Metasurfaces and flat optics - Capasso Group

Metasurface J-plates and metasurface-enhanced lasers ... Structured light refers to the tailoring or shaping of light in all its degrees of freedom, which can be ... Skiptomaincontent MainMenuUtilityMenuSearch HARVARD.EDU HomeNewsResearchFlatopticsRFPhotonicsOpticalforces2DopticsTerahertzsourcesPeopleProfCapassoAlumniPublicationsPh.D.ThesesGalleryApply HOME/RESEARCH/ GotoPublicationstoviewalljournalarticles. Introduction Traditionaloptics-lenses,waveplates,filters,andthelike-haveexistedforcenturies.Inmanycasestheseelementsarefashionedbytechniqueslikemachiningandturningglassthat,despiterefinements,havealsogonelargelyunchanged.Morerecently,metasurfaceopticshaveemergedwherephase-shiftingoccursatwavelength-scale,offeringcompactnessandnewfunctionalitynotaccessiblewithbulkopticalelements.Thesemetasurfacedevicesarefabricatedusinglithography,thinfilmdeposition,andetching,techniquesborrowedfromsemiconductormanufacturing.Theproductionofthesedevicescanbescaledup,withmajorconsequencesforoptics. Metalenses Metasurfacescomprisesub-wavelengthnanostructures.Bythedesignandarrangementoftheconstituentnanostructures,metasurfacesareabletoimpartcustomizedpolarization,amplitudeandphasetoincidentlight.Additionally,metasurfacescanbelithographicallymass-produced,enablingminiatureandmultifunctionalmetasurfaceopticalelements.Metalenses,asanexampleofmetasurfaceopticalelements,hasattractedwidespreadattentionandwashailedasoneofthetoptenemergingtechnologiesof2019bytheWorldEconomicForumandScientificAmerican.Thegroupisworkingondevelopinglargediameter,high-efficiencyandachromaticmetalensesforapplicationsinimaging,illumination,virtualandaugmentedrealityetc.HerearethreeYouTubevideosforthosewhoareinterestedtolearnmore: ScienceMagazine:Shrinkingmicroscopelenses TEDtalkgivenbyProf.FedericoCapasso Metalensdemonstrations MetasurfaceJ-platesandmetasurface-enhancedlasers  Structuredlightreferstothetailoringorshapingoflightinallitsdegreesoffreedom,whichcanbeusedformicromanipulationandenhancing thecapacityofopticalcommunicationchannels.Chirallightisforemostamongthefamilyofstructuredlightfieldswhichcarriesspinangular momentumandorbitalangularmomentum(OAM).ThemetasurfaceJ-plateisametasurfaceconverterforopticalstatesthatcouplesbetween arbitraryspinandopticalangularmomentumstatesoflightinacompactplanar.J-platesovercomeakeylimitationinalternativetechnologies suchasQ-platesandspatiallightmodulators:conjugatesymmetryoflight’sangularmomentum.AndtherelativelysmallpixelsizeofJ-plates improvesthebeamquality,efficiency,andcapabilityofgeneratinghigherOAMstates.  UsingaJ-plate,anewmetasurfacelaserthatproduceshigh-purityandnon-symmetricsuper-chirallightneveryetobservedfromlasers, creatingofarbitraryspin-orbitalchiralstatesofstructuredlightatthesource.Ourlaserconvenientlyoutputsinthevisible,offeringacompact andpower-scalablesourcethatharnessesintra-cavitystructuredmatterforthecreationofarbitrarychiralstatesofstructuredlight.The metasurface-enhancedlaserisanewmilestoneinthehistoryofstructuredlightlasersasitbreachesspin-orbitcouplingsymmetryaswellas setsupanovelrecordforwhathigh-purityandhigh-orderOAMstatescanbecreatedfromalaser.   