Fiber-OpticCommunicationTechnologyChapter3OpticalTransmittersFiber-OpticCommunicationTech2022/12/16OE,HUST2Chapter3.OpticalTransmittersIntroductionBasicconceptsSemiconductorlasers(LaserDiode)LaserCharacteristicsLight-EmittingDiodes(LED)TransmitterDesign2022/12/11OE,HUST2Chapter3.2022/12/16OE,HUST3Opticaltransmitter：光發射機LED:發光二極管LD：激光二極管Spontaneousemission：自發輻射Stimulatedemission：受激發射Stimulatedabsorption：受激吸收Boltzmanstatistics：玻爾茲曼統計分布Thermalequilibrium：熱平衡Spectraldensity：光譜密度Populationinversion：粒子數反轉Fermi-Diracdistribution：費米狄拉克分布Conductionband：導帶Valenceband：價帶Forward-biased：正向偏置Junction：結Fermilevel：費米能級Bandgap：帶隙Heavydoping：重摻雜Homojunction：同質結Heterojunction：異質結Doubleheterostructure：雙異質結Electron-holerecombination：電子空穴復合Claddinglayer：包層Augerrecombination：俄歇復合Kineticenergy：動能Nonradiativerecombination：非輻射復合Surfacerecombination：表面復合Internalquantumefficiency：內量子效率Directbandgap：直接帶隙Indirectbandgap：非直接帶隙Carrierlifetime：載流子壽命Latticeconstant：晶格常數Ternaryandquaternarycompound：三元系和四元系化合物Substrate:襯底LPE：液相外延VPE：汽相外延MBE：分子束外延MOCVD：改進的化學汽相沉積MQW:多量子阱2022/12/11OE,HUST3Opticaltra2022/12/16OE,HUST4Electron-holepairs電子空穴對Externalquantumefficiency外量子效率Fresneltransmissivity菲涅耳透射率Lambertiansource朗伯光源Power-conversionefficiency功率轉換效率Wall-plugefficiency電光轉換效率Responsivity響應度Rateequation速率方程Surface-emitting表面發射Beamdivergence光束發散Edge-emitting邊發射Resonantcavity諧振腔Gaincoefficient增益系數Differentialgain微分增益Laserthreshold激光閾值Thresholdcurrent閾值電流Groupindex群折射率Externalcavity外腔Broadarea寬面Stripegeometry條形Diffusion擴散Index-guided折射率導引Ridgewaveguidelaser脊波導激光器Buriedheterostructure掩埋異質結Lateral側向Transverse橫向SLM:SingleLongitudinalmode單縱模MSR:Modesuppressionratio模式抑制比DFB:DistributedFeedback分布式反饋Braggdiffraction布拉格衍射Braggcondition布拉格條件DBR:distributedBraggreflector分布式布拉格反射器Phase-shiftedDFBlaser相移DFB激光器Gaincoupled增益耦合Coupledcavity耦合腔2022/12/11OE,HUST4Electron-ho2022/12/16OE,HUST5Superstructuregrating超結構光柵VCSEL:verticalcavitysurface-emittinglasers垂直腔表面發射激光器Photonlifetime光子壽命Spontaneous-emissionfactor自發輻射因子Characteristicstemperature特征溫度Slopeefficiency斜率效率Differentialquantumefficiency微分量子效率Linewidthenhancementfactor線寬加強因子2022/12/11OE,HUST5Superstruct2022/12/16OE,HUST63.1Introduction3.1.1ComponentsofOpticalTransmittersBinarytosingleCoding/linecodingModulatorOpticalSourceDrivingCircuitPCMChannelcouplerOpticalsignaloutput2022/12/11OE,HUST63.1Introdu2022/12/16OE,HUST7BiasedcurrentModulationcurrent(≥10Gb/s)ModulationcurrentBiasedcurrent(≤2.5Gb/s)(a)DirectModulation(b)ExternalModulation2022/12/11OE,HUST7Biasedcurr2022/12/16OE,HUST81.stability:power&wavelength2.reliability:>25years(PouttoPout/2)3.smallemissiveareacompatiblewithfibercoredimensions4.rightwavelengthrange0.85μm:GaAlAs/GaAs1.31μm,1.55μm:InP/InGaAsP5.narrowlinewidth→dispersion,phasenoise6.directmodulation!?7.highefficiency&lowthreshold:MQW-LD,Ith~10mA3.1.2RequirementsforOpticalSourceMQWDFBLD2022/12/11OE,HUST81.stabilit2022/12/16OE,HUST9Chapter3.OpticalTransmittersIntroductionBasicconceptsSemiconductorlasers(LaserDiodes)LaserCharacteristicsLight-EmittingDiodes(LED)TransmitterDesign2022/12/11OE,HUST9Chapter3.2022/12/16OE,HUST103.2.1Threefundamentaltransitionprocesses 1.SpontaneousEmission→LED 2.StimulatedEmission→LD,SOA 3.StimulatedAbsorption→PIN/APD

