Experimental and theoretical investigation of semiconductor optical amplifier

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Experimental and theoretical investigation of semiconductor optical amplifier (SOA)
based all-optical switches
Nielsen, Mads Lønstrup
Publication date:
2004
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Citation (APA):
Nielsen, M. L. (2004). Experimental and theoretical investigation of semiconductor optical amplifier (SOA) based
all-optical switches. Technical University of Denmark.

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Experimental and Theoretical investigation of
Semiconductor Optical Amplifier (SOA) based
All-Optical Switches
Mads Lønstrup Nielsen
April 2004
Research Center COM
Technical University of Denmark
Acknowledgements
IwouldliketostartoutbythankingmyadvisorsLarsDittmann,AndersClausen,
and Jesper Mørk. Lars for providing a great social atmosphere, and allowing
me to pursue my interest in optics in the Networks Group, Anders for good
collaboration with the Systems area, and Jesper for invaluable inspiration and
theoretical assistance.
In addition, a great number of former and current colleagues at COM are
thanked for joint efforts in the lab, for solving computer-related problems (in-
cluding fejl 40), helpful scientific discussions, and all the non-scientific stuff
that made all it worth the effort. In particular, I would like to thank Tina
Fjelde, David Wolfson, Allan Kloch, Leif Oxenlöwe, Henrik N. Poulsen, Anders
Clausen,TommyBerg,KrestenYvind,ChristophePeucheret,JakobBuron,Hen-
ningChristiansen,JørnHedegaardPoulsen,MichaelBerger,HenrikChristiansen,
Martin Nordal Petersen and Martin "Havrenakke" Nord.
Alcatel Research and Innovation are acknowledged for supplying state-of-the-
art devices for the experiments, and in particular I would like to thank Beatrice
Dagens and Bruno Lavigne for a good collaboration during my three visits to
Marcoussis.
Moreover, I am grateful to Allan Kloch for boosting my self esteem every
weekend on the squash court, and to Dolkene & Co. for the good life.
Last,butnotleast,IamindebtedtoRikkeforputtingupwithme,andtaking
care of me, during the last four months.
Kgs. Lyngby, 14/4/2004 Mads Lønstrup Nielsen
i
List of Abbreviations
1R (regeneration) Re-amplification
2R (regeneration) 1R + Re-shaping
3R (regeneration) 2R + Re-timing
FD-BPM Finite-Difference Beam Propagation Model
A.O. Acousto-optic
A/N Any Number
A-P Active-Passive
A-A All-Active
AM Amplitude Modulation
AMZI/AMZ Asymmetric MZI
ASE Amplified Spontaneous Emission
BER Bit Error-Rate
BERT Bit Error-Rate Test Set
BPF Band-Pass Filter
BRF Birefringent Fiber
BRS Buried Ridge Structure
CDR Carrier Density Response
CH Carrier Heating
CLK Clock
CMR Carrier-to-Modulation Ratio
CR Contrast Ratio
CW Continuous Wave
DCF Dispersion Compensating Fiber
DEMUX Demultiplexing / Demultiplexer
DFB Distributed FeedBack
DFF Decision Flip-Flop
DFG Difference Frequency Generation
DISC Delayed-Interference Signal Converter
DM Differential-Mode / Dual-Mode
DOMO Dual-Order MOde
DPSK Differential Phase Shift Keying
DSF Dispersion Compensating Fiber
DUT Device Under Test
ii
EAM Electro-Absorption Modulator
ECL External Cavity Laser
EDFA Erbium-Doped Fiber Amplifier
EIM Effective Index Method
EO Electro-Optic
EPC Equivalent Photo Current
ER Extinction Ratio
ESA Electrical Spectrum Analyzer
FBG Fiber Bragg Grating
FEC Forward Error Correction
FFT-BPM Fast Fourier Transform Beam Propagation Model
FM Frequency Modulation
FSR Free Spectral Range
FWHM Full Width at Half Maximum
FWM Four Wave Mixing
GPIB General Purpose Interface Bus
GS-DFB Gain Switched DFB (laser)
IP In-Phase
IPDR Input Power Dynamic Range
IWC Interferometric Wavelength Converter
LCM Least Common Multiple
MEMS Micro Electro Mechanical Systems
MI Michelson Interferometer
