Integration of a GaAs/AlGaAs SQW laser and a tapered waveguide coupler

144 Pages·1996·4 MB·English

by  Xie, Suning, 1961-

INTEGRATIONOFAGaAs/AIGaAsSQWLASERAND
ATAPEREDWAVEGUIDECOUPLER
By
SUNINGXIE
ADISSERTATIONPRESENTEDTOTHEGRADUATESHOOL
OFTHEUNIVERSITYOFFLORIDAINPARTIALFULFILLMENT
OFTHEREQUIREMENTSFORTHEDEGREEOF
DOCTOROFPHILOSOPHY
UNIVERSITYOFFLORIDA
1996
Tomyparents
ACKNOWLEDGMENTS
First,IwanttothankDr.RamuV.Ramaswamy,myadvisor,forhissupportand
guidancethroughoutthecourseofthiswork.Hishardworkandsuccessingenerating
fundsforthePhotonicsResearchLaballowedmetocompletethisworkinaverywell
equippedlab.
IalsowanttothankDr.ShengS.Li,Dr.AmostNeugroschel,Dr.EwenThomson,
andDr.DavidTannerfortheirparticipationonmysupervisorycommittee.
ThanksalsogotomyfellowgroupmembersinthePhotonicsResearchLabfor
theirdirectorindirecthelp,particularly,DavidMaring,Dr.ScottSamson,MarkSkowron-
ski.Dr.RobertTavlykaev,Dr.WeidongWang,Dr.ChrisHussell,Dr.TizianaConese,Dr.
SanjaiSinha,Dr.Sang-KookHanandDr.HyoonSooKim.
Iwanttothankmyparents.Theyalwaysencouragemetoattainhighergoals.I
knowthattheprogressinmyendeavor,suchasthecompletionofthisdissertation,isthe
bestexpressionofgratitudetothem.
iii
TABLEOFCONTENTS
page
ACKNOLEDGMENTS
iii
ABSTRACT vi
CHAPTERS
1 INTRODUCTION 1
1.1 Motivation 2
1.2 TheLaser-WaveguideIntegrationStructures 8
1.3 OrganizationoftheDissertation 16
2 NOVELINTEGRATIONOFANSQWLASERAND
ATAPEREDCOUPLER 18
2.1 MultilayerOpticalWaveguide 18
2.2 QuantumWellLasers 24
2.3 TaperedWaveguideCoupler 30
2.4 TheSQWLaser-WaveguideIntegration 36
3 MULTIPLEQUANTUMWELLDISORDERING 39
3.1 Introduction 39
3.2 ZnDiffusionProfiles 46
3.3 CompositionalProfilesofDisorderedMQWs 56
3.4 RefractiveIndexProfilesofDisorderedMQWs 64
3.5 TheOpticalConfinementFactor 69
3.6 TheLasingThresholdCurrentDensity 77
4 GROOVEBETWEENTHELASERANDTHETAPER 84
4.1 TheCharacteristicMatrix 84
4.2 ReflectanceoftheGroove 88
IV
4.3 TheLasingThresholdVariation 93
4.4 ThePowerOutputVariation 94
5 FABRICATIONTECHNIQUESANDEXPERIMENTALRESULTS 98
5.1 MaterialGrowth 98
5.2 MQWDisorderingbyZnImplantationandAnnealing 101
5.3 GrooveEtchingByRIE 105
5.4 FabricationoftheTaperedCoupler 107
5.5 TheIntegration 114
6 SUMMARYANDCONCLUSIONS 120
REFERENCES 124
BIOGRAPHICALSKETCH 131
AbstractofDissertationPresentedtotheGraduateSchool
oftheUniversityofFloridainPartialFulfillmentofthe
RequirementsfortheDegreeofDoctorofPhilosophy
IntegrationofaGaAs/AlGaAsSQWLaserand
ataperedwaveguidecoupler
By
SuningXie
December1996
Chairman:RamuV.Ramaswamy
MajorDepartment:ElectricalandComputerEngineering
Future high speedoptical fibercommunicationsandsignalprocessingsystems
requirethemonolithicintegrationofalasersourceandotherpassiveaswellasactive
devices.Keytointegrationisthecouplingoflightfromthelasersourcetoawaveguide
circuitthatmakethelightavailableforotheropticalprocessingfunctionssuchasmodula-
tion,switchingandrouting.Existingintegrationschemeseitherrequirecomplicatedand
costlymaterialregrowthorimposeseveredesignandfabricationrestrictions.Thisdisser-
tationstudiesanovelmonolithicintegrationofasinglequantumwell(SQW)laseranda
taperedwaveguidecouplerintheGaAs/AlGaAsmaterialsystem.Theintegratedstructure
consists of two sections: the laser and the tapered waveguide coupler. The SQW
waveguideforthelaserandthemultiplequantumwell(MQW)waveguideastheoutput
waveguideareverticallystacked.Inthelasersection,theMQWsaredisorderedbyZn
VI
implantationandannealingthusbecomingthecladdinglayeroftheSQWlaser.Inthe
tapered waveguide coupler section, the MQWs are gradually disordered along the
waveguidebynitrogenimplantationandannealing.Thispermitsthelaseroutputcouples
totheMQW waveguide foroptical processing such as modulation.Agrooveetched
betweenthelaserandthetapersectionsfunctionsasapartiallytransmissivemirrorpro-
