光纖通信技術(shù)：Chapter 4 Optical Signal Detection and Recovery

Chapter4

OpticalSignalDetectionandRecoveryVocabularyopticalreceiver光接收機(jī)signaldistortion信號畸變BER(bit-errorrate)誤碼率APD雪崩光電二極管ISI碼間串?dāng)_darkcurrent暗電流photoncurrent光生電流directdetection直接探測coherentdetection相干探測noisefigure噪聲指數(shù)highsensitivity高靈敏度responsivity響應(yīng)度thermalnoise熱噪聲shotnoise散粒噪聲noiseequivalentpower噪聲等效功率currentfluctuation電流波動excessnoisefactor過剩噪聲因子quantumlimit量子受限automaticgaincontrol自動增益控制pre-amplifier前置放大器decisioncircuit判決電路decisionthresholdvalue判決閾值clockrecovery時(shí)鐘恢復(fù)electron-holepair電子空穴對driftvelocity漂移速率Gaussianstatistics高斯統(tǒng)計(jì)high-passfilter高通濾波器linearchannel線性信道electro-opticaldelay電光延遲samplingtime采樣時(shí)間powerfluctuation功率波動optimumgain最優(yōu)增益complementaryerrorfunction互補(bǔ)誤差函數(shù)multiplicationfactor倍增因子spectraldensity譜密度intensitynoise強(qiáng)度噪聲Chapter42SOEI,HUSTtimingjitter定時(shí)抖動mode-partitionnoise模式分配噪聲parasiticreflection寄生反射depletionregion耗盡區(qū)biasvoltage偏置電壓reversebias反向偏置tunnelingbreakdown隧道擊穿equalizer均衡器stimulatedabsorption受激吸收quantumefficiency量子效率straylight雜散光sensitivitydegradation靈敏度劣化diffusive擴(kuò)散gainflatness增益平坦ionizationcoefficient電離系數(shù)gainregion增益區(qū)boundarycondition邊界條件avalancheprocess雪崩過程pulsebroadening脈沖展寬stationaryrandomprocess平穩(wěn)隨機(jī)過程Poissonstatistics泊松統(tǒng)計(jì)Wiener-Khinchintheorem維納-辛欽定理pulseshaping脈沖整形transferfunction傳遞函數(shù)rectangularpulse矩形脈沖one/two-sided單/雙邊帶transparenttransmission透明傳輸wavelengthrouting波長路由point-to-point點(diǎn)對點(diǎn)topologystructure拓?fù)浣Y(jié)構(gòu)powerbudget功率預(yù)算powermargin功率余量powerpenalty功率代價(jià)Chapter43SOEI,HUSTChap.4OpticalSignalDetectionandRecovery4.1Opticaldetectordesign4.2Opticalreceiverstructure4.3Receivernoise4.4Receiversensitivity4.5CoherentopticalreceiverRequirementHighsensitivity,Highresponsespeed,Lowcost,Highreliability,robusttodistortions.Chapter45SOEI,HUSTopticalsignalvoltagesupplyO/Epre-amplifierautomaticgaincontrolamplifierfilterdecisioncircuitclockrecovery

PINorAPDelectricaldataFrontEndLinearChannelDataRecovery4.1.1Responsivity

andBandwidth1.StimulatedabsorptionSpontaneousEmissionStimulatedemissionStimulatedabsorptionLEDLDPDOpticalsourceChapter46SOEI,HUSTPhotodetector2.ResponsivityThephotocurrentgeneratedRistheresponsivityofthephotodetector(inunitsofA/W).3.HowtoincreaseR?Chapter47SOEI,HUSTwhenChapter48SOEI,HUST4.PDbandwidthChapter49SOEI,HUSTRCtimeconstantOpticalsignalPinVout(t)90%10%V0TrWTransittimeChapter410SOEI,HUST5.DarkcurrentOriginatesfromstraylightorthermallygeneratedelectron-holepairs4.1.2TypicalStructuresandPerformancesChapter411SOEI,HUSTP-NPhotodiodesareversebiasedp-njunctionFastSlowa)Ap-nphotodiodeunderreversebias;(b)variationofopticalpowerinsidethePD;(c)energy-banddiagramshowingcarriermovementthroughdriftanddiffusion.

