation Glossary xix

HEMT High electron mobility transistor

HFET Heterojunction field-effect transistor

HFSS High frequency simulation system

HPT Heterojunction bipolar phototransistor

IDFT Inverse discrete Fourier transform

IM-DD Intensity modulation-direct detection

IMEP Institut de microeacutelectronique eacutelectromagneacutetisme et optique (Institute of microelectronics electromagnetism and optics)

InAs Indium arsenide

InGaAs Indium gallium arsenide

InGaP Indium gallium phosphide

InP Indium phosphide

IR-UWB Impulse Radio ndash Ultra Wideband

KDP Potassium dihydrogen phosphate

LAHC Laboratoire drsquohyperfreacutequences et de caracteacuterisation (hyperfrequency and characterization laboratory)

LASER Light amplifier by stimulated emission of radiation

LF Low frequency

LiNbO3 Lithium niobate

LiTaO3 Lithium tantalate

MAG Maximum available gain

MASER Microwave amplifier by stimulated emission of radiation

MB-OFDM Multi-band ndash orthogonal frequency division modulation

MB-OOK Multi-band on off keying

MEMS Micro-electro-mechanical systems

MESFET Metal semiconductor field-effect transistor

MMIC Monolithic microwave integrated circuit

MODFET Modulation-doped field-effect transistor

MQW-EAM Multi-quantum well-EAM

xx Microwave Photonic Links

MSM Metal semiconductor metal

MZM Modulator Mach-Zehnder

NdYAG Neodymium-doped yttrium aluminum garnet

NF Noise factor Noise figure

nOI n order intermodulation

nOIP n order intercept point

NRA National Research Agency

OE Opticelectric

OEIC Optoelectronic integrated circuit

OEMMIC Optoelectronic millimeter-wave monolithic integrated circuit

OFDM Orthogonal frequency division modulation

PDFA Praseodymium-doped fiber amplifier

PDG Biased-dependent gain

PM Phase modulation

PMMA Poly(methyl methacrylate)

PRBS Pseudo-random bit sequence

PSK Phase-shift keying

QAM Quadrature amplitude modulation

QCSE Quantum confined stark effect

QW-EAM Quantum well-EAM

RCEPD Resonant cavity enhanced photodetectors

RFT Rapid Fourier transform

RIN Relative intensity noise

RoF Radio over fiber

SD-MZM Single drive ndashMZM

Si Silicon

SiGe Silicon-germanium

SiMOX Separation by implantation of oxygen

Abbreviation Glossary xxi

SiO2 Silicon dioxide

SOA Semiconductor optical amplifier

SOC System on a chip

SOI Substrate on insulator

TDFA Thulium-doped fiber amplifier

TEGFET Two-dimensional electron gas field-effect transistor

TW-MZM Travelling wave-MZM

UTC Uni-travelling carrier

UWB Ultra-wideband

VCSEL Vertical-cavity surface-emitting laser

VCSOA Vertical-cavity semiconductor optical amplifier

VMDP Velocity matched distributed photodetector

WDM Wavelength division multiplexing

YDFA Ytterbium-doped fiber amplifier

ZnS Zinc sulfide

Chapter 1

General Points

11 Microwave photonic links

All signals generated or observed due to human activity (measurement of different physical values remote control files sounds images etc) can be transformed into analog electrical signals These electrical signals can be processed or transmitted as they are but in most cases they are digitized beforehand Once digitized these signals have different forms regarding the digital coding or error-correcting algorithms used and protocols employed in the transmission systems To be processed or transmitted these analog or digital signals can use different mediums

If the transmission is performed via metallic lines or cables digital signals directly enter these lines or they modulate more or less complex subcarriers (ADSL Ethernet)

If transmission occurs with a radiowave a high-frequency carrier must be available Due to the congestion of the wireless spectrum carriers are now principally microwaves ie with frequencies of 1 to 100 GHz (GSM UMTS Wi-Fi Wimax etc) Wireless transmission can also be performed by very short pulses having a wide spectrum range including the microwave spectrum or these pulses can modulate a carrier in the millimeter wave spectrum This technique is known as ultra-wideband (UWB) [YAO 09]

If transmission is via fiber optics digital signals modulate one or several optical carriers (amplitude or soliton modulation) which are themselves

2 Microwave Photonic Links

transmitted over hundreds of kilometers on optical fibers This is the case for all passive optical networks (PON) and their different transmission protocols [LEC 97]

From these definitions the distinctive feature of microwave photonic links is to transmit a microwave signal analogically or for it be digitally modulated This microwave signal is transferred to an optical carrier which is guided with minimum loss by an optical fiber The microwave signal is then picked up by a photodetector at the end of the fiber

One of the first applications of microwave optical links was the distribution of the microwave carrier in radar or radio-astronomy systems comprising offset aerials or active phased-array antennas which benefited from the low weight and low volume of the fiber optics [COX 97 DEC 98]

Another important area comprises all radio over fiber (RoF) applications consisting of the extension of wireless networks using microwaves or UWB waves The optical tunnels produced are capable of reaching all rooms or buildings of a company university or diverse institutions or all the rooms of a house whilst benefiting from the very low loss associated with fiber optics [FRI 02]

Amongst the applications of RoF a promising domain is in the connection of internet transmission networks to the home These connections are increasingly popular with ever-increasing speeds (1 Gbs) due to fiber optics reaching households (fiber to the home or FTTH) whereby the house itself becomes a high-speed local network In this local network the signal distribution in each room is achieved by a 60 GHz millimeter-wave (wireless personal area network or WPAN) which stays confined in the room due to the extremely fast attenuation at this frequency All rooms are linked to each other by a network of passive fiber optics which extends the millimeter-wave UWB signal throughout the whole house (ultra broadband wireless home area network or UBB-WHAN) Examples of millimeter-wave over optical transmissions are presented in [CHU 07 KIM 04 WEI 08] and a demonstration of a UBB-WHAN with an up and down link is described in [HUC 08]

The length of a link ranges from 10 m to 1 km allowing several fiber types to be used (single mode or multimode silica or plastic) and several optical wavelengths ranging from 06 to 155 μm The light undergoes intensity modulation the signal is received via photodetection In just a few

General Points 3

years rates have risen from around 10 Mbs on carriers of a few gigahertz to rates of 1 or 10 Gbs on 60 GHz for microwave carriers

A microwave photonic link is constituted of three parts

ndash a coherent light source a laser that emits an optical carrier the intensity of which is directly modulated inside the laser or externally by an optical modulator In the case of external modulation the amplitude modulation is performed by a Mach-Zehnder or an electro-absorption modulator

ndash the modulated light is then transported by single or multi-mode optical fiber [GOM 08 KOO 08] made of silica or plastic [KOI 06] This part may include an optical amplification

ndash the modulated light is finally photodetected in a photodetector consisting of a photodiode or a phototransistor

After some deliberation regarding coherent and incoherent optical links [HAL 82] the solution finally adopted for these links was ldquointensity modulation (IM) direct detection (DD)rdquo As this is recalled in [COX 06] in this type of link the depth of optical modulation is sufficiently weak that we can initially use small signal or linear techniques for each aspect Because the signals applied to links or extracted from them are in microwaves the variables characterizing these systems are S-parameters gains and noise factors Also nonlinearities and hence intermodulation produced by each component on the signal introduced in the link must be considered The combination of these different characteristics leads to the notion of interference-free dynamic range (IFDR) This shall be evaluated regarding the properties of each element in the chapters concerning overall performances of such links

As a link includes electrical-to-optical optical-to-electrical and even optical-to-optical transducers each of the magnitudes in terms of S-parameters gains and noise factors should be presented in the form of optomicrowave magnitudes This aspect forces harmonization of notions from the optical optoelectronic and microwave disciplines This is described in Chapter 5

The term used initially to describe these links was ldquomicrowave optical linksrdquo However the techniques used have gradually distanced themselves from proper optical and optoelectronic techniques so that the more specific term ldquomicrowave photonic linksrdquo has been progressively used [SEE 02]

4 Microwave Photonic Links

12 Link description

Figures 11 and 12 represent a general diagram of an IM-DD microwave optical link

Figure 11 Diagram of directly modulated microwave optical link

Figure 11 represents a direct modulation link A laser emits a light of wavelength 08 or 13 or 155 μm this laser is modulated by a microwave signal (which is possibly itself modulated) through a driver circuit The modulated light enters an optical fiber coupled to a photodetector that detects the microwave modulation signal The optical modulation can have an amplitude frequency and phase However direct photodetection detects only the modulation in amplitude The detected microwave signal is then amplified by a low-noise amplifier

Figure 12 represents an external modulation link This time a light emitted from a laser is injected into a Mach-Zehnder or electro-absorption amplitude modulator In this case microwave modulation is also applied to the modulator through a driver circuit

After passing into an optical fiber the optical intensity modulation only is detected via a photodetector As in the previous diagram the detected microwave signal is amplified in a low-noise amplifier

Laser

Driver

Optical fiber Photodetector

Low noise amplifier

Microwave or UWB Microwave or UWB

λ = 155 or 13 or 08 μm

Amplitude modulation Direct detection

General Points 5

Figure 12 Diagram of externally modulated microwave optical link

13 Signal to transmit

131 Microwave signal

The first type of transmitted signal is a signal that constitutes a microwave frequency reference It can be used in offset aerial systems or active phased-array antenna After its reflection from a moving object the microwave signal emitted from an antenna can shift in frequency (Doppler modulation) and it is the spectral purity of the microwave that determines the minimum observed frequency shift and therefore the minimum relative speed of the moving object The spectral purity and degradation after transmission of the microwave by optical links must be watched closely to distinguish the frequency shift