3.2BasicConceptsLightEmission2022/12/11OE,HUST103.2.1Thre2022/12/16OE,HUST113.2.2EmissionandAbsorptionRatesE2N2N1E1:spectraldensityoftheelectromagneticenergyInthermalequilibrium,accordingtoBoltzmannStatistics:kB:BoltzmannConstantT:AbsoluteTemperatureAccordingtoPlanck’sformula:2022/12/11OE,HUST113.2.2Emis2022/12/16OE,HUST12visibleornear-infraredregion,roomtemperature,thermalsourcesN2>N1,Rstim>Rabs(populationinversion)thermalequilibrium laseroperation ?Operationconditionforlaser:Externalpumpingsourceisneeded:injectioncurrent,pumpinglightetc.2022/12/11OE,HUST12visibleor2022/12/16OE,HUST13原子是由原子核和繞原子核旋轉的電子組成。最里層的電子距原子核最近，受原子核束縛最強，能量最低（包括電子的動能和勢能）。越外層的電子受原子束縛越弱，能量越高；電子只能處于特定的能級之上；能級圖用一系列高低不同的水平橫線來表示電子所能取的確定能量；原子中的電子通過和外界交換能量的方式發生能級的躍遷——熱躍遷和光躍遷。Energybandsinsemiconductorconductionband&valenceband2022/12/11OE,HUST13原子是由原子核和繞原2022/12/16OE,HUST14實際物體是由大量原子構成的，每一原子的電子特別是外層電子除受本身原子的勢場作用外，還受到相鄰原子的作用。半導體材料中原子在共價鍵的作用下形成緊密相間、周期排列的晶格結構。電子能級受晶格作用發生分裂而形成能帶；Si2022/12/11OE,HUST14實際物體是由大量原子2022/12/16OE,HUST15價帶：由共價鍵束縛的價電子所占據的能帶為價帶；導帶：由自由電子占據的能帶為導帶，導帶位于價帶之上；禁帶：導帶和價帶之間被寬度為Eg的帶隙分開，稱為禁帶；絕緣體：Eg～7eV，電子不容易躍遷到導帶；半導體：Eg～1eV，電子容易躍遷到導帶；導體：Eg～0eV，沒有帶隙。2022/12/11OE,HUST15價帶：由共價鍵束縛的2022/12/16OE,HUST16EnergybandsinsemiconductorrecombinationbetweenelectronsandholesTheoccupationprobabilityforelectronsintheconductionandvalencebandsisgivenbytheFermi-Diracdistributions:Efc,EfvaretheFermilevelsinconductionbandandvalencebandrespectively2022/12/11OE,HUST16Energyban2022/12/16OE,HUST17:jointdensityofstates,whichdescribethenumberofstatesperunitvolumeperunitenergyrangeEg:bandgapmr:reducedmassmc,mv:effectivemassesofelectrons&holesinconductionandvalencebands,respectively2022/12/11OE,HUST17:jointd2022/12/16OE,HUST18population-inversioncondition:

inthermalequilibrium:pumpingenergyintosemiconductorbyinjectingcurrent

Togetlaseroutput,2022/12/11OE,HUST18population2022/12/16OE,HUST191.

TypeofsemiconductorIntrinsicsemiconductor:undoped,Fermilevelislyinginthemiddleofthebandgapn-typesemiconductor:Fermilevelmovestowardtheconductionbandasthedopantconcentrationincreasesp-typesemiconductor:Fermilevelmovestowardthevalencebandasthedopantconcentrationincreases3.2.3p-njunctions2022/12/11OE,HUST191.Typeof2022/12/16OE,HUST20

n-typeIntrinsic

p-typeforwardbiasedp-typesemiconductor

&n-typesemiconductor2022/12/11OE,HUST20n-typeInt2022/12/16OE,HUST21(a)inthermalequilibrium(b)underforwardbiased2.p-njunctionsunderforwardbiased:built-inelectricfieldisreduceddiffusionofelectronsandholesacrossthejunctionelectronsandholesarepresentsimultaneouslyindepletionregiongeneratelightthroughspontaneousemissionorstimulatedemissioninthermalequilibrium:

