复试笔试5g5电子器件-固态课件2009-2010chapter

LED(LightEmittingIndexofrefraction折射率Graded-indexfiber渐变型光纤Stepindexfiber突变型光纤Multimodefibers多模光纤

binary二元的ternary三元的quaternary四元Single-modefibers单模光 Spontaneousemission自发辐射Stimulatedemission受激辐射Infrared红 phonon声子Light-emittingdiode(LED)发光二极Underforwardbiased,theinjectedcarrierswilldiffuseUnderforwardbiased,theinjectedcarrierswilldiffuse process,theenergywillbereleased.PrincipleofForamaterialwithadirectbandgap,theenergywillbeForamaterialwithadirectbandgap,theenergywillbelightemission. ratorsoftkEfficient efectForamaterialwithanindirectbandgap,suchasSior releasestheheattothelattice.Themomentumwillchangewhenthe Aphononandaphotonwillbereleased.hForamaterialwithanindirectbandgap,suchasSior releasestheheattothelattice.Themomentumwillchangewhenthe Aphononandaphotonwillbereleased. kALEDisanincoherentlightsource,inthatphotonsareemittedrandomlyfromthejunctioninalldirectionsandnotinphasewitheachother.Light-EmittingMaterialandradiatingwavelengthsDifferentmaterialhavedifferentbandgap,therefore,differentemissionBinarycompounds:fromGaN(3.4eV)toInSb(0.18eV),correspondingtofromblue(orultraviolet)toinfrared; GaP:Eg=2.26eV(green) Ternarycompounds:Ternarycompounds:GaAs1-indisplayredQuaternarycompounds:InAlGaPetal.foryellowandgreenwavelengthregion.EnergyGaAs:Eg=1.43eV(infrared)?GaP:Eg=2.26eV(green) c

ch 1.24eV (mEhE EEh(GaAs)1.24 0.8671.4(GaP) 1.24 0.5492.2(GaN)1.24 0.3653.Somekindsof(1)EELED(EdgeEmittingLED,边发射发光二极管);(2)SELEDSurfaceEmittingLED，面OutputP-ICharacteristicsintP:outputpoweroflight

I:forwardbiasedP INq/

)/P[(It/q)E]/ (E/q)I Radiatedwavelengthoftenreferredtoasapeakwavelength,isdeterminedbybandgap,Eg;Spectrumwidth,,ismeasuredasfullwidthat um,~fromtoseveralhundredLightLightemittedfromaLEDisnotmonochromaticlight!FiberOpticLight ,

OpticalfiberAnouterlayerofverypurefusedsilicaAcoreofdopedglassIndexof

Single-mode单模光纤Multi-modefibers多模光纤（2a=50-突变型光纤(阶跃折射率光纤）index渐变（折射率）型光纤Indexprofile（折射率分布n r阶跃折射率分布(StepIndexfiber渐变折射率分布GI

n(r)n(r)n(r) )r121arr22

n r，22(cable)光缆Fabrication(光纤的制造硫硫化 Attenuationorloss(衰减或损耗I(x)I0

x

α(1/km)isattenuationcoefficient,andtheP(x)P0

x

attenuationisnotthesameforallwavelengths.A(dBA(dB/km)10log(out/in)/Loss(dB)10log(out/in1310nm:0.35-0.51550nm:0.2-850nm:2.3-3.4光纤熔接点损耗：0.2dB1点Dispersionisanotherimportantconsiderationinchoiceofoperatingwavelength.DispersioncancausesignalChromaticDispersion（材料色散）:wavelengthdependenceoftherefractiveindexAtλ=1.27μm,chromaticdispersionis Intermodaldispersion（模间色散）:differentmodespropagatewithdifferentpathlengths(itcanbereducedbygradingtheindexofthecore).Waveguidedispersion（波导色散）:smallpartofsignalpowerpropagateincladding,differentgroupvelocitiesbetweenthepowerpropagatingincoreandincladdingPhotonicCrystalPhotonicCrystalFiber(光子晶体光纤Bymakingasuitablegeometryoftheperiodicmedium,aphoniccrystalcanbeusedasanopticalLightofSomespontaneousemission(自发辐射)andstimulatedemission(受激辐射)StimulatedStimulatedStimulatedStimulatedThisradiationwillThisradiationwillmonochromaticsinceeachphotonwillhaveanenergyofpreciselyE21andwillbecoherent,allthephotonsreleasedbeindensity:thetotalenergyintheradiationfieldperunitvolumeandForclassicalparticles,at1ne(E2E1)/kT, 21fofo stead statW21：stimulatedemissionprobability;W12：stimulatedA21(dndt)sp/n2W21(dndt)st/2 2112);W12(dndt)st/ 11212)spontaneous ratestimulatedemission rateB21n2(12) rateA21,B21andB12arecalledEinsteindn1/dt (dn2/dt)sp(dn2/dt)sB12n1(12) A21n B21n2(12optical (Fabry- 腔stimulatedemissionrateB21n2(12)B21 Aspontaneous A

12Thewaytoenhancethestimulatedemissionistohavealargephotonfieldenergydensity(12):anopticalresonantinwhichthephotondensitycanbuilduptoalargevaluethroughmultipleinternalreflectionsatcertainfrequencies(12).L2HowHowtobuildThereTheremustbethemediuminthetoprovidethegain. stimulatedemissionrateB21n2(12)B21n2 Bn Ifstimulatedemissionistodominateoverabsorptionofphotonsfromtheradiationfield,wemusthaveaway