Unit-7：Fiber-Optic

专业英语——SpecializedEnglishUnit7：第二部分通信技术FiberOptic——光纤SpecializedEnglishonCommunicationEngineeringSnell’sLaw(斯涅尔定律)n1n2A1(angleofincidence)A2(angleofrefraction)211221sinsinVVKnnAASpecializedEnglishonCommunicationEngineeringNEWWORDSANDPHRASESinterferencen.干涉;干扰propagatev.传播;propagationn.refractionn.折射；refractiveindexv.折射率coren.（光纤）纤芯claddingn.包层dispersionn.色散profilen.曲线，分布图multimodefiber多模光纤single-modefiber单模光纤graded-indexfiber渐变（折射率）光纤stepped-indexfiber阶跃（折射率）光纤SpecializedEnglishonCommunicationEngineeringOpticalfibertransmissionhascomeofageasamajorinnovationintelecommunications.telecommunications：电讯,长途通讯,无线电通讯,电信学光纤传输作为电信业一项重大变革的时代已经到来。TEXTSpecializedEnglishonCommunicationEngineeringSuchsystemsofferextremelyhighbandwidth,freedomfromexternalinterference,immunityfrominterceptionbyexternalmeans,andcheaprawmaterial(silicon,themostabundantmaterialontheEarth).bandwidth：带宽；externalinterference：外界干扰interception：中途夺取,拦截,侦听；rawmaterial：原料光纤通信系统提供了极宽的带宽，它不受外界干扰，不能通过外部手段进行信号截取，它的原材料是廉价的（硅，地球上最丰富的物质）。SpecializedEnglishonCommunicationEngineeringOpticalfibersguidelightrayswithinthefibermaterial.Theycandothisbecauselightraysbendorchangedirectionwhentheypassfromonemediumtoanother.lightrays：光纤medium：介质，媒介FundamentalsofFiberOpticSystemSpecializedEnglishonCommunicationEngineeringTheybendbecausethespeedofpropagationoflightineachmediumisdifferent.Thisphenomenoniscalledrefraction.speedofpropagation：传播速度phenomenon：现象refraction：折射光线发生弯曲是因为光的传播速度在各种介质中是不同的。这种现象就称作折射。SpecializedEnglishonCommunicationEngineeringOnecommonexampleofrefractionoccurswhenyoustandattheedgeofapoolandlookatanobjectatthebottomofthepool.Unlessyouaredirectlyovertheobject,itappearstobefartherawaythanitreallyis.当你站在湖边，看湖底的一个物体时，就会发生最普通的折射的例子。如果你不是在物体的正上方，这个物体就会看起来比他真实的位置更远。SpecializedEnglishonCommunicationEngineeringThiseffectoccursbecausethespeedofthelightraysfromtheobjectincreasesasthelightrayspassfromthewatertotheair.lightrays：光线发生这种效应是因为，来自物体的光线从水中进入空气时，其速度会增加。SpecializedEnglishonCommunicationEngineeringThiscausesthemtobend,changingtheangleatwhichyouperceivetheobject.YoucanobtainanappreciationforthemannerbywhichlightflowsbyfocusinguponSnell’sLaw.perceive：察觉，感知,感到这使得光线发生弯曲，改变了观察物体的角度。通过Snell定律可以理解光线遵循的传播方式。SpecializedEnglishonCommunicationEngineeringHowopticalfibersworkcanbeexplainedbySnell’sLaw,whichstatesthattheratioofthesineoftheangleofincidencetothesineoftheangleofrefractionisequaltotheratioofthepropagationvelocitiesofthewaveinthetworespectivemedia.theratioofAtoB：表示A与B之比theangleofrefraction：折射角theangleofincidence：入射角propagationvelocities：传播速度光纤的工作原理可通过斯涅尔折射定律来解释，该定理阐明，入射角正弦值与折射角正弦值之比等于光波在两种媒介中的传输速度之比。SpecializedEnglishonCommunicationEngineering122121sinsinnnKVVAAtheangleofrefractiontheangleofincidenceconstantrefractiveindexofthesecondmediumrefractiveindexofthefirstmediumSnell’sLawSpecializedEnglishonCommunicationEngineering(a)RayEscapes1n2n1A2A(b)RayisAbsorbed1A902A(c)TotalInternalReflection1A2A21nnSpecializedEnglishonCommunicationEngineeringFig.2-1(b)demonstratestheconditionthatexistswhenA1isatthecriticalangleandangleA2isat90[dg].demonstrate:表示，表明criticalangle：临界角（定义为折射角为90度时的入射角）[dg]表示角度单位，dg=degree度。图2-1(b)表示当A1为临界角，A2为90度时的情况。SpecializedEnglishonCommunicationEngineeringAsshowninFig.2-1(c),anylightraysthatareincidentatanglesgreaterthanA1ofFig.2-1(b)willbereflectedbackintomaterial1withangleA2equaltoA1.incident：入射的reflect：反射如图2-1(c)所示，入射角大于图2-1(b)中的入射角A1的任何入射光线，都会被以反射角A2=A1反射回材料1。SpecializedEnglishonCommunicationEngineeringAnopticalfiberisadielectric(nonconductorofelectricity)waveguidemadeofglassorplastic.dielectric：电介质,绝缘体waveguide：波导plastic：塑料光纤是由玻璃或塑料制成的介质（电绝缘体）波导。FiberComposition(光纤结构)SpecializedEnglishonCommunicationEngineeringItconsistsofthreedistinctregions:acore,thecladding,andasheathorjacket.Thesheathorjacketprotectsthefiberbutdoesnotgovernthetransmissioncapabilityofthefiber.cladding：包层sheath：涂敷层，外壳jacket：护套govern：控制，统治,支配transmissioncapability：传输性能SpecializedEnglishonCommunicationEngineeringTheindexofrefractionoftheassemblyvariesacrosstheradiusofthecable,andthecorehasaconstantorsmoothlyvaryingindexofrefractioncallednc.Thecladdingregionhasanotherconstantindexofrefractioncalledn.assembly：集合，组装radius：半径constant：常数光纤的折射率沿着半径变化,纤芯的折射率nc是常数或者是平滑变化的。包层的折射率n是另一个常数。SpecializedEnglishonCommunicationEngineeringThecorepossessesahighrefractiveindex,whereasthecladdingisconstructedtohavealowerrefractiveindex.Theresultofthedifferenceintherefractiveindiceskeepslightflowingthroughthecoreafteritgetsintothecore,evenifthefiberisbentortiedintoaknot.assembly：集合，组装radius：半径constant：常数纤芯具有高的折射率，而构建的包层具有较低的折射率。折射率差异这一结果使得光进入光纤以后能够通过纤芯传播，即使光纤发生弯曲或者打结。SpecializedEnglishonCommunicationEngineeringForafiberdesignedtocarrylightinseveralmodesofpropagationatthesametime(calledamultimodefiber),thediameterofthecoreisseveraltimesthewavelengthofthelighttobecarried.mode：模式multimodefiber：多模光纤diameter：直径wavelength：波长能够同时携载多个传输模式的光纤（称作多模光纤），其纤芯直径是所携载波长的几倍。SpecializedEnglishonCommunicationEngineeringWavelengthisameasureofthedistancebetweentwocyclesofthesamewavemeasuredinna