電子與通信技術(shù)專業(yè)英語（第6版）課件 項目13 Optical Fiber Communications

劉騁蔡靜主編電子與通信技術(shù)專業(yè)英語（第6版）高職高專電子信息類“十三五”規(guī)劃教材EnglishonElectronicandTelecommunicationTechnology03UnitⅢCommunicationTechnologyLesson13OpticalFiberCommunications

UnitⅢNewWordsconvey [k?n'vei] vt. 搬運，傳達，轉(zhuǎn)讓transfer ['tr?nsf?:] n. 移動，傳遞，轉(zhuǎn)移Superimpose [,su:p?r?m'p??z] v. 添加，雙重microwave ['maikr?weiv] n. 微波conversion [k?n'v?:?n] n. 變換，轉(zhuǎn)化semiconductor [,semik?n'd?kt?] n. 半導體NewWordsdiode ['dai?ud] n. 二極管photodiode [,f?ut?u'dai?ud] n. 光敏二極管，光電二極管phototransistor [,f?ut?utr?n'zist?] n. 光電晶體管，光敏晶體管photoconductor [,f?ut?uk?n'd?kt?] n. 【物】光電導體，

光電導元件discrete [di'skri:t] adj. 不連續(xù)的，離散的NewWordsimplement ['implim?nt,'impliment] n.&vt. 工具，器具；貫徹，

實現(xiàn)，執(zhí)行encode [in'k?ud] vt. 編碼equalizer ['i:kw?laiz?] n. 均衡器，平衡裝置decode [,di:'k?ud] vt. 解碼，譯解PhrasesandExpressionsopticalfiber 光纖electromagneticwave 電磁波APD(AvalanchePhotoDiode) 雪崩發(fā)光二極管front-endamplifier 前置放大器Communicationmaybebroadlydefinedasthetransferofinformationfromonepointtoanother.Whentheinformationistobeconveyedoveranydistanceacommunicationsystemisusuallyrequired.Withinacommunicationsystemtheinformationtransferisfrequentlyachievedbysuperimposingormodulatingtheinformationontoanelectromagneticwavewhichactsasacarrierfortheinformationsignal.Lesson13OpticalFiberCommunicationsChineseTranslationofTexts廣義地說，把信息從一點傳送到另一點就稱為通信。當信息跨越一段距離被傳送時，就需要一個通信系統(tǒng)。在通信系統(tǒng)中，信息傳送是通過把信息疊加在電磁波上或?qū)﹄姶挪ㄟM行調(diào)制來實現(xiàn)的，電磁波起著載送信號的作用。第13課