theFermilevelmustbecontinuousacrossthep–njunctionachievedthroughdiffusionofelectronsandholesacrossthejunction.2022/12/11OE,HUST21(a)inthe2022/12/16OE,HUST22Homojunction:equalbandgapsthesamesemiconductormaterialwideregionforelectron-holerecombinationdifficulttorealizehighcarrierdensitiesHeterojunction:differentbandgapsDouble-heterojunction:

sandwichingathinlayerbetweenthep-typeandn-typelayerssuchthatthebandgapofthesandwicheslayerissmallerthanthelayersurroundingit.4.Homojunction&heterojunction2022/12/11OE,HUST22Homojuncti2022/12/16OE,HUST232022/12/11OE,HUST232022/12/16OE,HUST24Activelayer:lightisgeneratedinsideitasaresultofelectron-holerecombinationhigherdensityofcarriers→higherindex→waveguide(1D)Heterojunction:confinementofcarriers&opticalfield0.85μm:cladding/active:GaAlAs/GaAs1.31μm,1.55μm:cladding/active:InP/InGaAsP2022/12/11OE,HUST24Activelay2022/12/16OE,HUST251.electron-holerecombination3.2.4NonradiativeRecombinationTrapofdefectsSurfacerecombinationAugerNonradiativerecombination2022/12/11OE,HUST251.electro2022/12/16OE,HUST262.internalquantumefficiencyRrr:radiativerecombinationrateRnr:nonradiativerecombinationrateRtot:totalrecombinationrateτ:recombinationtimeNonradiativerecombination,especiallyAugerrecombination(temperaturedependent)isharmfultodevices!positivefeedback

2022/12/11OE,HUST262.interna2022/12/16OE,HUST27E0E0k1k2(1)direct-bandgap(GaAs,InP)(2)indirect-bandgap(Si,Ge)3.carrierlifetimeA:defects&trapsB:spontaneousradiationC:Auger2022/12/11OE,HUST27E0E0k1k2(12022/12/16OE,HUST28Qualityoftheheterojunctioninterfacedependsonthelatticeconstantofthetwomaterials.(matching!)3.2.5SemiconductorMaterialsternarycompound2022/12/11OE,HUST28Quali2022/12/16OE,HUST29quaternarycompound0.85μm:GaAlAs/GaAs(cladding/active)

1.31μm,1.55μm:InP/InGaAsP(cladding/active)2022/12/11OE,HUST29quaternary2022/12/16OE,HUST302022/12/11OE,HUST302022/12/16OE,HUST31Chapter3.OpticalTransmittersIntroductionBasicconceptsSemiconductorlasers(LaserDiodes)LaserCharacteristicsLight-EmittingDiodes(LED)TransmitterDesign2022/12/11OE,HUST31Chapter3.2022/12/16OE,HUST323.3Semiconductorlasers(LaserDiodes)Advantagesofstimulatedemissioncomparedwithspontaneousemissionofsemiconductormaterialsemittinghighpower(to100mW)narrowangularspreadnarrowspectralwidthdirectmodulationathighfrequency(to10GHz,becauseissmall)2022/12/11OE,HUST323.3Semico2022/12/16OE,HUST33ComponentsofSemiconductorLasers2022/12/11OE,HUST33Components2022/12/16OE,HUST34z=0z=LInjectioncurrentGainmediumResonantcavityResonantcavityModeloflaser2022/12/11OE,HUST34z=0z=LInje2022/12/16OE,HUST353.3.1OpticalGainPeakgainofmedium:

when :differentialgain(gaincrosssection) :injectioncarrierdensity :transparentcarrierdensity:thresholdcarrierdensityNTisequaltoNth?2022/12/11OE,HUST353.3.1Opti2022/12/16OE,HUST36Figure3.9:(a)Gainspectrumofa1.3-μmInGaAsPlaseratseveralcarrierdensitiesN.(b)Variationofpeakgaingp

withN.Thedashedlineshowsthequalityofalinearfitinthehighgainregion.Blueorredshiftingofpeakwavelengthwheninjectedcurrentincreases?2022/12/11OE,HUST36Figure3.92022/12/16OE,HUST373.3.2FeedbackandLaserThresholdFeedbackR1R2n0=1n2022/12/11OE,HUST373.3.2Feed2022/12/16OE,HUST38Threshold2022/12/11OE,HUST38Threshold2022/12/16OE,HUST39AmplitudeconditionPhaseconditionspacingofoscillatingfrequencyoscillatingfrequencythresholdgainMLM2022/12/11OE,HUST39Amplitude2022/12/16OE,HUST403.3.3LDStructuresBroad-areaLDFigure3.12:Abroad-areasemiconductorlaser.Theactivelayer(hatchedregion)issandwichedbetweenp-typeandn-typecladdinglayersofahigher-bandgapmaterial.light-confinementmechanisminthedirectionperpendiculartothejunctionplaneintroducedbydoubleheterostructure