ML-FRL Mode-Locked Fiber Ring Laser
MLL Mode-Locked Laser
MMI Multi-Mode Interference
MP Mark Patterning
MUX Multiplexing / Multiplexer
MZI Mach-Zehnder Interferometer
NLE Non-Linear Element
NLF NonLinear Fiber
NOLM Nonlinear Optical Loop Mirror
NRZ Non Return-to-Zero
OCS Optical Circuit Switching
OE Opto-Electronic
OOP Out-Of-Phase
OPC Optical Phase Conjugator
OPS Optical Packet Switching
OSA Optical Spectrum Analyzer
OSNR Optical Signal-to-Noise-Ratio
OTDM Optical Time Division Multiplexing
OXC Optical Cross Connect
P.C. Polarization Controller
iii
P.D. Photo Diode
PBS Polarization Beam Splitter
PCF Photonic Crystal Fiber
PD-EAM Photo Diode Electro-Absorption Modulator
Pdf Probability Density Function
PMD Polarization Mode Dispersion
PD-MZI Polarization Discriminating Mach-Zehnder Interferometer
PLC Planar Lightwave Circuit
PLL Phase-Locked Loop
PM Phase Modulation / Polarization Maintaining
PPG Pulse Pattern Generator
PPLN Periodically Poled Lithium Niobate
PPM Pulse Position Modulation
PRBS Pseudo-Random Bit Sequence
PRZ Pseudo Return-to-Zero
RF Radio Frequency
Rx Receiver
RZ Return-to-Zero
SE Spontaneous Emission
SHB Spectral Hole Burning
SI Sagnac Interferometer
SLALOM Semiconductor Laser Amplifier Loop Mirror
SM Standard-Mode / Single-Mode
SMF Single Mode Fiber
SM-MZI Standard-Mode MZI
SM-XPM Standard-Mode Cross-Phase Modulation
SOA Semiconductor Optical Amplifier
SPM Self-Phase Modulation
SRS Stimulated Raman Scattering
SSFR Small-Signal Frequency Response
StC Sideband-to-Carrier
SVEA Slowly Varying Envelope Approximation
TOAD TeraHertz Optical Asymmetric Demultiplexer
TOF Time Of Flight
Tx Transmitter
TW-EAM Traveling Wave Electro Absorption Modulator
UNI Ultra-fast Nonlinear Interferometer
UTC-PD Uni-Traveling-Carrier Photo Diode
WDM Wavelength Division Multiplexing
XAM Cross-Absorption Modulation
XGM Cross-Gain Modulation
XOR Exclusive OR
XPM Cross-Phase Modulation
iv
Abstract
This thesis analyzes semiconductor optical amplifier (SOA) based all-optical
switches experimentally and through numerical simulations. These devices are
candidatesforopticalsignalprocessingfunctionalitiessuchaswavelengthconver-
sion, regeneration, and logic processing in future transparent optical networks.
The factors governing the modulation bandwidth of SOAs are determined,
and schemes for reducing detrimental patterning effects are discussed. Three
types of SOA-based switches are investigated numerically: so-called standard-
mode and differential-mode switches, and the filtering assisted switch. Differen-
tial -mode switches are shown to eliminate one contribution to the patterning
effects, referred to as the linear patterning. This enables operation at bitrates far
beyond the limit set by the carrier lifetime, but ultimately a saturation-induced
patterning effect, nonlinear patterning, is found to limit the performance. Two
implementations of differential-mode switches, the Mach-Zehnder interferometer
(MZI) and the delayed-interferometer signal converter (DISC), are compared at
bitrates up to 160 Gb/s, and fundamental differences in terms of noise filtering
are demonstrated.
TheDISC, consisting of an SOAand an asymmetricMZI filter, is analyzed in
the small-signal regime, and the obtainable modulation bandwidth is expressed
analytically. A new optical spectrum approach to small-signal analysis is intro-
duced, and is used to assess the bandwidth enhancing effect of different optical
filters, as well the impact of the filter phase response. Experiments at 40 Gb/s
verify the predictions of the small-signal analysis.
Wavelength conversion is demonstrated experimentally at 40 Gb/s using a
simple filtering-assisted scheme with an ultra-low optical switching energy, and
up to 80 Gb/s employing MZIs operated in the standard-mode, also assisted by
bandwidth enhancing filtering.
