電子與通信技術專業(yè)英語UnitⅣ-17課件

UnitⅣCommunicationTechnologyLesson17OpticalFiberCommunicationsUnitⅣCommunicationTechnologNewWordsconvey[k?n'vei]vt.搬運,傳達,轉讓transfer[tr?ns'f?:]n.移動,傳遞,轉移superimpose[,sju:p?rim'p?uz]v.添加,雙重microwave['maikr?uweiv]n.微波conversion[k?n'v?:??n]n.變換,轉化NewWordssemiconductor[,semik?n'd?kt?]n.半導體diode['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[dis'kri:t]a.不連續(xù)的,離散的semiconductor[,semik?n'd?kt?]implement['implim?nt,'impliment]n.

工具,器具

vt.&v.貫徹,實現(xiàn),執(zhí)行encode[en'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implement['implim?nt,'impliPhrasesandExpressionsopticalfibern.光纖electromagneticwaven.電磁波avalanchephotodiode(APD)n.雪崩發(fā)光二極管front-endamplifiern.前置放大器PhrasesandExpressionsNotes1.…bysuperimposingormodulatingtheinformationontoanelectromagneticwavewhichactsasacarrierfortheinformationsignal.

⑴介詞by+動名詞短語充當狀語；

⑵which引導定語從句，修飾wave。Notes2.Thismodulatedcarrieristhentransmittedtotherequireddestinationwhereitisreceivedandtheoriginalinformationsignalisobtainedbydemodulation.

過去分詞短語required充當定語，whereitis…bydemodulation是定語從句，兩者均修飾destination。2.Thismodulatedcarrieristh3.…byusingelectromagneticcarrierwavesoperatingatradiofrequenciesaswellasmicrowaveandmillimeterwavefrequencies.

⑴介詞by+動名詞短語充當狀語；

⑵aswellas意思是“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)。3.…byusingelectromagneticca4.However,“communication”mayalsobeachievedbyusinganelectromagneticcarrierwhichisselectedfromtheopticalrangeoffrequencies.

Which引導定語從句，修electromagneticcarrier。4.However,“communication”maya5.Inthiscasetheinformationsourceprovidesanelectricalsignaltoatransmittercomprisinganelectricalstagewhichdrivesanopticalsourcetogivemodulationofthelightwavecarrier.

⑴inthiscase：“在這種場合下，既然這樣”；⑵which引導定語從句。5.Inthiscasetheinformation6.…toprovidegainaswellaslinearsignalprocessingandnoisebandwidthreduction.

此為不定式短語，充當目的狀語。6.…toprovidegainaswellasTranslationofTextsLesson17OpticalFiberCommunicationsCommunicationmaybebroadlydefinedasthetransferofinformationfromonepointtoanother.Whentheinformationistobeconveyedoveranydistanceacommunicationsystemisusuallyrequired.Withinacommunicationsystemtheinformationtransferisfrequentlyachievedbysuperimposingormodulatingtheinformationontoanelectromagneticwavewhichactsasacarrierfortheinformationsignal.TranslationofTextsLesson17第17課光纖通信廣義地說，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對電磁波進行調制來實現(xiàn)的，電磁波起著載送信號的作用。第17課光纖通信Thismodulatedcarrieristhentransmittedtotherequireddestinationwhereitisreceivedandtheoriginalinformationsignalisobtainedbydemodulation.Sophisticatedtechniqueshavebeendevelopedforthisprocessbyusingelectromagneticcarrierwavesoperatingatradiofrequenciesaswellasmicrowaveandmillimeterwavefrequencies.However,“communication”mayalsobeachievedbyusinganelectromagneticcarrierwhichisselectedfromtheopticalrangeoffrequencies.Thismodulatedcarrieris

這一經過調制的載波隨后被傳送到要求到達的目的地，在那里被接收，并且通過解調還原成原始信息。在運用電磁載波的領域，高新技術得到進一步的發(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。這一經過調制的載波隨后被傳送到要求到達的目的地，在那里TypicalopticalfibercommunicationssystemisshowninFig.20-1.Inthiscasetheinformationsourceprovidesanelectricalsignaltoatransmittercomprisinganelectricalstagewhichdrivesanopticalsourcetogivemodulationofthelightwavecarrier.Theopticalsourcewhichprovidestheelectrical-opticalconversionmaybeeitherasemiconductorlaserorlightemittingdiode(LED).Typicalopticalfibe

典型的光纖通信系統(tǒng)如圖17－1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動光源以完成對光載波的調制。光源是由發(fā)光二極管或半導體激光管構成的，它完成光—電變換。傳輸媒介由光纖（纜）組成。典型的光纖通信系統(tǒng)如圖17－1所示。信源