XYdistributioninnearfield2022/12/11OE,HUST403.3.3LDS2022/12/16OE,HUST41nosuchlight-confinementmechanisminthelateraldirectionparalleltothejunctionplane.thelightgeneratedspreadsovertheentirewidthofthelaser.relativelyhighthresholdcurrentandaspatialpatternthatishighlyellipticalandthatchangesinanuncontrollablemannerwiththecurrent.Howaboutspatialmodeinwaveguideanddistributioninfarfield?2022/12/11OE,HUST41nosuchli2022/12/16OE,HUST42Gain-guidedsemiconductorlasersFigure3.13:Crosssectionoftwostripe-geometrylaserstructuresusedtodesigngain-guidedsemiconductorlasersandreferredtoas(a)oxidestripeand(b)junctionstripe.Stripelasers

XY2022/12/11OE,HUST42Gain-guid2022/12/16OE,HUST43solvethelight-confinementproblembylimitingcurrentinjectionoveranarrowstripe.thespotsizeisstillnotstableasthelaserpowerisincreased.Injectioncurrentinducedindexvariety!2022/12/11OE,HUST43solvethe2022/12/16OE,HUST44Index-guidedsemiconductorlasersFigure3.14:Crosssectionoftwoindex-guidedsemiconductorlasers:(a)ridge-waveguidestructureforweakindexguiding;(b)etched-mesaburiedheterostructureforstrongindexguiding.

XY2022/12/11OE,HUST44Index-gui2022/12/16OE,HUST45Multi-Quantum-WellLD有源區厚度薄1~10nm周期結構，將窄帶隙的很薄的有源區夾在寬帶隙的半導體材料之間，形成勢能阱多個勢能阱--多量子阱（MQW）2022/12/11OE,HUST45Multi-Quan2022/12/16OE,HUST46homojunctionDoubleheterostructureStripegeometryMulti-quantum-wellRelativelystrongerconfinementofinjectedcarriersandoutputphotons,thuslowerthresholdcurrent,andhigherslopeefficiency!2022/12/11OE,HUST46homojuncti2022/12/16OE,HUST473.3.4ControlofLongitudinalModesSideModeSuppressionRatio(SMSR):orMLMLossSLM2022/12/11OE,HUST473.3.4Cont2022/12/16OE,HUST48DistributedFeedback(DFB)Lasers

相位光柵在波導中產生折射率的周期性變化，使正反向傳播的行波產生耦合。當光波長滿足布拉格條件時，耦合達到最大。在布拉格條件下，某一入射波長幾乎被全反射，光柵起到了對波長選擇性反射的作用。光柵周期滿足：2022/12/11OE,HUST48Distribute2022/12/16OE,HUST49Coupled-cavitylaserFigure3.18:Coupled-cavitylaserstructures(a)external-cavitylaser;(b)cleaved-coupledcavitylaser;(c)multisectionDBRlaser.2022/12/11OE,HUST49Coupled-ca2022/12/16OE,HUST50

增益介質反射鏡準直透鏡透鏡光纖增透膜濾光片高反膜λcExternalcavitylaser2022/12/11OE,HUST50增益介質2022/12/16OE,HUST51SampledGratingDBRLaserDBR:distributedBraggreflector2022/12/11OE,HUST51SampledGr2022/12/16OE,HUST52Cleaved-coupledcavitylaser2022/12/11OE,HUST52Cleaved-co2022/12/16OE,HUST53VCSEL2022/12/11OE,HUST53VCSEL2022/12/16OE,HUST54思考題1.現有半導體激光器的F-P諧振腔，長度為400m，材料折射率為3.5，諧振腔兩端面一端鍍有增反射膜，反射率為90％，另一端沒有鍍膜。現有半導體激光器工作在1550nm附近，要求諧振腔諧振的閾值增益系數小于75cm－1，請問：如何選擇半導體材料和組分？諧振腔內部損耗系數應滿足什么條件？2022/12/11OE,HUST54思考題1.現有半導2022/12/16OE,HUST55Chapter3.OpticalTransmittersIntroductionBasicconceptsSemiconductorlasers(LaserDiodes)LaserCharacteristicsLight-EmittingDiodes(LED)TransmitterDesign2022/12/11OE,HUST55Chapter3.2022/12/16OE,HUST563.4LaserCharacteristics