132 Microwave carrier for a digital signal

If the microwave signal serves as a carrier for a digital signal this carrier is previously modulated All the modulation techniques normally used such as amplitude frequency phase OFDM and combined amplitude-phase modulation (QAM) or more complex techniques can be considered such as those used in GSM GPRS EDGE and UMTS for mobile telephones or such as Bluetooth Wi-Fi and Wimax for data transmission These modulations are generally carried out on single sideband (SSB) When microwave signal modulation is implemented in phase or frequency spectral purity is also of great importance

Laser

Amplifier or driver

Optical fiber

λ = 155 or 13 or 08 μm

Microwave or UWB

Optical modulator MZ or EA

Amplitude modulation

Photodetector

Low noise amplifier

Microwave or UWB

Direct detection

6 Microwave Photonic Links

133 UWB signal

Another signal category is available for transmission by fiber optics These signals are relevant to UWB techniques without carriers and with the spectrum in the microwave region or up-converted to a millimeter-wave carrier UWB wireless links are largely used over short distances The optical fibers are particularly indicated to enable extensions of such networks

134 Optical carrier

Microwave signals can carry analog information (frequency shift due to the Doppler effect) or they can be modulated by a digital signal or be constituted of UWB signals which are themselves digitally modulated All these microwave signals must be up-converted to an optical carrier This transfer exclusively occurs by intensity modulation One of the advantages of this modulation is that the microwave signal can be recovered in a simple photodetection unit permitting the elimination of possible frequency fluctuations of the optical carrier Loss of sensitivity resulting from direct detection does not occur if the optical wavelength allows us to insert an optical amplifier or if the link is very short Usually this modulation is double sideband (DSB) especially if the modulation occurs directly in the laser but for slightly longer links this type of modulation can lead to extinction phenomena A single sideband modulation can hence be considered but this modulation must be carried out by an external modulator

135 Summary

The complexity of microwave photonic links comes from the stacking of an optical carrier and microwave or UWB subcarrier The optical carrier is exclusively intensity modulated whereas the microwave subcarrier can be modulated following all known modulation types amplitude frequency phase or their combination including a frequency shift due to the Doppler effect All these modulations can be recovered via photodetection

The use of microwave optical links will increase as the transmitted signals will be numerous and emitted in parallel communications and the data rates will increase accordingly Thus telecommunication optical

Abbreviation Glossary xix

HEMT High electron mobility transistor

HFET Heterojunction field-effect transistor

HFSS High frequency simulation system

HPT Heterojunction bipolar phototransistor

IDFT Inverse discrete Fourier transform

IM-DD Intensity modulation-direct detection

IMEP Institut de microeacutelectronique eacutelectromagneacutetisme et optique (Institute of microelectronics electromagnetism and optics)

InAs Indium arsenide

InGaAs Indium gallium arsenide

InGaP Indium gallium phosphide

InP Indium phosphide

IR-UWB Impulse Radio ndash Ultra Wideband

KDP Potassium dihydrogen phosphate

LAHC Laboratoire drsquohyperfreacutequences et de caracteacuterisation (hyperfrequency and characterization laboratory)

LASER Light amplifier by stimulated emission of radiation

LF Low frequency

LiNbO3 Lithium niobate

LiTaO3 Lithium tantalate

MAG Maximum available gain

MASER Microwave amplifier by stimulated emission of radiation

MB-OFDM Multi-band ndash orthogonal frequency division modulation

MB-OOK Multi-band on off keying

MEMS Micro-electro-mechanical systems

MESFET Metal semiconductor field-effect transistor

MMIC Monolithic microwave integrated circuit

MODFET Modulation-doped field-effect transistor

MQW-EAM Multi-quantum well-EAM

xx Microwave Photonic Links

MSM Metal semiconductor metal

MZM Modulator Mach-Zehnder

NdYAG Neodymium-doped yttrium aluminum garnet

NF Noise factor Noise figure

nOI n order intermodulation

nOIP n order intercept point

NRA National Research Agency

OE Opticelectric

OEIC Optoelectronic integrated circuit

OEMMIC Optoelectronic millimeter-wave monolithic integrated circuit

OFDM Orthogonal frequency division modulation

PDFA Praseodymium-doped fiber amplifier

PDG Biased-dependent gain

PM Phase modulation

PMMA Poly(methyl methacrylate)

PRBS Pseudo-random bit sequence

PSK Phase-shift keying

QAM Quadrature amplitude modulation

QCSE Quantum confined stark effect

QW-EAM Quantum well-EAM

RCEPD Resonant cavity enhanced photodetectors

RFT Rapid Fourier transform

RIN Relative intensity noise

RoF Radio over fiber

SD-MZM Single drive ndashMZM

Si Silicon

SiGe Silicon-germanium

SiMOX Separation by implantation of oxygen

Abbreviation Glossary xxi

SiO2 Silicon dioxide

SOA Semiconductor optical amplifier

SOC System on a chip

SOI Substrate on insulator

TDFA Thulium-doped fiber amplifier

TEGFET Two-dimensional electron gas field-effect transistor

TW-MZM Travelling wave-MZM

UTC Uni-travelling carrier

UWB Ultra-wideband

VCSEL Vertical-cavity surface-emitting laser

VCSOA Vertical-cavity semiconductor optical amplifier

VMDP Velocity matched distributed photodetector

WDM Wavelength division multiplexing

YDFA Ytterbium-doped fiber amplifier

ZnS Zinc sulfide

Chapter 1

General Points

11 Microwave photonic links

All signals generated or observed due to human activity (measurement of different physical values remote control files sounds images etc) can be transformed into analog electrical signals These electrical signals can be processed or transmitted as they are but in most cases they are digitized beforehand Once digitized these signals have different forms regarding the digital coding or error-correcting algorithms used and protocols employed in the transmission systems To be processed or transmitted these analog or digital signals can use different mediums

If the transmission is performed via metallic lines or cables digital signals directly enter these lines or they modulate more or less complex subcarriers (ADSL Ethernet)

If transmission occurs with a radiowave a high-frequency carrier must be available Due to the congestion of the wireless spectrum carriers are now principally microwaves ie with frequencies of 1 to 100 GHz (GSM UMTS Wi-Fi Wimax etc) Wireless transmission can also be performed by very short pulses having a wide spectrum range including the microwave spectrum or these pulses can modulate a carrier in the millimeter wave spectrum This technique is known as ultra-wideband (UWB) [YAO 09]

If transmission is via fiber optics digital signals modulate one or several optical carriers (amplitude or soliton modulation) which are themselves

2 Microwave Photonic Links

transmitted over hundreds of kilometers on optical fibers This is the case for all passive optical networks (PON) and their different transmission protocols [LEC 97]

From these definitions the distinctive feature of microwave photonic links is to transmit a microwave signal analogically or for it be digitally modulated This microwave signal is transferred to an optical carrier which is guided with minimum loss by an optical fiber The microwave signal is then picked up by a photodetector at the end of the fiber

One of the first applications of microwave optical links was the distribution of the microwave carrier in radar or radio-astronomy systems comprising offset aerials or active phased-array antennas which benefited from the low weight and low volume of the fiber optics [COX 97 DEC 98]

Another important area comprises all radio over fiber (RoF) applications consisting of the extension of wireless networks using microwaves or UWB waves The optical tunnels produced are capable of reaching all rooms or buildings of a company university or diverse institutions or all the rooms of a house whilst benefiting from the very low loss associated with fiber optics [FRI 02]

Amongst the applications of RoF a promising domain is in the connection of internet transmission networks to the home These connections are increasingly popular with ever-increasing speeds (1 Gbs) due to fiber optics reaching households (fiber to the home or FTTH) whereby the house itself becomes a high-speed local network In this local network the signal distribution in each room is achieved by a 60 GHz millimeter-wave (wireless personal area network or WPAN) which stays confined in the room due to the extremely fast attenuation at this frequency All rooms are linked to each other by a network of passive fiber optics which extends the millimeter-wave UWB signal throughout the whole house (ultra broadband wireless home area network or UBB-WHAN) Examples of millimeter-wave over optical transmissions are presented in [CHU 07 KIM 04 WEI 08] and a demonstration of a UBB-WHAN with an up and down link is described in [HUC 08]

The length of a link ranges from 10 m to 1 km allowing several fiber types to be used (single mode or multimode silica or plastic) and several optical wavelengths ranging from 06 to 155 μm The light undergoes intensity modulation the signal is received via photodetection In just a few

General Points 3

years rates have risen from around 10 Mbs on carriers of a few gigahertz to rates of 1 or 10 Gbs on 60 GHz for microwave carriers

A microwave photonic link is constituted of three parts

ndash a coherent light source a laser that emits an optical carrier the intensity of which is directly modulated inside the laser or externally by an optical modulator In the case of external modulation the amplitude modulation is performed by a Mach-Zehnder or an electro-absorption modulator

ndash the modulated light is then transported by single or multi-mode optical fiber [GOM 08 KOO 08] made of silica or plastic [KOI 06] This part may include an optical amplification

ndash the modulated light is finally photodetected in a photodetector consisting of a photodiode or a phototransistor