thepresenceofadiffusivecomponentdistortsthetemporalresponseofaphotodiode.

solution:decreasingthewidthsofthep-andn-regions;increasingthedepletion-regionwidth.Chapter412SOEI,HUST

i-layer→highresistance→largeelectricfield→thedepletionregionthroughoutit→driftcomponentdominatesoverthediffusioncomponentButdiffusioncomponentmaystillexist!2.PINPhotodiodesChapter413SOEI,HUSTEg(i)<hv<Eg(p,n)Chapter414SOEI,HUSTDouble-heterostructurePINsStimulatedabsorptiononlyoccursinthei-layer.Thediffusivecomponentcurrentiseliminatedcompletely(Highresponsespeed).

InPInGaAsInPChapter415SOEI,HUSTChapter416SOEI,HUSTTypicalstructure(a)AnAPDtogetherwiththeelectric-fielddistributioninsidevariouslayersunderreversebias;(b)designofasiliconreach-throughAPD.3.AvalanchePhotodiodes(APDs)Chapter417SOEI,HUSTOperationprinciple:impactionizationAnacceleratingelectrongivesapartofitskineticenergytoanotherelectroninthevalencebandthatendsupintheconductionband,leavingbehindahole.aphoton asingleprimaryelectronelectronwithhighkineticenergymanysecondaryelectrons&holesi-layer:absorption;gain-layer:multiplicationthroughimpactionizationMainparametersimpact-ionizationcoefficients:(αe:electrons;αh:holes)dependonmaterialandontheelectricfield.

Chapter418SOEI,HUSTMultiplicationfactorthecurrentflowwithinmultiplicationlayerie,ih:electron&holecurrentrespectivelythetotalcurrent:Chapter419SOEI,HUSTassumingthat:,theelectricfieldacrossthegainregionisuniform(areconstants),onlyelectronscrosstheboundarytoenterthen-region.

Consideringtheboundarycondition

Chapter420SOEI,HUSTChapter421SOEI,HUSTResponsivityM:averageAPDgainavalanchebreakdown!whenwhereisionizationcoefficientratio.Bandwidth

WhereM0isthelowfrequencygain,τeistheeffectivetransittimeChapter422SOEI,HUSTChapter423SOEI,HUST

DifferentAPDstructuresChapter424SOEI,HUSTReach-throughAPD0.85um:Si,KA<<1M~100,B~100Mb/s1.31um,1.55um:Ge,InGaAsSolution:largebandgap→canbeappliedhighreversevoltage

Absorption&Multiplicationlayersusethesamematerial.(ilayer)Chapter425SOEI,HUSTSAM-APD:SeparateabsorptionandmultiplicationAPDp+-InPn+-InPn-InPi-InGaAsMA-+Problem:largebandgapdifferencebetweenInP&InGaAsEInp=1.35eVEInGaAs=0.75eV1)holesgeneratedaretrappedattheheterojunction.2)slowresponse&smallbandwidth.Solution:Chapter426SOEI,HUSTChapter427SOEI,HUSTp+-InPn+-InPn-InPInGaAsMA-+InGaAsPGSAGM-APD(SeparateAbsorptionGrading&Multiplication)p+-InPN+-InPn-InPInGaAsMA-+InGaAsPGN+-InPCChapter428SOEI,HUSTSAGCM-APD(C-chargelayer)Chap.4OpticalSignalDetectionandRecovery4.1Opticaldetectordesign4.2Opticalreceiverstructure4.3Receivernoise4.4Receiversensitivity4.5CoherentopticalreceiverTIA4.2.1FrontEndChapter430SOEI,HUSTEquivalentcircuitfor(a)high-impedanceand(b)transimpedancefrontendsinopticalreceivers.Thephotodiodeismodeledasacurrentsourceinbothcases.DesignRequirementsAlargeloadresistorReceiverbandwidth

UsingEqualizertoincreasethebandwidthbyattenuatingthelow-frequencycomponentsHigherOutputVoltageLowThermalNoiseImprovedsensitivity

