通信工程光纖濾波器中英文對照外文翻譯文獻

中英文翻譯譯文一：基于一個高雙折射光纖雙Sagnac環(huán)的可調(diào)諧多波長光纖激光器1．引言工作在波長1550nm附近的多波長光纖激光器已經(jīng)吸引了許多人的興趣，它可以應用于密集波分復用（DWDM）系統(tǒng)，精細光譜學，光纖傳感和微波（RF）光電[1-4]等領(lǐng)域。多波長光纖激光器可以通過布拉格光纖光柵陣列[5]，鎖模技術(shù)[6-7]，光學參量振蕩器[8]，四波混頻效應[9]，受激布里淵散射效應實現(xiàn)[10-12]。摻鉺光纖（EDF）環(huán)形激光器可以提供大輸出功率，高斜度效率和大可調(diào)諧波長范圍。例如，作為一種可調(diào)諧EDF激光器，帶有單個高雙折射光纖Sagnac環(huán)的多波長光纖激光器已經(jīng)提出[13-15]。輸出波長可以通過調(diào)整偏振控制器（PC）進行調(diào)諧，波長間隔可以通過改變保偏光纖（PMF）的長度進行調(diào)諧。然而，對于單個Sagnac環(huán)光纖激光器來說，波長間隔和線寬都不能獨立調(diào)諧[16]。密集波分復用（DWDM）系統(tǒng)要求激光波長調(diào)諧更靈活，否則會限制這些激光器的應用。一個雙Sagnac環(huán)的多波長光纖激光器能提供更好的可調(diào)諧性和可控性。采用這種結(jié)構(gòu)，可以實現(xiàn)保持線寬不變的波長間隔可調(diào)諧，以及保持波長間隔不變的線寬調(diào)諧。本文提出和證明了一種雙Sagnac環(huán)可調(diào)諧多波長摻鉺光纖環(huán)形激光器。多波長選擇由兩個Sagnac環(huán)實現(xiàn)，而每個環(huán)由一個3dB耦合器，一個PC，和一段高雙折射PMF組成。本文模擬分析了單個和兩個Sagnac環(huán)的梳狀濾波器的特征。實驗中，得到輸出激光的半峰全寬（FWHM）是0.0187nm，邊模抑制比（SMSR）是50dB。通過調(diào)整兩個PC可以實現(xiàn)多波長激光器輸出的大范圍調(diào)諧。與單環(huán)結(jié)構(gòu)相比，改變PMF長度可以獨立調(diào)諧波長間隔和激光線寬。本文中提出的雙Sagnac環(huán)光纖激光器是先前單Sagnac環(huán)多段PMF多波長光纖激光器工作的延伸，其在DWDM系統(tǒng)，傳感和儀表測試中具有潛在應用。2．實驗裝置和操作原則提出的多波長光纖激光器的實驗裝置示意圖如圖1（a）中所示。一個980nm的泵浦激光二極管（LD）通過一個980/1550nm波分復用（WDM）耦合到一段EDF中。用一個能提供10%反饋功率的90/10光纖耦合器耦合出激光輸出。多波長光纖激光器通過雙Sagnac環(huán)進行調(diào)諧。如圖1（b）所示，高雙折射Sagnac環(huán)由一個3dB耦合器，一段PMF，一個PC組成。端口3和端口4通過一個PC和一段PMF連接起來。光束從端口1進入耦合器并被耦合器平均分成兩束。這兩束反向傳播的光束在環(huán)中重新耦合。由于PMF的高雙折射影響，光束在兩個軸（快軸和慢軸）上出現(xiàn)相位差。因此，當光通過PMF時會產(chǎn)生一個角度偏差，通過PC時會產(chǎn)生另一個角度偏差。當反向傳播過一個光纖環(huán)后，兩束光束在耦合器上干涉。Sagnac環(huán)的輸出特性可以用Jones矩陣分析。PMF的Jones傳播矩陣可以描述為：（1）這里的是光在快軸和慢軸傳播相同距離所產(chǎn)生的相位差，L是PMF的有效長度，是波長，是兩個軸的有效折射率差。還有，和是快軸和慢軸的有效折射率指數(shù)。因為當光傳播通過一個PC時偏振角偏轉(zhuǎn)為，通過PC的透射光束的Jones矩陣可以描述為：（2）端口1的入射光電矢量為，端口2的入射光電矢量為（=0）。被耦合器分成和。設(shè)為通過PC和PMF的光學矢量，為通過PC和PMF的光學矢量。因此，和相干疊加后在端口1反射，在端口2透過：（3）端口1的入射功率為，反射功率為。端口2的反射功率為。透射率為：（4）這個說明單Sagnac環(huán)的透射率與偏振偏轉(zhuǎn)角度和兩個軸的相位差有關(guān)。正如圖2的模擬結(jié)果所示，PMF長度越大，濾波周期越短和濾波帶寬越窄。但是，周期和帶寬不能單獨調(diào)諧。另外，PMF雙折射率越高，濾波周期越短和濾波帶寬越窄。對雙Sagnac環(huán)來說，在兩個Sagnac環(huán)之間安裝一個光纖隔離器可以消除反射光。因此，雙環(huán)的透射率可以描述為：（5）很明顯，雙Sagnac環(huán)的透射率與長度或者基于Eq（5）兩段PMF的折射率差有關(guān)。其次，濾波周期和帶寬分別由一段較短的PMF和一段較長的PMF決定，輸出激光可以通過單獨調(diào)整PC狀態(tài)和PMF長度進行調(diào)諧。在雙Sagnac環(huán)結(jié)構(gòu)中，兩段PMF長度分別為2m和1m，模擬結(jié)果如圖3（a）所示。圖中我們能看到濾波周期在變而濾波帶寬不變。