After some deliberation regarding coherent and incoherent optical links [HAL 82] the solution finally adopted for these links was ldquointensity modulation (IM) direct detection (DD)rdquo As this is recalled in [COX 06] in this type of link the depth of optical modulation is sufficiently weak that we can initially use small signal or linear techniques for each aspect Because the signals applied to links or extracted from them are in microwaves the variables characterizing these systems are S-parameters gains and noise factors Also nonlinearities and hence intermodulation produced by each component on the signal introduced in the link must be considered The combination of these different characteristics leads to the notion of interference-free dynamic range (IFDR) This shall be evaluated regarding the properties of each element in the chapters concerning overall performances of such links

As a link includes electrical-to-optical optical-to-electrical and even optical-to-optical transducers each of the magnitudes in terms of S-parameters gains and noise factors should be presented in the form of optomicrowave magnitudes This aspect forces harmonization of notions from the optical optoelectronic and microwave disciplines This is described in Chapter 5

The term used initially to describe these links was ldquomicrowave optical linksrdquo However the techniques used have gradually distanced themselves from proper optical and optoelectronic techniques so that the more specific term ldquomicrowave photonic linksrdquo has been progressively used [SEE 02]

4 Microwave Photonic Links

12 Link description

Figures 11 and 12 represent a general diagram of an IM-DD microwave optical link

Figure 11 Diagram of directly modulated microwave optical link

Figure 11 represents a direct modulation link A laser emits a light of wavelength 08 or 13 or 155 μm this laser is modulated by a microwave signal (which is possibly itself modulated) through a driver circuit The modulated light enters an optical fiber coupled to a photodetector that detects the microwave modulation signal The optical modulation can have an amplitude frequency and phase However direct photodetection detects only the modulation in amplitude The detected microwave signal is then amplified by a low-noise amplifier

Figure 12 represents an external modulation link This time a light emitted from a laser is injected into a Mach-Zehnder or electro-absorption amplitude modulator In this case microwave modulation is also applied to the modulator through a driver circuit

After passing into an optical fiber the optical intensity modulation only is detected via a photodetector As in the previous diagram the detected microwave signal is amplified in a low-noise amplifier

Laser

Driver

Optical fiber Photodetector

Low noise amplifier

Microwave or UWB Microwave or UWB

λ = 155 or 13 or 08 μm

Amplitude modulation Direct detection

General Points 5

Figure 12 Diagram of externally modulated microwave optical link

13 Signal to transmit

131 Microwave signal

The first type of transmitted signal is a signal that constitutes a microwave frequency reference It can be used in offset aerial systems or active phased-array antenna After its reflection from a moving object the microwave signal emitted from an antenna can shift in frequency (Doppler modulation) and it is the spectral purity of the microwave that determines the minimum observed frequency shift and therefore the minimum relative speed of the moving object The spectral purity and degradation after transmission of the microwave by optical links must be watched closely to distinguish the frequency shift

132 Microwave carrier for a digital signal

If the microwave signal serves as a carrier for a digital signal this carrier is previously modulated All the modulation techniques normally used such as amplitude frequency phase OFDM and combined amplitude-phase modulation (QAM) or more complex techniques can be considered such as those used in GSM GPRS EDGE and UMTS for mobile telephones or such as Bluetooth Wi-Fi and Wimax for data transmission These modulations are generally carried out on single sideband (SSB) When microwave signal modulation is implemented in phase or frequency spectral purity is also of great importance

Laser

Amplifier or driver

Optical fiber

λ = 155 or 13 or 08 μm

Microwave or UWB

Optical modulator MZ or EA

Amplitude modulation

Photodetector

Low noise amplifier

Microwave or UWB

Direct detection

6 Microwave Photonic Links

133 UWB signal

Another signal category is available for transmission by fiber optics These signals are relevant to UWB techniques without carriers and with the spectrum in the microwave region or up-converted to a millimeter-wave carrier UWB wireless links are largely used over short distances The optical fibers are particularly indicated to enable extensions of such networks

134 Optical carrier

Microwave signals can carry analog information (frequency shift due to the Doppler effect) or they can be modulated by a digital signal or be constituted of UWB signals which are themselves digitally modulated All these microwave signals must be up-converted to an optical carrier This transfer exclusively occurs by intensity modulation One of the advantages of this modulation is that the microwave signal can be recovered in a simple photodetection unit permitting the elimination of possible frequency fluctuations of the optical carrier Loss of sensitivity resulting from direct detection does not occur if the optical wavelength allows us to insert an optical amplifier or if the link is very short Usually this modulation is double sideband (DSB) especially if the modulation occurs directly in the laser but for slightly longer links this type of modulation can lead to extinction phenomena A single sideband modulation can hence be considered but this modulation must be carried out by an external modulator

135 Summary

The complexity of microwave photonic links comes from the stacking of an optical carrier and microwave or UWB subcarrier The optical carrier is exclusively intensity modulated whereas the microwave subcarrier can be modulated following all known modulation types amplitude frequency phase or their combination including a frequency shift due to the Doppler effect All these modulations can be recovered via photodetection

The use of microwave optical links will increase as the transmitted signals will be numerous and emitted in parallel communications and the data rates will increase accordingly Thus telecommunication optical

xx Microwave Photonic Links

MSM Metal semiconductor metal

MZM Modulator Mach-Zehnder

NdYAG Neodymium-doped yttrium aluminum garnet

NF Noise factor Noise figure

nOI n order intermodulation

nOIP n order intercept point

NRA National Research Agency

OE Opticelectric

OEIC Optoelectronic integrated circuit

OEMMIC Optoelectronic millimeter-wave monolithic integrated circuit

OFDM Orthogonal frequency division modulation

PDFA Praseodymium-doped fiber amplifier

PDG Biased-dependent gain

PM Phase modulation

PMMA Poly(methyl methacrylate)

PRBS Pseudo-random bit sequence

PSK Phase-shift keying

QAM Quadrature amplitude modulation

QCSE Quantum confined stark effect

QW-EAM Quantum well-EAM

RCEPD Resonant cavity enhanced photodetectors

RFT Rapid Fourier transform

RIN Relative intensity noise

RoF Radio over fiber

SD-MZM Single drive ndashMZM

Si Silicon

SiGe Silicon-germanium

SiMOX Separation by implantation of oxygen

Abbreviation Glossary xxi

SiO2 Silicon dioxide

SOA Semiconductor optical amplifier

SOC System on a chip

SOI Substrate on insulator

TDFA Thulium-doped fiber amplifier

TEGFET Two-dimensional electron gas field-effect transistor

TW-MZM Travelling wave-MZM

UTC Uni-travelling carrier

UWB Ultra-wideband

VCSEL Vertical-cavity surface-emitting laser

VCSOA Vertical-cavity semiconductor optical amplifier

VMDP Velocity matched distributed photodetector

WDM Wavelength division multiplexing

YDFA Ytterbium-doped fiber amplifier

ZnS Zinc sulfide

Chapter 1

General Points

11 Microwave photonic links

All signals generated or observed due to human activity (measurement of different physical values remote control files sounds images etc) can be transformed into analog electrical signals These electrical signals can be processed or transmitted as they are but in most cases they are digitized beforehand Once digitized these signals have different forms regarding the digital coding or error-correcting algorithms used and protocols employed in the transmission systems To be processed or transmitted these analog or digital signals can use different mediums

If the transmission is performed via metallic lines or cables digital signals directly enter these lines or they modulate more or less complex subcarriers (ADSL Ethernet)

If transmission occurs with a radiowave a high-frequency carrier must be available Due to the congestion of the wireless spectrum carriers are now principally microwaves ie with frequencies of 1 to 100 GHz (GSM UMTS Wi-Fi Wimax etc) Wireless transmission can also be performed by very short pulses having a wide spectrum range including the microwave spectrum or these pulses can modulate a carrier in the millimeter wave spectrum This technique is known as ultra-wideband (UWB) [YAO 09]

If transmission is via fiber optics digital signals modulate one or several optical carriers (amplitude or soliton modulation) which are themselves

2 Microwave Photonic Links

transmitted over hundreds of kilometers on optical fibers This is the case for all passive optical networks (PON) and their different transmission protocols [LEC 97]

From these definitions the distinctive feature of microwave photonic links is to transmit a microwave signal analogically or for it be digitally modulated This microwave signal is transferred to an optical carrier which is guided with minimum loss by an optical fiber The microwave signal is then picked up by a photodetector at the end of the fiber

One of the first applications of microwave optical links was the distribution of the microwave carrier in radar or radio-astronomy systems comprising offset aerials or active phased-array antennas which benefited from the low weight and low volume of the fiber optics [COX 97 DEC 98]

Another important area comprises all radio over fiber (RoF) applications consisting of the extension of wireless networks using microwaves or UWB waves The optical tunnels produced are capable of reaching all rooms or buildings of a company university or diverse institutions or all the rooms of a house whilst benefiting from the very low loss associated with fiber optics [FRI 02]

