Nanostructure Semiconductor Optical Amplifiers: Building Blocks for All-Optical Processing

189 Pages·2011·5.452 MB·English

by  Ali Rostami, Hamed Baghban, Reza Maram (auth.)

Engineering Materials
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Ali Rostami (cid:2) Hamed Baghban (cid:2) Reza Maram
Nanostructure
Semiconductor Optical
Amplifiers
Building Blocks for All-Optical Processing
123
Prof.AliRostami Reza Maram
NanophotonicsSchool ofEngineering- Faculty ofElectrical and
Emerging Technology Computer Engineering
Universityof Tabriz Universityof Tabriz
Bolv.29, Bahman Bolv.29, Bahman
51666Tabriz,Iran 51666Tabriz,Iran
e-mail: [email protected] e-mail: [email protected]
Hamed Baghban
Faculty ofElectrical and
Computer Engineering
Universityof Tabriz
Emam Khomeini Bolv.29,Bahman
51666Tabriz,Iran
e-mail: [email protected]
ISSN 1612-1317 e-ISSN1868-1212
ISBN 978-3-642-14924-5 e-ISBN 978-3-642-14925-2
DOI 10.1007/978-3-642-14925-2
SpringerHeidelbergDordrechtLondonNewYork
LibraryofCongressControlNumber:2010937667
(cid:2)Springer-VerlagBerlinHeidelberg2011
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Preface
Theimportanceofsemiconductoropticalamplifiers(SOAs)askeycomponentsin
optical communications and integrated optics, covering a wide range of applica-
tions for the 1550- and 1300-nm optical windows, has grown in recent years.
All-opticalsignalprocessing,includingwavelengthconversion,opticallogicgates
andsignalregeneration,etc,isoneofthemostimportantenablingtechnologiesto
realize optical switching, including optical circuit switching, optical burst
switchingandopticalpacketswitchingandSOAsareverypromisinginall-optical
signalprocessingsincetheyarecompact,easytomanufactureandpowerefficient.
The need for all-optical elements for increasing the capacity of current and
futurecommunicationnetworksandoptimizingtheoperationofopticalswitching
networkshas been oneofthe main motivations for consideringSOAs asessential
elements in all-optical switching scenarios in recent years. The present book tries
tomarkasmallportionoftheSOAsandspeciallyquantum-dotSOAs(QD-SOAs)
capabilities in the mentioned topics.
In Chap. 1 of this book authors have tried to introduce different aspects of a
SOAspeciallyaQD-SOAincludingstructural,opticalandelectricalspecifications
of a QDSOA. Different definitions in the field of a SOA such gain-related
mechanisms, SOA polarization characteristics, effect of impurity doping in the
active region and fabrication requirements are presented in this chapter.
Chapter2presentsageneraloverviewfordifferentsimulationmethodsofQD-
SOAs. One of the most accurate ways of modeling a SOA is to solve the Semi-
conductor Bloch Equation (SBE). However, this method is extremely time-con-
suming. The computation time is not acceptable for the system applications of
SOA-baseddevices,wheremanyopticalpulseshavetobetransmittedthroughthe
SOAtoevaluatethesystemperformance.Simplifiedapproachesincludingcertain
physicalprocessesphenomenologically,asitisdoneinrate-equationmodels,have
much faster calculation speeds and are quite successful in explaining the experi-
mental results.Althoughtheaccuracy forsub-picosecondpulsesis notasgoodas
the SBE calculation. Numerical modeling is always necessary to understand the
working principle of the devices and to optimize their performance. Physical
modelingofcomplexdevicesincludingSOA,suchasall-activeMZIs,isnecessary
v
vi Preface
inordertounderstandtheirpotentialandlimitations.Inthischapterthreedifferent
methods for investigation of the QD-SOA performances based on rate-equation
modeli.e.numericalmethods,equivalentcircuit-modelingmethodsandanalytical
methods is briefly described.
Chapter 3 of the book covers different techniques toward utilizing the high-
speed operation capabilities of SOAs for high-bit-rate signal processing. This
chapter reviewsthe mostrecent techniques inthe field ofbulk, quantumwell and
alsoquantumdot-basedSOAsandgivesaninsightforpossiblefutureoptimization
methods for increasing the response of SOA-based devices for high-speed
operations.
Chapter 4 covers the applications of SOAs in all-optical logic gates and
subsystems which seem to be essential elements in all-optical signal processing
scenarios. In this chapter it has been tried to introduce different techniques for
realization of SOA-based optical units and hence, it hasn’t suffice to QD-SOA
based structures. This diversity of introduced structures may provide inspiration
for novel ideas in eager readers. Authors believe that investigation of QD-SOA
specifications in the beginning chapters and presentation of practical methods
based on different types of SOAs provides this ability for researchers who are
interested in the topics.
Finally, in Chap. 5 of the present book, recent progresses in all-optical signal
processing and switching with considering SOAs as one of the main elements in
the proposed structures are presented. Although these applications are not the
wholeSOAbasedarchitecturesforopticalswitchingandsignalprocessing,asmall
part of recent development in this field is has been reviewed in this chapter.
