A 10 Gb/s Photonic Modulator and WDM MUX/DEMUX Integrated with Electronics in 0.13um SOI CMOS

High Speed Circuits & Systems Laboratory

Joungwook Moon

2011. 5.25

Contents

Introduction1.

Implementation2.

Conclusion3.

Introduction

• Author :Andrew Huang. Luxtera, Carlsbad, CA (ISSCC 2006)

• Manufacturable yield-frendly photonics components combined with electronics using a 0.13um SOI process for PowerPC processors

• A 10Gb/s optical modulator integrated with a driver and 4-channel WDM MUX/DEMUX w/ integrated tun-ing circuits– WDM MUX/DEMUX(Wavelength division multiplexing) : To in-

crease capacity and speed of commucation, different kind of data put into a single fiber. An optical fiber can carry maxi-mum 80 wavelength of data.

Implementation - Waveguide

• C-band (1.5um) optical waveguides are formed by a high reflective index core of transparent silicon & low reflective index index silicon dioxide

• C-band (conventional wavelength band) :1530nm ~ 1565nm

Waveguide structure & Optical profile@ Ref.[2]

Wavelength Band

Holographic Lens

• Holographic lens(HL) couples light normal to the surface of the die with < 1.5dB loss

• HL allows inexpensive wafer scale testability (Good replacement for the refract-

-ing lens in maching application)

10um fiber core

waveguides

SEM photograph of a holographc lens

Holographic lens

Modulator (1)

• Modulator uses a free-carrier-effect-based device in a Mach-Zender interferometer- Light is split evenly into two arms.- The light is phase-modulated.- Differential accumulation of phase (ΔΦ) causes

the recombined light to interefer. P= 0.5 + cos(∏/2 + ΔΦ)/2

Schematic diagram of a phase modulator in one arm of the MZI

• A reverse-biased lateral PIN diode (contrast to conventional method

based on diffusion/recombination)

• The speed of the resulting device is limited by RLC

Modulator (2)

• In a lumped configuration, junction length needed for sufficient phase shift would be parastic-limited to < 10Gb/s

To overcome this lumped-RC speed limit is to design a travelingwave electrode. (designed as a part of the microwave transmission line)

• On chip terminations are integrated at the end of the microwave transmission lines to supperss back-relfec-tions

• The characteristic impedance of the transmission line + PN diode : Total system impedance = 25Ω

• The modulator has a length of 2mm, microwave loss would be sufficiently small

Integrated Driver

• A cascoded thin-gate-oxide transister swich is used• Pre-driver chain drives the switch transistor• Cascode device is used to shield the high-performance

switch from the relatively high voltages required by the modulator elements

Integrated driver connected to one MZI arm

• The active area for the modulator driver is 0.08mm2

• Total area is 2.6mm2 including 2mm modulator, termination network, and pads

CMOS optical modulator with Differential Driver

Integrated Driver

• A cascoded thin-gate-oxide transister swich is used• Pre-driver chain drivesthe switch transistor• Cascode device is used to shield the high-performance

switch from the relatively high voltages required by the modulator elements

Optical eye of integrated modulator plus driver at 10Gb/s

• The integrated circuit yields a 10-12 BER with a 223-1 PRBS at 10Gb/s.

• Performance of the optical modu-lator is entirely limited by the driver

4-Channel DWDM AWG (1)

• A Key Advantage of integrated electronics and photonics on a single chip is to raise yield of an optical device by electronic control ciucuitry

• Optical 4-channel DWDM AWG with an 8b DAC array is integrated (< 0.6mm2)

• DWDM: Dense Wavelength Division Multiplexing • AWG: Arrayed waveguide grating generate a desired spectral function

Die shot of DAC array plus AWG element

Electrically Tunable AWG

4-Channel DWDM AWG (2)

• Forward-biased PIN junction phase Modulators inte-grated into each arm of the AWG.

offer great phase efficiency (90°/mA for 100um arm) but lower speed & higher loss• Each modulator is driven by an 8b 5/3 segmented DAC to restore phase relationship (inducing random delay)

• After tuning, the crosstalk suppression is improved by over 16db

Luxtera CMOS Photonic Tech.

from Luxtera (www.luxtera.com)

Conclusion

• Abstract– Motolithic integration of both photonic and

electronic components operating at 10Gb/s in a 0.13um SOI CMOS process

– A modulator uses free carrier plasma dis-persion in a reverse-biased PIN optical phase shifer in a Mach-Zender interferome-ter.

– An AWG demultiplexer uses a forward-bi-ased PIN phase shifter to compensate the optical path length improving the channel separation