电子与通信技术专业英语（第6版）课件 项目13 Optical Fiber Communications

刘骋蔡静主编电子与通信技术专业英语（第6版）高职高专电子信息类“十三五”规划教材EnglishonElectronicandTelecommunicationTechnology03UnitⅢCommunicationTechnologyLesson13OpticalFiberCommunications

UnitⅢNewWordsconvey [kən'vei] vt. 搬运，传达，转让transfer ['trænsfə:] n. 移动，传递，转移Superimpose [,su:pərɪm'pəʊz] v. 添加，双重microwave ['maikrəweiv] n. 微波conversion [kən'və:ʃn] n. 变换，转化semiconductor [,semikən'dʌktə] n. 半导体NewWordsdiode ['daiəud] n. 二极管photodiode [,fəutəu'daiəud] n. 光敏二极管，光电二极管phototransistor [,fəutəutræn'zistə] n. 光电晶体管，光敏晶体管photoconductor [,fəutəukən'dʌktə] n. 【物】光电导体，

光电导元件discrete [di'skri:t] adj. 不连续的，离散的NewWordsimplement ['implimənt,'impliment] n.&vt. 工具，器具；贯彻，

实现，执行encode [in'kəud] vt. 编码equalizer ['i:kwəlaizə] n. 均衡器，平衡装置decode [,di:'kəud] vt. 解码，译解PhrasesandExpressionsopticalfiber 光纤electromagneticwave 电磁波APD(AvalanchePhotoDiode) 雪崩发光二极管front-endamplifier 前置放大器Communicationmaybebroadlydefinedasthetransferofinformationfromonepointtoanother.Whentheinformationistobeconveyedoveranydistanceacommunicationsystemisusuallyrequired.Withinacommunicationsystemtheinformationtransferisfrequentlyachievedbysuperimposingormodulatingtheinformationontoanelectromagneticwavewhichactsasacarrierfortheinformationsignal.Lesson13OpticalFiberCommunicationsChineseTranslationofTexts广义地说，把信息从一点传送到另一点就称为通信。当信息跨越一段距离被传送时，就需要一个通信系统。在通信系统中，信息传送是通过把信息叠加在电磁波上或对电磁波进行调制来实现的，电磁波起着载送信号的作用。第13课

