AWGMlaserwithpulsedopticalpumpingfabricatedbysurroundingasmallsectionofaglasscapillarywithasolutionofRhodamine6G,andbycouplingthepumplightintothecapillarywall,wasdemonstratedin[175].Thelasingthresholdpumpenergywas100nJ/pulseatapumppulsedurationof6ns.2)LasinginDopedWGRs:AnotherwaytocreateaWGRlaseristheuseofsolidsdopedwithactiveelements;e.g.,rareearthionsasaWGRhostmaterial.
AWGMlaserbasedonneodymium-dopedsilicamicro-sphereswitha200nWthresholdwasrealized[176]withmicrospheresofradiusa～25–50µm,formedbyheat-fusingthetipofalengthofdopedsilica ber.Neodymiumionsprovideafavorablefour-levellasersystemthatcanbepumpedonthe4I9/2 4F5/2transitionat～810nmwithadiodelaser.Thelasertransition4F3/2 4I11/2inthe1.06–1.09µmrangeconnectsalonglivedupperleveltoalowerlevelthatisdepletedbystrongphononrelaxationsothatpopulationinversioniseasilyachieved.Similarexperimentswithaneodymium-dopedsilicamicrospherelaseroperatingat2Kandabsorbing200nWpumppowerwerereportedin[177].CWlaseroscillationonboththe4F3/2→4I11/2and4F3/2→4I13/2transitionsofNd3+ionsin uorideglassWGRswasalsoachieved[178].FabricationofNd-dopedtelluriteglassWGRsandobservations
WGM谐振腔综述
22IEEEJOURNALOFSELECTEDTOPICSINQUANTUMELECTRONICS,VOL.12,NO.1,JANUARY/FEBRUARY2006
oflaseroscillationcorrespondingtotheopticaltransition4
F3/2→4I11/2at1.06µmwasreportedin[179].
AWGMlaserutilizingamicrospheremadeofhighlydopederbium:ytterbiumphosphateglasswasusedtogeneratelightat1.5µm[180].Laserthresholdpumppowerof60µWand ber-coupledoutputpowerashighas3µWwithsingle-modeoperationwereobtained.Abispherelasersystemconsistingoftwomicrospheresattachedtoasingle bertaperwasalsodemonstrated.
AnEr3+-dopedtelluriteglassL-bandWGRlaserwasdemon-stratedanddiscussedin[181].Themicrospheresweremadebya“spinmethod.”Fibertaperswereutilizedtocouple975nmpumpintothesphereandcouplegeneratedlight(1.56–1.61µm)outofthesphere.Theerbiumionconcentrationofthetelluriteglasswas1.7×1020ions/cm3.
Agreenroomtemperatureup-conversionlaserwasdemon-stratedina120µmdiametermicrosphereofEr3+dopedZBLAN[182],[183].Lasingoccurredaround540nmwitha801nmdiodelaserpump.Thelasingthresholdwas30µWofabsorbedpumppower.
Experimentalresultsontherealizationandspectralcharac-terizationofEr:ZBLANmicrosphericallasersat1.56µmwerepresentedin[184],[185].Thelasingwasobtainedwiththeexternal1.48µmpumping.Multimodeoperationandalaserthresholdaslowas600µWwereobserved.
Greenlasinghaving4mWthresholdwasdemonstratedinanerbium-ion-doped uoro-zirconateglassWGR[186].Peri-odicnarrowpeaksoftheemissionspectracorrespondingtotheWGRswereobserved.
Anerbium-dopedmicrolaseronsilicon,operatingatwave-lengthof1.5µmandcharacterizedwithpumpthresholdaslowas4.5µW,wasdemonstratedin[187].The40-µmdi-ametertoroidallaserWGRwasmadeusingacombinationoferbiumionimplantation,photolithography,wetanddryetch-ing,andlaserannealing,usingathermallygrownSiO2 lmonaSisubstrateasastartingmaterial.Singlemodelasingwasobserved.
Anothererbium-dopedhigh-QsilicatoroidalWGRmicro-laser(25–80µmindiameter)wasdemonstratedin[188].TheWGRwascoupledwithataperedoptical ber.Erbiumioncon-centrationswereintherange0.009–0.09at.%.Thresholdpumppowerwasaslowas4.5µW.
ATm3+-dopedtelluriteglassWGRlaserwasdiscussedin[189].Thelaser,pumpedat800nmwithataperedopti-cal ber,oscillatesinboththeSbandandthe1.9-µmband.Thepeakat1.5µm(S-band)correspondstoemissionofthe3
H4→3F4transition,whilethepeakat1.9µmcorrespondstothe3F4→3H6transition.
Numericalanalysisofamicrodisklaser,takingintoaccountfullgainsaturationeffectandthevectorcharacterofthe eld,waspresentedin[190].TheauthorssuggestedthatNd:YAGmicrodisklasersaretheexcellentcandidatesforalightsourceforoptical bercommunicationsoperatingat1.064and1.3µm.Atheoreticalstudyofthein uenceofdeformationofaWGRonlasingpropertieswasreportedin[191].
3)LasinginCoatedWGRs:Insteadofusingdopedmateri-als,apassiveWGRcanbecoatedwithgainmedium.Forex-ample,erbium-dopedsolgel lmswereappliedtothesurfaceofsilicamicrospherestocreatelow-thresholdWGRlasers[192].Lasingactioninanultra-high-QsphericalWGRcoatedwithgainmediumwasreportedin[193].
LasinginasquarecavitywithroundcornerscoatedwithpolymethylmethacrylateandwithRhodamine6Gmolecules,wasstudiedin[194].Athingainlayerwascoatedonlyontheouterboundaryofcavity.Thethicknessofthegainlayervariedfromonemicrometertoseveralmicrometers.
Ultravioletmicrodisklasersonsiliconsubstratewithalayerofzincoxidegainmediumgrownontopofthesilicamicrodisksweredemonstratedin[195].LasingoccursintheWGRsatroomtemperature.ThehybridZnO–SiO2WGRwasopticallypumpedbythethirdharmonics(355nm)ofamode-lockedNd:YAGlaserwith～10Hzrepetitionrateand20pspulsewidth.Amicroscopeobjectivelensisusedforfocusingpumplightontheresonatoraswellasforcollectingtheultravioletemissionat～390nm.AWGM-enhancedinelasticemissionfromamonolayerofA488 uorophoresonthesurfaceofa9.8µmWGR(polystyrenebeadtrappedinanopticaltrap)wasobservedandreported[196].ItwaspointedoutthatitwaslikelythattheWGM-enhancedemissionisduetoA488lasing,withalasingthresholdbetween0.29and0.87W·cm 2.