保持一個Sagnac環(huán)中的PMF為2m長不變，圖3（b）表明改變另一個Sagnac環(huán)中較長PMF（>2m）的長度可以改變?yōu)V波帶寬但使濾波周期不變。因此，使用雙Sagnac環(huán)光纖激光器可以實現(xiàn)波長間隔和帶寬獨立調(diào)諧。圖1（a）基于雙Sagnac高雙折射光纖環(huán)干涉儀的可調(diào)諧多波長光纖激光器（b）Sagnac干涉環(huán)圖2（彩色線）單Sagnac環(huán)的透射率譜圖3（彩色線）雙Sagnac環(huán)的透射率譜（a）線寬不變時的可調(diào)諧濾波器的周期（b）周期不變時的可調(diào)諧濾波器的線寬3．實驗及結(jié)果在實驗中，隔離器1的作用是確保光單向傳播和降低噪聲。摻鉺光纖的長度，截至波長，數(shù)值孔徑和在1530nm附近的峰值吸收分別為12m，960nm，0.23，7dB/m。PMF的長度為5m和2m，雙折射拍長小于5.0mm。泵浦光功率為300mW，我們使用一種光譜分析儀（AQ6370B）監(jiān)視輸出激光。根據(jù)模擬結(jié)果可以得出改變短PMF長度可以調(diào)諧濾波周期，濾波器中所有的傳播光會產(chǎn)生多個激光。由于增益譜平坦度和偏振衰減的限制，濾波帶寬的部分光將被抑制。激射波長的數(shù)量對PC狀態(tài)敏感。中心波長在1549.6nm的三波長激光運行如圖4中所示，激光器的SMSR大于50dB。多波激光器不規(guī)則的輸出頻譜主要由不精確的PMF折射率差，不精確的PMF長度和接頭損耗引起。圖4（b）顯示了超過10分鐘周期，每隔2分鐘重新掃描得到的激光輸出光譜，其激光波長在1544.9、1549.6和1554.3nm，可以觀察到穩(wěn)定的輸出功率和波長。對三波長激光光功率的測量表明最大的功率起伏小于0.2dB，波長起伏小于0.02nm。偏振偏轉(zhuǎn)角度可以通過調(diào)整PC1和PC2進行調(diào)諧，因此輸出激光的波長和波長間隔也可以調(diào)諧。如圖5所示，調(diào)整兩個PC可以觀察到多波長輸出激光在C波段內(nèi)的（a）短波長和（b）長波長。圖5（c）整個C波段可以觀察到多波長輸出激光，并且激光器穩(wěn)定性隨著振蕩模式的增加而降低。在實驗中，我們觀察到輸出波長間隔可以通過調(diào)整兩個PC進行調(diào)諧。如圖6所示，多波長光纖激光器的波長間隔從2.82（a）降到1.76（b）nm。調(diào)整PC，濾波器帶寬中的部分光不會達到閾值。其次波長大小和波長間隔可以通過PC調(diào)諧。通過調(diào)整PC，我們觀察到能夠?qū)崿F(xiàn)穩(wěn)定輸出峰值的波長最大數(shù)目是6個。波長間隔可以通過改變基于Eq（5）的短PMF長度進行調(diào)諧。在實驗中，如圖7（a）所示，我們可以觀察到用5m長的長PMF和1m長的短PMF時波長間隔為2.81nm。另外，如圖7（b）所示，我們可以觀察到用2m長的短PMF時波長間隔為1.79nm。根據(jù)模擬和實驗的結(jié)果，波長間隔隨著短PMF長度增大而變小但帶寬保持不變。根據(jù)模擬結(jié)果，激光器線寬可以通過改變長PMF的長度進行調(diào)諧。如圖8（a）所示，當兩段PMF長度為1m時能觀察到0.036nm的3dB線寬；如圖8（b）所示，當長PMF為5m時能觀察到0.0187nm的3dB線寬。實驗結(jié)果表明了激光線寬隨著長PMF長度增大而變小但波長間隔保持不變。因此，模擬結(jié)果[圖3（b）]已經(jīng)用實驗結(jié)果證實。峰值線寬越小，光纖激光器的抗環(huán)境干擾能力越弱，但抖動起伏小于0.02nm。圖4（彩色線）多波長光纖激光器的輸出光譜（a）三波長激光光譜（b）10分鐘內(nèi)重復檢測輸出光譜圖5多波長激光輸出光譜（a）短波長帶（b）長波長帶（c）整個C波段圖6可調(diào)諧波長間隔在輸出激光光譜（a）波長間隔為2.82nm（b）波長間隔為1.76nm圖7改變短PMF長度的輸出多波長激光器光譜（a）1m長的短PMF（b）2m長的短PMF圖8改變長PMF長度的輸出多波長激光器光譜（a）1m長的長PMF（b）2m長的長PMF4．結(jié)論我們提出并證明了基于雙Sagnac環(huán)的可調(diào)諧多波長環(huán)型EDF激光器。通過Jones矩陣分析了單個和兩個Sagnac環(huán)梳狀濾波器的特性。模擬結(jié)果表明雙Sagnac環(huán)比單Sagnac環(huán)具有更好的可調(diào)諧性和可控性。3dB的輸出激光的線寬測量為0.0187nm，SMSR為50dB。通過調(diào)整兩個PC可以觀察到大范圍可調(diào)諧多波長光纖激光器的輸出，能夠?qū)崿F(xiàn)穩(wěn)定輸出峰值的波長最大數(shù)目是6個。改變短PMF長度可以調(diào)諧波長間隔而不改變線寬；改變長PMF長度可以獨立調(diào)諧激光線寬。