Amongst the applications of RoF a promising domain is in the connection of internet transmission networks to the home These connections are increasingly popular with ever-increasing speeds (1 Gbs) due to fiber optics reaching households (fiber to the home or FTTH) whereby the house itself becomes a high-speed local network In this local network the signal distribution in each room is achieved by a 60 GHz millimeter-wave (wireless personal area network or WPAN) which stays confined in the room due to the extremely fast attenuation at this frequency All rooms are linked to each other by a network of passive fiber optics which extends the millimeter-wave UWB signal throughout the whole house (ultra broadband wireless home area network or UBB-WHAN) Examples of millimeter-wave over optical transmissions are presented in [CHU 07 KIM 04 WEI 08] and a demonstration of a UBB-WHAN with an up and down link is described in [HUC 08]

The length of a link ranges from 10 m to 1 km allowing several fiber types to be used (single mode or multimode silica or plastic) and several optical wavelengths ranging from 06 to 155 μm The light undergoes intensity modulation the signal is received via photodetection In just a few

General Points 3

years rates have risen from around 10 Mbs on carriers of a few gigahertz to rates of 1 or 10 Gbs on 60 GHz for microwave carriers

A microwave photonic link is constituted of three parts

ndash a coherent light source a laser that emits an optical carrier the intensity of which is directly modulated inside the laser or externally by an optical modulator In the case of external modulation the amplitude modulation is performed by a Mach-Zehnder or an electro-absorption modulator

ndash the modulated light is then transported by single or multi-mode optical fiber [GOM 08 KOO 08] made of silica or plastic [KOI 06] This part may include an optical amplification

ndash the modulated light is finally photodetected in a photodetector consisting of a photodiode or a phototransistor

After some deliberation regarding coherent and incoherent optical links [HAL 82] the solution finally adopted for these links was ldquointensity modulation (IM) direct detection (DD)rdquo As this is recalled in [COX 06] in this type of link the depth of optical modulation is sufficiently weak that we can initially use small signal or linear techniques for each aspect Because the signals applied to links or extracted from them are in microwaves the variables characterizing these systems are S-parameters gains and noise factors Also nonlinearities and hence intermodulation produced by each component on the signal introduced in the link must be considered The combination of these different characteristics leads to the notion of interference-free dynamic range (IFDR) This shall be evaluated regarding the properties of each element in the chapters concerning overall performances of such links

As a link includes electrical-to-optical optical-to-electrical and even optical-to-optical transducers each of the magnitudes in terms of S-parameters gains and noise factors should be presented in the form of optomicrowave magnitudes This aspect forces harmonization of notions from the optical optoelectronic and microwave disciplines This is described in Chapter 5

The term used initially to describe these links was ldquomicrowave optical linksrdquo However the techniques used have gradually distanced themselves from proper optical and optoelectronic techniques so that the more specific term ldquomicrowave photonic linksrdquo has been progressively used [SEE 02]

4 Microwave Photonic Links

12 Link description

Figures 11 and 12 represent a general diagram of an IM-DD microwave optical link

Figure 11 Diagram of directly modulated microwave optical link

Figure 11 represents a direct modulation link A laser emits a light of wavelength 08 or 13 or 155 μm this laser is modulated by a microwave signal (which is possibly itself modulated) through a driver circuit The modulated light enters an optical fiber coupled to a photodetector that detects the microwave modulation signal The optical modulation can have an amplitude frequency and phase However direct photodetection detects only the modulation in amplitude The detected microwave signal is then amplified by a low-noise amplifier

Figure 12 represents an external modulation link This time a light emitted from a laser is injected into a Mach-Zehnder or electro-absorption amplitude modulator In this case microwave modulation is also applied to the modulator through a driver circuit

After passing into an optical fiber the optical intensity modulation only is detected via a photodetector As in the previous diagram the detected microwave signal is amplified in a low-noise amplifier

Laser

Driver

Optical fiber Photodetector

Low noise amplifier

Microwave or UWB Microwave or UWB

λ = 155 or 13 or 08 μm

Amplitude modulation Direct detection

General Points 5

Figure 12 Diagram of externally modulated microwave optical link

13 Signal to transmit

131 Microwave signal

The first type of transmitted signal is a signal that constitutes a microwave frequency reference It can be used in offset aerial systems or active phased-array antenna After its reflection from a moving object the microwave signal emitted from an antenna can shift in frequency (Doppler modulation) and it is the spectral purity of the microwave that determines the minimum observed frequency shift and therefore the minimum relative speed of the moving object The spectral purity and degradation after transmission of the microwave by optical links must be watched closely to distinguish the frequency shift

132 Microwave carrier for a digital signal

If the microwave signal serves as a carrier for a digital signal this carrier is previously modulated All the modulation techniques normally used such as amplitude frequency phase OFDM and combined amplitude-phase modulation (QAM) or more complex techniques can be considered such as those used in GSM GPRS EDGE and UMTS for mobile telephones or such as Bluetooth Wi-Fi and Wimax for data transmission These modulations are generally carried out on single sideband (SSB) When microwave signal modulation is implemented in phase or frequency spectral purity is also of great importance

Laser

Amplifier or driver

Optical fiber

λ = 155 or 13 or 08 μm

Microwave or UWB

Optical modulator MZ or EA

Amplitude modulation

Photodetector

Low noise amplifier

Microwave or UWB

Direct detection

6 Microwave Photonic Links

133 UWB signal

Another signal category is available for transmission by fiber optics These signals are relevant to UWB techniques without carriers and with the spectrum in the microwave region or up-converted to a millimeter-wave carrier UWB wireless links are largely used over short distances The optical fibers are particularly indicated to enable extensions of such networks

134 Optical carrier

Microwave signals can carry analog information (frequency shift due to the Doppler effect) or they can be modulated by a digital signal or be constituted of UWB signals which are themselves digitally modulated All these microwave signals must be up-converted to an optical carrier This transfer exclusively occurs by intensity modulation One of the advantages of this modulation is that the microwave signal can be recovered in a simple photodetection unit permitting the elimination of possible frequency fluctuations of the optical carrier Loss of sensitivity resulting from direct detection does not occur if the optical wavelength allows us to insert an optical amplifier or if the link is very short Usually this modulation is double sideband (DSB) especially if the modulation occurs directly in the laser but for slightly longer links this type of modulation can lead to extinction phenomena A single sideband modulation can hence be considered but this modulation must be carried out by an external modulator

135 Summary

The complexity of microwave photonic links comes from the stacking of an optical carrier and microwave or UWB subcarrier The optical carrier is exclusively intensity modulated whereas the microwave subcarrier can be modulated following all known modulation types amplitude frequency phase or their combination including a frequency shift due to the Doppler effect All these modulations can be recovered via photodetection

The use of microwave optical links will increase as the transmitted signals will be numerous and emitted in parallel communications and the data rates will increase accordingly Thus telecommunication optical

Abbreviation Glossary xxi

SiO2 Silicon dioxide

SOA Semiconductor optical amplifier

SOC System on a chip

SOI Substrate on insulator

TDFA Thulium-doped fiber amplifier

TEGFET Two-dimensional electron gas field-effect transistor

TW-MZM Travelling wave-MZM

UTC Uni-travelling carrier

UWB Ultra-wideband

VCSEL Vertical-cavity surface-emitting laser

VCSOA Vertical-cavity semiconductor optical amplifier

VMDP Velocity matched distributed photodetector

WDM Wavelength division multiplexing

YDFA Ytterbium-doped fiber amplifier

ZnS Zinc sulfide

Chapter 1

General Points

11 Microwave photonic links

All signals generated or observed due to human activity (measurement of different physical values remote control files sounds images etc) can be transformed into analog electrical signals These electrical signals can be processed or transmitted as they are but in most cases they are digitized beforehand Once digitized these signals have different forms regarding the digital coding or error-correcting algorithms used and protocols employed in the transmission systems To be processed or transmitted these analog or digital signals can use different mediums

If the transmission is performed via metallic lines or cables digital signals directly enter these lines or they modulate more or less complex subcarriers (ADSL Ethernet)

If transmission occurs with a radiowave a high-frequency carrier must be available Due to the congestion of the wireless spectrum carriers are now principally microwaves ie with frequencies of 1 to 100 GHz (GSM UMTS Wi-Fi Wimax etc) Wireless transmission can also be performed by very short pulses having a wide spectrum range including the microwave spectrum or these pulses can modulate a carrier in the millimeter wave spectrum This technique is known as ultra-wideband (UWB) [YAO 09]

If transmission is via fiber optics digital signals modulate one or several optical carriers (amplitude or soliton modulation) which are themselves

2 Microwave Photonic Links

transmitted over hundreds of kilometers on optical fibers This is the case for all passive optical networks (PON) and their different transmission protocols [LEC 97]

From these definitions the distinctive feature of microwave photonic links is to transmit a microwave signal analogically or for it be digitally modulated This microwave signal is transferred to an optical carrier which is guided with minimum loss by an optical fiber The microwave signal is then picked up by a photodetector at the end of the fiber

One of the first applications of microwave optical links was the distribution of the microwave carrier in radar or radio-astronomy systems comprising offset aerials or active phased-array antennas which benefited from the low weight and low volume of the fiber optics [COX 97 DEC 98]

Another important area comprises all radio over fiber (RoF) applications consisting of the extension of wireless networks using microwaves or UWB waves The optical tunnels produced are capable of reaching all rooms or buildings of a company university or diverse institutions or all the rooms of a house whilst benefiting from the very low loss associated with fiber optics [FRI 02]