3.4.1CWCharacteristicsForaSLMlaser,therateequations:P,N:numberofphotons&carriersNetrateofstimulatedemission—opticalgain:g:peakgainofmaterial:gaincrosssection,ordifferentialgain.Photonlifetime:2022/12/11OE,HUST563.4Laser2022/12/16OE,HUST57Thresholdofcurrent&carrierForI>Ith(R1=R2)CWoperation:2022/12/11OE,HUST57Threshold2022/12/16OE,HUST58ThresholdofP-IcurvesSpontaneousemissionStimulatedemissionI0:constantT0:characteristictemperatureGaAs:T0=120K,InGaAsP:T0=50~70KP-IcurvesBendingofP-Icurves

Rnr:mainlydependingonAugerrecombinationinInGaAsPLDsSolution:built-inthermoelectriccoolerisusedtodealwithtemperaturesensitivitiesofInGaAsPLDs2022/12/11OE,HUST58Threshold2022/12/16OE,HUST59EfficienciesInternalquantumefficiency:Slopeefficiency:Differentialquantumefficiency:Externalquantumefficiency:wall-plugefficiency:2022/12/11OE,HUST59Efficienci2022/12/16OE,HUST603.4.2Small-SignalModulationsmall-signalmodulation:Frequencyresponse2022/12/11OE,HUST603.4.2Smal2022/12/16OE,HUST61Figure3.21:Modulationresponseofalaserasafunctionofmodulationfrequencyatseveralbiaslevels.ModulationbandwidththeefficiencyisreducedwhenthemodulationfrequencyexceedsΩR

byalargeamount.2022/12/11OE,HUST61Figure3.22022/12/16OE,HUST623.4.3Large-SignalModulationExternalmodulationforhighspeedtransmission!Frequencychirp

leadingedge:modefrequencyshiftstowardtheblue

sidetrailingedge:modefrequencyshiftstowardtheredside:amplitude-phasecouplingparameter,ex.bulkmaterial:4~8;MQW:~32022/12/11OE,HUST623.4.3Larg2022/12/16OE,HUST63Electro-opticalDelay&RelaxationOscillation

Pre-biasedtoreducedelaytime!請參見江劍平編著的《半導體激光器》2022/12/11OE,HUST63Electro-op2022/12/16OE,HUST64Patterneffect

TBIP“11”“11”當電光延遲時間與電調制速率對應的的碼元持續時間相近時，會使“0”碼后的第一個“1”碼脈沖寬度變窄，幅度變小，嚴重時使單個“1”碼丟失，這種現象即“碼型效應”。連“0”數越多，調制速率越高，該效應越明顯。用適當的“過調制”補償，可以消除碼型效應。2022/12/11OE,HUST64Patternef2022/12/16OE,HUST65Self-pulsation不同于張弛振蕩，沒有阻尼，脈動頻率范圍為0.2~4GHz容易發生在閾值附近和P-I特性的扭曲區造成自脈動的機理涉及量子噪聲效應、有源區的缺陷及溫度感應的變化等因素抑制這種現象主要靠控制材料的質量，盡量減少有源區的缺陷。Operatedfarfromkinkzone!OPIPI2022/12/11OE,HUST65Self-pulsa2022/12/16OE,HUST66Simulation1-Directmodulation2022/12/11OE,HUST66Simulation2022/12/16OE,HUST67Simulation2-Externalmodulation

2022/12/11OE,HUST67Simulation2022/12/16OE,HUST68Ib&ImLD偏置電流的選擇合適與否直接影響激光器的高速調制輸出特性。加大直流偏置，使其接近閾值，可以減小電光延遲時間，也可使張馳振蕩得到一定程度的抑制。當激光器偏置在閾值附近時，較小的調制電流就能得到足夠高的輸出光脈沖，調制效率較高。而且由于偏置電流與最大電流相差不大，可以大大減小碼型效應和結發熱效應的不良影響。過大的偏置電流會使消光比惡化，影響接收機靈敏度。激光器恰好偏置在閾值時，散粒噪聲會增強，直接影響信號的信噪比。2022/12/11OE,HUST68Ib&ImLD偏2022/12/16OE,HUST69Chapter3.OpticalTransmittersIntroductionBasicconceptsSemiconductorlasers(LaserDiodes)LaserCharacteristicsLight-EmittingDiodes(LED)TransmitterDesign2022/12/11OE,HUST69Chapter3.2022/12/16OE,HUST703.5.1Power-CurrentCharacteristics3.5Light-EmittingDiodes(LEDs)aforward-biasedp-njunction→spontaneousemission→LED2022/12/11OE,HUST703.5Light-2022/12/16OE,HUST712022/12/11OE,HUST712022/12/16OE,HUST72Power-conversionefficiency(wall-plugefficiency)2022/12/11OE,HUST72Power-conv2022/12/16OE,HUST73P-ICurveResponsivity:(1)responsivityremainsconstantwhenIissmall(2)bendingofP-Icurve:(3)nothreshold