外文原文一：TunablemultiwavelengthfiberlaserbasedonadoubleSagnacHiBifiberloop1.IntroductionMultiwavelengthfiberlasersoperatingonthewavelengtharound1550nmhaveattractedmuchinterest,suchassourcesfordensewavelengthdivisionmultiplexing(DWDM)systems,precisespectroscopy,opticalfibersensingandRFphotonics[1–4].AmultiwavelengthfiberlasercanberealizedbyafiberBragggratingarray[5],themode-lockedtechnique[6,7],anopticalparametricoscillator[8],thefourwavemixingeffect[9],orthestimulatedBrillouinscatteringeffect[10–12].Ringerbium-dopedfiber(EDF)laserscanprovidelargeoutputpower,highslopeefficiency,andawidetunablewavelengthrange.AsakindoftunableEDFlasers,multiwavelengthfiberlaserswithsinglehighbirefringence(HiBi)fiberSagnacloophavebeenhighlighted[13–15].Theoutputwavelengthcanbetunedbyadjustingthepolarizationcontroller(PC),andthewavelengthspacingcanbetunedbychangingthelengthofpolarizationmaintainingfiber(PMF).However,neitherthewavelengthspacingnorthelinewidthcanbetunedindependentlyforsingleSagnacloopfiberlasers[16].DWDMsystemsrequirethattuningofthelaserwavelengthbemoreflexible,ortheapplicationsoftheselaserswillbelimited.However,amultiwavelengthfiberlaserwithdoubleSagnacloopscanprovidesbettertenabilityandcontrollability.Forthisstructure,wavelengthspacingcanbetunedwhilekeepingthelinewidthunchanged,andlinewidthcanbetunedwhilekeepingwavelengthspacingunchanged.Inthispaper,atunablemultiwavelengthringEDFlaserwithdoubleSagnacloopsisproposedanddemonstrated.ThemultiwavelengthselectionisperformedbytwoSagnacloops,andeachloopiscomposedofa3dBcoupler,aPC,andasegmentofHiBiPMF.ThecombfiltercharacteristicsofsingleanddoubleSagnacloopsaresimulatedandanalyzed.Inexperiment,theFWHMoftheoutputlaserismeasuredas0.0187nm,andthesidemodesuppressionratio(SMSR)is50dB.ByadjustingtwoPCs,themultiwavelengthlasercanbewidelytuned.BychangingthelengthofthePMF,thewavelengthspacingandthelinewidthcanbetunedindependently,comparedwithasingleloopstructure.Thedouble-Sagnac-loopfiberlaserproposedinthisworkisanextensionofpreviousworksonmultiwavelengthfiberlaserswithmultiplesectionsofPMFsinthesingleSagnacloop,andithaspotentialapplicationsinDWDMsystems,sensing,andinstrumenttesting.2.ExperimentalSetupandOperationPrincipleTheexperimentalsetupoftheproposedmultiwavelengthfiberlaserisshowninFig.