Amongst the applications of RoF a promising domain is in the connection of internet transmission networks to the home These connections are increasingly popular with ever-increasing speeds (1 Gbs) due to fiber optics reaching households (fiber to the home or FTTH) whereby the house itself becomes a high-speed local network In this local network the signal distribution in each room is achieved by a 60 GHz millimeter-wave (wireless personal area network or WPAN) which stays confined in the room due to the extremely fast attenuation at this frequency All rooms are linked to each other by a network of passive fiber optics which extends the millimeter-wave UWB signal throughout the whole house (ultra broadband wireless home area network or UBB-WHAN) Examples of millimeter-wave over optical transmissions are presented in [CHU 07 KIM 04 WEI 08] and a demonstration of a UBB-WHAN with an up and down link is described in [HUC 08]

The length of a link ranges from 10 m to 1 km allowing several fiber types to be used (single mode or multimode silica or plastic) and several optical wavelengths ranging from 06 to 155 μm The light undergoes intensity modulation the signal is received via photodetection In just a few

General Points 3

years rates have risen from around 10 Mbs on carriers of a few gigahertz to rates of 1 or 10 Gbs on 60 GHz for microwave carriers

A microwave photonic link is constituted of three parts

ndash a coherent light source a laser that emits an optical carrier the intensity of which is directly modulated inside the laser or externally by an optical modulator In the case of external modulation the amplitude modulation is performed by a Mach-Zehnder or an electro-absorption modulator

ndash the modulated light is then transported by single or multi-mode optical fiber [GOM 08 KOO 08] made of silica or plastic [KOI 06] This part may include an optical amplification

ndash the modulated light is finally photodetected in a photodetector consisting of a photodiode or a phototransistor

After some deliberation regarding coherent and incoherent optical links [HAL 82] the solution finally adopted for these links was ldquointensity modulation (IM) direct detection (DD)rdquo As this is recalled in [COX 06] in this type of link the depth of optical modulation is sufficiently weak that we can initially use small signal or linear techniques for each aspect Because the signals applied to links or extracted from them are in microwaves the variables characterizing these systems are S-parameters gains and noise factors Also nonlinearities and hence intermodulation produced by each component on the signal introduced in the link must be considered The combination of these different characteristics leads to the notion of interference-free dynamic range (IFDR) This shall be evaluated regarding the properties of each element in the chapters concerning overall performances of such links

As a link includes electrical-to-optical optical-to-electrical and even optical-to-optical transducers each of the magnitudes in terms of S-parameters gains and noise factors should be presented in the form of optomicrowave magnitudes This aspect forces harmonization of notions from the optical optoelectronic and microwave disciplines This is described in Chapter 5

The term used initially to describe these links was ldquomicrowave optical linksrdquo However the techniques used have gradually distanced themselves from proper optical and optoelectronic techniques so that the more specific term ldquomicrowave photonic linksrdquo has been progressively used [SEE 02]

4 Microwave Photonic Links

12 Link description

Figures 11 and 12 represent a general diagram of an IM-DD microwave optical link

Figure 11 Diagram of directly modulated microwave optical link

Figure 11 represents a direct modulation link A laser emits a light of wavelength 08 or 13 or 155 μm this laser is modulated by a microwave signal (which is possibly itself modulated) through a driver circuit The modulated light enters an optical fiber coupled to a photodetector that detects the microwave modulation signal The optical modulation can have an amplitude frequency and phase However direct photodetection detects only the modulation in amplitude The detected microwave signal is then amplified by a low-noise amplifier

Figure 12 represents an external modulation link This time a light emitted from a laser is injected into a Mach-Zehnder or electro-absorption amplitude modulator In this case microwave modulation is also applied to the modulator through a driver circuit

After passing into an optical fiber the optical intensity modulation only is detected via a photodetector As in the previous diagram the detected microwave signal is amplified in a low-noise amplifier

Laser

Driver

Optical fiber Photodetector

Low noise amplifier

Microwave or UWB Microwave or UWB

λ = 155 or 13 or 08 μm

Amplitude modulation Direct detection

General Points 5

Figure 12 Diagram of externally modulated microwave optical link

13 Signal to transmit

131 Microwave signal

The first type of transmitted signal is a signal that constitutes a microwave frequency reference It can be used in offset aerial systems or active phased-array antenna After its reflection from a moving object the microwave signal emitted from an antenna can shift in frequency (Doppler modulation) and it is the spectral purity of the microwave that determines the minimum observed frequency shift and therefore the minimum relative speed of the moving object The spectral purity and degradation after transmission of the microwave by optical links must be watched closely to distinguish the frequency shift

132 Microwave carrier for a digital signal

If the microwave signal serves as a carrier for a digital signal this carrier is previously modulated All the modulation techniques normally used such as amplitude frequency phase OFDM and combined amplitude-phase modulation (QAM) or more complex techniques can be considered such as those used in GSM GPRS EDGE and UMTS for mobile telephones or such as Bluetooth Wi-Fi and Wimax for data transmission These modulations are generally carried out on single sideband (SSB) When microwave signal modulation is implemented in phase or frequency spectral purity is also of great importance

Laser

Amplifier or driver

Optical fiber

λ = 155 or 13 or 08 μm

Microwave or UWB

Optical modulator MZ or EA

Amplitude modulation

Photodetector

Low noise amplifier

Microwave or UWB

Direct detection

6 Microwave Photonic Links

133 UWB signal

Another signal category is available for transmission by fiber optics These signals are relevant to UWB techniques without carriers and with the spectrum in the microwave region or up-converted to a millimeter-wave carrier UWB wireless links are largely used over short distances The optical fibers are particularly indicated to enable extensions of such networks

134 Optical carrier

Microwave signals can carry analog information (frequency shift due to the Doppler effect) or they can be modulated by a digital signal or be constituted of UWB signals which are themselves digitally modulated All these microwave signals must be up-converted to an optical carrier This transfer exclusively occurs by intensity modulation One of the advantages of this modulation is that the microwave signal can be recovered in a simple photodetection unit permitting the elimination of possible frequency fluctuations of the optical carrier Loss of sensitivity resulting from direct detection does not occur if the optical wavelength allows us to insert an optical amplifier or if the link is very short Usually this modulation is double sideband (DSB) especially if the modulation occurs directly in the laser but for slightly longer links this type of modulation can lead to extinction phenomena A single sideband modulation can hence be considered but this modulation must be carried out by an external modulator

135 Summary

The complexity of microwave photonic links comes from the stacking of an optical carrier and microwave or UWB subcarrier The optical carrier is exclusively intensity modulated whereas the microwave subcarrier can be modulated following all known modulation types amplitude frequency phase or their combination including a frequency shift due to the Doppler effect All these modulations can be recovered via photodetection

The use of microwave optical links will increase as the transmitted signals will be numerous and emitted in parallel communications and the data rates will increase accordingly Thus telecommunication optical

Chapter 1

General Points

11 Microwave photonic links

All signals generated or observed due to human activity (measurement of different physical values remote control files sounds images etc) can be transformed into analog electrical signals These electrical signals can be processed or transmitted as they are but in most cases they are digitized beforehand Once digitized these signals have different forms regarding the digital coding or error-correcting algorithms used and protocols employed in the transmission systems To be processed or transmitted these analog or digital signals can use different mediums

If the transmission is performed via metallic lines or cables digital signals directly enter these lines or they modulate more or less complex subcarriers (ADSL Ethernet)

If transmission occurs with a radiowave a high-frequency carrier must be available Due to the congestion of the wireless spectrum carriers are now principally microwaves ie with frequencies of 1 to 100 GHz (GSM UMTS Wi-Fi Wimax etc) Wireless transmission can also be performed by very short pulses having a wide spectrum range including the microwave spectrum or these pulses can modulate a carrier in the millimeter wave spectrum This technique is known as ultra-wideband (UWB) [YAO 09]

If transmission is via fiber optics digital signals modulate one or several optical carriers (amplitude or soliton modulation) which are themselves

2 Microwave Photonic Links

transmitted over hundreds of kilometers on optical fibers This is the case for all passive optical networks (PON) and their different transmission protocols [LEC 97]

From these definitions the distinctive feature of microwave photonic links is to transmit a microwave signal analogically or for it be digitally modulated This microwave signal is transferred to an optical carrier which is guided with minimum loss by an optical fiber The microwave signal is then picked up by a photodetector at the end of the fiber

One of the first applications of microwave optical links was the distribution of the microwave carrier in radar or radio-astronomy systems comprising offset aerials or active phased-array antennas which benefited from the low weight and low volume of the fiber optics [COX 97 DEC 98]

Another important area comprises all radio over fiber (RoF) applications consisting of the extension of wireless networks using microwaves or UWB waves The optical tunnels produced are capable of reaching all rooms or buildings of a company university or diverse institutions or all the rooms of a house whilst benefiting from the very low loss associated with fiber optics [FRI 02]

Amongst the applications of RoF a promising domain is in the connection of internet transmission networks to the home These connections are increasingly popular with ever-increasing speeds (1 Gbs) due to fiber optics reaching households (fiber to the home or FTTH) whereby the house itself becomes a high-speed local network In this local network the signal distribution in each room is achieved by a 60 GHz millimeter-wave (wireless personal area network or WPAN) which stays confined in the room due to the extremely fast attenuation at this frequency All rooms are linked to each other by a network of passive fiber optics which extends the millimeter-wave UWB signal throughout the whole house (ultra broadband wireless home area network or UBB-WHAN) Examples of millimeter-wave over optical transmissions are presented in [CHU 07 KIM 04 WEI 08] and a demonstration of a UBB-WHAN with an up and down link is described in [HUC 08]