2022/12/11OE,HUST73P-ICurveR2022/12/16OE,HUST743.5.2LEDSpectrumanapproximateexpression:LEDsaresuitableforLANwithlowbitrate&shortdistance!2022/12/11OE,HUST743.5.2LED2022/12/16OE,HUST75Figure3.7:(b)spectrumoftheemittedlightforatypical1.3-μmLED.超寬帶光源白光LED2022/12/11OE,HUST75Figure3.72022/12/16OE,HUST762022/12/11OE,HUST762022/12/16OE,HUST773.5.3ModulationResponseRateequation::injectioncarrier:carrierofrecombination(nonradiative&spontaneousemission)Sinusoidalmodulation:Ib:biascurrentIm:modulationcurrentωm:modulationfrequency2022/12/11OE,HUST773.5.3Modu2022/12/16OE,HUST78Sincemodulatedpowerisrelatedtolinearly2022/12/11OE,HUST78Sincemodu2022/12/16OE,HUST793.5.4LEDStructures(a)(b)(a)surface-emittingLED(b)edge-emittingLED2022/12/11OE,HUST793.5.4LED2022/12/16OE,HUST80思考題1.以下論述正確的是：（）A、非輻射復合會影響發光器件的發光效率；B、正向偏置的PN結中導帶和價帶的準費米能級趨于一致；C、半導體材料要發光，必須實現粒子數的反轉；D、LED中最初的光子來源于內部的自發輻射；E、電子與空穴復合不一定產生光子；F、雙異質結結構提高了半導體光源的量子效率；G、工作于1.55m處的半導體光源有源層材料為InP；

H、溫度升高發光器件的發光效率會下降；

I、間接帶隙半導體材料中非輻射復合效率高于輻射復合效率，不適合用作光源材料。2022/12/11OE,HUST80思考題1.以下論述2022/12/16OE,HUST811.以下論述正確的是：（）

A、非輻射復合會影響發光器件的發光效率；

B、正向偏置的PN結中導帶和價帶的準費米能級趨于一致；C、半導體材料要發光，必須實現粒子數的反轉；

D、LED中最初的光子來源于內部的自發輻射；

E、電子與空穴復合不一定產生光子；

F、雙異質結結構提高了半導體光源的量子效率；G、工作于1.55m處的半導體光源有源層材料為InP；

H、溫度升高發光器件的發光效率會下降；

I、間接帶隙半導體材料中非輻射復合效率高于輻射復合效率，

不適合用作光源材料。2022/12/11OE,HUST811.以下論述正確的2022/12/16OE,HUST82A、LD的激射波長一定是自發輻射的峰值波長；B、條形激光器中也存在雙異質結結構；C、雙異質結中對載流子的限制作用是因為存在內建折射率波導；D、通過選擇合適的組分x和y，基于In1-xGaxAsyP1-y的半導體光源可設計工作于0.85m處；E、LD有諧振腔，而LED沒有；F、LD的P-I曲線有閾值，而LED的P-I曲線沒有閾值；G、LD和SOA中最初的光子均來源于自發輻射；H、激光器的小信號調制帶寬會隨著偏置電流的增加而增大；I、偏置電流選擇合理可適當減小張馳振蕩和電光延時效應的影響；J、單縱模LD用作光源時，色散容限大。

2.以下關于半導體材料和發光機理論述錯誤的是：2022/12/11OE,HUST822.以下關于半導2022/12/16OE,HUST83

A、LD的激射波長一定是自發輻射的峰值波長；B、條形激光器中也存在雙異質結結構；

C、雙異質結中對載流子的限制作用是因為存在內建折射率波導；

D、通過選擇合適的組分x和y，基于In1-xGaxAsyP1-y的半導體光源可設計工作于0.85m處；E、LD有諧振腔，而LED沒有；F、LD的P-I曲線有閾值，而LED的P-I曲線沒有閾值；

G、LD和SOA中最初的光子均來源于自發輻射；H、激光器的小信號調制帶寬會隨著偏置電流的增加而增大；I、偏置電流選擇合理可適當減小張馳振蕩和電光延時效應的影響；J、單縱模LD用作光源時，色散容限大。