1(a).A980nmpumplaserdiode(LD)iscoupledintoasegmentofEDFthrougha980∕1550nmwavelengthdivisionmultiplexer(WDM).Thelaseroutputiscoupledoutwitha90/10fibercoupler,whichprovides10%powerforfeedback.ThemultiwavelengthfiberlaseristunedbythedoubleSagnacloops.AsshowninFig.1(b),theHiBiSagnacloopiscomposedofa3dBcoupler,asegmentofPMF,andaPC.Port3andport4areconnectedtogetherthroughaPCandasegmentofPMF.Thebeamentersintothecouplerfromport1,andisdividedintotwobeamsbythecoupleraverager.Thesetwocounterpropagatingbeamsrecombineintheloop.DuetoHiBieffectofthePMF,thereisaphasedifferenceofthelightsontwoaxes(fastaxisandslowaxis).Hence,whenthelightpassesthroughthePMF,thereisanangledeflection,andthereisanotherangledeflectionwhenthelightpassesthroughthePC.Aftertravelingthroughafiberloopoppositely,thetwobeamsinterfereinthecoupler.TheoutputcharacteristicsoftheSagnacloopcanbeanalyzedbyaJonesmatrix.TheJonestransmissionmatrixofthePMFcanbedescribedas（1）whereisthephasedifferencebetweenthelightonthefastaxisandthatontheslowaxisinthesametransmissiondistance,istheeffectivelengthofthePMF,isthewavelength,andistheeffectiverefractivedifferencebetweentwoaxes.Then,andaretheeffectiverefractiveindicesofthefastaxisandtheslowaxis.SincethepolarizationangledeflectionofthelightiswhenthelighttransmitsthroughaPC,theJonesmatrixofthepositivetransmittinglightbeamthroughthePCcanbedescribedas（2）Theelectricvectoroftheincidentbeamisatport1,andtheelectricvectoroftheincidentbeamisatport2(=0).issplitintoandbythecoupler.LetbetheopticalvectorofthethroughthePCandthePMF,andbetheopticalvectorofthethroughthePCandthePMF.Thus,andarereflectedatport1andtransmittedatport2aftercoherentsuperimposition:（3）Theincidentpoweratport1is,andthereflectivepoweris.Thereflectivepoweratport2is.Thetransmissivityis（4）Thisshowsthatsingle-Sagnac-looptransmissivityisrelatedtothepolarizationdeflectionangleandthephasedifferencebetweentwoaxes.AsshowninthesimulatedresultsinFig.2,thefilterperiodisshorterandthefilterbandwidthisnarrowerwhenthelengthofthePMFisincreased.However,theperiodandbandwidthcannotbetunedindependently.Inaddition,withthePMFbirefringenceshigher,thefilterperiodisshorterandthefilterbandwidthisnarrower.ForthedoubleSagnacloops,afiberisolatorismountedbetweentwoSagnacloopsforeliminatingthereflectivelight.So,thetransmissivityofdoubleloopscanbedescribedas（5）Obviously,thetransmissivityofdoubleSagnacloopsisrelatedtothelengthortherefractiondifferenceoftwosegmentsofPMFsbasedonEq.