光纖通信復習題英文

一一Makeachoice1)Ingraded-indexopticalfiber,thenumericalapertureNAcanbeexpressedasC.n nn n122

C. n1

D. a2n n2n n12A.<2.4 B.>2.4 C.=3 D.=3.5Whenthephasedifferenceisanintegralmultipleof_2_,thetwomodeswillbeatandtheinputpolarizationstatewillbereproduced.A.2 B. C.1800 D./2Itiswellknownthatthetotaldispersioninthesingle-moderegimeiscomposedoftwocomponents:C.A.mode-partitionnoise,inter-symbolInterferenceB.frequencychirp,modaldispersionC.materialdispersion,waveguidedispersionD.modaldispersion,waveguidedispersion5)WhichofthefollowingcodescannotbetransmittedinfibersB.5)WhichofthefollowingcodescannotbetransmittedinfibersB.A.CMI B.HDB3 C.5B6B D.8B1H6)Dispersion-shiftedfiber(DSF)isatypeofsingle-modefiberdesignedtohavezerodispersionnearAnm.6)Dispersion-shiftedfiber(DSF)isatypeofsingle-modefiberdesignedtohavezerodispersionnearAnm.A.1550 B.850 C.1310 D.15107)TomakesurethattheAPDphotodetectorworksproperly,asufficientlyDisappliedacrossthep-njunction.7)TomakesurethattheAPDphotodetectorworksproperly,asufficientlyDisappliedacrossthep-njunction.A.highforward-biasvoltage B.lowforward-biasvoltageC.lowreverse-biasvoltage D.highreverse-biasvoltage8)AsinglemodefiberusuallyhasacorediameterofA.A.10m B.62.5nm C.125nm D.50mm二二Blankfilling EachSDHframecomprisingthreeareas:asectionoverheadarea（SOH）,apointerarea,apayloadareaincludingthedatatobetransmitted.List three applications of FBG(fiber Bragg grating): filter、Optical Add DropMultiplexer(OADM)anddispersioncompensator. Accordingtowhetherthereiselectricormagneticfieldinthedirectionofpropagationornot,transversemodesoflightwavesareclassifiedintodifferenttypes:TEMmodes,TEmodes,TMmodesandhybridmodes. Transmissionofinformationinanopticalformatiscarriedoutnotbyfrequencymodulationofthecarrier,butbyvaryingtheintensityoftheopticalpower. Largelyduetoattenuationanddispersion,theopticalsignalsundergowaveformdistortionanddecreasedamplitude. Materialdispersionoccursbecausetheindexofrefractionvariesasafunctionoftheopticalwavelength.8) Alaserisconstructedfromthreeprincipalparts:apumpsource,againmedium,andanopticalresonator. ZDSFisadispersionshiftedsinglemodefiberthathasthezerodispersionwavelengthnearthe1550nmwindow,butoutsidethewindowactuallyusedtotransmit8) Alaserisconstructedfromthreeprincipalparts:apumpsource,againmedium,andanopticalresonator.9)10)9)10)11)Anopticalfibercomprisesatleasttwolayers,acoreandacladding.Opticaltransmitterconsistsofopticalsource,amodulatorandachannelcoupler.Fiberrefractiveindexprofilesclassifyfibersasstep-indexfibersandgraded-indexfibers.13) LASERisamechanism13) LASERisamechanismforemittinglightwithintheelectromagneticradiationregionofthespectrum,viatheprocessofstimulatedemission.14)Therearetwokindsof(TWA).SOA：Fabry-PerotAmplifier(FPA)andTraveling-WaveAmplifier Theprincipalnoisesassociatedwithphotodetectorsthathavenointernalgainarequantumnoise,dark-currentnoisegeneratedinthebulkmaterialofthephotodiode,andsurfaceleakagecurrentnoise. Inastep-indexfiber,therefractiveindexofthecoreisuniformandundergoesanabruptchangeatthecore-claddingboundary.Ingraded-indexfibers,therefractiveindexofthecorevariesgraduallyasafunctionofradialdistancefromthefibercenter.Themostcommonsemiconductorphotodetectoristhepinphotodiode.Themaincauseofintrinsicabsorptionintheinfraredregionisthecharacteristicvibrationfrequencyofatomicbonds.InSDHtransmissionstructures,aTU(TributaryUnit)includesalowlevelVCandaTUPTR.Themostcommonsemiconductorphotodetectoristhepinphotodiode.Themaincauseofintrinsicabsorptionintheinfraredregionisthecharacteristicvibrationfrequencyofatomicbonds.InSDHtransmissionstructures,aTU(TributaryUnit)includesalowlevelVCandaTUPTR.Extrinsicabsorptioniscausedbyimpuritiesintroducedintothefibermaterial. Theopticalamplifiersisdividedinto3groups:semiconductoropticalamplifier(SOA),opticalfiberamplifier(OPA)andRamanamplifier(FRA). Theopticalamplifiersisdividedinto3groups:semiconductoropticalamplifier(SOA),opticalfiberamplifier(OPA)andRamanamplifier(FRA).Therearetwokindsofdirectionalcouplers:aprism-fibreandafibre-fibrelappedcoupler. EDFAhasthreepumpingstructures:forwardpumpingstructure;backwardpumpingstructure;③thedoublepumpingstructure. Alaserconsistsofagainmediuminsideahighlyreflectiveopticalcavity,aswellasameanstosupplyenergytothegainmedium. Attenuationinanopticalfiberiscausedbyabsorptionlosses,scatteringlosses,andbendinglosses.STM-1framesprovideatransmissionbitrateof155Mbit/s. Fromthe point of viewof the wavetheory,light wavecould be describedas electromagneticwave. Atypicalopticaldigitalcommunicationsystemusuallycomprisesthreeparts:transmitter,opticalfiberchannel,andreceiver. ThepinPhotodetectorstructureconsistsofpandnregionsseparatedbyaverylightlyn-dopedintrinsic(i) Atypicalopticaldigitalcommunicationsystemusuallycomprisesthreeparts:transmitter,opticalfiberchannel,andreceiver. ThepinPhotodetectorstructureconsistsofpandnregionsseparatedbyaverylightlyn-dopedintrinsic(i)region.PleaselistthreestepsofSDHMultiplexing:aligning，multiplexing. TherearethreevariationsofWDMthatarecommonlyused:BroadWDM,CoarseWDM,andDenseWDM. TheSTM-1frameisthebasictransmissionformatforSDH.Theframelastsfor125microseconds;thereforethereare8000framespersecond. InSDHframestructure,theSOHismadeupofaregeneratorsectionoverhead(RSOH)andamultiplexingsectionoverhead(MSOH). Thesensitivityofaphotodetectorinanopticalfibercommunicationsystemisdescribableintermsoftheminimumdetectableopticalpower. PleaselistthreeapplicationsofEDFAinopticalfibercommunicationsystem:aspreamplifierofreceiver、aspoweramplifieroftransmitterandastheopticalrepeater.Anopticalisolator(opticaldiode),isanopticalcomponentwhichallowsthetransmissionoflightinonlyonedirection.三InterpretationoftermsandphrasesAON (all-opticalnetwork) 2)DBR(distributedBraggreflector)3）FDDI (fiberdistributeddatainterface) 4）HFC(hybridfiber-coaxial)5）ISDN (integratedservicesdigitalnetwork) 6）RA(ramanamplifier)7OC (opticalcarrier) 8OTDM (opticaltime-divisionmultiplexing)9）PON(passiveopticalnetwork) 10）SCM(subcarrier(synchronousdigitalhierarchy)12）SPM(self-phasemodulation)13）STS(synchronoustransporsignal) 14）TW(travelingwave)15）WGA (waveguide-gratingrouter) 16）IMD (intermodulationdisortion)17）AWG (arrayed-waveguidegrating) 18）AOTF (acousto-optictunable四畫圖題1)DrawtheelementblockofaDistributedforwardRamanamplifierWDMfiberinputWDMfiberinputPumpLaseroutput2)DrawanelementdiagramofaDoublepumpEDFAInputIsolatorWDMEDFIsolatorOutputPumpLaserPumpLaser3)Drawablockdiagram ofatypicalopticaldigitalcommunicationsystemandbrieflydescribethefunctionsofeachpart.fiberfiberfiberfiberOptical RepeatertransmitterOpticalreceiver4)Drawtheelementdiagramoftheapplicationofopticalamplifier.四簡答題1)Dispersion:Anyphenomenoninwhichthevelocityofpropagationofany4)Drawtheelementdiagramoftheapplicationofopticalamplifier.