Chapter6FrontiersChapter6FrontiersChapter22SOEI,HUST6.1Multi-dimensionalmultiplexing6.2Opticalamplification6.3Dispersionmanagementandcompensation6.4Forwarderrorcorrection(FEC)6.1.1IntroductionChapter63SOEI,HUSTMultiplexingisamethodbywhichmultipleanalogmessagesignalsordigitaldatastreamsarecombinedintoonesignalovera

sharedmedium.Themultiplexingdividesthecapacityofthehigh-levelcommunicationchannelintoseverallow-levellogicalchannels,andenhancesspectralefficiency.Multiplexingisperformedbyexploitingorthogonalityinoneormoreofthephysicaldimensions:Time,Frequency,Polarization,Code,SpaceWhatisMultiplexing?Chapter64SOEI,HUSTModulation&MultiplexingOTDMPDMOFDMWDMSDM6.1.2OTDM---OpticalTimeDomainMultiplexingChapter65SOEI,HUSTTime-divisionmultiplexing(TDM)isusedprimarilyfordigitalsignals,butmaybeappliedinanalogmultiplexinginwhichtwoormoresignalsorbitstreamsaretransferredappearingsimultaneouslyassub-channelsinonecommunicationchannel,butarephysicallytakingturnsonthechannel.Thetimedomainisdividedintoseveralrecurrenttimeslotsoffixedlength,oneforeachsub-channel.Chapter66SOEI,HUSTUltra-shortpulsegenerationOpticalMultiplexer/DemultiplexerAll-opticalclockrecovery/SamplingDispersionmanagementSinglewavelengthPrecisedelaylines6.1.2OTDM:CharacteristicsandkeytechniquesChapter67SOEI,HUSTIntelecommunications,frequency-divisionmultiplexing(FDM)isatechniquebywhichthetotalbandwidthavailableinacommunicationmediumisdividedintoaseriesofnon-overlappingfrequencysub-bands,eachofwhichisusedtocarryaseparatesignal.WDMisatechnologywhichmultiplexesanumberofopticalcarriersignalsontoasingleopticalfiberbyusingdifferentwavelengths(i.e.,colors)oflaserlight.Thistechniqueenablesbidirectionalcommunicationsoveronestrandoffiber,aswellasmultiplicationofcapacity.Inopticalcommunication,FDMiscalledWDM.6.1.3WDM---WavelengthDivisionMultiplexingChapter68SOEI,HUST6.1.3WDM:Characteristicsandkeytechniques光發(fā)射機(jī)光發(fā)射機(jī)光發(fā)射機(jī)光發(fā)射機(jī)N123光接收機(jī)光接收機(jī)光接收機(jī)光接收機(jī)N123EDFA功放線放預(yù)放MUXDEMUXWavelengthlockingintransmittersNonlinearitiesinopticalfiberCrosstalkinMUX/DMUXGainbandwidthofamplifierDispersionmanagementChapter69SOEI,HUST6.1.4PDM---Polarization-divisionmultiplexingPDMusesthepolarizationofelectromagneticradiationtoseparateorthogonalchannels.Itisinpracticaluseinbothradioandopticalcommunications,particularlyin100Gbit/sperchannel(PDM-QPSK)fiberoptictransmissionsystems.Chapter610SOEI,HUST6.1.4PDM:CharacteristicsandkeytechniquesSinglewavelengthDriftsinpolarizationstatePolarizationmodedispersionPolarization-dependentloss/gainCross-polarizationmodulationPBS/PBCPDMsignalgenerationChapter611SOEI,HUST6.1.5OFDM---Orthogonalfrequency-divisionmultiplexingConceptually,OFDMisaspecialized

