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1、复习一、Fillintheblank（30points,2%perblank）(1)Asthetemperatureincreases,thediode'sgaindecreases,thethresholdcurrentbecomesgreater.二、Judgement,onlyoneiscorrect（16points,4%perblank）(1)Whatistheoutputcurrentofaphotodetectorwhosequantumefficiencyis0.9.Thewavelengthis1
2、300nm,andtheincidentpowerlevelis-37dBm.(a)a.0.188mAb.0.190mAc.0.192mAd.0.194mA三、简述题（24points,8%perblank）1、简述光纤通信系统对光源、光纤和光检测器的要求。¨carrierSource:stable,single-frequency,sufficientpower,theinformationiscontainedinthevariationoftheopticpower¨fiber:attenuation,dis
3、tortion,acceptanceangle¨photodetectors:longlife,lowpowerconsumption,highsensitivity,fastresponse2、SiO2折射率特点Describethecharacteristicsofrefractiveindexforpuresilicondioxideglass.¨Therefractiveindexdecreaseswithincreasingwavelengths.¨Ataparticularwavelength,ther
4、eisaninflectionpointontherefractiveindexcurve.Themagnitudeoftheslopeisminimumatthiswavelength.¨Forpuresilica,therefractiveindexiscloseto1.45andtheinflectionpointisnear1.3mm.3、色散如何导致的模拟信号、数字信号畸变Howdoesdispersioncreatesignaldistortion?¨Digitalsignal:Theseveralpu
5、lsestravelatdifferentvelocities,reachingtheendofthefiberatslightlydifferenttimes.Whensummedattheoutput,theslightlydisplacedpulsesaddtogether,yieldinganoutputthatislengthened,orspread,relativetotheinputsignal.¨Analogsignal:Attheinputseveralwavelengthsvarytogeth
6、erinphasewitheachother,creatingalargesignalvariation.Aftertravelthroughthedispersivemedia,thesewavelengthsarenolongerinphase.Whenaddedtogethertheyproduceasignalvariationlowerinamplitudethantheinputsignalvariation.4、导模条件Explainingmodecondition.Stableinterferenc
7、epatternsoccurredonlywhenthephaseshiftforacompleteroundtripwasequaltoanintegralnumberof2pradians.Denotingtheround-tripphaseshiftbyDj,thecavityresonanceconditioncanbewrittenasDj=m2p,wheremisaninteger.Djisthesumofthephaseshiftalongthepathandthephaseshiftthattake
8、splaceateachofthetworeflectingboundaries.5、棱镜耦合的特点Describetheworkingprincipleofanopticalisolator¨Single-modeexcitationisparticularlyconvenientwithprismcoupling.¨High-refractive-ind
