復(fù)習(xí)題題庫1.Makeachoice(共十題每題1分)10p.Whichofthefollowingdispersiondosenotexistinsingle-modeopticalfiber?(D).Theunitofthefiberattenuationcoefficientis(C).thebandsofOpticalfibercommunicationis(B).IftheopticalinputpowerofaOpticalamplifierislOmW,andtheopticaloutputpowerislOOmWaswell,thenitsoutputgainlevelis(A)(5)InordertomakesureofthesystemBERconditions,iftheminimumopticalinputpowerofthereceiveris1uW,thesensitivityofthereceivermustbe(6)Theprincipallightsourcesusedforfiberopticalcommunicationsapplicationsare：(7)laseractionistheresultofthreekeyprocess,whichoneofthefollowingisnotbeincluded?Asinglemodefiberusuallyhasacorediameterof(9)TomakesurethattheAPDphoto-detectorworksproperly,asufficientlyisappliedacrossthep-njunction.WhenDFAfiberamplifierusesaslightRepeaters,itsmaineffectisA.amplifyingandregeneratingthesignalIngraded-indexopticalfiber,thenumericalapertureNAcanbeexpressedasInpracticalSMFs,thecorediameterisjustbelowthecutoffofthefirsthigher-ordermode;thatis,forVslightlyItiswellknownthatthetotaldispersioninthesingle-moderegimeiscomposedoftwocomponents:Atpresent,erbiumdopedfiberamplifier'smaximumsmallsignalgainisaroundA.40dBWhichofthefollowingdoesn'tbelongtopassiveopticalcomponentsThe_modehasnocutoffandceasestoexistonlywhenthecorediameteriszero.A.HE11(17)WhenthephasedifferenceisanintegralmultipleofA,thetwomodeswillbeatandtheinputpolarizationstatewillbereproduced.(18)whichoneofthefollowingmodecantransmitinthesingle-modeopticalfiber?(A)A.HE11(19)Lightattenuationinanopticalfiberiscausedby(B)(20)Whichofthefollowingwillreducetheattenuationoffiber-opticcableassembly?(21)Increasingafiber'slengthcan(22)Whatistheleastimportantcharacteristicofafiber-opticlightsource?(23)Whichofthefollowingcodescannotbetransmittedinfibers?(24)Dispersion-shiftedfiber(DSF)isatypeofsingle-modefiberdesignedtohavezerodispersionnear nm.(25)Ingraded-indexopticalfiber,thenumericalapertureNAcanbeexpressedasWritethefullnameofthefollowingacronym(l)OTDM:opticaltime-divisionmultiplexing(2)DTM:DynamicSynchronousTransferMode(3)DWDM:Densewavelengthdivisionmultiplexing(4)DFF:Dispersiion-flattenedfiber(5)AWF:Allwavefiber(6)EPON:EthernetPassiveOpticalNetwork(7)ARQ:automaticreaptrequest(8)SDH:Synchronousdigitalhierarchy(9)SONET:synchronousopticalnetwork(10)TDMA:time-divisionmultipleaccess(11)ISDN:integratedservicesdigitalnetwork(12)FDM:frequency-divisionmultiplexing(13)SIOF:stepindexopticalfiber(14)ATM:asynchronoustransfermode(15)SOA:Semiconductoropticalamplifier(16)APD:AvalanchePhotoDiode(17)WDM:wavelength-divisionmultiplexing(18)PCM:pulse-codemodulation(19)NRZ:nonreturn-to-zero(20)DSF:dispersionshiftfiber(21)TLLM:transmission-linelasermodel(22)ONSL:opticalnetworksimulationlayer(23)OVPO:outsidevapor-phaseoxidation(24)VAD:vapor-phaseaxialdeposition(25)MCVD:modifiedchemicalvapordeposition(26)EDFA:erbium-dopedfiberamplifier(27)FDDI:fiberdistributeddatainterface(28)GIOF:gradedindexopticalfiber(29)SQW:singlequantum-well(30)FEC:forwarderrorcorrectionThetransmissiondistanceofanyfiber-opticcommunicationsystemisinherentlylimitedby?Theroleoftheopticaltransmitteristoconvertthe( )intothecorresponding(opticalsignal)andthenlaunchitintothe( )servingasacommunicationchannel.TOC\o"1-5"\h\zTheLEDstructuresbeingusedforfiberopticscanbeclassifiedas( )or().ThetwobasicLEDconfigurationsbeingusedforfiberopticsare( )and().Thethreemaincomponentsoftheopticaltransmitterare( ),( ),( ).Theroleoftheopticalreceiveristoconvertthe( )backinto( )andrecoverthedatatransmittedthroughthe( ).Thedesignofthefrontendofreceiverrequiresatrade-offbetween( )and( ).Thetwofundamentalnoisemechanismsresponsibleforcurrentfluctuationsinallopticalreceiversarethe( )and( ).Fromanarchitecturalstandpoint,fiber-opticcommunicationsystemscanbeclassifiedintothreebroadcategories-point-to-pointlinks,( ),and( ).Opticalamplifiersareoftencascadedtoovercome( )inalong-haullightwavesystem.AfiberBragggratingactsasanopticalfilterbecauseoftheexistenceofa( ),thefrequencyregioninwhichmostoftheincidentlightisreflectedback.Theelectromagneticenergyofaguidedmodeiscarriedpartlyinthe( )andpartlyinthe().(13)Thebasicattenuationmechanismsinafiberare( ),( )and( )oftheopticalwaveguide.Thetwomainopticalamplifiertypescanbeclassifiedas( )and( ).Thetwomostcommonsamplesofthesespontaneousfluctuationsare( )and().(16)Accordingtotherefractiveindexofthecore,thefibercanbedividedinto( )fiberand( )fiber.(17)Thetotaldispersioninsingle-modefibersconsistsmainlyofThemostmeaningfulcriterionformeasuringtheperformanceofadigitalcommunicationsystemistheThesimplesttransmissionlinkisa.(20)Absorptionisrelatedtothefibermaterial,whereasscatteringisassociatedbothwiththe(fibermaterial)andwith(structuralimperfections)intheopticalwaveguide.Giveabriefdescriptionoffollowingtermsandquestions(共5題每題3分)15pPleasewritethreemainfactorsthatinfluencethesensitivityoftheopticalreceiver.Noise:shotnoiseandthermalnoiseExtinctionRatioFiberdispersionBrieflydescribetheremajorgoalsofSDH.AvoidtheproblemsofPDHAchievehigherbitratesBettermeansfbroperation,administrationandMaintenanceListatleastthreeadvantagesofopticalfiberinfibercommunication.WidebandwidthAnti-interferenceLowlossLargecapacityListatleastthreeadvantagesofSOA.Smallsize,andeasytobeintegratedwithsemiconductorcircuits.Fabricationissimpleandwithlowpowerconsumption,longlife-spanandlowcost.Gainresponseisveryquickandwellsuitedforswitchingandsignalprocessinginopticalnetworksapplication.Canamplifyopticalsignalandprocesssignalinthesametimesuchasswitch,socanbeusedinwavelengthconvertingandopticalswitch.ListmorethanthreedisadvantagesofSOA.ThecouplinglosswithopticalfiberistoolargeSensitivetopolarizationNoisefigureishigh(?8dB)crosstalkEasytobeaffectedbytemperature,lowstability(6)BERBit-Errorrate,definedastheprobabilityofincorrectidentificationofabitbythedecisioncircuitofthereceiver.Whatconditionsshouldbemettoachieveahighsignal-to-noiseratio?Thephotodetectormusthaveahighquantumefficiencytogeneratealargesignalpower.Thephotodetectorandamplifiernoisesshouldbekeptaslowaspossible.Pleasewritethethreebasiccategoriesofdegradationoflightsourcesinternaldamageohmiccontactdegradationdamagetothefacetsoflaserdiodes(9)ListthethreefactorslargelydeterminingthefrequencyresponseofanLEDthedopinglevelintheactiveregiontheinjectedcarrierlifetimeTiintherecombinationregiontheparasiticcapacitanceoftheLED.PleasewritethethreedifferentmechanismscausingabsorptionbrieflyAbsorptionbyatomicdefectsintheglasscomposition.Extrinsicabsorptionbyimpurityatomsintheglassmaterial.Intrinsicabsorptionbythebasicconstituentatomsofthefibermaterial.ThedisadvantageofRamanamplifierNeedlargeoutputpowerpumplaser.AsRamanScattering,theenergyistransferredfromhighfrequencytolowfrequency.Crosstalkwillaffectsignal.DynamicRangeSystemdynamicrangeisthemaximumopticalpowerrangetowhichanydetectormustbeabletorespond.ListatleastthreeadvantagesoffiberamplifiersinfibercommunicationlowinsertionlosslargebandwidthlownoiselowcrosstalkhighgainListatleastthreefactorsofattenuationinfibercommunicationI)materialabsorption2)Rayleighscattering3)miescattering4)connectionlosses5.Figure(共1題每題5分)5p(I)Pleasedrawthebasicstepforanautomatic-repeat-request(ARQ)error-correctionscheme.Solution:

(2)Pleasedrawoutthebasicelementsoftheopticalreceiver.(5p)Solution:(3)Pleasedrawoutthebasicelementsofananaloglinkandthemajornoisecontributions.Solution:□□□□□□□□□□□□APD(3)considertheencodershowninFig.1thatchangesNRZdataintoaPSKwaveform.usingthisencoder,drawtheNRZandPSKwaveformsforthedatasequence0001011101001101.Fig.lSolution:

NRZdata |]2aFr”JWWUWUUUWWULpsiinmjw-rLJwmCalculationProblems(共3-4題，統(tǒng)計40分)40pAwaveisspecifiedbyy=8COS27r(2,一0.8z),whereyisexpressedinmicrometersandthepropagationconstantisgivenin1.Find(a)theamplitude,(b)thewavelength,(c)theangularfrequency,and(d)thedisplacementattime/=0andz=4〃加.Solution:Thegeneralformis:y=(amplitude)cos(6X—kz)=Acos[2zr(vZ—z/A)].Thereforeamplitude=wavelength:1/=0.8//m-1sothat2=1.25//7?/co=2^rv=27r(2)=44At/=0andz=4〃加wehavey=8cos[2^(-0.8///n_I)(4/z/??)]=8cos[2](一3.2)]=2.472Acertainopticalfiberhasanattenuationof0.6dB/kmat1300nmand0.3dB/kmat1550nm.Supposethefollowingtwoopticalsignalsarelaunchedsimultaneouslyintothefibe亡anopticalpowerof150at1300nmandanopticalpowerof100/jWat1550nm.WhataretheSolution:powerlevelsin/jWofthesetwosignalsat(a)8kmand(b)20km?SincetheattenuationsaregivenindB/km,firstfindthepowerlevelsindBmfor100jlAVand150/jW.Theseare,respectively,P(100//W)=10log(100juW/\.OmW)=10log(0.10)=-10.0dBmP(150〃W)=10log(150pW/\.OmW)=10log(0.15)=-8.24dBm

