C2 Optical Fibers 光纤通信 第二章ppt课件.ppt

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1、Chapter2OpticalFibers:StructuresandWaveguiding2.1TheNatureofLight2.1.1LinearPolarization2.1.2EllipticalandCircularPolarization2.1.3TheQuantumNatureofLight2.2BasicOpticalLaws2.3OpticalFiberModes2.3.1FiberTypes2.3.2RaysandModes2.3.3Step-IndexFiberStructure2.3.4RayOpticsRepresentation2.4ModeTheoryfo

2、rCircularWaveguides2.4.1OverviewofModes2.4.2SummaryofKeyModalConcepts2.4.7ModesinStep-IndexFibers2.5Single-ModeFibers2.5.2PropagationModesinSMFs2.6Graded-IndexFiberStructureChapter2OpticalFibers:StructuresandWaveguidingLightwaveiselectromagneticinnature.Polarizationeffectsindicatedthatlightwavesa

3、retransverse(i.e.,thewavemotionisperpendiculartothedirectioninwhichthewavetravels).TheEMwavescanberepresentedbyatrainofsphericalwavefronts,asshowninFig.2-1.Awavefrontisthelocusofallpointsinthewavetrainhavingthesamephase.Thewavefronts(alsocalledphasefronts)areseparatedbyonewavelength.2.1TheNatureof

4、LightLightwavecanberepresentedasaplanewave;itsdirectionoftravelcanbeindicatedbyalightraydrawnperpendiculartothephasefront.Opticaleffectsofreflectionandrefractioncanbeanalyzedbythegeometricalprocessofraytracing.Thisisreferredtoasrayorgeometricaloptics.2.1TheNatureofLightFigure2-1.Sphericalandplanew

5、avefrontsandtheirassociatedrays.2.1.1LinearPolarizationTheEorHfieldofplanelinearlypolarizedwavestravelingindirectionkcanberepresentedinA(x,t)=eiAo.exp[j(wt–k.x)](2-1)withx=xex+yey+zezrepresentingageneralpositionvectorandk=kxex+kyey+kzezrepresentingthewavepropagationvector.Aoisthemaximumamplitudeof

6、thewave;w=2pn,withnthelightfrequency;themagnitudeofthewavevectorkisthewavepropagationconstantk=2p/l,withlbeingthewavelength;andeiisaunitvectorlyingparalleltoi-axis.Ifk=kezandAdenotestheelectricfieldEwiththecoordinateaxesei=exthentherealelectricfieldisgivenbyEx(z,t)=Re(E)=exEox.cos(wt-kz),(2-2)This

7、planewaveistravelinginthezdirectionandislinearlypolarizedwithpolarizationvectorex.2.1.1LinearPolarizationFigure2-2.ElectricandmagneticfieldsinatrainofEMplanewaves.ConsiderthelinearlypolarizedwaveEy(z,t)independen