四簡答題1)Dispersion:Anyphenomenoninwhichthevelocityofpropagationofanyelectromagneticwaveiswavelengthdependent.StimulatedEmissionsIfaphotonofenergyhv12impingesonthesystemwhiletheelectronisstillinitsexcitedstate,theelectronisimmediatelystimulatedtodroptothegroundstateandgiveoffaphotonofenergyhv12.Thereare3dispersiontypesintheopticalfibersingeneral:1-MaterialDispersionWaveguideDispersionPolarization-ModeDispersionPolarizationmodedispersion(PMD)isduetoslightlydifferentvelocityforeachpolarizationmodebecauseofthelackofperfectlysymmetric&anisotropicofthefiberLaserisanopticaloscillator.Itcomprisesaresonantopticalamplifierwhoseoutputisfedbackintoitsinputwithmatchingphase.Anyoscillatorcontains:Anamplifierwithagain-saturatedmechanismAfeedbacksystemAfrequencyselectionmechanismAnoutputcouplingschemeInthermalequilibriumthestimulatedemissionisessentiallynegligible,sincethedensityofelectronsintheexcitedstateisverysmall,andopticalemissionismainlybecauseofthespontaneousemission.Stimulatedemissionwillexceedabsorptiononlyifthepopulationoftheexcitedstatesisgreaterthanthatofthegroundstate.ThisconditionisknownasPopulationInversion.Populationinversionisachievedbyvariouspumpingtechniques.TurnonDelayWhenthedrivingcurrentsuddenlyjumpsfromlow(I1<Ith)tohigh(I2>Ith),(stepinput),thereisa finitetimebeforethelaserwillturnonTheQuantumLimitForanidealphoto-detectorhavingunityquantumefficiencyandproducingnodarkcurrent,itispossibletofindtheminimumreceivedopticalpowerrequiredforaspecificBERperformanceinadigitalsystem.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.Listtheadvantagesoffiber-opticcommunicationsoverothertypesofcommunicationtechnologies.Theadvantageofopticalfibercommunication:WeightandListtheadvantagesoffiber-opticcommunicationsoverothertypesofcommunicationtechnologies.Theadvantageofopticalfibercommunication:WeightandSizeMaterialcost(SiO2isplentiful)InformationCapacityNoelectromagneticinterferenceNoelectricalconnectionDistancebetweenrepeatersBetterBettersecurityLowcrosstalkThefabricationofamplifierOpticalisolator，Opticalmultiplexer,EDF,PumplaserWhataretheadvantagesanddisadvantagesofSDHsystemascomparedtoPDHsystem?ThemainlimitationsofPDHare:Inabilitytoidentifyindividualchannelsinahigher-orderbitstream;Insufficientcapacityfornetworkmanagement;MostPDHnetworkmanagementisproprietary;ThereisnostandardizeddefinitionofPDHbitratesgreaterthan140Mbit/s;and,Therearedifferenthierarchiesinusearoundtheworld.Specializedinterfaceequipmentrequiredtointerworkthetwohierarchies.Listthetypesoffiberattenuationanddispersion.Absorbing\scatteringandbendinglossMaterial/mode/waveguidedispersion.Theavalancheeffect.Thecreatedcarriersareacceleratedbythehighelectricfield,gainingenoughenergytocausefurtherimpactionization.Dynamicrange:21)Differentiatebetweenstepindexandgradedindexopticalfiber.Stepindexfiberhasacoreofoneindexofrefraction;gradedindexfiberhasacoreinwhichtheoutsideedgestartswithalowindexofrefractionthatgraduallyincreasestowardsthecenter.21)Differentiatebetweenstepindexandgradedindexopticalfiber.Stepindexfiberhasacoreofoneindexofrefraction;gradedindexfiberhasacoreinwhichtheoutsideedgestartswithalowindexofrefractionthatgraduallyincreasestowardsthecenter.五計算題1)Supposetwogradedindexfibersaremisalignedwithanaxialoffsetofd=0.3a.Trytocalculatethefractionofopticalpowercoupledfromthefirstfiberintothesecondfiber.（Parameteraisthecoreradius）Thefractionofopticalpowercoupledinthefiber：P 2

