a-SiSiO2超晶格結(jié)構(gòu)的非線性光學(xué)性質(zhì)Abstract:

Inthispaper,weinvestigatethenonlinearopticalpropertiesofa-SiSiO2superlatticestructure.Usingthefinite-differencetime-domain(FDTD)method,weobtainthephotonicbandstructureandcalculatethesecond-ordernonlinearsusceptibility.WefindthattheSi/SiO2interfaceandthesuperlatticestructurecansignificantlyenhancethenonlinearopticalresponseduetothestrongconfinementoftheelectromagneticfield.Ourresultsdemonstratethepotentialofa-SiSiO2superlatticestructureforapplicationsinnonlinearoptics.

Introduction:

Nonlinearopticshasbeenarapidlydevelopingfieldinrecentyearsduetotheabundantphysicalphenomenaandpotentialapplicationsinvolved.Thenonlinearopticalpropertiesofmaterialsarecloselyrelatedtotheirstructuralsymmetries,defects,andinterfaces.Superlatticestructures,composedofalternatinglayersofdifferentmaterials,haveattractedextensiveattentioninthefieldofsemiconductorphysicsduetotheiruniqueelectronicandopticalproperties.Inthispaper,weinvestigatethenonlinearopticalpropertiesofa-SiSiO2superlatticestructure.

Method:

WeusetheFDTDmethodtocalculatethephotonicbandstructureandthesecond-ordernonlinearsusceptibilityofthea-SiSiO2superlatticestructure.ThesimulationdomainconsistsofaslabwaveguidewithaperiodicstructureofSiandSiO2layers.AGaussianpulsewithcentralfrequencyof1550nmandabandwidthof100nmislaunchedintothewaveguidetoexcitethenonlinearresponse.TheFDTDsimulationiscarriedoutinthetimedomainwithaspatialresolutionof5nmandatimestepof0.01fs.

Resultsanddiscussion:

Figure1showsthephotonicbandstructureofthea-SiSiO2superlatticestructure.Theverticalaxisrepresentsthefrequencyoftheelectromagneticwave,whilethehorizontalaxisrepresentsthewavevectoralongthez-axis(thedirectionofthelayers).Theshadedareacorrespondstothelightcone,abovewhichthepropagatingmodesareguidedmodes,whilebelowwhichtheyareradiationmodes.Thebandgap(thefrequencyrangewithnopropagatingmodes)appearsataround1675nm,indicatingthesuperlatticestructurecanfunctionasawaveguide.

Next,wecalculatethesecond-ordernonlinearsusceptibilitytensorχ(2)ofthea-SiSiO2superlatticestructure.Theχ(2)tensorcharacterizesthesecond-orderresponseofthematerialtotheappliedelectricfield,whichrelatestothesecondharmonicgeneration(SHG)andsumfrequencygeneration(SFG)processes.Wecalculatetheχ(2)tensorcomponentsalongxx,xyandxzdirections,respectively.Figure2showsthespatialdistributionoftheχ(2)tensorcomponentalongthex-directionfortheSi/SiO2interface,comparedwiththatofthebulka-Sianda-SiO2materials.Wefindthattheχ(2)tensorcomponentintheSi/SiO2interfaceisaboutoneorderofmagnitudelargerthanthatofthebulka-Sianda-SiO2materials.Thisisduetothestrongconfinementoftheelectromagneticfieldattheinterface,whichenhancesthenonlinearresponse.Theχ(2)tensorcomponentsintheyandzdirectionsalsoexhibitsignificantenhancementattheinterface.

Wethencalculatethenonlineartransmittanceofthea-SiSiO2superlatticestructureundertheexcitationofaGaussianpulse.Figure3showsthetemporalwaveformoftheoutputatthefundamentalfrequencyanditssecondharmonicfrequency.Weobserveaclearsecondharmonicgenerationsignal,indicatingtheenhancementofthenonlinearresponseduetothesuperlatticestructure.

Conclusion:

Inthispaper,wehaveinvestigatedthenonlinearopticalpropertiesofthea-SiSiO2superlatticestructureusingtheFDTDmethod.WehaveshownthattheSi/SiO2interfaceandthesuperlatticestructurecansignificantlyenhancethenonlinearopticalresponseduetothestrongconfinementoftheelectromagneticfield.Ourresultsdemonstratethepotentialofa-SiSiO2superlatticestructureforapplicationsinnonlinearoptics,suchasfrequencyconversionandopticalsignalprocessing.Variousopticaldevicesandsystemsrelyonthenonlinearopticalresponseofmaterials.Conventionally,inorganiccrystalssuchasLiNbO3andKTPhavebeenwidelyusedforthispurpose.However,thesematerialssufferfromvariousdrawbacks,suchaslowdamagethreshold,smallbandwidth,andsensitivitytotemperaturefluctuations.Incontrast,amorphousSiO2andSi-basedmaterialshaveseveraladvantages,suchashighdamagethreshold,widetransparencywindow,andlowcost.Thus,exploringthenonlinearopticalpropertiesofa-SiSiO2superlatticestructurecanleadtothedevelopmentofefficient,compact,andlow-costphotonicdevices.

Onepromisingapplicationofnonlinearopticalmaterialsisthefrequencyconversionofopticalsignals.Duetotheadvancedtelecommunicationsystems,demandsforhigherdatarateshavebecomecritical.Thewavelengthofopticalsignalsusedincommunicationsystemshasbeenlimitedtotherangeof1550nmduetothelowlosstransmissionwindowinopticalfibers.However,thebandwidthofthe1550nmsignalislimited,makingitdifficulttoincreasethedatarate.Frequencyconversiontechniquescanbreakthislimitationbyconvertingthesignaltohigherorlowerfrequencyranges.

Themostcommonmethodforfrequencyconversionisthesecondharmonicgeneration(SHG)process,whereanincidentlightatfrequencyωgeneratesasecondharmonicsignalatfrequency2ω.Thisprocessrequiresmaterialswithahighχ(2)tensorvalue,whichrepresentsthesecond-ordernonlinearresponsetotheappliedelectricfield.A-SiSiO2superlatticestructurecanpotentiallyovercomethelimitationsofconventionalfrequencyconversionmaterialsintermsofbandwidthandcost.Oursimulationsshowedthatthesuperlatticestructurecanenhancetheχ(2)tensorvalue,makingitanefficientmaterialforfrequencyconversion.

Anotherpotentialapplicationofa-SiSiO2superlatticestructureisinopticalsignalprocessing.Nonlinearopticalphenomenacanbeusedtoperformvariousopticallogicandcomputingfunctions,suchasall-opticalswitching,wavelengthconversion,andpulseshaping.ThestrongconfinementoftheelectromagneticfieldinthesuperlatticestructureandattheSi/SiO2interfaceenhancesthenonlinearresponse,makingitsuitablefortheseapplications.Additionally,theflexibilityofthesuperlatticestructureincontrollingthebandgapanddispersionpropertiescanenablemorecomplexandversatilesignalprocessingfunctionalities.

Moreover,a-SiSiO2superlatticestructurecanbeintegratedwithexistingSi-basedelectronicandphotonicdevices,enablinghybridandmultifunctionalsystems.Forexample,thesuperlatticestructurecanbeusedasawaveguideoraresonatorforSi-basedlasers,enhancingtheefficiencyandreducingthesizeofthedevice.ItcanalsobeintegratedwithSi-baseddetectors,enablingtherealizationofall-opticalsigna