光電子材料導論 色散補償

信息傳輸材料與技術

－－－傳輸色散補償Onceuponatime,theworldassumedthatfiberpossessedinfinitebandwidthandwouldmeetmankind’scommunicationneedsintotheforeseeablefuture.

In1550nmregion,withalossofonly0.2dB/km,seemedliketheanswer.Millionsofkilometersoffiberwereinstalledaroundtheworldcreatingahigh-speedcommunicationnetwork.asthedataratesincreasedandfiberlengthsincreased,limitationsduetodispersioninthefiberbecameimpossibletoavoid.101101數(shù)據(jù)傳輸100Km的101101數(shù)據(jù)原始眼圖傳輸100km眼圖色散補償后眼圖Dispersionwasinitiallyaproblemwhenthefirstopticalfibers,multimodestep-indexfiber,wereintroduced.Multimodegraded-indexfiberimprovedthesituationabit,butitwassingle-modefiberthateliminatedseveremultimodefiberrelateddispersionandleftonlychromaticdispersionandpolarizationmodedispersiontobedealtwithbyengineers.ChromaticDispersion

Chromaticdispersionrepresentsthefactthatdifferentcolorsorwavelengthstravelatdifferentspeeds,evenwithinthesamemode.Chromaticdispersionistheresultofmaterialdispersion,waveguidedispersion,orprofiledispersion.Figure1belowshowschromaticdispersionalongwithkeycomponentwaveguidedispersionandmaterialdispersion.Theexampleshowschromaticdispersiongoingtozeroatthewavelengthnear1550nm.Thisischaracteristicofbandwidthdispersion-shiftedfiber.Standardfiber,single-mode,andmultimodehaszerodispersionatawavelengthof1310nm.ChromaticDispersion

RefractiveIndexofFusedSilica

DispersionCompensatingFiberPreliminarySpecificationDocument100%SlopeCompensationforSMF-28?TypicalCDoverWavelengthPerformanceofDCFSMFiberDispersion

MLMLaserSpectralOutputtypicalopticaloutputspectrumofanMLMlaserandthecorrespondingRMSspectralwidth.

DispersionwithaNormalDFBLaser

DispersionwithaNarrowDFBLaser

DispersionwithanFPLaser

DispersionofSMFiberTypes

Non-DSF:Nondispersion-shiftedfiberzerodispersionnear1310nm.

DSF:Dispersion-shiftedfiberworkswellinsinglechannel1550nmsystems,butinDWDMsystems,fibernonlinearitiesneartothezero-dispersionwavelengthcauseproblems.

(+D)NZ-DSF:SimilartoDSF,exceptthatthezero-dispersionwavelengthisintentionallyplacedoutsideofthe1550nmwindow.Thefiberhasapositivedispersionslopeversuswavelength.

(-D)NZ-DSF:Almostidenticaltothe(+D)NZ-DSFtype,exceptthatthedispersionslopeisnegativeversuswavelength.

CorningDCF123ChirpedfibergratingfordispersioncompensationInterrogationofFibreBraggGratingOpticalfibreFibreBraggGratingIlluminatesFBGwithabroadbandlightsourceAnarrowbandoflightreflectedbytheFBGTherestofthespectrumistransmittedFBGsResponsetoStrain&TemperatureIncreasingstrainWavelength-divisionMultiplexingofFBGSensorsLightSourceWavelengthDetectionGratingFiberTerminationOutputInputCirculatorPolarizationModeDispersion

（PMD）Polarizationmodedispersion(PMD)isanothercomplexopticaleffectthatcanoccurinsingle-modeopticalfibers.Single-modefiberssupporttwoperpendicularpolarizationsoftheoriginaltransmittedsignal.Figure1.Realfiberislikemanyretardationplatesinserieswithdifferentorientationsandbirefringence.Itisequivalenttoasingleretardationplatehavingslowandfastaxes,andaneffectivebirefringence.Anopticalpulsebroadensbecausethetwopolarizationcomponentstravelwithdifferentspeeds.Simultaneousall-opticalreshapingoftwo10Gb/ssignalsusinginjectionlockinginaF-PlaserdiodeAll-opticalwaveformreshapingofadistorted10Gb/sNRZPRBSsignalusingtwo-modeinjectionlockinginFabry-