d2

d d2 1T arccos( )1 5 1P 2a 2a6a 2a2 2

10.15

0.32

arccos(0.15)10.1522 5 3

2 0.748TurnitintodB,obtain10log

PT1.27dBP

Adouble-heterojunctionInGaAsPLEDemittingatapeakwavelengthof1310nmhasradiativeandnonradiativerecombinationtimesof30and100ns,respectively.Thedrivecurrentis40mA.Computeinternalquantumefficiencyandinternalopticalpower.Thentheinternalquantumefficiency

1 1/30int

r

1/301/100r nrtheinternalpowerlevelis：P

Ihc

0.770.046.62561034Js3108m/s

2.92mWint

int

q 1.60210191.31106AGaAslaseroperatingat800nmhasa500-μmlengthandarefractiveindexn=3.7.Whatarethefrequencyandwavelengthspacing?From

，2

obtain:2Ln 2Ln c

3108

81GHz，2Ln 25001063.7Ina100-nspulse,6×106photonsatawavelengthof1300nmfallonanInGaAsphotodetector.Ontheaverage,5.4×106electron-hole(e-h)pairsaregenerated.Pleasecalculatethequantumefficiency.ThequantumefficiencyNumberofe-hpairsgenerated= Numberofincidentphotons=5.41060.906106Consideragraded-indexopticalfiber,coreindexn1=1.50andthecorecladdingindexdifference

.1.Trytocalculate:Thecladdingindexn2ThenumericalapertureNA=1.50=0.01，1根據(jù)(1)由（1）式，可知n=n2-n2

(2)1 1 2n2=n2（1-2）2 112122 1將n、代入上式，可得11n12將n、代入（2）式，可得1

=1.50

=1.500.98995=1.484912NA=n21

=1.50

=1.500.14142=0.21213ThenumericalapertureNAis2NA=n12

=

0.22222an12V= =312an121

20.01=26.454>VC

=2.405Considera30-kmlongopticalfiberthathasanattenuationof0.8dB/km1300nm.If200ofopticalpowerislaunchedintothefiber,trytocalculatetheopti.caloutputpowerPoutFirstweturntheinputsignalpowerunitfrommWintodBmP)

P

200106W10log 10login 1103WFrom

10dBkmdBkm

P(0),asz=30k,z PP) P)theoutputpoweris

)

out

10log

in zout 7.dBm (0.dBkm)(3kmAlsoP(3km)1031.0/1(mW)0.79103mW 0.79WAphotodiodeisconstructedofGaAs,whichhasaband-gapenergyof1.43eVat300K.Whatisthecutoffwavelength?Thecutoffwavelengthis

hc

6.6251034J

3108m/s

869nmc E g

1.61019J/eV3.6GaAs1.48源在物理上緊密相接，于是分界面上發(fā)生菲涅爾反射：AGaAsopticalsourcewitharefractiveindexof3.6iscoupledtoasilicafiberthathasarefractiveindexof1.48.Ifthefiberendandthesourceareinclosephysicalcontact,then,theFresnelreflectionattheinterfaceisnn2 3.601.482nn 3.601.48Rnn 3.601.481這相當于17.4%的發(fā)射功率反射回光源，與這一R值相對應的耦合功率由下式給定：ThisvalueofRcorrespondstoareflectionof17.4percentoftheemittedopticalpowerbackintothesource.GiventhatPcoupled

