Optical modulators based on nanophotonic resonators in silicon-on-insulator [Elektronische Ressource] / Sophie Schönenberger Frey

Informations

• Publié par: rheinisch-westfalischen_technischen_hochschule_-rwth-_aachen
• Publié le: 01 janvier 2011
• Nombre de lectures: 25
• Poids de l'ouvrage: 20 Mo

Extrait

"OpticalModulatorsBasedon
Nanophotonic Resonatorsin
Silicon-On-Insulator"
VonderFakultätfürElektrotechnikundInformationstechnik
derRheinisch-WestfälischenTechnischenHochschuleAachen
zurErlangungdesakademischenGradeseinesDoktorsder
NaturwissenschaftengenehmigteDissertation
vorgelegtvon
Dipl.-Phys. EidgenössischenTechnischenHochschuleZürich(ETH),Schweiz
SophieSchönenberger Frey,geboreneSchönenberger
ausZürich(ZH),Schweiz
Berichter: UniversitätsprofessorDr.phil.(UniWien)HeinrichKurz
UniversitätsprofessorDr. AndreiVescan
TagdermündlichenPrüfung: 28. Juni2010
DieseDissertationistaufdenInternetseitenderHochschulbibliothekonlineverfügbar.CONTENTS
Contents
Introduction 1
1 Fundamentals 5
1.1 PhotonicCrystals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1.1 TheMacroscopicMaxwellEquations-LightinHomogeneousMedia . 6
1.1.2 1DPhotonicCrystal: AMultilayerFilm . . . . . . . . . . . . . . . . . 7
1.2 OpticalCavities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
1.2.1 Fabry-Pérot Cavity . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.2.2 PhotonicCrystalDefect Cavity . . . . . . . . . . . . . . . . . . . . . 14
1.2.3 Coupled-ModeTheoryforWaveguide-LoadedCavities . . . . . . . . . 15
1.2.4 Circular GratingResonators(CGRs) . . . . . . . . . . . . . . . . . . . 16
1.2.5 Waveguide-embedded1DPhotonicCrystalMicro-Cavities . . . . . . . 18
1.3 OpticalModulatorBased onCavities . . . . . . . . . . . . . . . . . . . . . . . 19
1.3.1 ModulationMechanismsinSilicon . . . . . . . . . . . . . . . . . . . 20
1.3.1.1 ElectricFieldEffects . . . . . . . . . . . . . . . . . . . . . 20
1.3.1.2 Carrier InjectionorDepletion . . . . . . . . . . . . . . . . . 21
1.3.1.3 Thermo-OpticEffect . . . . . . . . . . . . . . . . . . . . . . 23
1.3.2 FundamentalLimitationsfor(Electro-)OpticalModulation . . . . . . . 24
1.3.3 State oftheArt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
1.4 ComputationalMethodsforOpticalSimulations . . . . . . . . . . . . . . . . . 30
1.4.1 FrequencyDomainMethod . . . . . . . . . . . . . . . . . . . . . . . 30
1.4.2 TimeDomainMethod . . . . . . . . . . . . . . . . . . . . . . . . . . 31
iCONTENTS
2 FabricationandCharacterizationMethods 35
2.1 Fabrication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
2.1.1 PatternDefinition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
2.1.2 SiliconDoping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
2.2 OpticalandElectro-OpticalCharacterizationMethods . . . . . . . . . . . . . . 39
2.2.1 LinearOpticalTransmissionMeasurements . . . . . . . . . . . . . . . 39
2.2.2 ScanningNear-Field OpticalMicroscopy . . . . . . . . . . . . . . . . 41
2.2.2.1 BasicsofNear-FieldImaging . . . . . . . . . . . . . . . . . 41
2.2.2.2 SNOMconfiguration . . . . . . . . . . . . . . . . . . . . . 42
2.2.3 PumpandProbeSpectroscopy . . . . . . . . . . . . . . . . . . . . . . 44
2.2.4 Electro-OpticalCharacterization . . . . . . . . . . . . . . . . . . . . . 46
3 Waveguide-CoupledCircularGratingResonatorsasOpticalModulators 49
3.1 DesignOptimization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
3.1.1 Influence oftheCladding . . . . . . . . . . . . . . . . . . . . . . . . . 50
3.1.2 TMversusTEPolarization . . . . . . . . . . . . . . . . . . . . . . . . 54
3.2 OpticalandSimulationCharacterization . . . . . . . . . . . . . . . . . . . . . 56
3.2.1 LinearOpticalCharacterization . . . . . . . . . . . . . . . . . . . . . 57
3.2.2 ModalIntensityDistributionStudieswithSNOM . . . . . . . . . . . . 61
3.2.3 All-opticalSwitchingwithPumpandProbe . . . . . . . . . . . . . . . 63
3.2.4 Influence oftheCladding . . . . . . . . . . . . . . . . . . . . . . . . . 67
3.2.5 DifferencesbetweenTMandTEPolarization . . . . . . . . . . . . . . 68
3.3 TrenchesforSuppressingHigher-OrderModes . . . . . . . . . . . . . . . . . 69
3.4 ChirpedCircular GratingResonator . . . . . . . . . . . . . . . . . . . . . . . 70
3.4.1 OptimizationforHighQ-Factor andLowVerticalLosses . . . . . . . . 70
3.5 SummaryandConclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
4 Waveguide-Embedded1DPhotonicCrystalMicro-CavitiesasOpticalModulators 79
4.1 StateoftheArt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
4.2 ConceptandDesign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
iiCONTENTS
4.3 CavityStructurewithoutContactLeads . . . . . . . . . . . . . . . . . . . . . 81