2.以下關于半導體材料和發光機理論述錯誤的是：2022/12/11OE,HUST832.以下關于半導2022/12/16OE,HUST84Chapter3.OpticalTransmittersIntroductionBasicconceptsSemiconductorlasers(LaserDiodes)LaserCharacteristicsLight-EmittingDiodes(LED)TransmitterDesign2022/12/11OE,HUST84Chapter3.2022/12/16OE,HUST85

3.6.1BasicconceptAnalog&DigitalModulation3.6TransmitterDesign(a)LEDanalogmodulation(b)LEDdigitalmodulation(c)LDdigitalmodulationforLD,biasednearthreshold!2022/12/11OE,HUST85 3.6.1Bas2022/12/16OE,HUST86DigitalLogicElectricalLevel

0

1 TTL:0~0.8V 2.0~5.0V (-5V)ECL:-1.75V -0.85 V (+5V)PECL:+3.25V +4.15 VExtinctionRatioPP1P00t2022/12/11OE,HUST86DigitalLo2022/12/16OE,HUST87Source-fibercoupling

Packaging

sourcefiberRfcoatinglensedfiberdiesubmountPDheatsinkTECcoolerfibermetalshell2022/12/11OE,HUST87Source-fib2022/12/16OE,HUST882022/12/11OE,HUST882022/12/16OE,HUST89ButterflypackagedLD2022/12/11OE,HUST89Butterfly2022/12/16OE,HUST90ExternalModulator

LiNbO3modulatorinMach-ZehnderconfigurationV2022/12/11OE,HUST90ExternalM2022/12/16OE,HUST91EA