(5).Then,thefilterperiodandbandwidtharedeterminedbyashorterPMFandalongerPMF,respectively,andtheoutputlasercanbetunedbyadjustingthePCsandthelengthsofthePMFs.Inadouble-Sagnac-loopstructure,twosegmentsofPMFwere2mlongand1mlong.Figure3(a)showsthesimulatedresult.Fromthefigurewecanseethatthefilterperiodcanbechangedwhilethefilterbandwidthisunchanged.Keepinga2mlongPMFinoneSagnacloop,Fig.3(b)showsthatthefilterbandwidthcanbechangedwhilethefilterperiodisunchangedbychangingthelengthofalongerPMF(>2m)inanotherSagnacloop.Thus,byusingdoubleSagnacloopsinthefiberlaser,boththewavelengthspacingandthebandwidthcanbetunedindependently.Fig.1.(a)TunablemultiwavelengthfiberlaserbasedonadoubleSagnacHiBifiberloopinterferometer.(b)Sagnacinterferenceloop.Fig.2.(Coloronline)TransmissivityspectrumofsingleSagnacloop.Fig.3.(Coloronline)TransmissivityspectrumofdoubleSagnacloop.(a)Tunablefilterperiodwithoutchangingfilterbandwidth.(b)Tunablefilterbandwidthwithoutchangingfilterperiod.3.ExperimentsandResultsInexperiments,isolator1wasusedtoensuretheunidirectionalpropagationofthelightanddecreasethenoise.Thelength,cutoffwavelength,numericalaperture,andpeakabsorptionnear1530nmoftheEDFare12m,960nm,0.23,and7dB∕m,respectively.LengthsofPMFsare5and2m,andthebirefringencebeatlengthislessthan5.0mm.Tobepumpedat300mW,weusedanopticalspectrumanalyzer(AQ6370B)tomonitortheoutputlaser.Basedonsimulatedresults,thefilterperiodcanbetunedbychangingthelengthoftheshortPMF,andmultiplelaserswillbeproducedbyallthetransmittedlightofthefilter.Sincegainspectrumflatnessandpolarizationattenuationarelimited,partofthelightinthefilterbandwidthwillbesuppressed.ThenumberoflasingwavelengthswassensitivetothePC.Theoperationofthreewavelengthswiththecenterwavelengthat1549.6nmisillustratedinFig.4,andtheSMSRofthelaserisgreaterthan50dB.TheirregularoutputspectrumofthemultiwavelengthlaserwasmainlycausedbyinaccuraterefractivedifferenceofPMFs,inaccuratelengthofPMFs,andthesplicingloss.Fig.4(b)showstherepeatedscansoftheoutputspectrumwith1544.9,1549.6