《光纤通信课程设计》课件：Class2-03

FiberOpticNetworkDesignX.Wu,M.J.Li,H.M.YanDept.ofOpt.Engr.,ZJU2011Class2Outline

ChromaticdispersioneffectDispersioncompensatingtechniquesOptimizationofresidualdispersionoritsmapChromaticDispersion3SpectrumbroadeningDifferenceingroupvelocityWavelengthGroupvelocityΔλ110OriginalsignalTimeTransmitteroutputTimeReceiverinput111RegeneratedsignalWavelengthOpticalspectrumΔλ

Pulsebroadening(Waveformdistortion)OpticalfiberWaveformdistortionduetofibernonlinearityTransmitteroutReceivedwaveformLowopticalpowerHighpowerintensityFrequencychirpRefractiveindexchangeWaveformdistortionduetochromaticdispersionOpticalfiberSpectrumbroadeningDispersioncompensationexample40Gb/sopticalsignalTransmissionfiber

Positivedispersion(Negativedispersion)+

Negativedispersion

(Positivedispersion)Longerwavelength

Slow

(Fast)Shorterwavelength

Fast(Slow)Longerwavelength

Fast(Slow)Shorterwavelength

Slow(Fast)AfterfibertransmissionTransmitteroutput25psAfterdispersioncomp.ThreecompensationschemesFiber#1DCDCFiber#2Distance[km]R.D.[ps/nm]Post-comp.+-0Fiber#1DCDCFiber#2Distance[km]R.D.[ps/nm]Pre-comp.-+0Fiber#1DCDCFiber#2DCDistance[km]R.D.[ps/nm]Post-&Pre-comp.-+0FactorsinfluencecompensationNeedtoconsiderthevariationoftoleranceduetocharacteristicsoftransmitter,fibernon-lineareffectsanddispersionmap.Evenifresidualdispersionvaluesaresame,thereceivedwaveformsaredifferent,affectedbytheseparameters.ParametersaffectingtothetoleranceSignalbitrateChannelcountsandspacingDistanceornumberofspansFibertypeFiberinputpowerPre-chirpingoftransmitter-Modulationschemeoftransmitter-DCFallocation/valueDistance[km]Dispersion[ps/nm]Dispersiontoleranceofreceiver-+-Dispersion[ps/nm]+0Penalty[dB]LongerwavelengthShorterwavelengthCenterwavelengthAllowablepenaltyAPastFieldExampleAlookatBERagainLightinanopticalfiberslowlyvaryingcomponentpolarizationcarrierTransversefieldprofiledefinedbymodeThenonlinearSchrödingerequation(NLSE)Fibertransmission-TheNonlinearSchrödingerEquationLaunchedsignal:C.R.Menyuk,IEEEJ.QuantumElectron.25,12,2674-2682,December1,1989.L.F.Mollenaueretal.,inOpt.FiberTelecommunicationsiVA,(Academic,SanDiego,Calif.,1997).Fibertransmission–NLSEgeneraldefinitionsAttenuationDispersionNonlinearitya-Losscoefficient[km-1]b-dispersioncoefficient[ps2/km]g=2p

n2/(lAeff)-nonlinearcoefficient[W-1km-1]t=told–z/vgtoremovepropagationdelay-istheopticalpower[W]Fibertransmission–RenormalizingthelossesDefine:zLossnormalizedNLSEForsimplicityofphysicalinsightwemayassumeG(z)=1Chromaticdispersionorgroupvelocitydispersion(GVD)“Positive”or“negative”dispersiondependsonthedefinitionD>0b<0“anomalous”dispersionD<0b>0“normal”dispersionps/nm/km[b]ps2/kmLinearpropagationofpulsesNegligiblenonlinearitylowpower(|a|2issmall)TrivialsolutionintheFourierdomainQuadraticphaseterminfrequency:powerspectrumisunchangedImportantexample–TheGaussianpulseTimedomainFrequencydomainFTIFTexp(ibW2z/2)Where:isthepulse-widthisthechirpparameteristhedispersionlengthtimetimewL|a|2ThechirpofapulseinstantaneousfrequencyAmplitudev.s.timeFrequencyv.s.timetimeIfb<0,thebluepartofthepulsegoesfasterandarrivesearlierThechirpofapulse:shiftingcolorsReversingthesignofdispersiontimeDispersionisreversibleDCFb>0Transmissionfiberb<0…AmplifiermoduleTimeisaparameter.Thereisaclosed-formsolutionPropagationofpulses:zerodispersioncaseZerodispersion:SelfphasemodulationtimeThepulseacquiresachirp,butitsamplitudeprofiledoesnotchange.Bandwidthincreases.GenerationofnewfrequenciesThepulseleadingedgeshiftstotheredandthetrailingtotheblueThepulseacquiresachirpw(t,z)NonlinearlengthLengthoverwhichthenonlinearphaseshiftis1radianP:peakpowerofthepulsenonlinearlength,characteristiclengthofthenonlinearevolutionDispersion+nonlinearity:Thesplit-stepmethodDzDzDznonlinearityonlydispersiononlydispersion+nonlinearityG.P.Agrawal,NonlinearFiberOptics,ThirdEdition,(Academic,NewYork,2001).NonlinearityBalancingdispersionandnonlinearity–asimplifiedexampleNonlinearity:

leadingedgeshiftedtothered,trailingtotheblueb<0:thebluepartofthepulsetravelsfasterthantheredpartleadingtopulsecompressionandinversionofchirpPossibletoachieveaveragecompensationbetweennonlinearcompressionandthedispersivebroadeningStablepulsepropagationDispersionb<0MoreDispersionDispersionmanagementAccumulateddispersionDCMDCMDCMDCMTxRxLocaldispersionThereducedmap:Theeffectoflinearpropagation0.0120.0130.0140.0150.016-0.0400.040.08frequencydispersion1/Bandwidth2BandwidthisconstanttimeDispersiononly,nononlinearityLinearw(t,z)timeLinearw(t,z)timeqIqRCombinedEffectofDispersionandNonlinearity0.0120.0130.0140.0150.016-0.0400.040.08frequencydispersionTreatnonlinearityasaperturbation1/Bandwidth2timeLinearw(t,z)Nonlinearw(t,z)IncreasesthebandwidthtimeNonlinearw(t,z)ReducesthebandwidthLinearw(t,z)timeDCFb>0Transmissionfiberb<0Amplifiermoduletime0.01480.01520.01560.0160.016400.040.080.121/Bandwidth2frequencydispersionEvolutionalongthedispersionmapNonlineardynamicsofasinglepulseIflinearandnonlinearchirpcompensateexactlyafteronedispersionmapperiod~constantbandwidth.IflinearandnonlinearchirpdonotcompensateexactlybandwidthoscillationsoverascalelargerthantheamplifierspacingLargegapbetweenlinearandnonlinearchirpPulsedestroysDispersingpu