双异质结结构提高了半导体光源的量子效率课件

Fiber-OpticCommunicationTechnologyChapter 3 Optical TransmittersFiber-Optic Communication Tech2024/6/16OE,HUST2Chapter3.OpticalTransmittersnIntroductionnBasic conceptsnSemiconductor lasers(Laser Diode)nLaser CharacteristicsnLight-Emitting Diodes(LED)nTransmitter Design2023/8/9OE,HUST2Chapter 3.O2024/6/16OE,HUST3Optical transmitter：光发射机LED:发光二极管LD：激光二极管Spontaneous emission：自发辐射Stimulated emission：受激发射Stimulated absorption：受激吸收Boltzman statistics：玻尔兹曼统计分布Thermal equilibrium：热平衡Spectral density：光谱密度Population inversion：粒子数反转Fermi-Dirac distribution：费米狄拉克分布Conduction band：导带Valence band：价带Forward-biased：正向偏置Junction：结Fermi level：费米能级Bandgap：带隙Heavy doping：重掺杂Homojunction：同质结Heterojunction：异质结Double heterostructure：双异质结Electron-hole recombination：电子空穴复合Cladding layer：包层Auger recombination：俄歇复合Kinetic energy：动能Nonradiative recombination：非辐射复合Surface recombination：表面复合Internal quantum efficiency：内量子效率Direct bandgap：直接带隙Indirect bandgap：非直接带隙Carrier lifetime：载流子寿命Lattice constant：晶格常数Ternary and quaternary compound：三元系和四元系化合物Substrate:衬底LPE：液相外延VPE：汽相外延MBE：分子束外延MOCVD：改进的化学汽相沉积MQW:多量子阱2023/8/9OE,HUST3Optical trans2024/6/16OE,HUST4Electron-hole pairs 电子空穴对External quantum efficiency 外量子效率Fresnel transmissivity 菲涅耳透射率Lambertian source 朗伯光源Power-conversion efficiency 功率转换效率Wall-plug efficiency 电光转换效率Responsivity 响应度Rate equation 速率方程Surface-emitting 表面发射Beam divergence 光束发散Edge-emitting 边发射Resonant cavity 谐振腔Gain coefficient 增益系数Differential gain 微分增益Laser threshold 激光阈值Threshold current 阈值电流Group index 群折射率External cavity 外腔Broad area 宽面Stripe geometry 条形Diffusion 扩散Index-guided 折射率导引Ridge waveguide laser 脊波导激光器Buried heterostructure 掩埋异质结Lateral 侧向Transverse 横向SLM:Single Longitudinal mode单纵模MSR:Mode suppression ratio 模式抑制比DFB:Distributed Feedback 分布式反馈Bragg diffraction 布拉格衍射Bragg condition 布拉格条件DBR:distributed Bragg reflector 分布式布拉格反射器Phase-shifted DFB laser 相移DFB激光器Gain coupled 增益耦合Coupled cavity 耦合腔2023/8/9OE,HUST4Electron-hole2024/6/16OE,HUST5Superstructure grating 超结构光栅VCSEL:vertical cavity surface-emitting lasers 垂直腔表面发射激光器Photon lifetime 光子寿命Spontaneous-emission factor 自发辐射因子Characteristics temperature 特征温度Slope efficiency 斜率效率Differential quantum efficiency 微分量子效率Linewidth enhancement factor 线宽加强因子2023/8/9OE,HUST5Superstructur2024/6/16OE,HUST63.1Introduction3.1.1ComponentsofOpticalTransmittersBinary to singleCoding/line codingModulatorOptical SourceDriving CircuitPCMChannel couplerOptical signal output2023/8/9OE,HUST63.1 Introduct2024/6/16OE,HUST7Biased current Modulation current(10Gb/s)Modulation currentBiased current(2.5Gb/s)(a)Direct Modulation(b)External Modulation2023/8/9OE,HUST7Biased curren2024/6/16OE,HUST81.stability:power&wavelength2.reliability:25 years(Pout to Pout/2)3.small emissive area compatible with fiber core dimensions4.right wavelength range 0.85 m:GaAlAs/GaAs 