The length of a link ranges from 10 m to 1 km allowing several fiber types to be used (single mode or multimode silica or plastic) and several optical wavelengths ranging from 06 to 155 μm The light undergoes intensity modulation the signal is received via photodetection In just a few

General Points 3

years rates have risen from around 10 Mbs on carriers of a few gigahertz to rates of 1 or 10 Gbs on 60 GHz for microwave carriers

A microwave photonic link is constituted of three parts

ndash a coherent light source a laser that emits an optical carrier the intensity of which is directly modulated inside the laser or externally by an optical modulator In the case of external modulation the amplitude modulation is performed by a Mach-Zehnder or an electro-absorption modulator

ndash the modulated light is then transported by single or multi-mode optical fiber [GOM 08 KOO 08] made of silica or plastic [KOI 06] This part may include an optical amplification

ndash the modulated light is finally photodetected in a photodetector consisting of a photodiode or a phototransistor

After some deliberation regarding coherent and incoherent optical links [HAL 82] the solution finally adopted for these links was ldquointensity modulation (IM) direct detection (DD)rdquo As this is recalled in [COX 06] in this type of link the depth of optical modulation is sufficiently weak that we can initially use small signal or linear techniques for each aspect Because the signals applied to links or extracted from them are in microwaves the variables characterizing these systems are S-parameters gains and noise factors Also nonlinearities and hence intermodulation produced by each component on the signal introduced in the link must be considered The combination of these different characteristics leads to the notion of interference-free dynamic range (IFDR) This shall be evaluated regarding the properties of each element in the chapters concerning overall performances of such links

As a link includes electrical-to-optical optical-to-electrical and even optical-to-optical transducers each of the magnitudes in terms of S-parameters gains and noise factors should be presented in the form of optomicrowave magnitudes This aspect forces harmonization of notions from the optical optoelectronic and microwave disciplines This is described in Chapter 5

The term used initially to describe these links was ldquomicrowave optical linksrdquo However the techniques used have gradually distanced themselves from proper optical and optoelectronic techniques so that the more specific term ldquomicrowave photonic linksrdquo has been progressively used [SEE 02]

4 Microwave Photonic Links

12 Link description

Figures 11 and 12 represent a general diagram of an IM-DD microwave optical link

Figure 11 Diagram of directly modulated microwave optical link

Figure 11 represents a direct modulation link A laser emits a light of wavelength 08 or 13 or 155 μm this laser is modulated by a microwave signal (which is possibly itself modulated) through a driver circuit The modulated light enters an optical fiber coupled to a photodetector that detects the microwave modulation signal The optical modulation can have an amplitude frequency and phase However direct photodetection detects only the modulation in amplitude The detected microwave signal is then amplified by a low-noise amplifier

Figure 12 represents an external modulation link This time a light emitted from a laser is injected into a Mach-Zehnder or electro-absorption amplitude modulator In this case microwave modulation is also applied to the modulator through a driver circuit

After passing into an optical fiber the optical intensity modulation only is detected via a photodetector As in the previous diagram the detected microwave signal is amplified in a low-noise amplifier

Laser

Driver

Optical fiber Photodetector

Low noise amplifier

Microwave or UWB Microwave or UWB

λ = 155 or 13 or 08 μm

Amplitude modulation Direct detection

General Points 5

Figure 12 Diagram of externally modulated microwave optical link

13 Signal to transmit

131 Microwave signal

The first type of transmitted signal is a signal that constitutes a microwave frequency reference It can be used in offset aerial systems or active phased-array antenna After its reflection from a moving object the microwave signal emitted from an antenna can shift in frequency (Doppler modulation) and it is the spectral purity of the microwave that determines the minimum observed frequency shift and therefore the minimum relative speed of the moving object The spectral purity and degradation after transmission of the microwave by optical links must be watched closely to distinguish the frequency shift

132 Microwave carrier for a digital signal

If the microwave signal serves as a carrier for a digital signal this carrier is previously modulated All the modulation techniques normally used such as amplitude frequency phase OFDM and combined amplitude-phase modulation (QAM) or more complex techniques can be considered such as those used in GSM GPRS EDGE and UMTS for mobile telephones or such as Bluetooth Wi-Fi and Wimax for data transmission These modulations are generally carried out on single sideband (SSB) When microwave signal modulation is implemented in phase or frequency spectral purity is also of great importance

Laser

Amplifier or driver

Optical fiber

λ = 155 or 13 or 08 μm

Microwave or UWB

Optical modulator MZ or EA

Amplitude modulation

Photodetector

Low noise amplifier

Microwave or UWB

Direct detection

6 Microwave Photonic Links

133 UWB signal

Another signal category is available for transmission by fiber optics These signals are relevant to UWB techniques without carriers and with the spectrum in the microwave region or up-converted to a millimeter-wave carrier UWB wireless links are largely used over short distances The optical fibers are particularly indicated to enable extensions of such networks

134 Optical carrier

Microwave signals can carry analog information (frequency shift due to the Doppler effect) or they can be modulated by a digital signal or be constituted of UWB signals which are themselves digitally modulated All these microwave signals must be up-converted to an optical carrier This transfer exclusively occurs by intensity modulation One of the advantages of this modulation is that the microwave signal can be recovered in a simple photodetection unit permitting the elimination of possible frequency fluctuations of the optical carrier Loss of sensitivity resulting from direct detection does not occur if the optical wavelength allows us to insert an optical amplifier or if the link is very short Usually this modulation is double sideband (DSB) especially if the modulation occurs directly in the laser but for slightly longer links this type of modulation can lead to extinction phenomena A single sideband modulation can hence be considered but this modulation must be carried out by an external modulator

135 Summary

The complexity of microwave photonic links comes from the stacking of an optical carrier and microwave or UWB subcarrier The optical carrier is exclusively intensity modulated whereas the microwave subcarrier can be modulated following all known modulation types amplitude frequency phase or their combination including a frequency shift due to the Doppler effect All these modulations can be recovered via photodetection

The use of microwave optical links will increase as the transmitted signals will be numerous and emitted in parallel communications and the data rates will increase accordingly Thus telecommunication optical

2 Microwave Photonic Links

transmitted over hundreds of kilometers on optical fibers This is the case for all passive optical networks (PON) and their different transmission protocols [LEC 97]

From these definitions the distinctive feature of microwave photonic links is to transmit a microwave signal analogically or for it be digitally modulated This microwave signal is transferred to an optical carrier which is guided with minimum loss by an optical fiber The microwave signal is then picked up by a photodetector at the end of the fiber

One of the first applications of microwave optical links was the distribution of the microwave carrier in radar or radio-astronomy systems comprising offset aerials or active phased-array antennas which benefited from the low weight and low volume of the fiber optics [COX 97 DEC 98]

Another important area comprises all radio over fiber (RoF) applications consisting of the extension of wireless networks using microwaves or UWB waves The optical tunnels produced are capable of reaching all rooms or buildings of a company university or diverse institutions or all the rooms of a house whilst benefiting from the very low loss associated with fiber optics [FRI 02]

Amongst the applications of RoF a promising domain is in the connection of internet transmission networks to the home These connections are increasingly popular with ever-increasing speeds (1 Gbs) due to fiber optics reaching households (fiber to the home or FTTH) whereby the house itself becomes a high-speed local network In this local network the signal distribution in each room is achieved by a 60 GHz millimeter-wave (wireless personal area network or WPAN) which stays confined in the room due to the extremely fast attenuation at this frequency All rooms are linked to each other by a network of passive fiber optics which extends the millimeter-wave UWB signal throughout the whole house (ultra broadband wireless home area network or UBB-WHAN) Examples of millimeter-wave over optical transmissions are presented in [CHU 07 KIM 04 WEI 08] and a demonstration of a UBB-WHAN with an up and down link is described in [HUC 08]

The length of a link ranges from 10 m to 1 km allowing several fiber types to be used (single mode or multimode silica or plastic) and several optical wavelengths ranging from 06 to 155 μm The light undergoes intensity modulation the signal is received via photodetection In just a few

General Points 3

years rates have risen from around 10 Mbs on carriers of a few gigahertz to rates of 1 or 10 Gbs on 60 GHz for microwave carriers

A microwave photonic link is constituted of three parts

ndash a coherent light source a laser that emits an optical carrier the intensity of which is directly modulated inside the laser or externally by an optical modulator In the case of external modulation the amplitude modulation is performed by a Mach-Zehnder or an electro-absorption modulator

ndash the modulated light is then transported by single or multi-mode optical fiber [GOM 08 KOO 08] made of silica or plastic [KOI 06] This part may include an optical amplification

ndash the modulated light is finally photodetected in a photodetector consisting of a photodiode or a phototransistor

After some deliberation regarding coherent and incoherent optical links [HAL 82] the solution finally adopted for these links was ldquointensity modulation (IM) direct detection (DD)rdquo As this is recalled in [COX 06] in this type of link the depth of optical modulation is sufficiently weak that we can initially use small signal or linear techniques for each aspect Because the signals applied to links or extracted from them are in microwaves the variables characterizing these systems are S-parameters gains and noise factors Also nonlinearities and hence intermodulation produced by each component on the signal introduced in the link must be considered The combination of these different characteristics leads to the notion of interference-free dynamic range (IFDR) This shall be evaluated regarding the properties of each element in the chapters concerning overall performances of such links