,and1554.3nmat2minintervalsovera10minperiod.Stableoutputpowerandwavelengthcanbeobserved.Ameasurementoftheopticalpowersatthreewavelengthsshowedthatthemaximumpowerfluctuationwaslessthan0.2dBandthewavelengthfluctuationwaslessthan0.02nm.ThepolarizationdeflectionanglecanbetunedbyadjustingPC1andPC2.Thenthewavelengthandthewavelengthspacingoftheoutputlasercanbetuned.AsshowninFig.5,themultiwavelengthoutputlaserwasobservedin(a)theshortwavelengthand(b)thelongwavelengthwithintheC-bandbyadjustingtwoPCs.ThemultiwavelengthoutputlasercanbeobservedinthewholeC-bandinFig.5(c),andthelaserstabilitywasdecreasedwiththeincreasingoftheoscillationmodes.Intheexperiment,weobservedthattheoutputwavelengthspacingcanbetunedbyadjustingtwoPCs.AsshowninFig.6,thewavelengthspacingofthemultiwavelengthfiberlaserschangedfrom2.82(panela)to1.76nm(panelb).ByadjustingthePC,partsofthelightinthefilterbandwidthwerenotuptothreshold.ThenthenumberofwavelengthsandthewavelengthspacingcouldbetunedbythePC.Hence,byadjustingthePCs,weobservedthatsixwavelengthswasthemaximumnumberofstableoutputpeaks.ThewavelengthspacingcanbetunedbychangingthelengthoftheshortPMFbasedonEq.(5).Intheexperiment,witha5mlengthforthelongPMFand1mlengthfortheshortPMF,weobservedthatthewavelengthspacingwas2.81nm,asshowninFig.7(a).Therefore,witha2mlengthoftheshortPMF,weobservedthatthewavelengthspacingwas1.79nm,asshowninFig.7(b).Basedonbothsimulatedandexperimentalresults,thewavelengthspacingisbenarrowedbyincreasingthelengthoftheshortPMFwhilethelinewidthisunchanged.ThelaserlinewidthcouldbetunedbychangingthelengthofthelongPMFbasedonsimulatedresults.WhenthelengthsofthetwosegmentsofthePMFswere1m,0.036nmof3dBlinewidthwasobserved,asshowninFig.8(a).With5mlengthofthelongPMF,0.0187nmof3dBlinewidthwasobserved,showninFig.8(b).TheexperimentalresultsshowthatthelinewidthwillbenarrowerwhenthelengthofthelongPMFisincreased,withoutachangeinwavelengthspacing.Thus,thesimulatedresults[Fig.3(b)]wereverifiedbytheexperimentalresults.Withsmallerpeaklinewidth,thefiberlaserwasmorevulnerabletoenvironmentalperturbations,butthejitterrangewaslessthan0.02nm.Fig.4.(Coloronline)Outputopticalspectrumofthemulti-wavelengthfiberlaser.(a)Threewavelengthlaserspectrum.