FDM,theadditionalconstraintbeing:allthecarriersignalsareorthogonaltoeachother.InOFDM,thesub-carrierfrequenciesarechosensothatthesub-carriersare

orthogonal

toeachother,meaningthat

cross-talk

betweenthesub-channelsiseliminatedandinter-carrierguardbandsarenotrequired.Chapter612SOEI,HUST6.1.5OFDM:CharacteristicsandkeytechniquesDiscreteFourierTransformImplementation:IFFT&FFTPeak-to-AveragePowerRatioCyclicPrefixWindow/FrequencyOffsetSynchronizationSummaryChapter613SOEI,HUSTBycombingdifferentmultiplexingtechniquestogether,thespectralefficiencyandtransmissioncapacitycanbefurtherincreased.Themultiplexingtechniquesutilizeddifferentphysicaldimensionscanbecompatible,providedthemessagessentinthesedimensionscanbeuniquelyseparatedfromoneanotheratthereceiverwithoutimpactingeachother’sdetectionperformance.Theworldrecordtransmissioncapacitywereachievedbymulti-dimensionalmultiplexing.6.1Multi-dimensionalmultiplexing6.2Opticalamplification6.3Dispersionmanagementandcompensation6.4Forwarderrorcorrection(FEC)Chapter6FrontiersChapter214SOEI,HUST6.2.1IntroductionChapter615SOEI,HUSTSeveralkindsofopticalamplifiersweredevelopedinthe1980stosolvethelossproblem.Examplesinclude:semiconductoropticalamplifiers,Ramanamplifiers,anderbium-dopedfiberamplifiers(EDFAs).TheyamplifymultipleWDMchannelssimultaneouslyandthusaremuchmorecost-effective.AllmodernWDMsystemsemployopticalamplifiers.Amplifiercanbecascadedandthusenableonetotransmitoverdistancesaslongas10,000km.Classification&CharacteristicsChapter616SOEI,HUSTAnopticalamplifierischaracterizedby:Gain:

ratioofoutputpowertoinputpower(indB)Gainefficiency:gainasafunctionofinputpower(dB/mW)Gainbandwidth:rangeofwavelengthoverwhichtheamplifieriseffectiveGainsaturation:Maximumoutputpower,beyondwhichnoamplificationisreachedNoise:undesiredsignalduetophysicalprocessinginamplifierChapter617SOEI,HUSTRare-earthDopedFiberAmplifiersErbium-DopedFiberAmplifiers(EDFA):C,L-BandThulium-DopedFiberAmplifiers(TDFA):S-BandPraseodymium-DopedFiberAmplifiers(PDFA):O-BandFiberRamanAmplifiersDiscreteRamanAmplifiersDistributedRamanAmplifiers(DRA)SemiconductorOpticalAmplifiers(SOA)ConventionalSOAGain-ClampedSOA(GC-SOA)LinearOpticalAmplifier(LOA)Chapter618SOEI,HUSTMETASTABLESTATEPumpPhoton980or1480nmSIGNALPHOTON1550nmFUNDAMENTALSTATEFUNDAMENTALSTATEEXCITEDSTATETRANSITIONAmplifiedSignal1550nm6.2.2EDFA:Principle&CharacteristicsChapter619SOEI,HUST

CharacteristicsAllopticalandfibercompatibleWidebandwidth,20~70nmHighgain,20~40dBHighoutputpower,>200mW（10W）Bitrate,modulationformat,powerandwavelengthinsensitiveLowdistortionandlownoise(NF<5dB)Chapter620SOEI,HUSTGainflatness6.2.2EDFA:ProblemsandChallengesPopulationlevelsatdifferentbandsvary,andhencethegainvariationSeriouslyaffectsWDMsystemsToovercomethis:usegainequalizingfiler/usefluorideglassfiberChapter621SOEI,HUSTGainequalizingfilterChapter622SOEI,HUSTNaturallyFlat.Pumpedonlyat1480.brittle,difficulttosplicewithtypicalfiber.Silicafiberof20dBgain,Fluoridefiberof20dBgain.FluorideglassfiberChapter623SOEI,HUSTChapter624SOEI,HUST6.2.3RA:Principle&CharacteristicsRamanAmplifierwasdemonstratedinthe1980s;Unavailabilityofhigh-powerdiodelaserpumpsourceUseintrinsicopticalnonlinearityoffiber:StimulatedRamanScatteringRamanscatteringfrommolecularvibrationPumpphotongivesupenergytocreateasignalphotonResidualvibrationalenergyisabsorbedasphononsAmplificationtakesplacethroughoutthelengthoftransmissionfiberChapter625SOEI,HUSTChapter626SOEI,HUSTChapter627SOEI,HUSTChapter628SOEI,HUSTWhydoyouneedit:amplifysignalsfrom1270to1670nmanyopticalfibercanserveastheamplifyingmedium