1RPemitted由反射造成的功率損耗為：ThepowerlossLindecibelsisfoundfromPL10log

10log(1R)0.83dBPemitted有一個InGaAs100ns1300nm6×106生了5.4×106個電子空隙對，則其量子效率可以等于：Ina100-nspulse,6×106photonsatawavelengthof1300nmfallonanInGaAsphotodetector.Ontheaverage,5.4x106electron-holepairsaregenerated,quantumefficiencyis.5.41066106

90%1.53×10-19J的光子入射到光電二極管上，此二極管的響應度為0.65A/W10mW，則產(chǎn)生的光電流為：Photonsofenergy1.53×10-19Jareincidentonaphotodiodewhichhasaresponsivityof0.65A/W.Iftheopticalpowerlevelis10μW,thephotocurrentisI Pp in

(0.65A/W)(10μW)6.5μA如上圖所示，波長范圍為1300nm-1600nmInGaAspin，量子效率約為90%應度為：Asshowninabovefigure,forthewavelengthrange1300nm<λ <1600nm,thequantumefficiencyforInGaAsisaround90%.Soresponsivityis

0.901.61019C 7.25105hv hc 6.6251034Js3108m/s1300nm時：Responsivityat1300nm

7.25105A/W

/m1.30106m0.942A/W一種硅APD900nm0.5mW10M。初級光電流為：Agivensiliconavalanchephotodiodehasaquantumefficiencyof65%atawavelengthof900nm.Suppose0.5μWofopticalpowerproducesamultipliedphotocurrentof10μA.FindthemultiplicationM.theprimaryphotocurrentisI P

q Pp in

hv hc in 1019C)(9 5107W0.235A6.6251034Js3108m/s倍增因子M為： I 10AThemultiplicationMis M M

43I 0.235 ApInGaAs1300nmID=4=1000Wh=0.90，表面暗電流可以忽略，入射光功率為300nW(-35dBm)，20MHz，計算接收機的各種噪聲。首先計算初級光電流：AgivenInGaAspinphotodiodehasthefollowingparametersatawavelengthof1300nm:ID=4nA,η =0.9,RL=1000Ω,andthesurfaceleakagecurrentisnegligible.Theincidentopticalpoweris300nW(-35dBm),andthereceiverbandwidthis20MHz.Letusfindthevariousnoisetermsofthereceiver.First,weneedtofindtheprimaryphotocurrent.I P

P Pp

in 0.901.61019C1.3 3107W0.282A6.6251034Js3108m/s量子噪聲均方電流：Themean-squarequantumnoisecurrentforapinphotodiodeisi2 Q

B1019C)(0.282106A)(20106Hz)1.801018A2p光檢測器均方暗電流：Themean-squaredarkcurrentforphotodetectorisi2 2qI B2(1.61019C)(4109A)(20106Hz)2.561020A2DB D負載均方熱噪聲電流為：Themean-squarethermalnoisecurrentcontributedbyRLforthereceiveris4Ki2 T RL