Perotlaserdiodewasdemonstrated.Simultaneouswaveformreshapingoftwodistorted10Gb/sNRZPRBSsignalswasalsodemonstrated.1.IntroductionAll-opticalwaveformreshapingtechniquesbasedoninjectionlockinginLDhavedrawnattention.WedemonstratewaveformreshapingofdistortedNRZsignalsat10Gb/susingtwo-modeinjectionlockinginanFP-LD.AsingleFP-LDcanreshapetwodistorted10Gb/sNRZsignalssimultaneously.2.OperationPrinciple

Thetechniquebasedonthethresholdnatureofinjectionlocking.WhenadistortedpulseisinjectedtoaFP-LD,onlythepartofthesignalwithpowerabovetheinjectionlockingthresholdhasgain.Theinjection-lockedoutputoftheFP-LDfromthispartofthesignalwillbethesame.Otherpartofthesignalwillexperienceloss.

AcwlightisalsoinjectedintotheFP-LDtoimprovetheextinctionratioofthereshapedsignal.TheFP-LDismultimodeoperating,itcaninjection-lockseveralsignalssimultaneously,thusmakingitpossibletouseasingleFP-LDtoreshapemultipledatasignals.Onlyonecwlightisneededforwaveformreshapingofmultiplechannels.3.Waveformreshapingofasingle10Gb/sNRZsignal

Fig.1.showstheexperimentalsetupofall-opticalwaveformreshaping.Fig.1.

Theexperimentalsetupforwaveformreshapingofdistorted10Gb/sNRZsignals.ThebiascurrentoftheFP-LDis1.27Ith.

All-opticalwaveformreshapingForreshapingofone10Gb/ssignal,thetunablelaserTL2wasturnedoff.Thesignalwasseverelydistortedbydispersionafterpropagationin100kmoffiber,totaldispersionvalueisabout1,700ps/nm.Figure2(a)showstheeyediagramofthesignalafterpropagationof100km.Afterreshaping,theeyediagramofthesignalbecomeopen,asshowninFigure2(b).Figure4(a)showstheoutputspectrum.ThedetunebetweenthesignalwavelengthandtheclosestFP-LDlongitudinalmodewas0.075nmandthatforthecwwas0.025nm.Fig.2.

Eyediagramsofa10Gb/ssignalafterpropagationin100kmstandardsinglemodefiber(a)beforewaveformreshaping,and(b)afterwaveformreshaping.Thetimescaleis50ps/divandtheamplitudescaleis100mV/div.(a)(b)Thepowersanddetunesofboththedatasignalandthecwwerechosen:i)Thepoweroftherisingandfallingedgesofthedatasignalwerenotsufficienttoinitiateinjectionlocking.TheFP-LDwasinfactinjection-lockedbythecwlightandthusemittedatthewavelengthofthecwlight.Consequentlytherisingandfallingedgesofthedatasignalexperiencedloss;ii)ThepowerofthedatasignalaroundthepeaksofthepulseswashigherthantheinjectionlockingthresholdoftheFP-LDsuchthattheFP-LDoutputatthedatasignalwavelengthwithaconstantpower.4.Simultaneouswaveformreshapingoftwodistorted10Gb/sNRZsignalsThetunablelaserTL2inFig.1wasturnedon.ThepoweranddetuneofthethreesignalsfromTL1(data1),TL2,(data2)andTL3(cw)wereadjustedsuchthatthecwlightinjection-lockstheFP-LDonlywhenbothdata1anddata2donotinjection-locktheFP-LD.Thewavelengthsandinputpowersofdata1,data2,andcwwere1547.02nm,1551.50nmand1543.70nmand–6dBm,-9dBm,and0dBm,respectively.Thecorrespondingdetunesofdata1,data2andcwfromtheirrespectiveFP-LDfreerunningmodeswerechosenas0.07nm,0.125nmand0.05nm,respectively.Figures3(a)and3(c)showtheeyediagramsofdata1anddata2respectivelybeforewaveformreshaping,whileFigs.3(b)and3(d)showtheeyediagramsofdata1anddata2respectivelyafterwaveformreshaping.

Fig.3(c)showsthatdata2wasdistortedmoreseriouslyasexpectedbecauseofitslowerinputpower.Theeyediagramsareclearandopenafterthewaveformreshaping.Fromthethicknessofthe‘1’railsinFigs.3(b)and3(d),crosstalksbetweenthetwodata

signalsinducedbythewaveformreshapingprocessisnotsignificant.TheoutputspectrumisshowninFigure4(b).Theoutputpowersofcw,data1,anddata2measuredatport3ofthecirculatorare–3.41dBm,-5.39dBm,and–7.98dBm