The resonant tunneling diode-laser diode optoelectronic ...w3.ualg.pt/~jlongras/2009-SPIEFinal-JF-Dresden-Germany-May2009.pdf · diode optoelectronic integrated circuit operating

The resonant tunneling diode-laser

diode optoelectronic integrated

circuit operating as a voltage

controlled oscillator

C. N. Ironside a, J. M. L. Figueiredo b, B. Romeira b ,T. J. Slight a, L. Wang a and E. Wasige a,

aDepartment of Electronics and Electrical Engineering, University of Glasgow, Glasgow G12 8LT, United Kingdom

bCentro de Electrónica, Optoelectrónica e Telecomunicações, Universidade do Algarve, Campus de Gambelas, 8005-139

Faro, Portugal

http://userweb.elec.gla.ac.uk/i/ironside/RTD/

http://userweb.elec.gla.ac.uk/i/ironside/RTD/ 2

Introduction We report on a novel OptoElectronic Integrated circuit (OEIC) the

Resonant Tunneling Diode- Laser Diode (RTD-LD) part of a family

of RTD OEICs that includes the RTD- photodiode (RTD-PD) and the

RTD-ElectroAbsorption Modulator RTD-EAM

We show that the RTD-LD can be made as monolithic chip and as

a hybrid (2 chip) device.

We show that the RTD-LD acts as an optoelectronic voltage

controlled oscillator (OVCO) that can described as a Liénard’s

Oscillator

We discuss an application as a wireless to optical interface device


Outline

Resonant Tunnelling Diode (RTD) operation principle.

The integrated RTD-LD OEIC

The hybrid RTD-LD OEIC

The Liénard’s oscillator model and the optoelectronic voltage

controlled oscillator

Application of the injection locked RTD-LD as a wireless-photonics

interface

Also a chaos generator

Summary and conclusion.


Resonant Tunnelling Diode (RTD)


Resonant Tunneling Diode

Resonant Tunneling Diodes (RTD) are nonlinear devices that use quantum effects to

produce negative differential conductance.

n InGaAs

n InGaAs

Emittern+ InGaAs

Substrate InP

AlAs

AlAsInGaAsDouble-Barrier

n+ InGaAs

Collector

DBQW-RTD Structure

The effect of bias on the conduction band profile

The Electron transmission probability

~10

nm

Conduction

band

profile

NDRR=1/G<0

Typical I-V characteristic

2 nm

2 nm

6 nm

Zero Bias (i) Off Resonance (iii)Resonance (ii)

E0 V=VvV=VpEF EF

EF

EC EC

EC

EF

EC

EF

EC

EC

EF

I

V


The integrated RTD-LD OEIC

“Investigation into the integration of a resonant tu nnelling diode and an optical communications laser: model and expe riment”, Slight, T. J.; Ironside, C. N. IEEE J. Quant. Elec. 43, 7, 580-587, 2007


Wafer Design

Layer no. Material Comp. fraction

Thickness µµµµm/ Å

Doping type

Doping conc.

Comments

Wafer InP i

1 InGaAs X=0.53 0.2µm p 5*1018cm-3 Bottom contact layer

2 InAlAs X=0.52 1 µm p 5*1017cm-3 Cladding

3 Inx Aly

Ga1-x-y As

X=0.53 Y=0.20

0.25 µm i Waveguiding core

4 Active Layer i Six quantum wells

5 Inx Aly

Ga1-x-y As

X=0.53

Y=0.20 0.25 µm i Waveguiding core

6 InAlAs X=0.52 1 µm n 5*1017cm-3 Cladding

7 InxGa1-xAs X=0.53 0.1µm n 1*1018cm-3 Laser isolation contact

8 InGaAs X=0.53 20 Å i Spacer

9 AlAs 25Å i Barrier (strained)

10 InGaAs X=0.53 50Å i Quantum well

11 AlAs 25Å i Barrier (strained)

12 InGaAs X=0.53 20A i Spacer

13 InGaAs X=0.53 0.1µm n 1*1018cm-3

14 InGaAs X=0.53 0.2µm n 5*1018cm-3 Cap layer

Quantum wells

Material Comp. fraction

Thickness Å/ ML

Doping type

Doping conc.