光纖通信ChineseTranslationofTextsThismodulatedcarrieristhentransmittedtotherequireddestinationwhereitisreceivedandtheoriginalinformationsignalisobtainedbydemodulation.Sophisticatedtechniqueshavebeendevelopedforthisprocessbyusingelectromagneticcarrierwavesoperatingatradiofrequenciesaswellasmicrowaveandmillimeterwavefrequencies.However,“communication”mayalsobeachievedbyusinganelectromagneticcarrierwhichisselectedfromtheopticalrangeoffrequencies.ChineseTranslationofTexts這一經(jīng)過調(diào)制的載波隨后被傳送到要求到達的目的地，在那里被接收，并且通過解調(diào)還原成原始信息。在運用電磁載波的領(lǐng)域，高新技術(shù)得到進一步的發(fā)展，比如射頻、微波以及毫米波的頻率都被用來作為載波頻率。在通信中，也可選擇光波的頻率作為載波頻率。ChineseTranslationofTextsTypicalopticalfibercommunicationssystemisshowninFig.13-1.Inthiscasetheinformationsourceprovidesanelectricalsignaltoatransmittercomprisinganelectricalstagewhichdrivesanopticalsourcetogivemodulationofthelightwavecarrier.Theopticalsourcewhichprovidestheelectrical-opticalconversionmaybeeitherasemiconductorlaserorlightemittingdiode(LED).ChineseTranslationofTexts典型的光纖通信系統(tǒng)如圖13－1所示。信源提供電信號給發(fā)射機，發(fā)射機組成一個電子平臺來驅(qū)動光源以完成對光載波的調(diào)制。光源是由發(fā)光二極管或半導體激光管構(gòu)成的，它完成光—電變換。傳輸媒介由光纖（纜）組成。ChineseTranslationofTextsThetransmissionmediumconsistsofanopticalfibercableandthereceiverconsistsofanopticaldetectorwhichdrivesafurtherelectricalstageandhenceprovidesdemodulationoftheopticalcarrier.Photodiodes(p-n,p-i-noravalanche)and,insomeinstances,phototransistorandphotoconductorsareutilizedforthedetectionoftheopticalsignalandtheoptical-electricalconversion.Thusthereisarequirementforelectricalinterfacingateitherendoftheopticallinkandatpresentthesignalprocessingisusuallyperformedelectrically.ChineseTranslationofTexts光接收機由驅(qū)動后面電路平臺的光探測器構(gòu)成，用以完成對已調(diào)光載波的解調(diào)。用于檢測光信號和進行光—電轉(zhuǎn)換的器件有：光電二極管（P-N、P-I-N或雪崩管）、發(fā)光三極管以及光敏電阻等。因此，在光系統(tǒng)鏈路的兩端都要求有電接口，并且在現(xiàn)階段，信號處理通常是通過電路實現(xiàn)的。ChineseTranslationofTextsTheopticalcarriermaybemodulatedbyusingeitherananalogordigitalinformationsignal.Analogmodulationinvolvesthevariationofthelightemittedfromtheopticalsourceinacontinuousmanner.Withdigitalmodulation,however,discretechangesinthelightintensityareobtained(i.e.on-offpulses).ChineseTranslationofTexts模擬或數(shù)字的信號均可用來調(diào)制光載波。模擬調(diào)制是指從光源處發(fā)射的連續(xù)光強度的變化，而數(shù)字調(diào)制則不然，它是通過光強度離散的變化（比如，有無光脈沖）來實現(xiàn)的。ChineseTranslationofTextsAlthoughoftensimplertoimplement,analogmodulationwithanopticalfibercommunicationsystemislessefficient,requiringafarhighersignaltonoiseratioatthereceiverthandigitalmodulation.Also,thelinearityneededforanalogmodulationisnotalwaysprovidedbysemiconductoropticalsource,especiallyathighmodulationfrequencies.Forthesereasons,analogopticalfibercommunicationlinkaregenerallylimitedtoshorterdistancesandlowerbandwidthsthandigitallinks.ChineseTranslationofTexts雖然簡單易行，但模擬調(diào)制在光通信系統(tǒng)調(diào)制中調(diào)制效率較低，而且與數(shù)字調(diào)制相比，需要高得多的信噪比。模擬調(diào)制所必需的線性不總是來源于半導體光源，尤其是在高頻調(diào)制中?；谏鲜鲈?，與數(shù)字光通信系統(tǒng)相比較，模擬光通信鏈路通常被限制使用在更短的通信距離和更窄的帶寬上。ChineseTranslationofTextsInitially,theinputdigitalsignalfromtheinformationsourceissuitablyencodedforopticaltransmission.Thelaserdrivecircuitdirectlymodulatestheintensityofthesemiconductorlaserwiththeencodeddigitalsignal.Henceadigitalopticalsignalislaunchedintotheopticalfibercable.Theavalanchephotodiode(APD)detectorisfollowedbyafront-endamplifierandequalizerorfiltertoprovidegainaswellaslinearsignalprocessingandnoisebandwidthreduction.Finally,thesignalobtainedisdecodedtogivetheoriginaldigitalinformation.ChineseTranslationofTexts首先，輸入的信源數(shù)字信號被適當?shù)鼐幋a以進行光傳輸。激光器的驅(qū)動電路通過這些已編碼的數(shù)字信號來直接調(diào)制激光器的發(fā)光強度，然后數(shù)字光信號被注入光纖電纜。在接收端，信號通過雪崩發(fā)光二極管（APD）后進入前置放大器和均衡器或濾波器，放大器用來提供增益、濾波器用來對信號進行線性處理和減少噪聲帶寬。最后，信號通過解碼得到原始數(shù)字信號。ChineseTranslationofTextsNotes…bysuperimposingormodulatingtheinformationontoanelectromagneticwavewhichactsasacarrierfortheinformationsignal.（1）介詞by+動名詞短語充當狀語。（2）which引導定語從句，修飾wave。1NotesThismodulatedcarrieristhentransmittedtotherequireddestinationwhereitisreceivedandtheoriginalinformationsignalisobtainedbydemodulation.這一經(jīng)過調(diào)制的載波隨后被傳送到要求到達的目的地，在那里被接收，并且通過解調(diào)還原成原始信息。過去分詞短語required充當定語，whereitis…bydemodulation是定語從句，兩者均修飾destination。2Notes…byusingelectromagneticcarrierwavesoperatingatradiofrequenciesaswellasmicrowaveandmillimeterwavefrequencies.（1）介詞by+動名詞短語充當狀語。（2）aswellas：“以及”，相當于and，常用于句中，下文中仍有這種用法。再如，HecanspeakEnglishaswellasChinese.請比較：HecanspeakEnglish,andhecanspeakChineseaswell.（aswell用于句末，相當于too）。3NotesHowever,“communication”mayalsobeachievedbyusinganelectromagneticcarrierwhichisselectedfromtheopticalrangeoffrequencies.在通信中，也可選擇光波的頻率作為載波頻率。which引導定語從句，修飾electromagneticcarrier。4NotesInthiscasetheinformationsourceprovidesanelectricalsignaltoatransmittercomprisinganelectricalstagewhichdrivesanopticalsourcetogivemodulationofthelightwavecarrier.信源提供電信號給發(fā)射機，發(fā)射機組成一個電子平臺來驅(qū)動光源以完成對光載頻的調(diào)制。（1）inthiscase：在這種場合下、既然這樣。（2）which引導定語從句。5Notes…toprovidegainaswellaslinearsignalprocessingandnoisebandwidthreduction.此為不定式短語，充當目的狀語。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.廣義地說，把信息從一點傳送到另一點就稱為通信。當信息跨越一段距離被傳送時，就需要一個通信系統(tǒng)。在通信系統(tǒng)中，信息傳送是通過把信息疊加在電磁波上或?qū)﹄姶挪ㄟM行調(diào)制來