光纤通信ChineseTranslationofTextsThismodulatedcarrieristhentransmittedtotherequireddestinationwhereitisreceivedandtheoriginalinformationsignalisobtainedbydemodulation.Sophisticatedtechniqueshavebeendevelopedforthisprocessbyusingelectromagneticcarrierwavesoperatingatradiofrequenciesaswellasmicrowaveandmillimeterwavefrequencies.However,“communication”mayalsobeachievedbyusinganelectromagneticcarrierwhichisselectedfromtheopticalrangeoffrequencies.ChineseTranslationofTexts这一经过调制的载波随后被传送到要求到达的目的地，在那里被接收，并且通过解调还原成原始信息。在运用电磁载波的领域，高新技术得到进一步的发展，比如射频、微波以及毫米波的频率都被用来作为载波频率。在通信中，也可选择光波的频率作为载波频率。ChineseTranslationofTextsTypicalopticalfibercommunicationssystemisshowninFig.13-1.Inthiscasetheinformationsourceprovidesanelectricalsignaltoatransmittercomprisinganelectricalstagewhichdrivesanopticalsourcetogivemodulationofthelightwavecarrier.Theopticalsourcewhichprovidestheelectrical-opticalconversionmaybeeitherasemiconductorlaserorlightemittingdiode(LED).ChineseTranslationofTexts典型的光纤通信系统如图13－1所示。信源提供电信号给发射机，发射机组成一个电子平台来驱动光源以完成对光载波的调制。光源是由发光二极管或半导体激光管构成的，它完成光—电变换。传输媒介由光纤（缆）组成。ChineseTranslationofTextsThetransmissionmediumconsistsofanopticalfibercableandthereceiverconsistsofanopticaldetectorwhichdrivesafurtherelectricalstageandhenceprovidesdemodulationoftheopticalcarrier.Photodiodes(p-n,p-i-noravalanche)and,insomeinstances,phototransistorandphotoconductorsareutilizedforthedetectionoftheopticalsignalandtheoptical-electricalconversion.Thusthereisarequirementforelectricalinterfacingateitherendoftheopticallinkandatpresentthesignalprocessingisusuallyperformedelectrically.ChineseTranslationofTexts光接收机由驱动后面电路平台的光探测器构成，用以完成对已调光载波的解调。用于检测光信号和进行光—电转换的器件有：光电二极管（P-N、P-I-N或雪崩管）、发光三极管以及光敏电阻等。因此，在光系统链路的两端都要求有电接口，并且在现阶段，信号处理通常是通过电路实现的。ChineseTranslationofTextsTheopticalcarriermaybemodulatedbyusingeitherananalogordigitalinformationsignal.Analogmodulationinvolvesthevariationofthelightemittedfromtheopticalsourceinacontinuousmanner.Withdigitalmodulation,however,discretechangesinthelightintensityareobtained(i.e.on-offpulses).ChineseTranslationofTexts模拟或数字的信号均可用来调制光载波。模拟调制是指从光源处发射的连续光强度的变化，而数字调制则不然，它是通过光强度离散的变化（比如，有无光脉冲）来实现的。ChineseTranslationofTextsAlthoughoftensimplertoimplement,analogmodulationwithanopticalfibercommunicationsystemislessefficient,requiringafarhighersignaltonoiseratioatthereceiverthandigitalmodulation.Also,thelinearityneededforanalogmodulationisnotalwaysprovidedbysemiconductoropticalsource,especiallyathighmodulationfrequencies.Forthesereasons,analogopticalfibercommunicationlinkaregenerallylimitedtoshorterdistancesandlowerbandwidthsthandigitallinks.ChineseTranslationofTexts虽然简单易行，但模拟调制在光通信系统调制中调制效率较低，而且与数字调制相比，需要高得多的信噪比。模拟调制所必需的线性不总是来源于半导体光源，尤其是在高频调制中。基于上述原因，与数字光通信系统相比较，模拟光通信链路通常被限制使用在更短的通信距离和更窄的带宽上。ChineseTranslationofTextsInitially,theinputdigitalsignalfromtheinformationsourceissuitablyencodedforopticaltransmission.Thelaserdrivecircuitdirectlymodulatestheintensityofthesemiconductorlaserwiththeencodeddigitalsignal.Henceadigitalopticalsignalislaunchedintotheopticalfibercable.Theavalanchephotodiode(APD)detectorisfollowedbyafront-endamplifierandequalizerorfiltertoprovidegainaswellaslinearsignalprocessingandnoisebandwidthreduction.Finally,thesignalobtainedisdecodedtogivetheoriginaldigitalinformation.ChineseTranslationofTexts首先，输入的信源数字信号被适当地编码以进行光传输。激光器的驱动电路通过这些已编码的数字信号来直接调制激光器的发光强度，然后数字光信号被注入光纤电缆。在接收端，信号通过雪崩发光二极管（APD）后进入前置放大器和均衡器或滤波器，放大器用来提供增益、滤波器用来对信号进行线性处理和减少噪声带宽。最后，信号通过解码得到原始数字信号。ChineseTranslationofTextsNotes…bysuperimposingormodulatingtheinformationontoanelectromagneticwavewhichactsasacarrierfortheinformationsignal.（1）介词by+动名词短语充当状语。（2）which引导定语从句，修饰wave。1NotesThismodulatedcarrieristhentransmittedtotherequireddestinationwhereitisreceivedandtheoriginalinformationsignalisobtainedbydemodulation.这一经过调制的载波随后被传送到要求到达的目的地，在那里被接收，并且通过解调还原成原始信息。过去分词短语required充当定语，whereitis…bydemodulation是定语从句，两者均修饰destination。2Notes…byusingelectromagneticcarrierwavesoperatingatradiofrequenciesaswellasmicrowaveandmillimeterwavefrequencies.（1）介词by+动名词短语充当状语。（2）aswellas：“以及”，相当于and，常用于句中，下文中仍有这种用法。再如，HecanspeakEnglishaswellasChinese.请比较：HecanspeakEnglish,andhecanspeakChineseaswell.（aswell用于句末，相当于too）。3NotesHowever,“communication”mayalsobeachievedbyusinganelectromagneticcarrierwhichisselectedfromtheopticalrangeoffrequencies.在通信中，也可选择光波的频率作为载波频率。which引导定语从句，修饰electromagneticcarrier。4NotesInthiscasetheinformationsourceprovidesanelectricalsignaltoatransmittercomprisinganelectricalstagewhichdrivesanopticalsourcetogivemodulationofthelightwavecarrier.信源提供电信号给发射机，发射机组成一个电子平台来驱动光源以完成对光载频的调制。（1）inthiscase：在这种场合下、既然这样。（2）which引导定语从句。5Notes…toprovidegainaswellaslinearsignalprocessingandnoisebandwidthreduction.此为不定式短语，充当目的状语。5Exercises1.WriteT(True)orF(False)besidethefollowingstatementsaboutthetext.a.Thismodulatedcarrieristhentransmittedtotherequireddestinationwhereitisreceivedandtheoriginalinformationsignalisobtainedbymodulation.b.Sophisticatedtechniqueshavebeendevelopedforthisprocessbyusingmagneticcarrierwavesoperatingatradiofrequenciesaswellasmicrowaveandmillimeterwavefrequencies.c.Theinformationsourceprovidesanelectricalsignaltoatransmittercomprisinganelectricalstagewhichdrivesanopticalsourcetogivemodulationofthelightwavecarrier.d.Thetransmissionmediumconsistsofanopticalfibercableandthereceiver.Exercises1.WriteT(True)orF(False)besidethefollowingstatementsaboutthetext.a.Thismodulatedcarrieristhentransmittedtotherequireddestinationwhereitisreceivedandtheoriginalinformationsignalisobtainedbymodulation.b.Sophisticatedtechniqueshavebeendevelopedforthisprocessbyusingmagneticcarrierwavesoperatingatradiofrequenciesaswellasmicrowaveandmillimeterwavefrequencies.c.Theinformationsourceprovidesanelectricalsignaltoatransmittercomprisinganelectricalstagewhichdrivesanopticalsourcetogivemodulationofthelightwavecarrier.d.Thetransmissionmediumconsistsofanopticalfibercableandthereceiver.FFTFExercises1.WriteT(True)orF(False)besidethefollowingstatementsaboutthetext.e.Theopticalcarrierismodulatedbyusingneitherananalognordigitalinformationsignal.f.Withdigitalmodulation,discretechangesinthelightintensityarenotobtained.g.Analogmodulationwithanopticalfibercommunicationsystemismoreefficient,requiringafarlowersignaltonoiseratioatthereceiverthandigitalmodulation.h.Theinputdigitalsignalfromtheinformationsourceisnotsuitablyencodedforopticaltransmission.Exercises1.WriteT(True)orF(False)besidethefollowingstatementsaboutthetext.e.Theopticalcarrierismodulatedbyusingneitherananalognordigitalinformationsignal.f.Withdigitalmodulation,discretechangesinthelightintensityarenotobtained.g.Analogmodulationwithanopticalfibercommunicationsystemismoreefficient,requiringafarlowersignaltonoiseratioatthereceiverthandigitalmodulation.h.Theinputdigitalsignalfromtheinformationsourceisnotsuitablyencodedforopticaltransmission.FFFFExercises2.Fillinthemissingwordsaccordingtothetext.a.Withinacommunicationsystemtheinformationtransferis