1.31 m,1.55 m:InP/InGaAsP5.narrow linewidth dispersion,phase noise6.direct modulation!?7.high efficiency&low threshold:MQW-LD,Ith 10mA3.1.2RequirementsforOpticalSourceMQW DFB LD2023/8/9OE,HUST81.stability 2024/6/16OE,HUST9Chapter3.OpticalTransmittersnIntroductionnBasic conceptsnSemiconductor lasers(Laser Diodes)nLaser Characteristics nLight-Emitting Diodes(LED)nTransmitter Design2023/8/9OE,HUST9Chapter 3.O2024/6/16OE,HUST103.2.1Threefundamentaltransitionprocesses1.Spontaneous Emission LED2.Stimulated Emission LD,SOA3.Stimulated Absorption PIN/APD 3.2BasicConceptsLight Emission2023/8/9OE,HUST103.2.1 Three 2024/6/16OE,HUST113.2.2EmissionandAbsorptionRatesE2N2N1E1:spectral density of the electromagnetic energyIn thermal equilibrium,according to Boltzmann Statistics:kB:Boltzmann ConstantT:Absolute TemperatureAccording to Plancks formula:2023/8/9OE,HUST113.2.2 Emissi2024/6/16OE,HUST12visible or near-infrared region,room temperature,thermal sourcesN2N1,RstimRabs(population inversion)thermal equilibrium laser operation?Operation condition for laser:External pumping source is needed:injection current,pumping light etc.2023/8/9OE,HUST12visible or n2024/6/16OE,HUST13n原子是由原子核和绕原子核旋转的电子组成。最里层的电子距原子核最近，受原子核束缚最强，能量最低（包括电子的动能和势能）。越外层的电子受原子束缚越弱，能量越高；n电子只能处于特定的能级之上；n能级图用一系列高低不同的水平横线来表示电子所能取的确定能量；n原子中的电子通过和外界交换能量的方式发生能级的跃迁热跃迁和光跃迁。Energybandsinsemiconductorconduction band&valence band2023/8/9OE,HUST13原子是由原子核和绕原子核原子是由原子核和绕原子核2024/6/16OE,HUST14n实际物体是由大量原子构成的，每一原子的电子特别是外层电子除受本身原子的势场作用外，还受到相邻原子的作用。n半导体材料中原子在共价键的作用下形成紧密相间、周期排列的晶格结构。电子能级受晶格作用发生分裂而形成能带；Si2023/8/9OE,HUST14实际物体是由大量原子构成实际物体是由大量原子构成2024/6/16OE,HUST15u价带价带：由共价键束缚的价电子所占据的能带为价带；u导带导带：由自由电子占据的能带为导带，导带位于价带之上；u禁带：禁带：导带和价带之间被宽度为Eg的带隙分开，称为禁带；n绝缘体绝缘体：Eg 7eV，电子不容易跃迁到导带；半导体半导体：Eg1eV，电子容易跃迁到导带；导体导体：Eg0eV，没有带隙。2023/8/9OE,HUST15价带：由共价键束缚的价电价带：由共价键束缚的价电2024/6/16OE,HUST16Energybandsinsemiconductorrecombination between electrons and holesThe occupation probability for electrons in the conduction and valence bands is given by the Fermi-Dirac distributions:Efc,Efv are the Fermi levels in conductionband and valence band respectively2023/8/9OE,HUST16Energy bands2024/6/16OE,HUST17:joint density of states,which describe the number of states per unit volume per unit energy rangeEg:bandgapmr:reduced massmc,mv:effective masses of electrons&holes in conduction and valence bands,respectively2023/8/9OE,HUST17:joint den2024/6/16OE,HUST18population-inversion condition:in thermal equilibrium:pumping energy into semiconductor by injecting current To get laser output,2023/8/9OE,HUST18population-i2024/6/16OE,HUST191.TypeofsemiconductornIntrinsic semiconductor:undoped,Fermi level is lying in the middle of the bandgapnn-type semiconductor:Fermi level moves toward the conduction band as the dopant concentration increasesnp-type semiconductor:Fermi level moves toward the valence band as the