Nano-opticendoscopeswithmetalenses Improvementintheaccuracyofendoscopicbiopsyforsmallperipherallesionsisnecessaryifbronchoscopywillplayamajorrolein lungcancerdiagnosis.Endoscopicopticalcoherencetomography(OCT)withcommercialcathetersthatrelyongraded-index(GRIN)lensesorballlenses, however,exhibitstrongastigmatismandsphericalaberrationandthusdeviatefromdiffraction-limitedfocusing.Shownisanartisticimpressionof thenano-opticendoscopethatusesametalens,withtheabilitytomodifythephaseofincidentlightatsubwavelengthlevel, toenablehigh-resolutionendoscopicimagingatextendeddepth-of-focusbyavoidingmonochromaticaberrations.High-resolutionthree-dimensionalimagesarecapturedbyinsertingthenano-opticendoscopeintothelungsendo-bronchiallyvisualizeairwaytissuemicrostructures.Thecombinationofthesuperiorresolutionandhigherimagingdepthoffocusofthenano-opticendoscopeislikelytoincreasetheclinicalutilityofendoscopicopticalimaging.   PolarizationImagingwithMetasurfaces Conventionalcamerasandimagingsystemsarenotsensitivetolight’spolarizationstate.Inordertomeasurethisfundamentaldegree-of-freedomoflight,imagingsystemsmustoftenrelyoncomplexbeampaths,movingparts,orspecialsensors.Usingametasurface,however,allpolarizationcomponentsnecessaryforafullmeasurementoflight’spolarizationstatecanbecombinedintoasingleopticalelement,renderingapolarization-measuringcameranotaltogethermorecomplicatedthananordinaryone;thishasbroadpotentialapplicationsinremotesensingandmachinevision.Formoreinformation,see HarvardSEASnews. Large-areametalenseswithDeepUVlithography Metalensesareflatlensesthatareultrathinandlightweight,andaretypicallyrealizedbyplacingmillionstobillionsofnano-structuresonasurface.Thelargenumberofstructuresmakesscalabilityinbothsizeandproductionscaleamajorconcern.Inourrecentwork,wedemonstratemass-producible,all-glass,centimeter-scalemetalensescapableoffocusingvisiblelight,usingdeep-ultraviolet(DUV)projectionlithography,amanufacturingtechniquewidelyusedbycomputerchipfoundries.Thesemetalensesexhibitdiffraction-limitedperformanceandaresuitableforpotentialapplicationsinvirtualreality(VR)devicesandbiologicalimagingtechniques.Sincethemetalensesarealsoverylight,webelievethattheyareidealforcameraapplicationswherepayloadweightandfootprintsizeareimportant,suchasindronesandcubesats.  Metasurfacespectrometer Oneoftheapplicationsofflatlensesisinspectroscopy.Opticalspectroscopyisanessentialtoolusedinmanyareassuchasfoodmonitoringandmedicaldiagnostics.However,spectrometerstypicallyfaceatrade-offbetweentheirspectralresolution,workingwavelengthrangeandoveralldevicesizeduetoopticalaberrationsintheirfocusingelements.Topreservehighspectralresolutionoverabroadbandwidth,additionalcorrectiveopticalcomponentsmustbeused.Theseaddsignificantbulkandpreventeasyintegrationwithportabledevices.Herewepresentahighlycompact,aberration-correctedspectrometerusingmeta-lenses,whicharecomprisedofsubwavelengthscalenanostructures.Itachievesnanometerresolutionacross200nminthevisiblespectrum,withanoverallfootprintatthecentimeter-scale. Metasurfaceaberrationcorrectors Inlensdesign,themostwidelyusedapproachforchromaticaberrationcorrectionisbasedonaddingrefractivelensesmadeofdifferentglasses.Thisapproachnotonlyincreasesvolumeandweight,butalsorelieson the difficultprocessofdevelopingnewglasseswithsuitabledispersionproperties.Here,wedemonstratedametasurfaceaberrationcorrector(metacorrector)whosephaseanddispersion(groupdelayandgroupdelaydispersion)profilesaretailoredtocorrectthemonochromaticandchromaticaberrationsofafusedsilicasinglet.Themetacorrectorwasdesignedbyengineeringtheeffectiverefractiveindexofeachconstituentnanostructureoveralargebandwidth.Theimagesaboveshowexperimentalimagingresultsunderincoherentwhite-lightilluminationforcaseswithandwithoutthemetacorrector.Thesamedesignmethodisapplicableforsophisticatedmicroscopeobjectivesandispromisingforrealizingsuper-achromaticanddiffraction-limitedlenses. 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