As a link includes electrical-to-optical optical-to-electrical and even optical-to-optical transducers each of the magnitudes in terms of S-parameters gains and noise factors should be presented in the form of optomicrowave magnitudes This aspect forces harmonization of notions from the optical optoelectronic and microwave disciplines This is described in Chapter 5

The term used initially to describe these links was ldquomicrowave optical linksrdquo However the techniques used have gradually distanced themselves from proper optical and optoelectronic techniques so that the more specific term ldquomicrowave photonic linksrdquo has been progressively used [SEE 02]

4 Microwave Photonic Links

12 Link description

Figures 11 and 12 represent a general diagram of an IM-DD microwave optical link

Figure 11 Diagram of directly modulated microwave optical link

Figure 11 represents a direct modulation link A laser emits a light of wavelength 08 or 13 or 155 μm this laser is modulated by a microwave signal (which is possibly itself modulated) through a driver circuit The modulated light enters an optical fiber coupled to a photodetector that detects the microwave modulation signal The optical modulation can have an amplitude frequency and phase However direct photodetection detects only the modulation in amplitude The detected microwave signal is then amplified by a low-noise amplifier

Figure 12 represents an external modulation link This time a light emitted from a laser is injected into a Mach-Zehnder or electro-absorption amplitude modulator In this case microwave modulation is also applied to the modulator through a driver circuit

After passing into an optical fiber the optical intensity modulation only is detected via a photodetector As in the previous diagram the detected microwave signal is amplified in a low-noise amplifier

Laser

Driver

Optical fiber Photodetector

Low noise amplifier

Microwave or UWB Microwave or UWB

λ = 155 or 13 or 08 μm

Amplitude modulation Direct detection

General Points 5

Figure 12 Diagram of externally modulated microwave optical link

13 Signal to transmit

131 Microwave signal

The first type of transmitted signal is a signal that constitutes a microwave frequency reference It can be used in offset aerial systems or active phased-array antenna After its reflection from a moving object the microwave signal emitted from an antenna can shift in frequency (Doppler modulation) and it is the spectral purity of the microwave that determines the minimum observed frequency shift and therefore the minimum relative speed of the moving object The spectral purity and degradation after transmission of the microwave by optical links must be watched closely to distinguish the frequency shift

132 Microwave carrier for a digital signal

If the microwave signal serves as a carrier for a digital signal this carrier is previously modulated All the modulation techniques normally used such as amplitude frequency phase OFDM and combined amplitude-phase modulation (QAM) or more complex techniques can be considered such as those used in GSM GPRS EDGE and UMTS for mobile telephones or such as Bluetooth Wi-Fi and Wimax for data transmission These modulations are generally carried out on single sideband (SSB) When microwave signal modulation is implemented in phase or frequency spectral purity is also of great importance

Laser

Amplifier or driver

Optical fiber

λ = 155 or 13 or 08 μm

Microwave or UWB

Optical modulator MZ or EA

Amplitude modulation

Photodetector

Low noise amplifier

Microwave or UWB

Direct detection

6 Microwave Photonic Links

133 UWB signal

Another signal category is available for transmission by fiber optics These signals are relevant to UWB techniques without carriers and with the spectrum in the microwave region or up-converted to a millimeter-wave carrier UWB wireless links are largely used over short distances The optical fibers are particularly indicated to enable extensions of such networks

134 Optical carrier

Microwave signals can carry analog information (frequency shift due to the Doppler effect) or they can be modulated by a digital signal or be constituted of UWB signals which are themselves digitally modulated All these microwave signals must be up-converted to an optical carrier This transfer exclusively occurs by intensity modulation One of the advantages of this modulation is that the microwave signal can be recovered in a simple photodetection unit permitting the elimination of possible frequency fluctuations of the optical carrier Loss of sensitivity resulting from direct detection does not occur if the optical wavelength allows us to insert an optical amplifier or if the link is very short Usually this modulation is double sideband (DSB) especially if the modulation occurs directly in the laser but for slightly longer links this type of modulation can lead to extinction phenomena A single sideband modulation can hence be considered but this modulation must be carried out by an external modulator

135 Summary

The complexity of microwave photonic links comes from the stacking of an optical carrier and microwave or UWB subcarrier The optical carrier is exclusively intensity modulated whereas the microwave subcarrier can be modulated following all known modulation types amplitude frequency phase or their combination including a frequency shift due to the Doppler effect All these modulations can be recovered via photodetection

The use of microwave optical links will increase as the transmitted signals will be numerous and emitted in parallel communications and the data rates will increase accordingly Thus telecommunication optical

General Points 3

years rates have risen from around 10 Mbs on carriers of a few gigahertz to rates of 1 or 10 Gbs on 60 GHz for microwave carriers

A microwave photonic link is constituted of three parts

ndash a coherent light source a laser that emits an optical carrier the intensity of which is directly modulated inside the laser or externally by an optical modulator In the case of external modulation the amplitude modulation is performed by a Mach-Zehnder or an electro-absorption modulator

ndash the modulated light is then transported by single or multi-mode optical fiber [GOM 08 KOO 08] made of silica or plastic [KOI 06] This part may include an optical amplification

ndash the modulated light is finally photodetected in a photodetector consisting of a photodiode or a phototransistor

After some deliberation regarding coherent and incoherent optical links [HAL 82] the solution finally adopted for these links was ldquointensity modulation (IM) direct detection (DD)rdquo As this is recalled in [COX 06] in this type of link the depth of optical modulation is sufficiently weak that we can initially use small signal or linear techniques for each aspect Because the signals applied to links or extracted from them are in microwaves the variables characterizing these systems are S-parameters gains and noise factors Also nonlinearities and hence intermodulation produced by each component on the signal introduced in the link must be considered The combination of these different characteristics leads to the notion of interference-free dynamic range (IFDR) This shall be evaluated regarding the properties of each element in the chapters concerning overall performances of such links

As a link includes electrical-to-optical optical-to-electrical and even optical-to-optical transducers each of the magnitudes in terms of S-parameters gains and noise factors should be presented in the form of optomicrowave magnitudes This aspect forces harmonization of notions from the optical optoelectronic and microwave disciplines This is described in Chapter 5

The term used initially to describe these links was ldquomicrowave optical linksrdquo However the techniques used have gradually distanced themselves from proper optical and optoelectronic techniques so that the more specific term ldquomicrowave photonic linksrdquo has been progressively used [SEE 02]

4 Microwave Photonic Links

12 Link description

Figures 11 and 12 represent a general diagram of an IM-DD microwave optical link

Figure 11 Diagram of directly modulated microwave optical link

Figure 11 represents a direct modulation link A laser emits a light of wavelength 08 or 13 or 155 μm this laser is modulated by a microwave signal (which is possibly itself modulated) through a driver circuit The modulated light enters an optical fiber coupled to a photodetector that detects the microwave modulation signal The optical modulation can have an amplitude frequency and phase However direct photodetection detects only the modulation in amplitude The detected microwave signal is then amplified by a low-noise amplifier

Figure 12 represents an external modulation link This time a light emitted from a laser is injected into a Mach-Zehnder or electro-absorption amplitude modulator In this case microwave modulation is also applied to the modulator through a driver circuit

After passing into an optical fiber the optical intensity modulation only is detected via a photodetector As in the previous diagram the detected microwave signal is amplified in a low-noise amplifier

Laser

Driver

Optical fiber Photodetector

Low noise amplifier

Microwave or UWB Microwave or UWB

λ = 155 or 13 or 08 μm

Amplitude modulation Direct detection

General Points 5

Figure 12 Diagram of externally modulated microwave optical link

13 Signal to transmit

131 Microwave signal

The first type of transmitted signal is a signal that constitutes a microwave frequency reference It can be used in offset aerial systems or active phased-array antenna After its reflection from a moving object the microwave signal emitted from an antenna can shift in frequency (Doppler modulation) and it is the spectral purity of the microwave that determines the minimum observed frequency shift and therefore the minimum relative speed of the moving object The spectral purity and degradation after transmission of the microwave by optical links must be watched closely to distinguish the frequency shift

132 Microwave carrier for a digital signal

If the microwave signal serves as a carrier for a digital signal this carrier is previously modulated All the modulation techniques normally used such as amplitude frequency phase OFDM and combined amplitude-phase modulation (QAM) or more complex techniques can be considered such as those used in GSM GPRS EDGE and UMTS for mobile telephones or such as Bluetooth Wi-Fi and Wimax for data transmission These modulations are generally carried out on single sideband (SSB) When microwave signal modulation is implemented in phase or frequency spectral purity is also of great importance

Laser

Amplifier or driver

Optical fiber

λ = 155 or 13 or 08 μm

Microwave or UWB

Optical modulator MZ or EA

Amplitude modulation

Photodetector

Low noise amplifier

Microwave or UWB

Direct detection

6 Microwave Photonic Links

133 UWB signal

Another signal category is available for transmission by fiber optics These signals are relevant to UWB techniques without carriers and with the spectrum in the microwave region or up-converted to a millimeter-wave carrier UWB wireless links are largely used over short distances The optical fibers are particularly indicated to enable extensions of such networks