bysuperimposingormodulatingtheinformationontoanelectromagneticwavewhichactsasacarrier.b.Photodiodes(p-n,p-i-noravalanche)and

and

areutilizedforthedetectionoftheopticalsignalandtheoptical-electricalconversion.c.Thelaserdrivecircuitdirectlymodulatestheintensityofthesemiconductorlaserwiththeencodeddigitalsignal.Hencea

islaunchedintotheopticalfibercable.d.Thereisarequirementforelectricalinterfacingateitherendoftheopticallinkandatpresentthe

isusuallyperformedelectrically.Exercises2.Fillinthemissingwordsaccordingtothetext.a.Withinacommunicationsystemtheinformationtransferisfrequentlyachievedbysuperimposingormodulatingtheinformationontoanelectromagneticwavewhichactsasacarrier.b.Photodiodes(p-n,p-i-noravalanche)andphototransistorandphotoconductorsareutilizedforthedetectionoftheopticalsignalandtheoptical-electricalconversion.c.Thelaserdrivecircuitdirectlymodulatestheintensityofthesemiconductorlaserwiththeencodeddigitalsignal.Henceadigitalopticalsignalislaunchedintotheopticalfibercable.d.Thereisarequirementforelectricalinterfacingateitherendoftheopticallinkandatpresentthesignalprocessingisusuallyperformedelectrically.Exercises3.TranslatethefollowingparagraphintoChinese.Communicationmaybebroadlydefinedasthetransferofinformationfromonepointtoanother.Whentheinformationistobeconveyedoveranydistance,acommunicationsystemisusuallyrequired.Withinacommunicationsystem,theinformationtransferisfrequentlyachievedbysuperimposingormodulatingtheinformationontoanelectromagneticwavewhichactsasacarrierfortheinformationsignal.Exercises3.TranslatethefollowingparagraphintoChinese.Communicationmaybebroadlydefinedasthetransferofinformationfromonepointtoanother.Whentheinformationistobeconveyedoveranydistance,acommunicationsystemisusuallyrequired.Withinacommunicationsystem,theinformationtransferisfrequentlyachievedbysuperimposingormodulatingtheinformationontoanelectromagneticwavewhichactsasacarrierfortheinformationsignal.广义地说，把信息从一点传送到另一点就称为通信。当信息跨越一段距离被传送时，就需要一个通信系统。在通信系统中，信息传送是通过把信息叠加在电磁波上或对电磁波进行调制来