Comments

1 InxGa1-xAs X=0.53 67 Å i Quantum well (*6)

2 Inx Aly

Ga1-x-y As

X=0.53 Y=0.20

90 Å i Barrier (*5)

MQW Laser

RTD

LaserActive Region


Integrated RTD-LD Chip layout

p-type contact

n-type contact

Laser active region

RTD

Silica InsulatingLayer

3µm wide laser ridge

22µm wide ridge

Semi-insulating substrate

Heavily p-doped InGaAs

contact layer

Laseremission


Images of fabricated device

Scanning electron microscope images of the bare

etched wafer and completed device.

Etched wafer- laser ridge and contact ridge

Complete device-inset shows 3µm ridge detail.


Monolithically Integrated Device- results

CW results from a 500µm

cavity length ridge waveguide

laser cooled to 130K. Fig 1

shows current vs voltage, fig

2 shows Log optical power vs

voltage.

There is clear hysteresis in

both the current and optical

power.

The hysteresis loop is wide

(~1.5V) and the optical power

on-off ratio is approximately

20dB.

0

50

100

150

200

250

300

0 1 2 3 4 5

Voltage (V)

Cur

rent

(m

A)

Voltage Forward

Voltage Back

0 2 4 61E-9

1E-8

1E-7

1E-6

1E-5

1E-4

1E-3

0.01

0.1

1

Log

Pop

t (a.

u.)

Voltage (V)

Voltage forward

Voltage back

Fig 1 – current vs voltage

Fig 2- Log Optical output vs voltage


The hybrid RTD-LD OptoElectronic Integrated

circuit (OEIC)

“A Liénard Oscillator Resonant Tunnelling Diode-Laser Diode Hybrid Integrated Circuit: Model and Experiment”, Slight, T. J. Romeira, B. Wang, L. Figueiredo, J. M. L. Wasige, E. Ironside, C. N.,IEEE J. Quantum Electron., Vol. 44, No. 12, pp. 1158-1163, December 2008.


The monolithic RTD-LD ->Hybrid RTD-LD

The monolithic RTD-LD showed hysteresis – good for NRZ

operation- but no oscillation and only pulsed room

temperature operation

To gain a further insight into the operation of RTD-LD we

moved to a hybrid version – with a RTD chip and a LD

chip connected by a bond wire

The work we now present is based on the hybrid version

From this work it was clear the monolithic version had a

large series resistance probably a contact resistance –

thus heating and hysteresis


The hybrid RTD–LD

Electro-photonic self-sustained oscillations.

Photo-detected output

RF

outputd. c. bias

Laser Diode

Au

Printed Circuit Board

Microstrip line

Shunt

Capacitor

n

p

RTDfiber

Current-voltage (I-V) characteristics


The Model

Experimental and modeled I-V curves

Equivalent Liénard’s oscillator circuit

F(V)C

LR

V(t)

Vin(t)= VDC+VAC sin(2πfint)

( ) ( ) ( ) ( ) 0V t H V V t G V+ + =&& &

( ) ( ) ( )dV t i t F V

dt C

−=

The circuit can be

described by the following

equations:

Which are equivalent to the

Liénard’s second-order differential

equation:

( ) ( )( ) bV Ri t V tdi t

dt L

− −=

Laser model introduced through

single mode rate equations


The Optoelectronic Voltage Controlled Oscillator (VCO)


RTD-LD as

an Injection Locked Oscillator (ILO)


RTD-LD Circuit's Optoelectronic Model with injected

signal Nonlinear dynamical system based on the Liénard’s driven

oscillator and laser diode single mode rate equations.