Iran, October 2010 Ali Rostami
Contents
1 Quantum-Dot Semiconductor Optical Amplifiers, Basic
Principles, Design Methods, and Optical Characterizations . . . . . . 1
1.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Operation Principles. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.3 SOA Gain. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3.1 Gain Saturation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.3.2 Confinement Factor . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.4 Refractive Index. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.5 Linewidth Enhancement Factor . . . . . . . . . . . . . . . . . . . . . . . 10
1.6 Comparison of Operating Characteristics. . . . . . . . . . . . . . . . . 12
1.6.1 Amplified Spontaneous Emission. . . . . . . . . . . . . . . . . 16
1.6.2 Noise Figure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
1.7 Polarization Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
1.8 Doped QD-SOAs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
1.8.1 p-doped QD-SOAs. . . . . . . . . . . . . . . . . . . . . . . . . . . 28
1.8.2 n-doped QD-SOAs. . . . . . . . . . . . . . . . . . . . . . . . . . . 37
1.9 Fabrication Process. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
1.9.1 Quantum-Dot Growth. . . . . . . . . . . . . . . . . . . . . . . . . 38
1.9.2 Epitaxial Structure of QD-SOA. . . . . . . . . . . . . . . . . . 40
1.9.3 Waveguide Requirements of QD-SOA . . . . . . . . . . . . . 43
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
2 Simulation Methods of QD-SOAs . . . . . . . . . . . . . . . . . . . . . . . . . 53
2.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
2.2 Numerical Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
2.3 Equivalent Circuit Methods. . . . . . . . . . . . . . . . . . . . . . . . . . 58
2.4 Analytical Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
vii
viii Contents
3 Techniques Toward High Speed Operation of SOAs . . . . . . . . . . . 71
3.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
3.2 Gain Recovery Improvement Techniques in Bulk
and QW-SOAs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
3.2.1 Carrier Reservoir. . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
3.2.2 Optical Pulse Injection and Holding Beam . . . . . . . . . . 75
3.2.3 Optical Filtering . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
3.2.4 Active Region Modification . . . . . . . . . . . . . . . . . . . . 87
3.3 Gain Recovery Improvement Techniques in QD-SOAs. . . . . . . 90
3.3.1 Two-Photon Absorption-assisted Recovery . . . . . . . . . . 90
3.3.2 Control Pulse-assisted Recovery . . . . . . . . . . . . . . . . . 94
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
4 Applications and Functionalities. . . . . . . . . . . . . . . . . . . . . . . . . . 109
4.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
4.2 SOA-MZI Gate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
4.3 SOA-MZI Transfer Function . . . . . . . . . . . . . . . . . . . . . . . . . 112
4.4 Michelson Interferometer . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
4.5 Wavelength Conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
4.5.1 XGM-Based Wavelength Conversion. . . . . . . . . . . . . . 114
4.5.2 XPM-Based Wavelength Conversion . . . . . . . . . . . . . . 116
4.5.3 FWM-Based Wavelength Conversion. . . . . . . . . . . . . . 117
4.5.4 Wavelength Conversion in SOA-BPF Configuration. . . . 118
4.6 All-Optical Regeneration. . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
4.7 Logic Gates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
4.7.1 XOR Gate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
4.7.2 AND Gate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
4.7.3 OR Gate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
4.7.4 NOR Gate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
4.7.5 XNOR Gate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134
4.7.6 NAND Gate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
4.7.7 NOT Gate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
4.8 All-Optical Multiplexing and Demultiplexing . . . . . . . . . . . . . 138
4.8.1 SOA-MZI-Based Multiplexing. . . . . . . . . . . . . . . . . . . 139
4.8.2 SOA-MZI-Based Demultiplexing. . . . . . . . . . . . . . . . . 141
4.9 Data Format Conversion. . . . . . . . . . . . . . . . . . . . . . . . . . . . 144
4.9.1 NRZ-to-RZ Data Format Conversion . . . . . . . . . . . . . . 144
4.9.2 NRZ-to-PRZ Data Format Conversion . . . . . . . . . . . . . 146
4.9.3 RZ-to-NRZ Data Format Conversion . . . . . . . . . . . . . . 148
4.10 All-Optical Flip-Flop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
4.11 All-Optical PRBS Generation . . . . . . . . . . . . . . . . . . . . . . . . 153
4.12 All-Optical Clock Recovery. . . . . . . . . . . . . . . . . . . . . . . . . . 155
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
Contents ix
5 Applications of SOA-Based Circuits in All-Optical Signal
Processing and Switching. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163
5.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163
5.2 All-Optical Header/Payload Separation. . . . . . . . . . . . . . . . . . 163
5.3 All-Optical Correlator. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165
5.4 All-Optical Packet Routing . . . . . . . . . . . . . . . . . . . . . . . . . . 170
5.5 All-Optical Header Processing. . . . . . . . . . . . . . . . . . . . . . . . 172
5.6 All-Optical Packet Switching Based on In-Band Filtering. . . . . 175
5.7 All-Optical Self-Routing Node and Network Architecture. . . . . 177
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182
Chapter 1
Quantum-Dot Semiconductor Optical
Amplifiers, Basic Principles, Design Methods,
and Optical Characterizations
1.1 Introduction
Thedevelopmentofsemiconductoropticalamplifiers(SOAs)happenedsoonafter
the invention of the semiconductor laser. A SOA is very similar to a semicon-
ductor laser without (or with negligible) optical facet feedback. An incoming
signal injected into the SOA propagates along its optical waveguide and is
amplified by stimulated emission. The optical gain is achieved by inverting the
carrier population in the active region via electrical pumping. During the 1990s
due to the development of the erbium doped optical amplifier (EDFA) the popu-
larityoftheSOAasalinearamplifierdeclinedastheEDFAsprovidedhighergain
without the detrimental nonlinearities associated with an SOA.
