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级联光纤布拉格光栅光谱特性研究.docx

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级联光纤布拉格光栅光谱特性研究 Abstract Inthispaper,westudiedthespectralcharacteristicsofacascadedfiberBragggrating(FBG)usingcascadeopticalfiber.TheexperimentalresultsshowthatthespectralresponseofthecascadedFBGisconsistentwiththetheoreticalmodel.ThecascadedFBGhasanarrowerreflectionbandwidth,higherreflectivity,andbetterspectralisolationthanasingleFBG.Theresearchprovidesguidanceforthedesignandfabricationofhigh-performanceFBGs. Introduction FiberBragggratings(FBGs)havebeenwidelyusedinopticalcommunication,sensingandotherfieldsfortheirexcellentspectralfilteringproperties.CascadedFBGs,formedbyconnectingmultipleFBGsinseries,canfurtherenhancespectralfilteringperformance,increasethereflectiondepth,andimprovethestabilityandaccuracyofthemeasurementsystem.ThecascadedFBGhasattractedmuchattentionduetoitsuniqueopticalpropertiesandpotentialapplications.Inthispaper,westudiedthespectralcharacteristicsofacascadedFBGusingcascadeopticalfiberandexploreditsperformanceadvantagesoverasingleFBG. ExperimentalSetupandResults TheexperimentalsetupisshowninFigure1.Weusedanerbium-dopedfiberamplifier(EDFA)asalightsourceandapowermeterasadetector.ThecascadedFBGiscomposedoftwoidenticalFBGswithalengthof20mm.TheFBGiswrittenonahydrogen-loadedopticalfiberwithaBraggwavelengthof1550nmandanindexmodulationofabout1.5x10^-4.TheFBGsareconnectedbyastandardopticalfiber,whichenablesthecouplingofthereflectedlightofthefirstFBGtothesecondFBG. ThemeasuredreflectionspectraofthecascadedFBGandasingleFBGareshowninFigure2.ThecascadedFBGhasareflectionbandwidthofabout0.13nm,whichisnarrowerthanthatofasingleFBG.ThereflectivityofthecascadedFBGis99.3%,whichishigherthanthatofasingleFBG.Moreover,thecascadedFBGhasahigherisolationbetweenthereflectionpeaks,whichindicatesbetterspectralselectivity. ThetheoreticalmodelofthecascadedFBGisshowninFigure3.TheBraggwavelengthsofthetwoFBGsaredenotedasλB1andλB2,respectively.λB1isassumedtobelocatedatthecentralwavelengthoftheEDFAoutputspectrum.ThereflectioncoefficientsofthetwoFBGsaredenotedasR1andR2,respectively.