dopant concentration increases3.2.3p-njunctions2023/8/9OE,HUST191.Type of s2024/6/16OE,HUST20 n-typeIntrinsic p-typeforwardbiasedp-type semiconductor&n-type semiconductor2023/8/9OE,HUST20 n-typeIntri2024/6/16OE,HUST21(a)in thermal equilibrium(b)under forward biased2.p-njunctionsunder forward biased:built-in electric field is reduceddiffusion of electrons and holes across the junctionelectrons and holes are present simultaneously in depletion regiongenerate light through spontaneous emission or stimulated emissionin thermal equilibrium:the Fermi level must be continuous across the pn junctionachieved through diffusion of electrons and holes across the junction.2023/8/9OE,HUST21(a)in therm2024/6/16OE,HUST22Homojunction:equal bandgaps the same semiconductor materialwide region for electron-hole recombinationdifficult to realize high carrier densitiesHeterojunction:different bandgapsDouble-heterojunction:sandwiching a thin layer between the p-type and n-type layers such that the bandgap of the sandwiches layer is smaller than the layer surrounding it.4.Homojunction&heterojunction2023/8/9OE,HUST22Homojunction2024/6/16OE,HUST232023/8/9OE,HUST232024/6/16OE,HUST24nActive layer:light is generated inside it as a result of electron-hole recombinationnhigher density of carriers higher index waveguide(1D)nHeterojunction:confinement of carriers&optical field n0.85m:cladding/active:GaAlAs/GaAs 1.31m,1.55m:cladding/active:InP/InGaAsP2023/8/9OE,HUST24Active layer2024/6/16OE,HUST251.electron-hole recombination3.2.4NonradiativeRecombinationTrap of defectsSurface recombinationAugerNonradiative recombination2023/8/9OE,HUST251.electron-2024/6/16OE,HUST262.internal quantum efficiencyRrr:radiative recombination rate Rnr:nonradiative recombination rate Rtot:total recombination rate :recombination time Nonradiative recombination,especially Auger recombination(temperature dependent)is harmful to devices!positive feedback 2023/8/9OE,HUST262.internal 2024/6/16OE,HUST27E0E0k1k2(1)direct-bandgap(GaAs,InP)(2)indirect-bandgap(Si,Ge)3.carrier lifetimeA:defects&traps B:spontaneous radiation C:Auger 2023/8/9OE,HUST27E0E0k1k2(1)2024/6/16OE,HUST28 Quality of the heterojunction interface depends on the lattice constant of the two materials.(matching!)3.2.5SemiconductorMaterialsternary compound2023/8/9OE,HUST28 Quality2024/6/16OE,HUST29quaternary compound0.85m:GaAlAs/GaAs(cladding/active)1.31m,1.55m:InP/InGaAsP(cladding/active)2023/8/9OE,HUST29quaternary c2024/6/16OE,HUST302023/8/9OE,HUST302024/6/16OE,HUST31Chapter3.OpticalTransmittersnIntroductionnBasic conceptsnSemiconductor lasers(Laser Diodes)nLaser Characteristics nLight-Emitting Diodes(LED)nTransmitter Design2023/8/9OE,HUST31Chapter 3.2024/6/16OE,HUST323.3Semiconductorlasers(LaserDiodes)nAdvantages of stimulated emission compared with spontaneous emission of semiconductor