Thetransmissionmediumconsistsofanopticalfibercableandthereceiverconsistsofanopticaldetectorwhichdrivesafurtherelectricalstageandhenceprovidesdemodulationoftheopticalcarrier.Photodiodes(p-n,p-i-noravalanche)and,insomeinstances,phototransistorandphotoconductorsareutilizedforthedetectionoftheopticalsignalandtheoptical-electricalconversion.Thusthereisarequirementforelectricalinterfacingateitherendoftheopticallinkandatpresentthesignalprocessingisusuallyperformedelectrically.Thetransmissionmediumco

光接收機由驅動后面電路平臺的光探測器構成，用以完成對已調光載波的解調。用于檢測光信號和進行光—電轉換的器件有：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。光接收機由驅動后面電路平臺的光探測器構成，用以完成對已Theopticalcarriermaybemodulatedbyusingeitherananalogordigitalinformationsignal.Analogmodulationinvolvesthevariationofthelightemittedfromtheopticalsourceinacontinuousmanner.Withdigitalmodulation,however,discretechangesinthelightintensityareobtained(i.e.on-offpulses).Theopticalcarrier

模擬或數字的信號均可用來調制光載波。模擬調制是指從光源處發(fā)射的連續(xù)光強度的變化，而數字調制則不然，它是通過光強度離散的變化（比如，有無光脈沖）來實現(xiàn)的。模擬或數字的信號均可用來調制光載波。模擬Althoughoftensimplertoimplement,analogmodulationwithanopticalfibercommunicationsystemislessefficient,requiringafarhighersignaltonoiseratioatthereceiverthandigitalmodulation.Also,thelinearityneededforanalogmodulationisnotalwaysprovidedbysemiconductoropticalsource,especiallyathighmodulationfrequencies.Forthesereasons,analogopticalfibercommunicationlinkaregenerallylimitedtoshorterdistancesandlowerbandwidthsthandigitallinks.Althoughoftensimplerto

雖然簡單易行，但模擬調制在光通信系統(tǒng)調制中調制效率較低，而且與數字調制相比，需要高得多的信噪比。模擬調制所必需的線性不總是來源于半導體光源，尤其是在高頻調制中。基于上述原因，與數字光通信系統(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。雖然簡單易行，但模擬調制在光通信系統(tǒng)調制中調制效率較低

Initially,theinputdigitalsignalfromtheinformationsourceissuitablyencodedforopticaltransmission.Thelaserdrivecircuitdirectlymodulatestheintensityofthesemiconductorlaserwiththeencodeddigitalsignal.Henceadigitalopticalsignalislaunchedintotheopticalfibercable.Theavalanchephotodiode(APD)detectorisfollowedbyafront-endamplifierandequalizerorfiltertoprovidegainaswellaslinearsignalprocessingandnoisebandwidthreduction.Finally,thesignalobtainedisdecodedtogivetheoriginaldigitalinformation.Initially,theinpu

首先，輸入的信源數字信號被適當地編碼以進行光傳輸。激光器的驅動電路通過這些已編碼的數字信號來直接調制激光器的發(fā)光強度，然后數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字信號。首先，輸入的信源數字信號被適當地編碼以進Exercises1.WriteT(True)orF(False)besidethefollowingstatementsaboutthetext.Exercisesa.Thismodulatedcarrieristhentransmittedtotherequireddestinationwhereitisreceivedandtheoriginalinformationsignalisobtainedbymodulation.b.Sophisticatedtechniqueshavebeendevelopedforthisprocessbyusingmagneticcarrierwavesoperatingatradiofrequenciesaswellasmicrowaveandmillimeterwavefrequenciesa.Thismodulatedcarrieristc.Theinformationsourceprovidesanelectricalsignaltoatransmittercomprisinganelectricalstagewhichdrivesanopticalsourcetogivemodulationofthelightwavecarrier.d.Thetransmissionmediumconsistsofanopticalfibercableandthereceiverc.Theinformationsourceprovie.Theopticalcarrierismodulatedbyusingneitherananalognordigitalinformationsignal.f.Withdigitalmodulation,discretechangesinthelightintensityarenotobtained.e.Theopticalcarrierismodug.Analogmodulationwithanopticalfibercommunicationsystemismoreefficient,requiringafarlowersignaltonoiseratioatthereceiverthandigitalmodulation.h.Theinputdigitalsignalfromtheinformationsourceisnotsuitablyencodedforopticaltransmission.g.Analogmodulationwithano2.Fillinthemissin