( )τ

βτε

NS

S

SNNgS

p

+−+

−=100

&

( )S

SNNg

N

q

IN

ετϑ +−−−=

100&

( )[ ]tfπVVVVRIL

I inAC+THDC 2sin-+--1

=&

[ ])(1

VFIC

V −=&

( ) ( ) ( ) ( ) sin(2 ),AC inV t H V V t G V V f tπ+ + =&& &

Electrical model:

Optical model:

Rate equations

Liénard’s driven oscillator

N – electron density

S – photon density

I – current through

the laser given by

Liénard’s model

Damping

factor

Nonlinear

force

Injected

signal


Application of the RTD-LD – ILO

as

a wireless to optical interface


Synchronisation and the Injection Locked

Oscillator

Synchronisation is well known phenomena in nonlinear

dynamics

Using the RTD-LD we could apply this wireless to optical

conversion

Wireless signals are often phase modulated – phase shift

keyed (PSK) – a small injected signal (-40dB compared to

the output) controls the phase of the RTD-LD and thus

the phase of the optical sub-carrier

Digital information can be transferred from the wireless

to the optical domain


Injection phase locking Injection locking of the laser output to the broadcasted signal

fundamental and second harmonic

Fundamental Second harmonic


Liénard’s RTD-LD 2D Synchronization Map

fin/3

fin/4

RTD-LD frequency locking structure showing the Arnold Tongues map: a comparison of theory with experimental results

fin/1

fin/2

fin/3

fin/4 fin/1 - when the injected

wireless signal is at the same frequency as the natural oscillation frequency

fin/2 - when the injected wireless signal is twice the frequency of the natural oscillation

The y axis is the amplitude of the injected wireless signal

fin/1 fin/2 fin/3


Adler’s equation – the short version of

Arnold’s tongues

0

0

2=∆

P

P

Q

ff

inj

0

0

- locking range

- oscillator frequency

- power of injected signal

- output power of the free-running oscillator

- oscillator quality factor

inj

f

f

P

P

Q

∆


RTD-LD based RF-to-optical conversion

The optoelectronic interface includes the RTD-LD electric-to-

optic (E/O) converter and patch antenna for RF broadcasting.

3 GHz

Patch antenna

RF output

Laser Diode

Au

Printed Circuit Board

Microstrip line

Shunt

Capacitor

n

p

RTD

d. c. bias

The RTD-LD responds to the wireless

electromagnetic radiation which is amplified

by the negative conductance

The optical fibre delivers microwave

broadcasted signals

Microwave to optical conversion

Wireless

RF Emission

Optical Signal

Measurement Setup

SCOPE/Spectrum Analyzer

PD

RF generator

50 ΩΩΩΩ

1.4 V

50 ΩΩΩΩ


Analogue Phase Modulation The laser diode output, locked with a broadcasted signal,

shows the same modulation features of the injected signal

with the same sidebands at 1 MHz offset of the radio carrier.

Most digital wireless signals are phase shift keyed (PSK) and so, because of the

fixed phase relationship, the phase synchronization of the RTD-LD can be used to

translate the digital information from the wireless to the optical domain.


Pico and Femtocell wireless networks Next generation of wireless access networks will have short range

cells – each office in a building with its own cell and base station

Lots of cells so a RTD-LD offers a cheap single chip solution


Chaos generation with the RTD-LD

"Self-oscillation and period adding from resonant tunnelling diode-laser diode circuit" Figueiredo, J.M.L.; Romeira, B.; Slight, T.J.; Wang, L.; Wasige, E.; Ironside, C.N. Electronics Letters 44 14 876-877 2008


Chaos-Liénard’s RTD-LD Bifurcation Maps

If sufficient injection signal power is applied at frequencies that are not a

rational fraction of the fundamental frequency – then chaotic output

Chaotic regions C1 (exponent > 0)

Opt

ical

Out

put (

a. u

.)

fin/3

fin/4

fin/1

fin/2

fin/3

fin/4


Summary and Conclusion There is a family of OEICs based on vertically integrated RTDs

The RTD-LD can be monolithically integrated

The hybrid RTD-LD has allowed us to verify the Lienard’s oscillator model

Modulation of the phase of the radio frequency sub-carrier was

demonstrated in the laser output.

First demonstration of wireless to optical conversion using

synchronization of a nonlinear oscillator.

The RTD-LD applications include: single chip platform with reduced size

for low cost microwave/photonics devices.

The Liénard’s model can be used to predict the frequency locking and

the chaotic behaviour – this model and technology could be extend to

much higher frequencies

Documents

The resonant tunneling diode-laser diode optoelectronic ...w3.ualg.pt/~jlongras/2009-SPIEFinal-JF-Dresden-Germany-May2009.pdf · diode optoelectronic integrated circuit operating