应用于VCSEL的宽角度光束控制非周期性高对比度光栅阵列（英文）-豆柴文库

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应用于VCSEL的宽角度光束控制非周期性高对比度光栅阵列（英文）
Introduction
VerticalCavitySurfaceEmittingLasers(VCSELs)havebecomeanintegralcomponentinarangeofapplicationsowingtotheirhighefficiency,lowthresholdcurrentandeaseoffabrication.However,oneofthechallengesfacedwithVCSELsisthecontroloftheemittedlightbeam,astheynaturallyemitbeamswithabroaddivergenceangle(typicallyaround30-40degrees).Thismakesitdifficulttocoupletheoutputintoopticalfibersorefficientlycollimatetheoutputforimagingapplications.TherehasbeensignificantresearchindevelopingtechniquestocontrolthebeamdivergenceangleofVCSELs,withoneapproachbeingtheuseofnon-periodichighcontrastgrating(NHCG)arraystomanipulatetheoutcouplingpropertiesofVCSELs.ThispaperreviewstheprogressthathasbeenmadeindevelopingNHCGarraysforwide-anglebeamcontrolinVCSELs.
Background
VCSELsarecompactsourcesofcoherentlightthatarevitalinarangeofapplicationssuchasopticalcommunications,sensing,andaspumpingsourcesforsolid-statelasers.Theyaretypicallyconstructedfromasemiconductormaterialandoperateundertheprincipleofopticalgainandfeedback.Unlikestandardsemiconductorlasers,theresonantcavityinVCSELsisperpendiculartothesubstrate,whichresultsinefficient,low-thresholdcurrent,single-frequencyoperation.However,thenaturalemissionprofileofVCSELsisabroad,nearlyGaussian-shapedbeamwithalargehalf-angledivergence.
NHCGsareachirpedformofhighcontrastgratingsthatarenon-periodicandcanbedesignedtohavearangeofoutcouplingproperties.Theyworkbymodifyingthephaseandamplitudeofthelightinsidethecavityandreflectacertainpercentageoftheguidedmodelightbackintothecavity.Thisback-reflectedlightinterfereswithincidentlightandcreatesastandingwaveinthecavitythatallowsforoutcouplingoflightinaparticulardirection.ItistheabilityofNHCGstoselectivelyoutcouplespecificdirectionsoflightthathasmadethemanattractiveapproachforVCSELbeamcontrol.
DevelopmentofNHCGsforVCSELs
ThefirststudiesonusingNHCGsforVCSELbeamcontrolwerereportedin2008byKuznetsovetal.Theyfabricatedanon-periodicNHCGstructureontopofaVCSELgainregiontoselectivelyoutc