At8kmwehavethefollowingpowerlevels:Pi300(8km)=-8.2dBm-(0.6dB/km)(8km)=-13.0dBm=50/jWPi550(8km)=-10.0dBm-(0.3dB/km)(8km)=-12.4dBm=57.5At20kmwehavethefollowingpowerlevels:Pi3oo(2Okm)=-8.2dBm-(0.6dB/km)(20km)=-20.2dBm=9.55/jWPi55o(2Okm)=-10.0dBm-(0.3dB/km)(20km)=-16.0dBm=25.1/jWAdouble-heterojunctionInGaAsPLEDemittingatapeakwavelengthof1310nmhasradiativeandnonradiativerecombinationtimesof25and90ns,respectively.Thedrivecurrentis35mA.Findtheinternalquantumefficiencyandtheinternalpowerlevel.Iftherefractiveindexofthelightsourcematerialisn=3.5,findthepoweremittedfromthedevice.Solution:1t, .(a)FromEq.7nl= =——，theinternalquantumefficiencyis1+M/「nr耳7int117int11+25/90=0.783,andfromEq.piMandfromEq.piM=7nt~hv=7ntqhcl

qktheinternalpowerlevelisPm=(0.783)/zc(35/M)

q(1310Pm=(0.783)/zc(35/M)

q(1310〃〃z)=26mW(b)Fr°mEq.P=-PX^＞，3.5(3.5+3.5(3.5+l)226mW=0.37/nWAnLEDwithacircularemittingareaofradius20fdmhasalambertianemissionpatternwitha100W(c/W?sr)axialradianceata100mAdrivecurrent.Howmuchopticalpowercanbecoupledintoastep-indexfiberhavinga100jjtncorediameterandNA=0.22?Howmuchopticalpowercanbecoupledfromthissourceintoa50〃〃？core-diametergraded-indexfiberhavinga=2.0,Wj=1.48andA=0.01?Solution:Thesourceradiusislessthanthefiberradius,so國PLED.step=7T2r2sB()(NA)2=2%2r2/泗2Aholds:

PLED^ep=^r2r2A(^)2=^2(2xl0-3cm)2(100W/c/n2)(0.22)2=191/zW、 2 1Fr°mEq，Pled…=2k廣紇〃「加—(尹]Pled,…=2,(2x1(J-0機)2(]oow/加)(L48)2(0.01)[l-|(|)2]=159〃W(5)Supposeanavalanchephotodiodehasthefollowingparameters:IL=1/1A,1D=1/zA,7/=0.85,F=A/12,=103Q,andB=\kHz.Considerasinusoidallyvarying850nmsignal,whichhasamodulationindexm=0.85andanaveragepowerlevelFq=-50dBm,tofallonthedetectoratroomtemperature.AtwhatvalueofMdoesthemaximumsignal-to-noiseratiooccur?Solution:.S <i^>M2UsingEq.—= wehaveN2q(IP+Id)M2F(M)B+2qILB+4kBTB/RLS 1(4甚機)2M22_= 2 N2qB(琮馬+1D)M5/2+2qI,B+4kBTB/RL1.21?TW22qL+4krT/Rf— 生 L,withx2qL+4krT/Rf— 生 L,withx=0.5:xq(Ip+ID)ThevalueofMformaximumS/NisfoundfromEq.M卯:2Moptimum=62.1.(6)AnLEDoperatingat1300nminjects25pWofopticalpowerintoafiber.IftheattenuationbetweentheLEDandthephotodetectoris40dBandthephotodetectorquantumefficiencyis0.65,whatistheprobabilitythatfewerthan5electronholepairswillbegeneratedatthedetectorina1-nsinterval?Solution:isFrom1Ehv,theaveragenumberofelectron-holepairsgeneratedinatimeFrom1Ehv,theaveragenumberofelectron-holepairsgeneratedinatimet“r/Er/Pt 0.65(25x10-10W)(lx10-95)(l.3x10-6w)N=—= = hvhdk(6.6256x1O-34J5)(3xl(//7z/5)Then,fromEq.(7-2)0-N 1^7277P(n)=Nn—=(10.6)5--=e106=0.05=5%nl 5! 120Anengineerhasthefollowingcomponentsavailable:GaAlAslaserdiodeoperatingat850nmandcapableofcoupling1mW(0dBm)intoafiber.Tensectionsofcableeachofwhichis500mlong,asa4-dB/kmattenuation,andhasconnectorsonbothends.Connectorlossof2dB/connector.Apinphotodiodereceiver.Anavalanchephotodiodereceiver.Usingthesecomponents,theengineerwishestoconstructa5-kmlinkoperatingat20Mb/s.IfthesensitivitiesofthepinandAPDreceiversare-45and-56dBm,respectively,whichreceivershouldbeusedifa6-dBsystemoperatingmarginisrequired?Solution:(a)Use4=—Pr=2lc+ argin,toanalyzethelinkpowerbudget.