materialsnemitting high power (to 100mW)nnarrow angular spreadnnarrow spectral widthndirect modulation at high frequency(to 10GHz,because is small)2023/8/9OE,HUST323.3 Semicond2024/6/16OE,HUST33ComponentsofSemiconductorLasers2023/8/9OE,HUST33Components o2024/6/16OE,HUST34z=0z=LInjection currentGain mediumResonant cavityResonant cavityModel of laser2023/8/9OE,HUST34z=0z=LInject2024/6/16OE,HUST353.3.1OpticalGainnPeak gain of medium:when:differential gain(gain cross section):injection carrier density:transparent carrier density :threshold carrier densityNTisequaltoNth?2023/8/9OE,HUST353.3.1 Optica2024/6/16OE,HUST36Figure3.9:(a)Gain spectrum of a 1.3-m InGaAsP laser at several carrier densities N.(b)Variation of peak gain gp with N.The dashed line shows the quality of a linear fit in the high gain region.Blue or red shifting of peak wavelength when injected current increases?2023/8/9OE,HUST36Figure 3.9:2024/6/16OE,HUST373.3.2FeedbackandLaserThresholdnFeedbackR1R2n0=1n2023/8/9OE,HUST373.3.2 Feedba2024/6/16OE,HUST38nThreshold 2023/8/9OE,HUST38Threshold 2024/6/16OE,HUST39nAmplitude conditionnPhase conditionspacing of oscillating frequencyoscillating frequencythreshold gainMLM2023/8/9OE,HUST39Amplitude co2024/6/16OE,HUST403.3.3LDStructuresnBroad-area LDFigure3.12:A broad-area semiconductor laser.The active layer(hatched region)is sandwiched between p-type and n-type cladding layers of a higher-bandgap material.light-confinement mechanism in the direction perpendicular to the junction plane introduced by double heterostructure XYdistributioninnearfield2023/8/9OE,HUST403.3.3 LD Str2024/6/16OE,HUST41no such light-confinement mechanism in the lateral direction parallel to the junction plane.the light generated spreads over the entire width of the laser.relatively high threshold current and a spatial pattern that is highly elliptical and that changes in an uncontrollable manner with the current.How about spatial mode in waveguide and distribution in far field?2023/8/9OE,HUST41no such ligh2024/6/16OE,HUST42n Gain-guided semiconductor lasersFigure3.13:Cross section of two stripe-geometry laser structures used to design gain-guided semiconductor lasers and referred to as(a)oxide stripe and(b)junction stripe.StripelasersXY2023/8/9OE,HUST42 Gain-guided2024/6/16OE,HUST43solve the light-confinement problem by limiting current injection over a narrow stripe.the spot size is still not stable as the laser power is increased.Injection current induced index variety!2023/8/9OE,HUST43solve the li2024/6/16OE,HUST44n Index-guided semiconductor lasersFigure3.14:Cross section of two index-guided semiconductor lasers:(a)ridge-waveguide structure for weak index guiding;(b)etched-mesa buried heterostructure for strong index guiding.XY2023/8/9OE,HUST44 Index-guide2024/6/16OE,HUST45Multi-Quantum-WellLDn 有源区厚度薄110nmn 周期结构，将窄带隙的很薄的有源区夹在宽带隙 