lowNFandthusbetterOSNRduetolowASEfastresponsetimeramanprocessitselfprovideshigh-powerlaserDisadvantage:Cross-talkHighpumppowersrequiredHighpowerpumpsareexpensiveatthewavelengthsofinterest6.2.3RA:ProblemsandChallengesChapter629OEI,HUSTHybridEDFA+RFAChapter630SOEI,HUST6.2.4OpticalAmplifierNoiseAllamplifiersdegradetheSNRofanopticalbitstream.Theyaddnoisetothesignalthroughspontaneousemission.Chapter631SOEI,HUSTSourcesofamplifiernoiseThermalNoiseSignalShotnoise

SignalRINSignal-spontaneousbeatnoiseSpontaneous-spontaneousbeatnoise

Chapter632SOEI,HUSTNoisefigure(NF)andnoisefactor(F)aremeasuresofdegradationofthesignal-to-noiseratio(SNR)NFdefinitionissimilarasforelectricalamplifiers,essentiallyadegradationofsignal.NFdefinitionassumesshot-noiselimitedsource.Lasernoiseanddetectorthermalnoiseisignored/negligible.6.1Multi-dimensionalmultiplexing6.2Opticalamplification6.3Dispersionmanagementandcompensation6.4Forwarderrorcorrection(FEC)Chapter6FrontiersChapter233SOEI,HUSTChapter6SOEI,HUST346.3.1IntroductionChapter6SOEI,HUST35DispersionmapPre-compensation:Dispersionaccumulatedovertheentirelinkiscompensatedatthetransmitterend.Post-compensation:ADCFofappropriatelengthisplacedatthereceiverend.Periodiccompensation:Dispersioniscompensatedinaperiodicfashionallalongthelink.Foratrulylinearsystem(nononlineareffects),allthreeschemesareidentical.Threeconfigurationsbehavedifferentlywhennonlineareffectsareincluded.Systemperformanceimprovedbyoptimizingdispersionmap.6.3.2DCFChapter6SOEI,HUST36Modifiesinputpulsesbeforetheyarelaunchedintofiberlink.Pre-chirpingofinputpulsemodifiesaGaussianpulseasSuitablychirpedpulsescanpropagateoverlongerdistancesbeforetheybroadenoutsideitsbitslot.Assumingbroadeningbyistolerable,MaximizeLwithrespecttothechirpparameterC.for(41%increase).6.3.3Pre-chirpTechniqueChapter6SOEI,HUST37Fourwavemixingusedtogeneratephaseconjugatedidlerfieldinthemiddleoffiberlink.reversedforthephaseconjugatedfield:Pulseshaperestoredatthefiberend.Basicideapatentedin1979.

Firstexperimentaldemonstrationin19OpticalPhaseConjugationChapter6SOEI,HUST38TimedomainequalizationTDEFreq.domainequalizationFDEFIRfilter6.3.5DSPalgorithmincoherentdetection6.1Multi-dimensionalmultiplexing6.2Opticalamplification6.3Dispersionmanagementandcompensation6.4Forwarderrorcorrection(FEC)Chapter6FrontiersChapter239SOEI,HUSTChapter6SOEI,HUST406.4.1IntroductionFECisamethodofencodingtheoriginalsignalwithadditionalerrordetectionandcorrectionoverheadinformation(i.e.paritybytes),sotheopticalreceiverscandetectandcorrecterrorsthatoccurinthetransmissionpath.ItdramaticallylowerstheBERandextendsthedistancesthatopticalsignalscanbetransmittedwithoutregeneration.ImprovementinBERisquantifiedthroughthecodinggain.Chapter6SOEI,HUST41Terminologies6.4.2BasicConceptChapter6SOEI,HUST42CodingGa