(a)Forthepinphotodiode,with11jointsPT=Ps—PR=Il(/c)+crAL+systemmargin=0dBm-(-45dBiri)=11(2dB)+(4dBIhn)L+6dBWhichgivesL=4.25km.theteansmissiondistancecannotbemetwiththesecomponents.(b)FortheAPDGdBm-{-56dBni)=1\(2dB)+(4dB/kni)L+6dBWhichgivesL=7.0km.thetransmissiondistancecanbemetwiththesecomponents.Supposewewanttofrequency-divisionmultiplex60FMsignals.If30ofthesesignalshaveaper-channelmodulationindex叫=3percentandtheother30signalshave町=4percent,findtheopticalmodulationindexofthelaser.Solution:Thetotalopticalmodulationindexism=琮]"2=[30(.03)2+30(.04)2]i/2=27.4%iAnopticaltransmissionsystemisconstrainedtohave500-GHzchannelspacings.Howmanywavelengthchannelscanbeutilizedinthe1536-to-1556-nmspectralband?Solution:Intermsofwavelength,atacentraiwavelengthof1546nma500-GHzchannelspacingisA^=—Af=(1547m)：500.i=4〃加c3x108w/.v

Thenumberofwavelengthchannelsfittingintothe1536-to-1556spectralbandthenisN=(1556—15362㈤/4〃m=5TheoutputsaturationpowerP(naisdefinedastheamplifieroutputpowerforwhichtheamplifiergainGisreducedby3dB(afactorof2)fromitsunsaturatedvalueG°.AssumingG()?1,showthatintermsoftheamplifiersaturationpower匕中,theoutputsaturationpowerisp=In2poui,sat 'cunp,sal(gT)Solution:LetG=Go/2andPin=P0ati2=2PMstt/Go.thenEq.(11-15)yields%=]+。。曦2%=]+。。曦2E22P“Solvingfor以…〃andwithGo?1,wehaveGoIn2Go-2Ps.GoIn2Go-2Ps. In2)以PM=0.693以…選擇題、填空題、問答題、計算題題庫一MakeachoiceIngraded-indexopticalfiber,thenumericalapertureNAcanbeexpressedasC.A.-n2B.aV2AC.ri|V2AD.a^/nj-n2InpracticalSMFs,thecorediameterisjustbelowthecutoffofthefirsthigher-ordermode;thatis,forVslightlyA.A.<2.4 B.>2.4 C.=3 D.=3.5Whenthephasedifferenceisanintegralmultipleofthetwomodeswillbeatandtheinputpolarizationstatewillbereproduced.A.2n B.兀 C.1800 D.n/2Itiswellknownthatthetotaldispersioninthesingle-moderegimeiscomposedoftwocomponents:C.A.mode-partitionnoise,inter-symbolInterferenceB.frequencychirp,modaldispersionC.materialdispersion,waveguidedispersionD.modaldispersion,waveguidedispersionWhichofthefollowingcodescannotbetransmittedinfibersB.A.CMI B.HDB3 C.5B6B D.8B1HDispersion-shiftedfiber(DSF)isatypeofsingle-modefiberdesignedtohavezerodispersionnearAnm.A.1550 B.850 C.1310 D.1510TomakesurethattheAPDphotodetectorworksproperly,asufficientlyDisappliedacrossthep-njunction.A.highforward-biasvoltage B.lowforward-biasvoltageC.lowreverse-biasvoltage D.highreverse-biasvoltageAsinglemodefiberusuallyhasacorediameterofA.A.10m B.62.5nm C.125nm D.50mm二BlankfillingEachSDHframecomprisingthreeareas:asectionoverheadarea(SOH),apointerarea,apayloadareaincludingthedatatobetransmitted.ListthreeapplicationsofFBG(fiberBragggrating):filter、OpticalAddDropMullipluxer(OADM)anddispersioncompensator.Accordingtowhetherthereiselectricormagneticfieldinthedirectionofpropagationornot,transversemodesoflightwavesareclassifiedintodifferenttypes:TEMmodes,TEmodes,TMmodesandhybridmodes.Transmissionofinformationinanopticalformatiscarriedoutnotbyfrequencymodulationofthecarrier,butbyvaryingtheintensityoftheopticalpower.Largelyduetoaliennationanddispersion,theopticalsignalsundergowaveformdistortionanddecreasedamplitude.Materialdispersionoccursbecausetheindexofrefractionvariesasafunctionoftheopticalwavelength.ZDSFisadispersionshiftedsinglemodefiberthathasthezerodispersionwavelengthnearthe1550nmwindow,butoutsidethewindowactuallyusedtotransmitsignals.Alaserisconstructedfromthreeprincipalparts:apumpsource,againmedium,andanopticalresonator.Anopticalfibercomprisesatleasttwolayers,acoreandacladding.Opticaltransmitterconsistsofopticalsource,amodulatorandachannelcoupler.Fiberrefractiveindexprofilesclassifyfibersasstep-indexfibersandgraded-indexfibers.BER(Thebiterrorrate)performanceandjitteraretwoimportantindicatorsinaopticaldigitalcommunicationsystem.LASERisamechanismforemittinglightwithintheelectromagneticradiationregionofthespectrum,viatheprocessofstimulatedemission.TherearetwokindsofSOA：Fabry-PerotAmplifier(FPA)andTraveling-WaveAmplifier(TWA).Theprincipalnoisesassociatedwithphotodetectorsthathavenointernalgainarequantumnoise,dark-currenlnoisegeneraiedinihebulkmalerialofthephotodiode,andsurfaceleakagecurrentnoise.Inastep?indexfiber,therefractiveindexofthecoreisuniformandundergoesanabruptchangeatthecore-claddingboundary.Ingraded-indexfibers,therefractiveindexofthecorevariesgraduallyasafunctionofradialdistancefromthefibercenter.Iftheinputpulseexcitesbothpolarizationcomponents,itbecomesbroaderasthetwocomponentsdispersealongthefiberbecauseoftheirdifferentgroupvelocities.ThisphenomenoniscalledthePMD.Themostcommonsemiconductorphotodetectoristhepinpholodiode.Themaincauseofintrinsicabsorptionintheinfraredregionisthecharacteristicvibrationfrequencyofatomicbonds.InSDHtransmissionstructures,aTU(TributaryUnit)includesalowlevelVCandaTUPTR.Extrinsicabsorptioniscausedbyimpuritiesintroducedintothefibermaterial.Intramodaldispersionisaresultofthegroupvelocitybeingafunctionofthewavelength.Theopticalamplifiersisdividedinto3groups:semiconductoropticalamplifier(SOA).oplicalfiberamplifier(OPA)andRamanamplifier(FRA).Therearetwokindsofdirectionalcouplers:aprism-fibreandafibrefbrelappedcoupler.EDFAhasthreepumpingstructures:?theforwardpumpingstructure;②thebackwardpumpingstructure;③thedoublepumpingstructure.Alaserconsistsofagainmediuminsideahighlyreflectiveopticalcavity,aswellasameanstosupplyenergytothegainmedium.Attenuationinanopticalfiberiscausedbyabsorptionlosses,scatteringlosses,andbendinglosses.STM-1framesprovideatransmissionbitrateof155Mbit/s.Fromthepointofviewofthewavetheory,lightwavecouldbedescribedasaneleclromagneticwave.Intermodaldispersionisaresultofeachmodehavingadifferentvalueofthegroupvelocityatasinglefrequency.Atypicalopticaldigitalcommunicationsystemusuallycomprisesthreeparts:transmitter,oplicalfiberchannel,andreceiver.

