2019 光电子学第4章(lpl-2019)ppt课件.ppt

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1、1.Introduction2.SpontaneousandStimulatedEmission3.Thelaserstructure:theopticalcavity(光学谐振腔)4.Thelaserbelowandabovethresholdandstaticoutputproperties5.Advancedstructures:tailoringelectronicstructure6.Advancedstructures:tailoringthecavityChapter4LaserDi

2、ode:StaticProperties1.IntroductionThemainadvantageoftheLED:simplicityofthefabricationprocessLEDisanincoherentlightsource.ThekeydrawbacksoftheLED:smalloutputpower(several10mW)thebroadspectrumoftheemittedlightthedifficultyinpushingthemodulationbandwidtha

3、bove1GHzLEDisanincoherentlightsource.LASERDIODEe-hrecombinationinahighqualityopticalcavityLEDSpectraloutputisbroadTemporalresponseislimitedbyspontaneousemissionUseanopticalcavitytoenhanceemissionofcertainphotonstatesUsestimulatedemissiontoenhancee-hrec

4、ombinationratesImprovementsLDisacoherentlightsource,whichcanovercomethelimitsofLED.theoutputpowerofLDisupto3000WthelinewidthofLDistwoordersofmagnitudenarrowerthanthatofLEDthemodulationbandwidthofLDapproaches50GHzThestimulatedemissionprocessprovidesnarr

5、owspectrallinewidthofthephotonoutput,providescoherentphotons,andoffershighspeedperformance.Thus,thekeydifferencebetweentheLEDandthelaserdiodearisesfromdifferencebetweenspontaneousandsimulatedemission.2.SpontaneousandStimulatedEmissionAssumedtwoenergygr

6、adesbasicstateenergygradeatthetopofvalencebandstimulatedstateenergygradeatthebottomofconductionband●●●●StimulatedAbsorption(受激吸收)SpontaneousEmission(自发辐射)StimulatedEmission(受激辐射)Spontaneousemission:randomprocessemittingincoherentphotonsStimulatedemissi

7、on:emittingcoherentphotons(samephaseasthephotonscausingtheemission)(sameinenergy;differentinphaseanddirection)RateforspontaneousemissionRateforstimulatedemissionPhotonoccupationnumberWhensemiconductorstimulatedbyphotonswiththestimulatedradiationandthea

8、bsorptionbothmayoccur.Whichisdominant?Atequilibriumstate:thenumberofparticlesatE1:Reverseddistributionofparticles(粒子分布反转)thenumberofparticlesatE2:Atnon-equilibriumstatebycarriersinjectedtheoccupationprobabilities:Whensemiconductorstimul