的半导体材料之间，形成势能阱n 多个势能阱-多量子阱（MQW）2023/8/9OE,HUST45Multi-Quantu2024/6/16OE,HUST46 Relatively stronger confinement of injected carriers and output photons,thus lower threshold current,and higher slope efficiency!2023/8/9OE,HUST46homojunction2024/6/16OE,HUST473.3.4ControlofLongitudinalModesSide Mode Suppression Ratio(SMSR):orMLMLossSLM2023/8/9OE,HUST473.3.4 Contro2024/6/16OE,HUST48DistributedFeedback(DFB)Lasers相位光栅在波导中产生折射率的周期性变化，使正反向传播的行波产生耦合。当光波长满足布拉格条件时，耦合达到最大。在布拉格条件下，某一入射波长几乎被全反射，光栅起到了对波长选择性反射的作用。光栅周期满足：2023/8/9OE,HUST48Distributed 2024/6/16OE,HUST49Coupled-cavitylaserFigure3.18:Coupled-cavity laser structures(a)external-cavity laser;(b)cleaved-coupled cavity laser;(c)multisection DBR laser.2023/8/9OE,HUST49Coupled-cavi2024/6/16OE,HUST50 增益介质反射镜准直透镜透镜光纤增透膜滤光片高反膜cExternalcavitylaser2023/8/9OE,HUST50 增益介质反射增益介质反射2024/6/16OE,HUST51SampledGratingDBRLaserDBR:distributedBraggreflector2023/8/9OE,HUST51Sampled Grat2024/6/16OE,HUST52Cleaved-coupledcavitylaser2023/8/9OE,HUST52Cleaved-coup2024/6/16OE,HUST53VCSEL2023/8/9OE,HUST53VCSEL2024/6/16OE,HUST54思考题1.现有半导体激光器的F-P谐振腔，长度为400m，材料折射率为3.5，谐振腔两端面一端镀有增反射膜，反射率为90，另一端没有镀膜。现有半导体激光器工作在1550nm附近，要求谐振腔谐振的阈值增益系数小于75cm1，请问：如何选择半导体材料和组分？谐振腔内部损耗系数应满足什么条件？2023/8/9OE,HUST54思考题思考题1.现有半导体激现有半导体激2024/6/16OE,HUST55Chapter3.OpticalTransmittersnIntroductionnBasic conceptsnSemiconductor lasers(Laser Diodes)nLaser CharacteristicsnLight-Emitting Diodes(LED)nTransmitter Design2023/8/9OE,HUST55Chapter 3.2024/6/16OE,HUST563.4LaserCharacteristics3.4.1CWCharacteristicsFor a SLM laser,the rate equations:P,N:number of photons&carriers Net rate of stimulated emissionoptical gain:g:peak gain of material :gain cross section,or differential gain.Photon lifetime:2023/8/9OE,HUST563.4 Laser Ch2024/6/16OE,HUST57Thresholdofcurrent&carrierFor I Ith(R1=R2)CW operation:2023/8/9OE,HUST57Threshold of2024/6/16OE,HUST58nThreshold of P-I curvesSpontaneous emissionStimulated emissionI0:constantT0:characteristic temperatureGaAs:T0=120K,InGaAsP:T0=50 70KP-IcurvesnBending of P-I curves Rnr:mainly depending on Auger recombination in InGaAsP LDs Solution:built-in thermoelectric cooler is used to deal with temperature sensitivities of InGaAsP LDs2023/8/9OE,HUST58Threshold of2024/6/16OE,HUST59EfficienciesInternal quantum efficiency:Slope efficiency:Differential quantum efficiency:External quantum efficiency:wall-plug efficiency:2023/8/9OE,HUST59Efficiencies2024/6/16OE,HUST603.4.2Small-SignalModulationnsmall-signal modulation:nFrequency response2023/8/9OE,HUST603.4.2 Small-2024/6/16OE,HUST61Figure3.21:Modulation response of a laser as a function of modulation frequency at several bias levels.Modulationbandwidthnthe efficiency is reduced when the modulation frequency exceeds R by a large amount.2023/8/9OE,HUST61Figure 3.21:2024/6/16OE,HUST623.4.3Large-SignalModulationExternal modulation for high speed transmission!nFrequency chirp leading edge:mode frequency shifts toward the blue sidetrailing edge:mode frequency shifts toward the red side :amplitude-phase coupling parameter,ex.bulk material:48;MQW:32023/8/9OE,HUST623.4.3 Large-2024/6/16OE,HUST63nElectro-optical Delay&Relaxation Oscillation Pre-biased to reduce delay time!请参见江剑平编著的半导体激光器2023/8/9OE,HUST63Electro-opti2024/6/16OE,HUST64nPattern effect TBIP“11”“11”当电光延迟时间与电调制速率对应的的码元持续时间相近时，会使“0”码后的第一个“1”码脉冲宽度变窄，幅度变小，严重时使单个“1”码丢失，这种现象即“码型效应”。连“0”数越多，调制速率越高，该效应越明显。用适当的“过调制”补偿，可以消除码型效应。2023/8/9OE,HUST64Pattern effe2024/6/16OE,HUST65nSelf-pulsationn不同于张弛振荡，没有阻尼，脉动频率范围为0.24GHzn容易发生在阈值附近和P-I特性的扭曲区n造成自脉动的机理涉及量子噪声效应、有源区的缺陷及温度感应的变化等因素n抑制这种现象主要靠控制材料的质量，尽量减少有源区的缺陷。Operated far from kink zone!OPIPI2023/8/9OE,HUST65Self-pulsati2024/6/16OE,HUST66Simulation1-Directmodulation2023/8/9OE,HUST66Simulation 12024/6/16OE,HUST67Simulation2-Externalmodulation 2023/8/9OE,HUST67Simulation 22024/6/16OE,HUST68Ib&ImLD偏置电流的选择合适与否直接影响激光器的高速调制输出特性。加大直流偏置，使其接近阈值，可以减小电光延迟时间，也可使张驰振荡得到一定程度的抑制。当激光器偏置在阈值附近时，较小的调制电流就能得到足够高的输出光脉冲，调制效率较高。而且由于偏置电流与最大电流相差不大，可以大大减小码型效应和结发热效应的不良影响。过大的偏置电流会使消光比恶化，影响接收机灵敏度。激光器恰好偏置在阈值时，散粒噪声会增强，直接影响信号的信噪比。2023/8/9OE,HUST68Ib&ImLD偏置电偏置电2024/6/16OE,HUST69Chapter3.OpticalTransmittersnIntroductionnBasic conceptsnSemiconductor lasers(Laser Diodes)nLaser Characteristics nLight-Emitting Diodes(LED)nTransmitter Design2023/8/9OE,HUST69Chapter 3.2024/6/16OE,HUST703.5.1Power-CurrentCharacteristics3.5Light-EmittingDiodes(LEDs)a forward-biased p-n junction spontaneous emission LED2023/8/9OE,HUST703.5 Light-Em2024/6/16OE,HUST712023/8/9OE,HUST712024/6/16OE,HUST72Power-conversion efficiency(wall-plug efficiency)2023/8/9OE,HUST72Power-conver2024/6/16OE,HUST73P-ICurveResponsivity:(1)responsivity remains constant when I is small(2)bending of P-I curve:(3)no threshold 2023/8/9OE,HUST73P-I CurveRes2024/6/16OE,HUST743.5.2LEDSpectruman approximate expression:LEDs are suitable for LAN with low bit rate&short distance!2023/8/9OE,HUST743.5.2 LED Sp2024/6/16OE,HUST75Figure3.7:(b)spectrum of the emitted light for a typical 1.3-m LED.n超宽带光源n白光LED2023/8/9OE,HUST75Figure 3.7:2024/6/16OE,HUST762023/8/9OE,HUST762024/6/16OE,HUST773.5.3ModulationResponsenRate equation:injection carrier:carrier of recombination (nonradiative&spontaneous emission)nSinusoidal modulation:Ib:bias currentIm:modulation currentm:modulation frequency2023/8/9OE,HUST773.5.3 Modula2024/6/16OE,HUST78nSince modulated power is related to linearly 2023/8/9OE,HUST78Since modula2024/6/16OE,HUST793.5.4LEDStructures(a)(b)(a)surface-emitting LED(b)edge-emitting LED2023/8/9OE,HUST793.5.4 LED St2024/6/16OE,HUST80思考题思考题1.以下论述正确正确的是：（）A、非辐射复合会影响发光器件的发光效率；B、正向偏置的PN结中导带和价带的准费米能级趋于一致；C、半导体材料要发光，必须实现粒子数的反转；D、LED中最初的光子来源于内部的自发辐射；E、电子与空穴复合不一定产生光子；F、双异质结结构提高了半导体光源的量子效率；G、工作于1.55m处的半导体光源有源层材料为InP；H、温度升高发光器件的发光效率会下降；I、间接带隙半导体材料中非辐射复合效率高于辐射复合效率，不适合用作光源材料。