T 4(1.381023J/K)(293K)B 20106Hz32310188.5(18.5dB)時，BER=10-51.544Mb/sDS1電BER導致每0.065是通過增加信號功率使S/N=12.0(21.6dB),BER就會降到10-DS650秒或11)才有一位誤碼，通常這是可以容忍的。Forarmssignal-to-noiseratioof8.5(18.5dB)wehaveIfthisisthereceivedsignallevelforastandardDS1telephonerateof1.544Mb/s,thisBERresultsinamisinterpretedbitevery0.065swhichishighlyunsatisfactory.However,byincreasingthesignalstrengthsothatthermsS/N=12.0(21.6dB),theBERdecreasesto10-9.FortheDS1case,thismeansthatabitismisinterpretedevery650s(or11min),which,ingeneral, istolerate.對于高速SONET(光纖同步網(wǎng)）鏈路，OC-12速率是622Mb/s,要求BER為10-11或10-12,這就表示至少要求V/σ=S/N=13.0(22.3dB)Forhigh-speedSONETlinks,saytheOC-12ratewhichoperatesat622Mb/s,BERsof10 -1110-12arerequired.ThismeansthatweneedtohaveatleastrmsS/N=13.0(22.3dB)9）20Mb/s10-9850nmSipin-42dBm。系統(tǒng)光源為GaAlAsLED-13dBm的平均光功率耦合進纖芯直徑為5029dB1dB6dBa，其傳輸距離可以由上式得到fWeshallbeginbyspecifyingadatarateof20Mb/sandaBERof10-9(i.e.atmostoneerrorcanoccurforevery109bitssent).Forthereceiver,weshallchooseasiliconpinphotodiodeoperatingat850nm.Checkthefigureonthelastslide,weknowthattherequiredreceiverinputsignalis-42dBm.WenextselectaGaAlAsLEDthatcancouplea50μ W(-13dBm)averageopticalpowerintoafiberflyleadwitha50μmcorediameter.Wethushavea29dBallowablepowerloss.Assumefurtherthata1dBlossoccurswhenthefiberflyleadisconnectedtothecableandanother1dBlossoccursatthecable-photodetectorinterface.Includinga6-dBsystemmargin,thepossibletransmissiondistanceforacablewithanattenuationofa=3.5dB/km,thena6.0kmftransmissionpathispossible.PPPt s r

29dB2(1dB)

L6dBf如果af=3.5dB/km，則傳輸距離為6kmIfαf=3.5dB/km，thenL=6km假定一個1550nm3dBInGaAsAPD2.5Gb/s-32dBm60km0.3dBm/km。由于設(shè)備安裝需要，在傳輸光纜的末端與SONET3dB的損耗。另外，假設(shè)每個光纖連接點上有1dB(由子有跳線，每一端)。Considera1550nmlaserdiodethatlauncheda3dBmopticalpowerlevelintoafiberflylead,anInGaAsAPDwitha-32dBmsensitivityat2.5Gb/s,anda60kmlongopticalcablewitha0.3dB/kmattenuation.Assumethathere,becauseofthewaytheequipmentisarranged,aopticaljumpercableisneededateachendbetweentheendofthetransmissioncableandtheSONETequipmentrack.Assumethateachjumpercableintroducesalossof3dB.Inaddition,assumea1dBconnectorlossoccursateachfiberjoint(twoateachendbecauseofthejumpercables).假定LED15ns的展寬時間。采用40nm寬的LED6km的鏈路上21ns25MHz14400q=3.9ns。WeshallassumethattheLEDtogetherwithitsdrivecircuithasarisetimeof15ns.TakingatypicalLEDspectralwidthof40nm,wehaveamaterial-dispersion-relatedrise-timedegradationof21nsoverthe6-kmlink.Assumingthereceiverhasa25MHzbandwidththenfromtheequation(7-17)thecontributiontotherise-timedegradationfromthereceiveris14ns.Ifthefiberwe elect has a 400 MHz.km bandwidth-distance product and with q=0.7, then modal-dispersion-inducedfiberrisetimeis3.9ns.Substitutingallthesevaluesbackintoequation(7-17)resultsinalinkrisetimeof30ns. t sys

15ns22ns23.9ns214ns21/2

30ns20Mb/s(50的NRZ數(shù)字流，這個結(jié)果低于允許的35ns件的選擇符合系統(tǒng)設(shè)計標準。Thisvaluefallsbelowthemaximumallowable35nsrise-timedegradationforour20Mb/sNRZdatastream.Thechoiceofcomponentswasthusadequatetomeetoursystemdesigncriteria.假定LD0.025ns0.11550nm的半導體激光器，所采用光纖的平均色