光纤通信练习题汇总.docx

光纤通信练习题汇总.docx

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光纤通信练习题汇总

1-1Whoisthefatherofthefiber?

Solution:

Gaohun

1-2Abasiccommunicationssystemconsistsofthreecomponents,whichare?

Solution:

Abasiccommunicationsystemconsistsofatransmitter,areceiver,andaninformationchannel.

1-3Thefunctionofamessageorigin?

Solution:

Itisatransducerthatconvertsanonelectricalmessageintoanelectricalsignal.

1-4Thefunctionofamodulator?

Solution:

Themodulatorhastwomainfunctions.First,itconvertstheelectricalmessageintotheproperformat.Second,itimpressthissignalontothewavegeneratedbythecarriersource.

1-5Whataretwocategoriesofmodulationformat?

Solution:

Twocategoriesofmodulationformatarealonganddigital.

1-6Thefunctionofacarriersource?

Solution:

Thecarriersourcegeneratesthewave.

1-7Whatarethecommondevicesusedascarriersourceinthefiberopticsystem?

Solution:

LDandLED

1-8Thefunctionofachannelcoupler?

Solution:

Thefunctionofachannelcoupleristhatfeedspowerintotheinformationchannel.

1-9Whatcanbeusedasinformationchannelinfiberopticcommunications?

Solution:

Glassandplastic.

1-10Whatarethedesirablepropertiesoftheinformationchannel?

Solution:

Lowloss,smalldistortion

1-11Whataredifferencesbetweenopticalamplifiersandrepeaters?

Solution:

1）Repeatercanbeusedonlyfordigitalsystems;opticalamplifiersaresuitableforbothanaloganddigitalsignals.

2）Opticamplifierscompensateonlyforsignalattenuation,butrepeatersreconstituteboththeamplitudeandwaveshapeofadigitalsignal.

3）Beingmuchmorecomplex,repeatersaremoreexpensivethanamplifiers.

1-12Foradetector,what’stheideallyrelationshipbetweentheoutputcurrentandinputopticalpower?

Solution:

Thecurrentdevelopedbythesedetectorsisproportionaltothepowerintheincidentopticwave.

1-13Howtoconvertananalogsignaltoadigitalsignal?

Solution:

Sample,Quantization,coding

1-14Whatisusedtodefinethequalityofanalogsignalanddigitalsignal?

Solution:

SNRandBER

1-15WhatisthedefinitionofdB?

Solution:

1-16Talkabouttheadvantagesoffiber.

Solution:

Toomuch,wocanrefertoourbookinpassage24

2-1What’sthedefinitionoff-number?

Solution:

Theratio

iscalledthef-numberofthelens.

2-2What’sthefunctionofGRINrodlens?

What’stheadvantagesofGRINrodlens?

Solution:

1）TheGRINrodhasfocusingandcollimatingproperties.

2）TheGRINrodisusefulforimaging.

3）TheGRINrodisdesirablebecausesmallfocallengthscanbeobtained,permittingconstructionofshort,solidopticstructures.

2-3Howisnumericalaperture（NA）defined?

WhatabilitydoesNAshow?

Solution:

ThelowNAdoesmakecouplingefficiencytendtobepoorbutimprovesthefiber'sbandwidth.

2-4Therearethreekindsoflensesoftenusedascouplerintheopticscommunicationsystem.Whatarethey?

Solution:

Thinlens,cylindricallens,GRIN

3-1What’sthedispersion?

Therearetwokindsofdispersion,whatarethey?

Solution:

Dispersionisthenamegiventothepropertyofvelocityalsovarieswithwavelength.

Materialdispersionandwaveguidedispersion.

3-2Whydosematerialdispersionexist?

Solution:

Becausetherefractiveindexdecreaseswithincreasingwavelengths.

3-3whatistheunitofmaterialdispersionM?

Solution:

3-4Forpuresilica,atwhichwavelengthMisequalto0?

Solution:

1.3um

3-5Whatissolitons?

Howcanithappen?

3-6HowdosepulsespreadlimitthedatarateofRZdigitalsignal?

Solution:

Adjacentpulsesarewellseparatedbyrequiringthatthepulsespreadbelessthan35%ofthetimeslot.Whenthisisnotaccomplished,portionsofthepulsemayspreadintotheneighboringtimeslot,producingintersymbolinterferencetheprobabilityofdetectionerrors.

Theinitialpulseconsistsofasumofplusesthatareidentical,exceptfortheirwavelengths.Theseveralpulsestravelatdifferentvelocities,reachingtheendofthefiberatslightlydifferenttimes.Whensunnedattheoutput,theslightlydisplacedplusesaddtogether,yieldinganoutputthatislengthened,orspread,relativetotheinputsignal.

4-1ConsideranAlGaAsLaserDiode,,givetherangeofeffectiverefractiveindexplease.

Solution:

4-2Whatisthemodeconditionofdielectricslabwaveguide?

Solution:

Thestableinterferencepatternsoccurredonlywhenthephaseshiftforacompleteroundtripwasequaltoanintegralnumberof

radians.

4-3Lookatthefigurebelow.IsthemodeofthepropagationTEorTM?

Solution:

TE

4-4what’sthedegeneratemodes?

Solution:

Waveswhoserayanglesdonotsatisfy

willquicklybeattenuatedbydestructiveinterference,whichisdegenerate.

4-5writeoutthemthmodecutoffconditionofsymmetricslabwaveguide.

Solution:

CutoffforthemthTEmode:

4-6Inmodepattern,themodeindexmisthenumberoftimestheelectricfieldcrossingthroughzerointhetransverseplane.Isitright?