During the development of SOAs, there were three main challenges related to
SOAsperformancemakingthemacceptableforpracticalapplications:polarisation
sensitivityreduction,opticalfeedbackreduction,anddecreasingthenoiselevelof
SOAs. However, attentions turned to SOAs in the late 1990s as SOA design
techniques developed, and thus its possibilities for integration and cost effec-
tiveness led the SOA to become a competitive component in comparison to the
EDFA.ThedesignofSOAsdevelopedintwodirections:asalinearamplifier,itis
needed to reduce optical nonlinearities of SOA and as a nonlinear medium; the
nonlineareffectsshouldbeexploitedforuseinvarietyofapplicationssuchasall-
optical signal processing. The advantages of SOAs are their versatility and pos-
sibility of monolithic integration with other optical components like passive
waveguides and couplers to perform more complex functions. They are compact,
electrically pumped and have a large optical bandwidth. Moreover, they allow a
wideflexibilityinthechoiceofthegainpeakwavelength.Inlinearoperationsuch
as a power booster, as an inline amplifier and as a preamplifier EDFAs are the
dominantamplifiersspeciallyinlong-haulsystemsastheyhavelowernoiselevels
andmuchbettercrosstalkpropertiesformulti-channelamplificationincomparison
to SOAs. However, the SOA offers a cost competitive alternative to the EDFA
A.Rostamietal.,NanostructureSemiconductorOpticalAmplifiers, 1
EngineeringMaterials,DOI:10.1007/978-3-642-14925-2_1,
(cid:2)Springer-VerlagBerlinHeidelberg2011
2 1 Quantum-DotSemiconductorOpticalAmplifiers
when used as an inline amplifier in metro networks, as a power booster and as a
preamplifier. Also, in nonlinear operation they can perform all-optical signal
processing due to their strong nonlinearities and their fast dynamics.
AdventofnewSOAgenerationinthelastdecade(i.e.quantumwell-SOAsand
quantum dot-SOAs) has promised enormous improvements over traditional bulk-
SOAs. SOAs with quantum wells or dots in their active region have presented
higher output power, lower threshold current, good temperature stability, lower
noise characteristics and interesting nonlinear properties compared with bulk
SOAs. Quantum-dot SOAs (QD-SOAs) specially have attracted great interest
recently due to interesting specifications of quantum dots and have developed
alongwithquantumdotlasersinrecentyears. Low-thresholdcurrent,highoutput
saturation power, fast gain dynamics and low noise level of QD-SOAs have been
provedandithasemphasizedthattheseelementscanbeutilizedasbuildingblocks
of all-optical systems. Multi-channel operation capability of QD-SOAs such as
multi-channel amplification and wavelength conversion provides a great chance
for development of WDM network as well as demonstration of all-optical
networks.
In this chapter, a brief overview of the operation principles of SOAs will be
given and to prevent presentation of redundant subjects in the field of SOAs that
have previously discussed in other valuable and outstanding books, specifications
of QD-SOAs will be introduced as the main roadmap of this chapter. Optical
properties of QD-SOAs, fabrication methods, polarisation-sensitivity, and prop-
erties of doped QD-SOAs are the main subjects that will be covered during the
next pages.
1.2 Operation Principles
The operation principle of the SOA lies in the creation of an inversion in the
carrierpopulationusedtoamplifytheinputopticalsignalviastimulatedemission.
The population inversion is achieved by electric current injection into the SOA.
Figure 1.1showsthesimplifiedbandstructureofadirect-gapsemiconductor.The
conduction band and the valence band are separated by the band-gap energy E .
g
Thecurrentinjectionleadstofreeelectron–holepairgenerationintheconduction
bandandvalenceband,respectively.Inquasi-equilibriumtherelaxationtimesfor
transitions within either of the bands are much shorter than the relaxation time
between the two bands. So, the carrier distribution within each band can be
described by two quasi-Fermi levels denoted by E and E . The position of the
fc fv
quasi-Fermilevelsisdeterminedbythecurrentinjection.Ifthecurrentinjectionis
sufficientlylargetheseparationbetweenthequasi-Fermilevelsexceedstheband-
gapenergy(E - E [E )andthesemiconductoractsasanamplifierforoptical
fc fv g
frequencies(m)withE \hm\E - E .Theabsorptionprocessdominatesover
g fc fv
stimulated emission for photon energies larger than DE = E - E (hm[DE)
f fc fv f
and the material acts as an attenuator [1].