vidingthefeedbackforthelaser.Thetaperedwaveguidecoupleremploysanadiabatic
powertransferprocessandallowsforindependentoptimizationofindividualcomponents
tobeintegrated.Theverticalconfiguration ofthetwowaveguidesandthecontrolled
impurity-induceddisorderingeliminatetheregrowthrequirementswithoutsacrificingthe
devicedesignandfabricationflexibility.
Inthisdissertation,thekeytechnologiesfortheintegrationoftheSQWlaserand
thetaperedwaveguidecouplerhavebeeninvestigatedtheoreticallyandexperimentally.
TheMQWsinthelasersectionaredisorderedbyZnimplantationandsubsequentanneal-
ing.Afinitedifferenceapproachhasbeendevelopedtodeterminetheconcentration(Zn)
dependentinterdiffusionandthemodelleadstoapredictionofasharpreductioninthresh-
oldcurrentdensityduetothedisorderingoftheMQWsinthelasersection,whichagreed
wellwithourexperimentalresults.Inaddition,dependenceofthelasingconditiondueto
thegrooveareinvestigated.ThefabricationtechniquesincludingtheMQWsdisordering
byimplantationandannealingandthereactiveionetching(RIE)forthegroovehavebeen
developed. Utilizingthesetechniques,theintegrationofanSQWlaserandatapered
waveguidecouplerintheGaAs/AlGaAsmaterialsystemhasbeenaccomplished.
vii
CHAPTER
1
INTRODUCTION
Thebreakthroughinsemiconductordiodelasersinthe1960sandthedevelopment
oflowlossopticalfiberinthe1970swereresponsiblefortheexplosioninthefiberoptical
communicationandopticalsignalprocessingsystems.Theprogressintheseopticalsys-
tems,inturn,hasstimulatedthegrowthofanewclassofpassiveandactiveopticalcom-
ponentsinthindielectriclayersusingguidedwaveoptics.Thehighlypromisingand
sophisticatedtechnologyresponsibleforthenewclassofdevicesisknownasintegrated
optics.Inadditiontotheadvantagesofgreaterbandwidthandimmunityfromelectromag-
neticinterference,integratedopticdevicesincorporateincreasedcomplexcircuitryand
functionalityalongwithhighreliability. Successfulfuturedeploymentofopticalfiber
communicationsandopticalsignalprocessingsystemsreliesonthemonolithicintegration
ofalasersourcewithvariouspassiveandactivedevices.Oneofthekeyintegrationsisthe
couplingoflightfromthelasersourcetoawaveguidecircuitinvolvingotheropticalpro-
cessingsuchasmodulation,switchingandrouting.Inthisdissertation,wetheoretically
andexperimentallyinvestigateanovellaser-taperedwaveguidecouplerintegration;inpar-
ticular,wedevelopthekeyfabricationtechniques,anddemonstratethemonolithicintegra-
tionintheAlGaAs/GaAsmaterialsystem.Thefirstsectionofthisintroductorychapter
1
2
describesthemotivationforthiswork.Insection1.2,wecomparevariousexistinglaser-
waveguideintegrationstructuresandintroducethenovelstructureweproposed.Theorga-
nizationoftheremainingchaptersofthisdissertationispresentedinsection1.3.
1.1Motivation
Opticalfiberofferstransmissioncapacityofmanyordersofmagnitudegreatthan
thatofconventionaltransmissionlines.Theoverallbandwidththatisavailableforoptical
transmissionisintheorderofTHz.Thisenormouscapacitycanbeaccessedbyusing
techniquessuchaswavelengthdivisionmultiplex(WDM);itallowsfortheimplementa-
tionofmanynewservicessuchasHDTVdistribution,broadbanddatahighwaysand
WDM
videotelephony.Ina system,theoveralldatastreamisdividedintoasetofsub-
streamseachhavingadifferentwavelength.Theopticalsignalsaremultiplexedbyan
opticalpowercombinerandthendemultiplexedbyopticalfiltersatthereceiverends.Fig-
ure 1 shows amultiwavelengthopticalbroadcastnetwork.Thenetworkbasedonthe
LAMBDANETarchitecture[1]iscomposedofaclusterofNcommunicationnodes.Each
nodetransmitsitsinformationatauniquewavelengthandeachnodereceivesalltheinfor-
mationfromtheothernodes.Thenodesareopticallycoupledtogetherusingatransmis-
siveopticalstarcoupleratahublocationwhichbroadcastsinformationatallwavelengths
toallnodes.
3
NODE#2
Figure1.1TheLAMBDANETmultiwavelengtharchitecture.