EE230OpticalFiberCommunicationLecture6EE230光纤通信讲座

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1、EE230:OpticalFiberCommunicationLecture6FromthemovieWarriorsoftheNetNonlinearProcessesinOpticalFibersPolarizationInmolecules,P=μ+αE+βE2+γE3+…Inmaterials,P=X(o)+X(1)E+X(2)E2+X(3)E3+…Ifmultipleelectricfieldsareapplied,everypossiblecrosstermisgenerated.Atsuffici

2、entlyhighvaluesofE,quadraticorhighertermsbecomeimportantandnonlineareffectsareinducedinthefiber.PolarizationMoleculesandtheirdipolemomentsDistortionofanelectroncloudinresponsetoanE-fieldNon-linearPolarizationNonlinearEffectsStimulatedRamanscatteringStimulate

3、dBrillouinscatteringFour-waveMixingSelf-phaseModulationCross-phaseModulationIndexofRefractionImaginarypartofindex:absorptionForasampleofabsorbanceAandthicknessd,theimaginarypartoftherefractiveindexisequaltoIndexofRefractionvsWavelengthRefractiveindexvsFreque

4、ncyforsilicaRefractiveIndexforvariousmaterialsWaveslowinginamediumofhigherIndexNonlinearindexofrefractionRealpartofindexisbestdescribedasapowerseriesn=n1+n2(P/Aeff)Terminparenthesesistheintensity.Forsilicafiber,n22.6x10-11μm2/mWInteractionLengthwhereα(incm-

5、1)isthelosscoefficientofthefiber.0.1dB/km=2.3x10-7cm-1.NonlinearparameterPropagationconstantispower-dependentPropagationinSingleModeFiberUnderstandingFiberOptics-HechtGeometricalopticsisnotusefulforsinglemodefiber,mustbehandledbyfullE&MtreatmentThinkofguidin

6、gasdiffractionconstrainedbyrefractionFieldsareevanescentlydampedinthecladdingEffectiveLengthandeffectiveareaSingleModeGaussianApproximationFundamentalsofPhotonics-SalehandTeichFiberOpticCommuniocationSystems-AgrawalGaussianPulseModeFieldDiameterFiberOpticsCo

7、mmunicationTechnology-Mynbaev&ScheinerMitigationIfPishighinafiberapplication,thenonlinearcomponentoftheindexisminimizedbyincreasingtheeffectiveareaofthefiber.FiberdesignedforthispurposeiscalledLEAFfiber(LargeEffectiveArea).PhasemodulationSelf-modulation:φNL=

8、γPLeffCross-modulation:φNL=2γPotherLeffEffectofthesephasechangesisafrequencychirp(frequencychangesduringpulse),broadeningpulseandreducingbitrate-lengthproductSelfPhaseModulationPulseSpreadingdue