The impact of 2R regeneration (re-amplification and re-shaping) is explained
through simulations, and demonstrated using MZIs at 10 Gb/s. In addition, the
2R regenerative capability of a novel all-active 2x2 coupler is verified, also at
10 Gb/s. 3R regeneration (2R + re-timing), based on a cross-gain modulation
wavelength converter and a MZI, is demonstrated at 40 Gb/s in a recirculating
loop experiment over 4000 km. Moreover, an optical subsystem for NRZ clock
recovery, based on self-phase modulation and cross-phase modulation in an SOA,
v
and capable of generating the 40 GHz spectral component from a 40 Gb/s NRZ
signal, is presented.
All-optical Boolean logic gates and functionalities involving several gates are
investigated experimentally and numerically. Boolean AND and XOR gates are
realizedexperimentallywithMZIs,at20Gb/sand10Gb/s,respectively,whereas
combinations of Boolean functions in MZIs are used to demonstrate a 3-input
XORgate,adatasegmentbitcomparator,andacompactparitycheckingscheme,
all at 10 Gb/s.
vi
Resumé (in Danish)
Denne afhandling analyserer rent optiske switche baseret på optiske halvleder-
forstærkeregennemeksperimenterognumeriskesimuleringer. Dissekomponenter
er kandidater til at realisere optisk signalprocessering såsom bølgelængdekon-
vertering, regenerering og logisk processering i fremtidens transparente optiske
netværk.
Faktorer bestemmende for halvlederforstærkeres modulationsbåndbredde er
bestemt, og metoder til reducering af skadelige mønstereffekter diskuteres. Tre
typerhalvlederforstærker-baseredeswitcheerundersøgtnumerisk: Såkaldtestan-
dard -mode og differentiel-mode switche og den filtreringsassisterede switch. Det
visesatdifferentiel-modeswitcheeliminereretafbidragenetilmønstereffekterne,
kaldet lineær mønstereffekt, mens den endelige begrænsning for ydelsen sættes af
en mætningsinduceret effekt, kaldet ulineær mønstereffekt. To implementationer
af differentiel-mode switche, Mach-Zehnder interferometret (MZI) og delayed-
interferometer signal convertereren (DISC), sammenlignes for bitrater op til 160
Gb/s og fundamentale forskelle i deres støj-filtrerende egenskaber demonstreres.
DISC komponenten, der består af en halvlederforstærker og et asymmetrisk
MZIfilter,eranalyseretismå-signalgrænsen,ogdenopnåeligemodulationsbånd-
bredde er udtrykt analytisk. En ny metode til små-signal analyse, der baserer
sig på det optiske spektrum, introduceres og benyttes til at bestemme den bånd-
breddeforøgelse der kan opnås med forskellige optiske filtre. Ydermere analyseres
effekten af filtres faserespons på modulationsbåndbredden. Eksperimenter ved
40 Gb/s bekræfter små-signal analysens forudsigelser.
Bølgelængdekonvertering er demonstreret eksperimentelt ved 40 Gb/s v. hj.
a. enfiltreringsassisteretteknikmedultra-lavswitch-energi,ogvedbitrateroptil
80 Gb/s v. hj. a. MZI’er opereret i standard-mode konfiguration, også assisteret
af båndbreddeforøgende filtrering.
Indvirkningen og betydningen af 2R regenerering (forstærkning og støjun-
dertrykkelse) forklares gennem simuleringer, og demonstreres ved 10 Gb/s med
MZI’er. Ydermere verificeres de regenererende egenskaber af en ny type rent-
aktiv2x2kobler, ogsåved10Gb/s. 3Rregenerering(2R+jitterundertrykkelse),
baseret på en bølgelængdekonverter opereret i kryds-gain modulation og et MZI,
er demonstreret ved 40 Gb/s i et loopeksperiment over 4000 km. Derudover
præsenteres et delsystem til klokkegendannelse for NRZ signaler, baseret på selv-
vii
fasemodulation (SPM) og kryds-fasemodulation (XPM) i en halvlederforstærker.
Systemet genererer den spektrale komponent ved 40 GHz udfra et 40 GHz NRZ
signal.
Rent-optiske Boolske logiske gates, og funktionaliteter der involverer flere
gates, er undersøgt eksperimentelt og numerisk. Boolsk AND og XOR er re-
aliseret eksperimentelt v. hj. a. MZI’er, ved henholdsvis 20 Gb/s og 10 Gb/s,
hvorimod kombinationer af Boolske funktioner i MZI’er anvendes til at demon-
strere en 3-input XOR gate, en datasegment bit-komparator og en kompakt
paritetschecker. Alle funktionaliteter er undersøgt ved 10 Gb/s.
viii