InvitedPaperNovelLaserBeamSteeringTechniquesHansDieterThollDept.ofOptronics&LaserTechniquesDiehlBGTDefencePOBox101155,88641Überlingen,GermanyABSTRACTThepapersummarizeslaserbeamsteeringtechniquesforpowerbeaming,sensing,andcommunicationapplications.Principlesandcharacteristicsofnovelmechanical,micro-mechanicalandnon-mechanicaltechniquesarecompiled.Micro-lensbasedcoarsebeamsteeringincombinationwithliquidcrystalorelectro-opticalphasecontrolforfinesteeringispresentedinmoredetail.Thisreviewaddressesbeamsteeringdeviceswhichmodulatethephasedistributionacrossalaserbeamandexcludesintra-cavitybeamsteering,beamsteeringbasedoncombiningtuneablelaserswithdispersiveopticalelements,activeopticalphasedarrays,andopticalwaveguides.Keywords:Laserbeamsteering,opticalphasedarrays,decenteredmicro-lenses,spatiallightmodulators1.INTRODUCTIONTheintegrationoflaserpowerbeaming,laser-assistedsensing,andlasercommunicationsubsystemsintoautonomousvehicles,airborneandspaceplatformsdemandsnewtechniquestosteeralaserbeam.Thenewtechniquesshouldpromotetherealizationofbeamsteeringdeviceswithlargeopticalapertureswhichareconformallyintegratedintothemechanicalstructureoftheplatform.Thewishlistofrequirementscomprisewell-knownproperties:compact,lightweight,lowpower,agile,multi-spectral,largefieldofregard.Theangularspreadofalaserbeam,especiallyforlongrangeapplications,isinherentlysmallbecauseofthehighantennagainofaperturesatopticalwavelengths.Consequently,thedirectionofpropagationofalaserbeamisgenerallycontrolledintwosteps:(1)Aturretwithgimballedopticalelementspointsthefield-of-viewofatransmitting/receivingtelescopeintotherequireddirectionandcompensatesforplatformmotionswithmoderateaccuracyandspeed.(2)Abeamsteeringdevicesteersthelaserbeamwithinthefield-of-viewofthetelescopeinordertoacquireandtrackatarget.Thesubjectmatterofthisreviewarenovellaserbeamsteeringtechniques.Beamsteeringdevicesarecapableof•pointingalaserbeamrandomlywithinawidefield-of-regard,•steppingthebeaminsmallincrementsfromoneangularpositiontothenext,•dwellingineachpositionfortherequiredtimeontarget.Incontrast,scanningdevicesmovethebeamaxiscontinuouslyandswitchingdevicesareonlyabletoaddresspredefineddirections.Reviewsofcurrenttechnologiesforsteering,scanning,andswitchingoflaserbeamsarefoundinreferences[1,2,3,4].Correspondence.Email:hans.tholl@diehl-bgt-defence.de;Phone:+497551894224TechnologiesforOpticalCountermeasuresIII,editedbyDavidH.Titterton,Proc.ofSPIEVol.6397,639708,(2006)·0277-786X/06/$15·doi:10.1117/12.689900Ingeneral,beamsteeringisaccomplishedbyimposingalinearphaseretardationprofileacrosstheapertureofthelaserbeam.Theslopeofthecorrespondingwavefrontrampdeterminesthesteeringangle:largesteeringanglescorrespondtolargeslopesandviceversa.Largewavefrontslopesincombinationwithlargeaperturesrequirelargeopticalpathdifferences(OPD)acrosstheaperturewhichhavetoberealizedbythebeamsteeringdevice.Largewavefrontslopesmaybegenerateddirectlybymacro-opticalelementssuchasrotating(Risley)prismsandmirrorsordecenteredlenses.Comparedtogimballedmirrorsthesesteeringdevicesarerelativecompact,possesslowmomentsofinertiaanddonotrotatetheopticalaxis.Recently,thesemacro-opticalapproachesgainedrenewedpopularity.Thewayforcompact,lightweight,lowpowerbeamsteeringdevicesissmoothedbymicro-opticstechnology.Singlemicro-opticalelementssuchaselectro-opticprisms,dual-axisscannin...