134 Optical carrier

Microwave signals can carry analog information (frequency shift due to the Doppler effect) or they can be modulated by a digital signal or be constituted of UWB signals which are themselves digitally modulated All these microwave signals must be up-converted to an optical carrier This transfer exclusively occurs by intensity modulation One of the advantages of this modulation is that the microwave signal can be recovered in a simple photodetection unit permitting the elimination of possible frequency fluctuations of the optical carrier Loss of sensitivity resulting from direct detection does not occur if the optical wavelength allows us to insert an optical amplifier or if the link is very short Usually this modulation is double sideband (DSB) especially if the modulation occurs directly in the laser but for slightly longer links this type of modulation can lead to extinction phenomena A single sideband modulation can hence be considered but this modulation must be carried out by an external modulator

135 Summary

The complexity of microwave photonic links comes from the stacking of an optical carrier and microwave or UWB subcarrier The optical carrier is exclusively intensity modulated whereas the microwave subcarrier can be modulated following all known modulation types amplitude frequency phase or their combination including a frequency shift due to the Doppler effect All these modulations can be recovered via photodetection

The use of microwave optical links will increase as the transmitted signals will be numerous and emitted in parallel communications and the data rates will increase accordingly Thus telecommunication optical

4 Microwave Photonic Links

12 Link description

Figures 11 and 12 represent a general diagram of an IM-DD microwave optical link

Figure 11 Diagram of directly modulated microwave optical link

Figure 11 represents a direct modulation link A laser emits a light of wavelength 08 or 13 or 155 μm this laser is modulated by a microwave signal (which is possibly itself modulated) through a driver circuit The modulated light enters an optical fiber coupled to a photodetector that detects the microwave modulation signal The optical modulation can have an amplitude frequency and phase However direct photodetection detects only the modulation in amplitude The detected microwave signal is then amplified by a low-noise amplifier

Figure 12 represents an external modulation link This time a light emitted from a laser is injected into a Mach-Zehnder or electro-absorption amplitude modulator In this case microwave modulation is also applied to the modulator through a driver circuit

After passing into an optical fiber the optical intensity modulation only is detected via a photodetector As in the previous diagram the detected microwave signal is amplified in a low-noise amplifier

Laser

Driver

Optical fiber Photodetector

Low noise amplifier

Microwave or UWB Microwave or UWB

λ = 155 or 13 or 08 μm

Amplitude modulation Direct detection

General Points 5

Figure 12 Diagram of externally modulated microwave optical link

13 Signal to transmit

131 Microwave signal

The first type of transmitted signal is a signal that constitutes a microwave frequency reference It can be used in offset aerial systems or active phased-array antenna After its reflection from a moving object the microwave signal emitted from an antenna can shift in frequency (Doppler modulation) and it is the spectral purity of the microwave that determines the minimum observed frequency shift and therefore the minimum relative speed of the moving object The spectral purity and degradation after transmission of the microwave by optical links must be watched closely to distinguish the frequency shift

132 Microwave carrier for a digital signal

If the microwave signal serves as a carrier for a digital signal this carrier is previously modulated All the modulation techniques normally used such as amplitude frequency phase OFDM and combined amplitude-phase modulation (QAM) or more complex techniques can be considered such as those used in GSM GPRS EDGE and UMTS for mobile telephones or such as Bluetooth Wi-Fi and Wimax for data transmission These modulations are generally carried out on single sideband (SSB) When microwave signal modulation is implemented in phase or frequency spectral purity is also of great importance

Laser

Amplifier or driver

Optical fiber

λ = 155 or 13 or 08 μm

Microwave or UWB

Optical modulator MZ or EA

Amplitude modulation

Photodetector

Low noise amplifier

Microwave or UWB

Direct detection

6 Microwave Photonic Links

133 UWB signal

Another signal category is available for transmission by fiber optics These signals are relevant to UWB techniques without carriers and with the spectrum in the microwave region or up-converted to a millimeter-wave carrier UWB wireless links are largely used over short distances The optical fibers are particularly indicated to enable extensions of such networks

134 Optical carrier

Microwave signals can carry analog information (frequency shift due to the Doppler effect) or they can be modulated by a digital signal or be constituted of UWB signals which are themselves digitally modulated All these microwave signals must be up-converted to an optical carrier This transfer exclusively occurs by intensity modulation One of the advantages of this modulation is that the microwave signal can be recovered in a simple photodetection unit permitting the elimination of possible frequency fluctuations of the optical carrier Loss of sensitivity resulting from direct detection does not occur if the optical wavelength allows us to insert an optical amplifier or if the link is very short Usually this modulation is double sideband (DSB) especially if the modulation occurs directly in the laser but for slightly longer links this type of modulation can lead to extinction phenomena A single sideband modulation can hence be considered but this modulation must be carried out by an external modulator

135 Summary

The complexity of microwave photonic links comes from the stacking of an optical carrier and microwave or UWB subcarrier The optical carrier is exclusively intensity modulated whereas the microwave subcarrier can be modulated following all known modulation types amplitude frequency phase or their combination including a frequency shift due to the Doppler effect All these modulations can be recovered via photodetection

The use of microwave optical links will increase as the transmitted signals will be numerous and emitted in parallel communications and the data rates will increase accordingly Thus telecommunication optical

General Points 5

Figure 12 Diagram of externally modulated microwave optical link

13 Signal to transmit

131 Microwave signal

The first type of transmitted signal is a signal that constitutes a microwave frequency reference It can be used in offset aerial systems or active phased-array antenna After its reflection from a moving object the microwave signal emitted from an antenna can shift in frequency (Doppler modulation) and it is the spectral purity of the microwave that determines the minimum observed frequency shift and therefore the minimum relative speed of the moving object The spectral purity and degradation after transmission of the microwave by optical links must be watched closely to distinguish the frequency shift

132 Microwave carrier for a digital signal

If the microwave signal serves as a carrier for a digital signal this carrier is previously modulated All the modulation techniques normally used such as amplitude frequency phase OFDM and combined amplitude-phase modulation (QAM) or more complex techniques can be considered such as those used in GSM GPRS EDGE and UMTS for mobile telephones or such as Bluetooth Wi-Fi and Wimax for data transmission These modulations are generally carried out on single sideband (SSB) When microwave signal modulation is implemented in phase or frequency spectral purity is also of great importance

Laser

Amplifier or driver

Optical fiber

λ = 155 or 13 or 08 μm

Microwave or UWB

Optical modulator MZ or EA

Amplitude modulation

Photodetector

Low noise amplifier

Microwave or UWB

Direct detection

6 Microwave Photonic Links

133 UWB signal

Another signal category is available for transmission by fiber optics These signals are relevant to UWB techniques without carriers and with the spectrum in the microwave region or up-converted to a millimeter-wave carrier UWB wireless links are largely used over short distances The optical fibers are particularly indicated to enable extensions of such networks

134 Optical carrier

Microwave signals can carry analog information (frequency shift due to the Doppler effect) or they can be modulated by a digital signal or be constituted of UWB signals which are themselves digitally modulated All these microwave signals must be up-converted to an optical carrier This transfer exclusively occurs by intensity modulation One of the advantages of this modulation is that the microwave signal can be recovered in a simple photodetection unit permitting the elimination of possible frequency fluctuations of the optical carrier Loss of sensitivity resulting from direct detection does not occur if the optical wavelength allows us to insert an optical amplifier or if the link is very short Usually this modulation is double sideband (DSB) especially if the modulation occurs directly in the laser but for slightly longer links this type of modulation can lead to extinction phenomena A single sideband modulation can hence be considered but this modulation must be carried out by an external modulator

135 Summary

The complexity of microwave photonic links comes from the stacking of an optical carrier and microwave or UWB subcarrier The optical carrier is exclusively intensity modulated whereas the microwave subcarrier can be modulated following all known modulation types amplitude frequency phase or their combination including a frequency shift due to the Doppler effect All these modulations can be recovered via photodetection

The use of microwave optical links will increase as the transmitted signals will be numerous and emitted in parallel communications and the data rates will increase accordingly Thus telecommunication optical

6 Microwave Photonic Links

133 UWB signal

Another signal category is available for transmission by fiber optics These signals are relevant to UWB techniques without carriers and with the spectrum in the microwave region or up-converted to a millimeter-wave carrier UWB wireless links are largely used over short distances The optical fibers are particularly indicated to enable extensions of such networks

134 Optical carrier

Microwave signals can carry analog information (frequency shift due to the Doppler effect) or they can be modulated by a digital signal or be constituted of UWB signals which are themselves digitally modulated All these microwave signals must be up-converted to an optical carrier This transfer exclusively occurs by intensity modulation One of the advantages of this modulation is that the microwave signal can be recovered in a simple photodetection unit permitting the elimination of possible frequency fluctuations of the optical carrier Loss of sensitivity resulting from direct detection does not occur if the optical wavelength allows us to insert an optical amplifier or if the link is very short Usually this modulation is double sideband (DSB) especially if the modulation occurs directly in the laser but for slightly longer links this type of modulation can lead to extinction phenomena A single sideband modulation can hence be considered but this modulation must be carried out by an external modulator

135 Summary

The complexity of microwave photonic links comes from the stacking of an optical carrier and microwave or UWB subcarrier The optical carrier is exclusively intensity modulated whereas the microwave subcarrier can be modulated following all known modulation types amplitude frequency phase or their combination including a frequency shift due to the Doppler effect All these modulations can be recovered via photodetection

The use of microwave optical links will increase as the transmitted signals will be numerous and emitted in parallel communications and the data rates will increase accordingly Thus telecommunication optical