《光纖通信課程設(shè)計(jì)》課件：Class7-03

FiberOpticNetworkDesignX.Wu,M.Y.Li,C.S.YanDept.ofOpt.Engr.,ZJU2011Class7

RamanFiberAmplificationEDFAStructureParametersSelectionGainflatteningExerciseReasonstousetheopticalamplifiers:

Broadband:possiblefortheS-bandandeven2ndwindowExcellentforultralong-haulHighchannelcount(morethan80)Highmodulationspeed(40Gbit/s)LownoiseLongerdistancesbetweenregenerationRamanFiberAmplifierAmplificationMechanismSRSStimulatedRamanScatteringElasticscatteringInelasticscatteringAlowerfrequency'signal'photon

Induces!!!

theinelasticscatteringofahigher-frequency'pump'photoninanopticalmediuminthenonlinearregime.RamanEffect:InelasticscatteringofaphotonDiscoveredbyC.V.Ramanin1928,NobelPrizein1930

Whenlightisscatteredfromanatomormolecule,mostphotonsareelasticallyscattered(Rayleighscattering),asmallfractionofthescatteredlight(approximately1in10millionphotons)isscatteredbyanexcitation,withthescatteredphotonshavingafrequencydifferentfrom,andusuallylowerthan,thefrequencyoftheincidentphotons.Inagas,Ramanscatteringcanoccurwithachangeinvibrationalorrotationalenergyofamolecule.Occursinliquids,gases,andsolidsRamanEffect:InelasticscatteringofaphotonRamanEffectinSilicateGlassOnesignalphotonin,twoout!RamanFiberAmp:Characteristics

Noneedofdopedfiber，transmissionfiber->gainmediumNonlineareffectDetune100nm,amplifyanybandbychoosingappropriatepumpwavelengthsMulti-pumpconfiguration->flat-gainbroadbandamplificationSimplestructureDisadvantagesStrongpumpingpowerRamaneffect:conversionfromhigher->lowerfrequency->cross-talk->noiseRamanEffect:InelasticscatteringofaphotonDiscoveredbySirChandrasekharaVenkataRaman,NobelPrizein1930

Whenlightisscatteredfromanatomormolecule,mostphotonsareelasticallyscattered(Rayleighscattering),asmallfractionofthescatteredlight(approximately1in10millionphotons)isscatteredbyanexcitation,withthescatteredphotonshavingafrequencydifferentfrom,andusuallylowerthan,thefrequencyoftheincidentphotons.[4]Inagas,Ramanscatteringcanoccurwithachangeinvibrationalorrotationalenergyofamolecule(seeenergylevel).ChemistsareconcernedprimarilywiththevibrationalRamaneffect.Occursinliquids,gases,andsolidsRamanFiberAmp:History

SRSinfiberobservedin19721973StolenandIppenmeasuredStokesshiftinfusedsilica~13.2THz1976AnyeungandYarivestablishedtheory1995Emoriutilized14xxnmpumpingtoobtain100nmbroadbandamplificationwithaflatnessof<1dB1997Nissovprovedthat7200kmtransmissiondistanceat10x10Gbit/susingdistributedRamanamplifiersTypesofRamanAmplifiers2typesofRamanamplifiersDiscreteRamanamplifiers:Signalisnotamplifiedinthetransmissionfiber,butinaspecialfiberwithinaboxwithothercomponents,likeEDFA!DistributedRamanamplifiers:Thetransmissionmedium(fiber)isusedtoachievegain.DistributedRamanamplifiersbenefits:ReducestheoverallNoiseFigure(NF)→longerlinkswithoutregeneration&highermodulationratesbecomepossible.Flatgaincanbeachievedwiththeuseofmorethanonepumplaserwithdifferentwavelengths(AlsopossiblewithDiscreteRamanamplifiers).DiscreteRamanAmplifierCounter-propagationpumpingGainisamaximumclosetothereceiveranddecreasesinthetransmitterdirectionAdvantagesVariablewavelengthamplificationpossibleCompatiblewithinstalledSMfiberCanbeusedto"extend"EDFAsCanresultinaloweraveragepowerovera

span,goodforlowercrosstalkVerybroadbandoperationmaybepossibleLimitations

HighpumppowerrequirementsSophisticatedgaincontrolneededNoiseisalsoanissueSRSTheorySignalPowerincreases,Pumpingpowerdecreasesw/zGainProfile:dependsonmediumBetweenpumpingandsignalfrequencyTypicalApplicationBandsfromStoLS+

Band:1450~1480nm(ExtendedShortBand)S-

Band:1480~1530nm(ShortBand)C

Band

:1530~1570nm(CenterBand)L

Band:1570~1610nm(LongBand)L+Band

:1610~1650nm(LongerBand)WaterpeakBandsfromStoLGainSaturationPumpingPowerConversionEfficiencyGainSaturationSourcesofNoiseinRamanAmplifiersDoubleRayleighscattering(DRS)Twoscatteringevents,backwardandforward,duetomicroscopicglasscompositionnon-uniformity,e.g.backwardASEreflectedbyDRS->forward->noiseShortupper-statelifetime(3-6fs)

Virtuallyinstantaneousgain:pumpfluctuationcouplestosignal->RINASEPhonon-stimulatedopticalnoiseThermallyinducedphononsinfiberthatcanspontaneouslyexperiencegainfromthepumps,therebycreatingnoiseforsignalsclosetopumpwavelengthsNoiseFigureinEDFAEnergyTransferinRamanAmplificationNoiseFigureNoisefigurev.s.alpha,fiberl