Atrade-offbetweenreceiversensitivityandbandwidth!Chapter431SOEI,HUSTTransimpedanceamplifier(TIA)HighSensitivityandLargeBandwidth4.2.2LinearChannelChapter432SOEI,HUST1.ComponentsAmplifierwithAGC:limitingtheaverageoutputvoltageforacceptingawiderangeofinputACvoltagesandprovidingconstant-amplitudevoltage.Low-passfilter:reducingthenoise;determiningthereceiverBWandthusshapingthevoltagepulsetoreducetheISI.2.Optimizationofthelow-passfilterChapter433SOEI,HUSTTheinputsignal:Theoptimizedshapeoftheoutputpulsefordecision:Consecutiveraised-cosineimpulses,demonstratingzero-ISIpropertyChapter434SOEI,HUSTThetransferfunctionofthelinearchannelisgivenas:raised-cosineFormationofEyediagram(NRZ)Chapter435SOEI,HUST4.2.3DecisionCircuitChapter436SOEI,HUSTComponents:clockrecovery(CR)+decisioncircuit.TheCRisolatesaspectralcomponentatf=Bfromthereceivedsignalandprovidesinformationaboutthebitslottothedecisioncircuitandhelpstosynchronizethedecisionprocess.CRiseasyincaseofRZformatwhiledifficultincaseofNRZformat.Thebestsamplingtimecanbedeterminedfromtheeyediagram.Chap.4OpticalSignalDetectionandRecovery4.1Opticaldetectordesign4.2Opticalreceiverstructure4.3Receivernoise4.4Receiversensitivity4.5CoherentopticalreceiverShotnoise:electronsaregeneratedatrandomtimes,depictedasastationaryrandomprocesswithPoissonstatistics(approximatedbyGaussianstatistics)Chapter438SOEI,HUST4.3.1NoiseMechanismsphotodiodecurrentwithshotnoisetheautocorrelationfunctionisrelatedtothespectraldensitybytheWiener-Khinchintheoremconsideringthedarkcurrentthetwo-sidedspectraldensitytheone-sidedspectraldensityChapter439SOEI,HUST2.Thermalnoise:Atafinitetemperate,electronsmoverandomlyinaresistorintheabsenceofanappliedvoltage.ThecurrentfluctuationinducedbythermalnoiseisastationaryrandomprocesswithGaussianstatistics.photodiodecurrentwithshotnoisepowerspectraldensityFn:factorbywhichthermalnoiseisenhancedbyvariousresistorsusedinpre-andmain-amplifierthetwo-sidedspectraldensitytheone-sidedspectraldensityChapter440SOEI,HUST3.Totalnoisepower

Thephotodiodecurrentwithshotandthermalnoise:

Notethatis(t),iT(t)

areindependentrandomprocesses.Chapter441SOEI,HUST1.PINreceiver4.3.2SNRofOpticalReceiversChapter442SOEI,HUSTThermalnoiselimitNoise-equivalentpower

(NEP):opticalpowerperunitbandwidthrequiredtoproduceSNR=1Detectivity:(NEP)-1Shot-noiselimitSNRcanbewrittenintermofthenumberofphotonNpcontaininthe“1”bit.bychoosingChapter443SOEI,HUST2.APDreceiverFA(M):excessnoisefactor,Chapter444SOEI,HUSTShotnoiseenhancement:Secondaryelectron-holepairsgeneratesatrandomtimesthroughtheprocessofimpactionization.Thermal-noiselimitShot-noiselimitOptimumAPDgainChapter445SOEI,HUSTChap.4OpticalSignalDetectionandRecovery4.1Opticaldetectordesign4.2Opticalreceiverstructure4.3Receivernoise4.4Receiversensitivity4.5CoherentopticalreceiverBit-ErrorRate(BER)：probabilityofincorrectidentificationofabitbythedecisioncircuitofthereceiver.Chapter447SOEI,HUST4.4.1BERandSensitivity(assumingp(1)=p(0)=1/2)

