Fiber Bragg grating原理与应用

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1、光纖光柵原理與應用梁財春教授T.C.Liang1光纖與光纜T.C.Liang2Classificationofopticalfibers1/5一、依折射率在core橫截面上的分佈形狀︰Æ級射率光纖(stepindexfiber)Æ斜射率光纖(gradedindexfiber)claddingn2二、依光纖中傳輸模態的多少分類︰corenÆsingle-modefiber1Æmultimodefiber三、依製造光纖所使用的材料來分類︰Æ石英系列(All-glass)Æ塑膠外殼石英核心Æ全塑膠光纖(All-plastic)T.C.Liang3Classificatio

2、nofopticalfibers2/5(a)SingleModeFibern1n1nn22r0Corediameter~8um(b)MultimodeFibern1n1n2n20Corediameter>50um(c)GradedIndexMultimodeFibern1n(r)n2n2T.C.Liang04Classificationofopticalfibers3/5(a)SingleModeFibern1n1nn22r0n2Corediameter~8umn1nfT.C.Liang5Classificationofopticalfibers4/5(b)Mult

3、imodeFibern1n1n2n20Corediameter>50umdispersionn2n1nfT.C.Liang6Classificationofopticalfibers5/5(c)GradedIndexMultimodeFibern1n(r)n2n20Corediameter>50umn2n1nfGRINT.C.Liang7DispersioninSingleModeFibers1/5ΔfΔλ=fλΔλ:linewidthorspectralwidthλ:centralwavelengthf:centralfrequencyΔf:therangeoff

4、requenciesradiatedThesmallerthelinewidth,themorecoherentthesource.Ifithaszerolinewidthandisperfectlymonochromatic.TypicalSourceSpectralWidthsSourceLinewidth(nm)Light-emittingdiode20-100Laserdiode1-5Nd:YAGlaser0.1T.C.LiangHeNelaser0.0028DispersioninSingleModeFibers2/5Fig.Pulsespreadingc

5、ausedbypropagationthroughadispersivematerial.Thecompletepulsecontainswavelengthsλ,λ,12andλ,eachtravelingatadifferentspeed.3T.C.Liang9DispersioninSingleModeFibers3/5Fig.Dispersioncauseslossinamplitudeofananalogsignal.Dispersiondoesnotchangetheaveragepowerorthemodulationfrequencies,butit

6、doeslowerthesignalvariation.T.C.Liang10DispersioninSingleModeFibers4/5Forλ<1.3μm,λ,VForλ>1.3μm,λ,VForλ<1.3μmFig.Usingchirped-fiberBragggratingfordispersioncompensationT.C.Liang11DispersioninSingleModeFibers5/5Totaldispersionforconventional,dispersion-flattenedanddispersion-shiftedfiber

7、s.T.C.Liang12Attenuation1/3T.C.Liang13Attenuation2/3Fig.Attenuationofagermanium-dopedsilicaglassfiber.Thelossesoccurringinglassfiberscanbeclassifiedasabsorption,scattering,andgeometriceffect.Absorption:intrinsicabsorption(UVabsorptionandIRabsorption)Æowingtostrongelectronicandmolecul