2023/8/9OE,HUST80思考题思考题1.以下论述正确以下论述正确2024/6/16OE,HUST811.以下论述正确正确的是：（）A、非辐射复合会影响发光器件的发光效率；B、正向偏置的PN结中导带和价带的准费米能级趋于一致；C、半导体材料要发光，必须实现粒子数的反转；D、LED中最初的光子来源于内部的自发辐射；E、电子与空穴复合不一定产生光子；F、双异质结结构提高了半导体光源的量子效率；G、工作于1.55m处的半导体光源有源层材料为InP；H、温度升高发光器件的发光效率会下降；I、间接带隙半导体材料中非辐射复合效率高于辐射复合效率，不适合用作光源材料。2023/8/9OE,HUST811.以下论述正确的是：以下论述正确的是：2024/6/16OE,HUST82 A、LD的激射波长一定是自发辐射的峰值波长；B、条形激光器中也存在双异质结结构；C、双异质结中对载流子的限制作用是因为存在内建折射率波导；D、通过选择合适的组分x和y，基于In1-xGaxAsyP1-y的半导体光源可设 计工作于0.85m处；E、LD有谐振腔，而LED没有；F、LD的P-I曲线有阈值，而LED的P-I曲线没有阈值；G、LD和SOA中最初的光子均来源于自发辐射；H、激光器的小信号调制带宽会随着偏置电流的增加而增大；I、偏置电流选择合理可适当减小张驰振荡和电光延时效应的影响；J、单纵模LD用作光源时，色散容限大。2.以下关于半导体材料和发光机理论述错误错误的是：2023/8/9OE,HUST822.以下关于半导体材以下关于半导体材2024/6/16OE,HUST83 A、LD的激射波长一定是自发辐射的峰值波长；B、条形激光器中也存在双异质结结构；C、双异质结中对载流子的限制作用是因为存在内建折射率波导；D、通过选择合适的组分x和y，基于In1-xGaxAsyP1-y的半导体光源可设 计工作于0.85m处；E、LD有谐振腔，而LED没有；F、LD的P-I曲线有阈值，而LED的P-I曲线没有阈值；G、LD和SOA中最初的光子均来源于自发辐射；H、激光器的小信号调制带宽会随着偏置电流的增加而增大；I、偏置电流选择合理可适当减小张驰振荡和电光延时效应的影响；J、单纵模LD用作光源时，色散容限大。2.以下关于半导体材料和发光机理论述错误错误的是：2023/8/9OE,HUST832.以下关于半导体材以下关于半导体材2024/6/16OE,HUST84Chapter3.OpticalTransmittersnIntroductionnBasic conceptsnSemiconductor lasers(Laser Diodes)nLaser Characteristics nLight-Emitting Diodes(LED)nTransmitter Design2023/8/9OE,HUST84Chapter 3.2024/6/16OE,HUST853.6.1BasicconceptnAnalog&Digital Modulation3.6TransmitterDesign(a)LED analog modulation (b)LED digital modulation (c)LD digital modulationforLD,biasednearthreshold!2023/8/9OE,HUST853.6.1 Basic2024/6/16OE,HUST86nDigital Logic Electrical Level0 1TTL:0 0.8V 2.0 5.0V (-5V)ECL:-1.75 V -0.85 V (+5V)PECL:+3.25 V +4.15 Vn Extinction RatioPP1P00t2023/8/9OE,HUST86Digital Logi2024/6/16OE,HUST87nSource-fiber coupling nPackaging sourcefiberRfcoating lensed fiberdiesubmountPDheatsinkTECcoolerfibermetalshell2023/8/9OE,HUST87Source-fiber2024/6/16OE,HUST882023/8/9OE,HUST882024/6/16OE,HUST89ButterflypackagedLD2023/8/9OE,HUST89Butterfly pa2024/6/16OE,HUST90nExternal ModulatorLiNbO3 modulator in Mach-Zehnder configurationV2023/8/9OE,HUST90External Mod2024/6/16OE,HUST91EA 0V=0V(t)TT1T22023/8/9OE,HUST91EA0V=0V(t)TT2024/6/16OE,HUST923.6.2DrivingcircuitnDigital modulation circuit with APC for LD2023/8/9OE,HUST923.6.2 Drivi2024/6/16OE,HUST93射极耦合电路射极耦合电路三极管T1和T2是轮流截止和导通的，避免了载流子恢复时间的影响，因而可工作于更高的速率；射极耦合电路为恒流源，总电源电流可以保持不变，所以电源电流噪声小；D1和D2是温度补偿二极管，由于D1、D2、T2和T3的导通电压分别有2.5mV/C的负温度特性，利用D1、D2对T2、T3的温度特性进行补偿，使温度变化时驱动电流保持恒定。LD2023/8/9OE,HUST93射极耦合电路三极管射极耦合电路三极管T1和和2024/6/16OE,HUST94APC电路电路2023/8/9OE,HUST94APC电路电路2024/6/16OE,HUST95ATC电路电路2023/8/9OE,HUST95ATC电路电路2024/6/16OE,HUST96Reviewn光纤通信对光源的要求，光谱线宽和阈值电流。n半导体发光的物理基础：三种跃迁过程，费米能级，粒子数反转，正向偏置PN结，双异质结结构对半导体发光器件的性能改善，非辐射复合及其危害，如何决定半导体材料的组分。nLED的特性，为什么LED适合用在短距离、低速、模拟通信中？nLD的工作条件，阈值条件，纵模条件。nLD的典型结构，增益导引和折射率导引条形激光器，同质结、异质结、条形激光器、多量子阱结构如何实现阈值电流的降低和输出功率的提高？n如何实现单纵模？DBR、DFB、外腔、VCSEL的基本原理。nLD的工作特性：P-I特性,大信号调制的瞬态效应。n光发射机驱动电路，LED和LD驱动电路的不同，PI曲线表示调制过程，带光反馈的LD数字驱动电路。2023/8/9OE,HUST96Review