(complementaryerrorfunction)Chapter448SOEI,HUSTDecisionthreshold:IDshouldbeoptimizedtominimizetheBER.TheminimumoccurswhenIDischosenas:QfactorChapter449SOEI,HUSTRelationbetweenQandBER

Chapter450SOEI,HUSTChapter451SOEI,HUST2.Sensitivity:theminimumaveragereceivedpowerPrecrequiredbythereceivertooperateataBERof10-9

.AveragereceivedpowerChapter452SOEI,HUSTPINreceiver

APDreceiverChapter453SOEI,HUST4.4.2BERandSNRShot–noiselimitThermal–noiselimitChapter454SOEI,HUST4.4.3SensitivityDegradationPowerpenalty:Theincreaseintheminimumaveragereceivedpowerbecauseofnon-idealconditions:extinctionratio;intensitynoise;timingjitter;mode-partitionnoise;parasiticreflectionsExtinctionratioideal:rex=0infact:rex≠0Ib<Ith,P0=0,relaxationoscillationandelectro-opticaldelayriseup.Ib>Ith,P0≠0,rex≠0,modulationbandwidthrisesup.ForaPINreceiver,inthethermalnoiselimit:Powerpenalty:ForaAPDreceiver,δexislargerbyafactorofabout2Chapter455SOEI,HUSTChapter456SOEI,HUSTPowerpenaltyversustheextinctionratioPowerpenaltyversustheintensitynoiseparameterIntensityNoisemodepartitionnoise;parasiticreflectionPowerfluctuationcurrentfluctuationChapter457SOEI,HUSTRZ,Error-freeTimingjitterChapter458SOEI,HUSTProblem光接收機(jī)靈敏度分析某PIN光接收機(jī)等效噪聲帶寬近似等于接收光信號比特速率的一半，工作在1550nm時(shí)量子效率為0.9，前端總電容為0.003pF，放大器噪聲指數(shù)為3dB，忽略暗電流，分別計(jì)算下面受限情況下，該接收機(jī)工作在10Gb/s時(shí)誤碼率要求為10－12時(shí)對應(yīng)的靈敏度（單位為dBm）：1）熱噪聲受限；2）散粒噪聲受限。注：普朗克常數(shù)：；基本電荷電量：；玻爾茲曼常數(shù)：Chapter459SOEI,HUSTChap.4OpticalSignalDetectionandRecovery4.1Opticaldetectordesign4.2Opticalreceiverstructure4.3Receivernoise4.4Receiversensitivity4.5CoherentopticalreceiverDirectdetectionistheconventionalwaytodetectopticalsignal.QUADRATICdetectionofelectricfield.OnlyIntensity!4.5.1OperationPrinciplesAmplitude,phaseandpolarization!LOfrequency≈carrierfrequency：intradynedetectionCoherentdetection:LINEARdetectionoftheelectricfield,bybeatingwithlocaloscillator.1.Comparisonbetweendirectdetectionandcoherentdetection

Chapter461SOEI,HUSTRef1.Fiber-OpticCommunicationSystems(Edition4),pp158~1614.5.2TypicalStructure1.Phasediversity:ThephotocurrentsI1，I2，I3，I4providefullinformationonrealandimaginarypartsoftheincomingsignalfield.I1I4Chapter462SOEI,HUSTRef2.OpticalFiberTelecommunicationsVB,pp95~113Chapter463SOEI,HUSTPhotocurrentI1-4andresultingcurrentsi(t)andq(t)Phaseinformation(+phasenoise)AmplitudeFrequencyoffsetWiththeλ/4waveplate(QWP),thepolarizationoftheLObecomescircular,whilethesignalremainslinearlypolarizedandis45degreewithrespecttoprincipalaxesofthePBSs.Afterpassingthroughthehalfmirror(HM),thePBSsseparatethetwopolarizationcomponentsoftheLOandsignalwhiletwobalancedphotodiodesPD1andPD2detectthebeatbetweentheLOandsignalineachpolarization.WhenthecircularlypolarizedLOissplitwithaPBS,thephasedifferenceis90degree.Incontrast,thereisnophasedifferencebetweent