ThepinPhotodetectorstructureconsistsofpandnregionsseparatedbyaverylightlyn-dopedintrinsic(i)region.PleaselistthreestepsofSDHMultiplexing:mapping,aligning,multiplexing.TherearethreevariationsofWDMthatarecommonlyused:BroadWDM.CoarseWDM,andDenseWDM.TheSTM-1frameisthebasictransmissionformatforSDH.Theframelastsfor125microseconds;thereforethereare8000framespersecond.InSDHframestructure,theSOHismadeupofaregeneratorsectionoverhead(RSOH)andamultiplexingsectionoverhead(MSOH).Thesensitivityofaphotodetectorinanopticalfibercommunicationsystemisdescribableintermsoftheminimumdetectableopticalpower.PleaselistthreeapplicationsofEDFAinopticalfibercommunicationsystem:aspreamplifierofreceiver>aspoweramplifieroftransmitterandastheopticalrepeater.Anopticalisolator(opticaldiode),isanopticalcomponentwhichallowsthetransmissionoflightinonlyonedirection.三lightinonlyonedirection.三Interpretationoftermsandphrases1)AON(all-opticalnetwork)3)FDDI(fiberdistributeddatainterface)5)ISDN(integratedservicesdigitalnetwork)7)OC(opticalcarrier)9)PON(passiveopticalnetwork)11)SDH(synchronousdigitalhierarchy)13)STS(synchronoustransporsignal)15)WGA(waveguide-gratingrouter)17)AWG(arrayed-waveguidegrating)四畫圖題2)DBR(distributedBraggreflector)4)HFC(hybridfiber-coaxial)6)RA(ramanamplifier)8)OTDM(opticaltime-divisionmultiplexing)10)SCM(subcarriermultiplexing)12)SPM(self-phasemodulation)14)TW(travelingwave)16)IMD(intermodulationdisortion)18)AOTF(acousto-optictunablefilter)DrawtheelementblockofaDistributedforwardRamanamplifierinnutOUtDUtinnutOUtDUtDrawanelementdiagramofaDoublepumpEDFAInputIsolatorWDMEDF空『utInputIsolatorWDMEDF空『utPumpLaserDrawablockdiagramofatypicalopticaldigitalcommunicationsystemandbrieflydescribethefunctionsofeachpart.fiberfiberfiberfiberAnopticalcommunicationsystemconsistsofatransmitter,whichencodesamessageintoanopticalsignal,achannel,whichcarriesthesignaltoitsdestination,andareceiver,whichreproducesthemessagefromthereceivedopticalsignal.Theopticalrepeateristoextendthetransmissiondistanceofopticalsignal.Drawtheelementdiagramoftheapplicationofopticalamplifier.Optical

transmitterOptical

transmitterTheapplicationofopticalamplifier四簡答題Dispersion:Anyphenomenoninwhichthevelocityofpropagationofanyelectromagneticwaveiswavelengthdependent.StimulatedEmissionsIfaphotonofenergyhv)2impingesonthesystemwhiletheelectronisstillinitsexcitedstate,theelectronisimmediatelystimulatedtodroptothegroundstateandgiveoffaphotonofenergyhvI2.Thereare3dispersiontypesintheopticalfibersingeneral:MaterialDispersionWaveguideDispersionPolarization-ModeDispersionPolarizationmodedispersion(PMD)isduetoslightlydifferentvelocityforeachpolarizationmodebecauseofthelackofperfectlysymmetric&anisotropicofthefiberLaserisanopticaloscillator.Itcomprisesaresonantopticalamplifierwhoseoutputisfedbackintoitsinputwithmatchingphase.Anyoscillatorcontains:Anamplifierwithagain-saturatedmechanismAfeedbacksystemAfrequencyselectionmechanismAnoutputcouplingschemeInthermalequilibriumthestimulatedemissionisessentiallynegligible,sincethedensityofelectronsintheexcitedstateisverysmall,andopticalemissionismainlybecauseofthespontaneousemission.Stimulatedemissionwillexceedabsorptiononlyifthepopulationoftheexcitedstatesisgreaterthanthatofthegroundstate.ThisconditionisknownasPopulationInversion.Populationinversionisachievedbyvariouspumpingtechniques.TurnonDelayWhenthedrivingcurrentsuddenlyjumpsfromlow(Il<Ith)tohigh(12>Ith),(stepinput),thereisafinitetimebeforethelaserwillturnonTheQuantumLimitForanidealphoto-detectorhavingunityquantumefficiencyandproducingnodarkcurrent,itispossibletofindtheminimumreceivedopticalpowerrequiredfbraspecificBERperformanceinadigitalsystem.Thisminimumreceivedpowerlevelisknownasthequantumlimit.Gainflatness:Thedifferencebetweenthebiggestgainandthesmallestgainofthedifferentfrequencysignal.TheadvantageofRamanamplifier:SimplefabricationLownoise,becauseamplifyingactiontakeplaceinsidetheordinarilyfiber.Thewavelengthcanbeselectedinthelowlosswaveband.Verywidegainbandwidth.MicrobendingLoss:microscopicbendsofthefiberaxisthatcanarisewhenthefibersareincorporatedintocables.Thepowerisdissipatedthroughthemicrobendedfiber,becauseoftherepetitivecouplingofenergybetweenguidedmodes&theleakyorradiationmodesinthefiber.Gainsaturation:whennearsaturation,thegainisnonlinear;saturation,thesignalcannotbeamplified.ThedisadvantageofRamanamplifier:Needlargeoutputpowerpumplaser.AsRamanScattering,theenergyistransferredfromhighfrequencytolowfrequency.Crosstalkwillaffectsignal.Theprincipalnoisesassociatedwithphotodetectorsare:Quantum(Shot)noise:arisesfromstatisticalnatureoftheproductionandcollectionofphoto-generatedelectronsuponopticalillumination.IthasbeenshownthatthestatisticsfollowaPoissonprocess.Darkcurrentnoise:isthecurrentthatcontinuestoflowthroughthebiascircuitintheabsenceofthelight.Thisisthecombinationofbulkdarkcurrent,whichisduetothermallygeneratedeandhinthepnjunction,andthesurfacedarkcurrent,duetosurfacedefects,biasvoltageandsurfacearea.Listtheadvantagesoffiber-opticcommunicationsoverothertypesofcommunicationtechnologies.Theadvantageofopticalfibercommunication:WeightandSizeMaterialcost(SiO2isplentiful)InformationCapacityNoelectromagneticinterferenceNoelectricalconnectionDistancebetweenrepeatersBettersecurityLowcrosstalkThefabricationofamplifierOpticalisolator,Opticalmultiplexer,EDEPumplaserWhataretheadvantagesanddisadvantagesofSDHsystemascomparedtoPDHsystem?ThemainlimitationsofPDHare:Inabilitytoidentifyindividualchannelsinahigher-orderbitstream;Insufficientcapacityfornetworkmanagement;MostPDHnetworkmanagementisproprietary;ThereisnostandardizeddefinitionofPDHbitratesgreaterthan140Mbit/s;and,Therearedifferenthierarchiesinusearoundtheworld.Specializedinterfaceequipmentisrequiredtointerworkthetwohierarchies.Listthetypesoffiberattenuationanddispersion.Absorbing\scatteringandbendinglossMaterial/mode/waveguidedispersion.Theavalancheeffect.Thecreatedcarriersareacceleratedbythehighelectricfield,gainingenoughenergytocausefurtherimpactionization.Dynamicrange:Systemdynamicrangeisthemaximumopticalpowerrangetowhichanydetectormustbeabletorespond.Differentiatebetweenstepindexandgradedindexopticalfiber.Stepindexfiberhas