0V=0V(t)TT1T2λ2022/12/11OE,HUST91EA0V=0V(t)2022/12/16OE,HUST923.6.2DrivingcircuitDigitalmodulationcircuitwithAPCforLD2022/12/11OE,HUST923.6.2Dri2022/12/16OE,HUST93射極耦合電路三極管T1和T2是輪流截止和導通的，避免了載流子恢復時間的影響，因而可工作于更高的速率；射極耦合電路為恒流源，總電源電流可以保持不變，所以電源電流噪聲小；D1和D2是溫度補償二極管，由于D1、D2、T2和T3的導通電壓分別有－2.5mV/C的負溫度特性，利用D1、D2對T2、T3的溫度特性進行補償，使溫度變化時驅動電流保持恒定。LD2022/12/11OE,HUST93射極耦合電路三極管T2022/12/16OE,HUST94APC電路2022/12/11OE,HUST94APC電路2022/12/16OE,HUST95ATC電路2022/12/11OE,HUST95ATC電路2022/12/16OE,HUST96Review光纖通信對光源的要求，光譜線寬和閾值電流。半導體發光的物理基礎：三種躍遷過程，費米能級，粒子數反轉，正向偏置PN結，雙異質結結構對半導體發光器件的性能改善，非輻射復合及其危害，如何決定半導體材料的組分。LED的特性，為什么LED適合用在短距離、低速、模擬通信中？LD的工作條件，閾值條件，縱模條件。LD的典型結構，增益導引和折射率導引條形激光器，同質結、異質結、條形激光器、多量子阱結構如何實現閾值電流的降低和輸出功率的提高？如何實現單縱模？DBR、DFB、外腔、VCSEL的基本原理。LD的工作特性：P-I特性,大信號調制的瞬態效應。光發射機驅動電路，LED和LD驅動電路的不同，PI曲線表示調制過程，帶光反饋的LD數字驅動電路。2022/12/11OE,HUST96ReviewFiber-OpticCommunicationTechnologyChapter3OpticalTransmittersFiber-OpticCommunicationTech2022/12/16OE,HUST98Chapter3.OpticalTransmittersIntroductionBasicconceptsSemiconductorlasers(LaserDiode)LaserCharacteristicsLight-EmittingDiodes(LED)TransmitterDesign2022/12/11OE,HUST2Chapter3.2022/12/16OE,HUST99Opticaltransmitter：光發射機LED:發光二極管LD：激光二極管Spontaneousemission：自發輻射Stimulatedemission：受激發射Stimulatedabsorption：受激吸收Boltzmanstatistics：玻爾茲曼統計分布Thermalequilibrium：熱平衡Spectraldensity：光譜密度Populationinversion：粒子數反轉Fermi-Diracdistribution：費米狄拉克分布Conductionband：導帶Valenceband：價帶Forward-biased：正向偏置Junction：結Fermilevel：費米能級Bandgap：帶隙Heavydoping：重摻雜Homojunction：同質結Heterojunction：異質結Doubleheterostructure：雙異質結Electron-holerecombination：電子空穴復合Claddinglayer：包層Augerrecombination：俄歇復合Kineticenergy：動能Nonradiativerecombination：非輻射復合Surfacerecombination：表面復合Internalquantumefficiency：內量子效率Directbandgap：直接帶隙Indirectbandgap：非直接帶隙Carrierlifetime：載流子壽命Latticeconstant：晶格常數Ternaryandquaternarycompound：三元系和四元系化合物Substrate:襯底LPE：液相外延VPE：汽相外延MBE：分子束外延MOCVD：改進的化學汽相沉積MQW:多量子阱2022/12/11OE,HUST3Opticaltra2022/12/16OE,HUST100Electron-holepairs電子空穴對Externalquantumefficiency外量子效率Fresneltransmissivity菲涅耳透射率Lambertiansource朗伯光源Power-conversionefficiency功率轉換效率Wall-plugefficiency電光轉換效率Responsivity響應度Rateequation速率方程Surface-emitting表面發射Beamdivergence光束發散Edge-emitting邊發射Resonantcavity諧振腔Gaincoefficient增益系數Differentialgain微分增益Laserthreshold激光閾值Thresholdcurrent閾值電流Groupindex群折射率Externalcavity外腔Broadarea寬面Stripegeometry條形Diffusion擴散Index-guided折射率導引Ridgewaveguidelaser脊波導激光器Buriedheterostructure掩埋異質結Lateral側向Transverse橫向SLM:SingleLongitudinalmode單縱模MSR:Modesuppressionratio模式抑制比DFB:DistributedFeedback分布式反饋Braggdiffraction布拉格衍射Braggcondition布拉格條件DBR:distributedBraggreflector分布式布拉格反射器Phase-shiftedDFBlaser相移DFB激光器Gaincoupled增益耦合Coupledcavity耦合腔2022/12/11OE,HUST4Electron-ho2022/12/16OE,HUST101Superstructuregrating超結構光柵VCSEL:verticalcavitysurface-emittinglasers垂直腔表面發射激光器Photonlifetime光子壽命Spontaneous-emissionfactor自發輻射因子Characteristicstemperature特征溫度Slopeefficiency斜率效率Differentialquantumefficiency微分量子效率Linewidthenhancementfactor線寬加強因子2022/12/11OE,HUST5Superstruct2022/12/16OE,HUST1023.1Introduction3.1.1ComponentsofOpticalTransmittersBinarytosingleCoding/linecodingModulatorOpticalSourceDrivingCircuitPCMChannelcouplerOpticalsignaloutput2022/12/11OE,HUST63.1Introdu2022/12/16OE,HUST103BiasedcurrentModulationcurrent(≥10Gb/s)ModulationcurrentBiasedcurrent(≤2.5Gb/s)(a)DirectModulation(b)ExternalModulation2022/12/11OE,HUST7Biasedcurr2022/12/16OE,HUST1041.stability:power&wavelength2.reliability:>25years(PouttoPout/2)3.smallemissiveareacompatiblewithfibercoredimensions4.rightwavelengthrange0.85μm:GaAlAs/GaAs1.31μm,1.55μm:InP/InGaAsP5.narrowlinewidth→dispersion,phasenoise6.directmodulation!?7.highefficiency&lowthreshold:MQW-LD,Ith~10mA3.1.2RequirementsforOpticalSourceMQWDFBLD2022/12/11OE,HUST81.stabilit2022/12/16OE,HUST105Chapter3.OpticalTransmittersIntroductionBasicconceptsSemiconductorlasers(LaserDiodes)LaserCharacteristicsLight-EmittingDiodes(LED)TransmitterDesign2022/12/11OE,HUST9Chapter3.2022/12/16OE,HUST1063.2.1Threefundamentaltransitionprocesses 1.SpontaneousEmission→LED 2.StimulatedEmission→LD,SOA 3.StimulatedAbsorption→PIN/APD

3.2BasicConceptsLightEmission2022/12/11OE,HUST103.2.1Thre2022/12/16OE,HUST1073.2.2EmissionandAbsorptionRatesE2N2N1E1:spectraldensityoftheelectromagneticenergyInthermalequilibrium,accordingtoBoltzmannStatistics:kB:BoltzmannConstantT:AbsoluteTemperatureAccordingtoPlanck’sformula:2022/12/11OE,HUST113.2.2Emis2022/12/16OE,HUST108visibleornear-infrared