Optical Resonators With Whispering-Gallery applications

WGM谐振腔综述

OpticalResonatorsWithWhispering-Gallery

Modes—PartII:Applications

VladimirS.IlchenkoandAndreyB.Matsko

(InvitedPaper)

Abstract—Wereviewphotonicapplicationsofdielectricwhispering-gallerymode(WGM)resonators—tracingthegrowthofthetechnologyfromexperimentswithlevitatingdropletsofaerosolstoultrahigh-Qsolidstatecrystallineandintegratedon-chipmicroresonators.

IndexTerms—Four-wavemixing(FWM),high-orderoptical lters,lasers,laserresonators,monolithicopticaltotalinternalre ectionresonators,morphologydependentresonances,nonlin-earoptics,optical lters,opticalresonators,parametricoptics,Q-factor,solidstatelasers,spectroscopy,tunable lters,wavemix-ing,whispering-gallerymode(WGM)resonators.

I.INTRODUCTION

I

NTHISpaper,weaddressapplicationsofopendielectricres-onatorsandleavethedetaileddescriptionsoftheirpropertiestotextbooks[1],[2]andreviews[3]–[8].Thebasicpropertiesofresonatorsthatareimportanttotheirpracticalapplicationsarealsosummarizedinthepreviouspaperofthisissue[9].

Antalkingabout“photonicapplications,”weuseabroadmeaningofphotonics,whichincludeslinear,nonlinear,andquantumoptics,opticalengineering,andotherrelatedbranchesofscienceandtechnology.Specialattentionisgiventomi-crowavephotonics,wheredielectricresonatorsareusedtopro-cessmicrowavesignalsbyopticalmeans.

Wediscusstheresonatorsthataremadeoftransparentopti-caldielectricsandhavemonolithicringresonatordesign(wedonotconsidermacroscopic berringresonatorsbasedondirectionalcouplers).Theopticalmodesinsuchresonators;e.g.,morphology-dependentresonancesorwhisperinggallerymodes(WGMs),canbeunderstoodasclosedcircularbeamssupportedbytotalinternalre ectionsfromboundariesoftheresonators.

Modernopendielectricopticalresonatorshavecylindrical,spherical,spheroidal/toroidal,ring,andothershapesandtopolo-gieswithvariouscon ningprinciples.Forthesakeofuni ca-tion,weusethroughoutthisreviewthetermswhisperinggalleryresonators(WGRs)andwhisperinggallerymodestodescribethoseresonatorsandtheirmodes.

Itisusefultonotethat,strictlyspeaking,thetermWGMcannotbeappliedtoquasi-one-dimensionalobjectssuchasmi-

crorings.Insuchcases,thecurvatureoftheresonatordoesnotplayasigni cantroleintheformationofthespatialmodestruc-tures,andtheseobjectscouldsimplybedescribedasloopsmadeoutofanopticalwaveguide.

OriginalWGMsdonothavealotincommonwithsuchawaveguidepropagation.OriginallystudiedassoundwavespropagatingveryclosetothecylindricalwallofthegalleryinSt.Paul’scathedral,London[10],theWGMs(LordRayleighs’sterm)werefoundtobepartiallycon nedduetothesuppressionofthewavediffractionbythesoundre ectionfromthecurveddomewalls.Theeffectivevolumesand elddistributionsofthosemodesdependontheradiusofthe“resonator”[11].

Toavoidthisdiscrepancy,inourreview,werede neanopticalWGRasamonolithicringresonatorbasedontotalinternalre ectionoflight.

II.DEVICESWITHPASSIVEWGMRESONATORS

UniquespectralpropertiesofWGMs,includingnarrowlinewidth,tunability,andhighstabilityunderenvironmentalconditions,makeWGRsattractivefornumerouspracticalappli-cations.Inthissection,wereviewapplicationsofpassiveWGRsfor ltering,frequencystabilization,andsensing.

Photonic ltersbasedonopticalWGRsarecurrentlyamongthemostdevelopeddevicesthatinvolveWGMs.Foropticaltelecommunicationpurposes,themaintaskofthe ltersistoselectchannelsinwavelengthdivisionmultiplexing(WDM)schemes.Inthisdomain,wherechannelspacingisusuallynolessthan10GHz,planarringresonatorswithWGMandsimilardeviceswithQ<1×105areadequate.

Ultra-high-QWGRswithMHzrangeresonancebandwidthsofferauniqueopportunityforcreationofphotonicmicrowave ltersinwhichopticaldomainselectionisusedforseparatingtheRFchannelsimprintedassidebandsonastableopticalcar-rier.ImportantapplicationsofWGRsoccurinmetrologyforopticalandmicrowavefrequencystabilization,wherealongphotonstoragetimehelpstosuppressphaseandfrequencyde-viationofoscillators.

High-QandlongrecirculationoflightincompactWGRsofferinterestingnewcapabilitiesinspectroscopyandsensing,wherethechangeinQorresonancefrequencyofWGMscanserveasameasureofabsorptioninthesurroundingmedium,orinasmall(downtosinglemolecule)quantityofdepositedsubstanceonaresonatorsurface.Theresonatorcanalsobeusedformeasurementofchangeinambientparameters,suchastemperature,pressure,motion,etc.

ManuscriptreceivedApril10,2005;revisedOctober31,2005.ThisworkwassupportedinpartbytheNationalAeronauticsandSpaceAdministrationandinpartbyDefenseAdvancedResearchProjectsAgency(DARPA).

TheauthorsarewiththeJetPropulsionLaboratory,CaliforniaInstituteofTechnology,Pasadena,CA91109-8099USA(e-mail:vladimir@jpl.nasa.gov;andery.matsko@jpl.nasa.gov).

DigitalObjectIdenti er10.1109/JSTQE.2005.862943

1077-260X/$20.00©2006IEEE

WGM谐振腔综述

A.OpticalandPhotonicSingleResonatorFilters

Thesimplestresonator-based lterincludesaWGRandanopticalcoupler;e.g.,aprismcoupler.TransmissionofamonochromaticelectromagneticwaveoffrequencyωbyanopticalWGRinasingleprismcon gurationmaybecharacterizedbythecoef cient

T=

γc γ i(ω ω0)

γγ+i(ω ω(1)c+0)

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