Solution:

No,N=m+1

4-7what’sthelongitudinalpropagationfactor?

Solution:

Theguidedwave'snetdirectionoftravelishorizontal.Thecomponentofthepropagationfactoralongthisdirectionis

.wewillcallthisthelongitudinalpropagationfactor.

4-8Whatisthesingle-modepropagationconditioninsymmetricslabwaveguide?

Solution:

Thesingle-modepropagationconditioninsymmetricslabwaveguideis

4-9What’sthemaindifferencesbetweensymmetricwaveguideandasymmetricmodecharts?

Solution:

2

4-10forslabwaveguide,thehigherthemodesare,the（larger/smaller）thepropagationanglesare.

Solution:

larger

4-11therearethreemethodstocouplethelightintothedielectricslabwaveguide,whatarethey?

Solution:

Edgecoupling,prismcoupling,gratingcoupling.

4-12therearethreereasonsleadtopulsespread,whatarethey?

Solution:

Materialdispersion,waveguidedispersion,multimodedistortion.

4-13writedownsomepassiveandactivecomponentsoffiberopticalcommunicationssystem.

5-1Whichonehasthelowestlossinallglassfiber,plastic-cladglassfiberandallplasticfiber?

WhichonehasthelargestNA?

Solution:

Allglassfiberhasthelowestloss.

AllplasticfiberhasthelargestNA

5-2TheacceptanceangleofSIfiberisindependentofwheretheincidentrayentersthecore.Isitright?

5-3HowdoestheNAofaGRINfiberchange?

Solution:

TheNAdecreasewithradialdistancefromtheaxis.

5-4Howmanykindsoflossesoccursinglassfibers?

Whatarethey?

Solution:

Absorption,scattering,geometriceffects.

5-5Whichlosscanbecontrolledbypropermanufacturingtechniques?

3intrinsicabsorption（B）Rayleighscattering（C）inhomogeneities（D）infraredabsorption

Solution:

（C）

5-6Inthelow-lossregionofallglassfiberconsideringthetotalattenuation,whichfactorboundstheshort-wavelengthsideandwhichoneboundsthelong-wavelengthside?

Solution:

Thelow-lossregionforallglassfiberisboundedontheshort-wavelengthsidebyscatteringandonthelong-wavelengthsidebyinfraredabsorption.

5-7whichcommunicationwindowisconventionalband?

whichcommunicationwindowisoriginalband?

（A）1260nm-1360nm;（B）1460nm-1530nm;（C）1530nm-1565nm;（D）1565nm-1625nm

Solution:

（C）isconventionalband（A）isoriginalband

5-8Whichdeviceisoftenusedtomeasurethefiberattenuation?

Solution:

OTDR

5-10Asweallknow,formultimodefibers,GRINfibersareoftenchosen;forsinglemodefibers,SIfibersareoftenchosen.Why?

Multimodegraded-indexfibersproducelessmodalpulsedistortionthanmultimodestep-indexfibers.

Single-modegraded-indexfibersprovidenoadvantageoversingle-modestep-indexfiberswithrespecttopulsespreading.

5-12IfsinglemodeSIfibersareinformationchannel,whatkindoflightsourceshouldbeused?

Why?

LD

5-13Thelowestabsorptionregionofglassfibersisat1550nm,thesmallestpulsedispersionregionisjustabove1300nm.Whatkindsoffiberscanworkatbothlowestabsorptionregionandthesmallestpulsedispersionregion?

Howcangetsuchkindsoffiber?

DSF

Thishasbeenaccomplishedbyconstructingasingle-modefiberwithatriangular-shapedrefractiveindexvariation.

5-14whatkindofsinglemodefiberisusedin1550nmsystemtocounterdispersion.

6-1comparetherelativeadvantagesanddisadvantagesofLEDandLD.

Solution:

4）LDsaremuchfasterthanLEDs.

5）LDstypicallypossesslinewidthsof1-5nm,considerablysmallerthantheoutputspectraofLEDs.

6）ThelightformLDwhichiscomparedwithLEDiscontainedwithinamuchsmallerangularregion,makingcouplingtoafibereasierandmoreefficient.

7）LEDsaremuchcheaperthanLDs.

6-2WhatistherelationshipbetweeninputcurrentandoutputopticalpowerofLEDs?

Solution:

TheopticpowergeneratedbyanLEDislinearlyproportionaltotheinputcurrent:

6-3therearetwofactorsdecreasetheoutputopticalpowerofLEDs.Whatarethey?

Solution:

Timeandtemperature.

6-4whatisthedifferencebetweenthedigitalmodulationofLDandthedigitalmodulationofLED?

Solution:

DigitalmodulationofLDdiffersfromdigitalmodulationofLED.Adcbiascurrent,

isadded,toplacethecurrentatthresholdwhenthesignalcurrent

iszero.

6-5HowdotheoperatingcharacteristicsofLDdependonthetemperature?

Solution:

1）Asthetemperatureincreases,LD'sgaindecreases,andsomorecurrentisrequiredbeforeoscillationcanbebegin-thatis,thethresholdcurrentbecomesgreater.

2）Ataconstantcurrent,theoutputpowerofaLDwilldiminishifthetemperaturerises.

3）Thelaseremissionwavelengthalsodependsuponthetemperature.

6-6whichLDhasnarrowbandwidth?

Solution:

DFB

6-7What’stheworkingmaterialinHeNeLaser?

Solution:

Ne

6-8InLDs,theatomsofworkingmaterialintheu