4.3.1 OptimizationofUnloadedCavitiesforHighQ-Factor . . . . . . . . . 82
4.3.2 AssessmentofFabricationVariations . . . . . . . . . . . . . . . . . . 84
4.3.3 OpticalCharacterization . . . . . . . . . . . . . . . . . . . . . . . . . 91
4.3.3.1 LinearOpticalTransmissionMeasurements . . . . . . . . . 91
4.3.3.2 Temperature-DependentTransmissionMeasurements . . . . 95
4.3.3.3 All-OpticalSwitchingwithPumpandProbe . . . . . . . . . 96
4.3.3.4 DeviceResponseasaFunctionofthePumpSpotPosition . . 102
4.4 ActiveResonantModulators . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
4.4.1 OptimizingtheCavityfor AbsorbingContactLeads . . . . . . . . . . 103
4.4.2 LinearOpticalCharacterizationoftheStructure withContactLeads . . 105
4.4.3 Performance CharacterisationoftheElectro-OpticalModulator . . . . 108
4.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
5 Summary 113
6 Outlook 117
A FurtherOptimizationofthe1DPCMicrocavitywithoutContactLeads 121
B Abbreviations 125
B.1 RomanSymbolsandAcronyms . . . . . . . . . . . . . . . . . . . . . . . . . 125
B.2 GreekSymbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
B.3 DevicesandMethods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
B.4 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
C SiliconProperties 133
D PhysicalConstants 135
Publicationsrelatedtothisthesis 149
iiiCONTENTS
Acknowledgements 153
CurriculumVitae 155
ivIntroduction
Introduction
The evolution of data communication is driven by the need of the world’s information infras-
tructure to be able to provide instantaneous availability of data, video and voice. This results
in an exponential growth of computational performances raising the necessity of higher band-
width technologies to keep track with the desired data rates. Therefore, shorter and shorter
distancesand thushigher integrationdensitiesare required. But cooper-based solutionsfor the
data transmissionbuild the main bottleneck of the performance on chip level. When shrinking
device dimensions the metal interconnection lines, which act as communicationpaths, have to
become smaller and closer to each other because of an increase in integration density. The
maximum achievable density is than limited by crosstalk and resistance which both affect the
performance. Thus, in the past decades, a new technology started to revolutionize the field of
datacom: photonics. They main advantage is related to the carrier frequency of light, which is
100000timeshigherthanelectronicsignal. ThisThisItenablesbandwidthdensitiesthatcanbe
ordersofmagnitudehigher.
Startinginthe1980swithdatatransmissionthroughopticalfibersoverthousandsofkilometers,
thereisatrendalsotoshorterandshortertransmissiondistances. Whilethecurrentstateofthe
art for practical applications bridges distances of several meters, there is a clear roadmap for
this to proceed down to sub-meter region. The ultimate goal is a so-called optoelectronic inte-
grated circuit (OEIC): a real "superchip" [1]. It will consist of various integrated components
for light generation, modulation, manipulation, amplification, and detection. Therefore, ultra-
small, low-power consuming, and cost-efficient active as well as passive optical components
are necessary.
Akeyfactorfordatacomisthecostperbit. Hence,thematerialinvolvedinthefabricationis
veryimportant. Inthepast,opticalswitchesandmodulatorsweredemonstratedinferroelectric
materials, such as lithium niobate (LiNbO ) and III-V semiconductor materials, in particular3
because of their large electro-optic coefficient in the case of LiNbO or the direct band gap3
in the case of III-V semiconductor materials. Most optical switches and modulators in III-V
semiconductor materials harness the photo-excited free charge carriers concentration resulting
from one- or two-photon absorption [2, 3]. However, both materials are difficult to combine
1Introduction
withthestandardcomplementarymetal-oxidesemiconductor(CMOS)fabricationplatformand
donotallowthefabricationoflow-costdevicesbecause theyare ratherexpensive.
Since silicon (Si) is relatively inexpensive, plentiful, robust, and well understood for pro-
ducing electronic devices it is a desirable material. It enables the fabrication and integration
of photonic and electronic components on a single silicon chip using the CMOS fabrication
technology. Inparticularhigh-qualitysilicon-on-insulator(SOI)wafersofferanidealplatform.
SOIexhibitsstrongopticalconfinementduetothelargeindexcontrastbetweenSi(n = 3.46)Si
and SiO (n = 1.46), which makes it possible to shrink the size of photonic devices to a2 SiO2
few micrometers. Therefore, silicon-based optical interconnects could le