(b)Repeatedscansoftheoutputspectrumin10min.Fig.5.Outputmultiwavelengthlaserspectrum.(a)Shortwavelengthband.(b)Longwavelengthband.(c)WholeC-band.Fig.6.Tunablewavelengthspacingintheoutputlaserspectrum.(a)2.82nmofthewavelengthspacing.(b)1.76nmofthewavelengthspacing.Fig.7.SpectrumoftheoutputmultiwavelengthlaserwithchanginglengthoftheshortPMF.(a)1mlengthoftheshortPMF.(b)2mlengthoftheshortPMF.Fig.8.SpectrumoftheoutputmultiwavelengthlaserwithchanginglengthofthelongPMF.(a)1mlengthofthelongPMF.(b)5mlengthofthelongPMF.4.ConclusionAtunablemultiwavelengthringEDFlaserbasedondoubleSagnacloopshasbeenproposedanddemonstrated.ByJonesmatrix,thecombfiltercharacteristicsofsingleanddoubleSagnacloopswereanalyzed.ThesimulationresultsshowedthattherearebettertunabilityandcontrollabilityofdoubleSagnacloopsthanasingleSagnacloop.Thelinewidthoftheoutputlaserwasmeasuredas0.0187nmat-3dB,andtheSMSRwas50dB.ByadjustingtwoPCs,themultiwavelengthwidetunablefiberlaseroutputwasobservedandthemaximumnumberofstableoutputpeakswassixwavelengths.BychangingthelengthoftheshortPMF,thewavelengthspacingcanbetunedwiththelinewidthunchanged.Inaddition,bychangingthelengthofthelongPMF,thelinewidthcanbetunedindependently.譯文二：可調(diào)諧全光纖雙折射梳狀濾波器1、引言可調(diào)諧光梳狀濾波器已經(jīng)被證明可用于發(fā)展波分復用光學光纖通信系統(tǒng)中的多波長激光器。這種濾波器實現(xiàn)方式是使用光纖光柵、高雙折射率光纖和法布里-珀羅諧振器1。在所有這些情況下，梳狀濾波器的信道間隔是固定的，而對于布拉格光纖來說，光譜調(diào)諧是有限的。本文我們將實驗證明低插入損耗、大消光比和偏振不敏感的可調(diào)頻道間隔梳狀濾波器。這種濾波器可以很容易應用于多波長光纖激光器結(jié)構(gòu)中。2、基本調(diào)諧概念一個基本的Lyot光纖濾波器通過把一個高雙折射光纖（PM光纖）放置在兩個偏振裝置之間，并且快軸相對于偏振鏡的軸旋轉(zhuǎn)45°構(gòu)成2。PM光纖兩個軸的波長相關(guān)相位差產(chǎn)生了一個正弦曲線的波長相關(guān)濾波傳輸函數(shù)，如方程式1所示，其中是光纖雙折射，是光纖長度。如方程式2所示，波長間隔取決于傳輸峰的相鄰距離。（1）（2）波長間隔可以通過改變PM光纖長度進行調(diào)諧，但這種方法不適合動態(tài)波長間隔調(diào)諧。在近期工作中，我們證明了有效的一種方法即通過使用兩段PM光纖的Lyot濾波器實現(xiàn)光纖長度的離散變化3。這個結(jié)構(gòu)中，光纖分段放置在兩個偏振器件之間并且每段都可以獨立旋轉(zhuǎn)。旋轉(zhuǎn)每段光纖可以改變有效長度，比如快軸相對于慢軸為+45°或-45°。增加光纖分段數(shù)量隨之可以增加合適波長間隔的數(shù)量。2段、3段、4段的波長間隔數(shù)量分別為4、13、40。這里我們的工作是把一個兩段Lyot濾波器擴展成一個三段Lyot濾波器和三、四段Sagnac-Lyot濾波器。這個工作展現(xiàn)了多段雙折射濾波器獨特的濾波特性。3、濾波器透射譜測量光纖型梳狀濾波器可以通過兩種方式實現(xiàn)：1）使用光纖偏振器件的標準Lyot雙折射濾波器；2）使用帶有一個50：50耦合器的Sagnac干涉儀裝置的Sagnac-Lyot濾波器。圖1a-3a顯示了兩種結(jié)構(gòu)的實驗裝置。在PM光纖片段的兩邊都使用光纖半波片，從而有效控制偏振態(tài)。Sagnac-Lyot濾波器只有兩個有效的旋轉(zhuǎn)角度：+45°和-45°。另外，二元Sagnac-Lyot梳狀濾波器的有效長度為和。通常n元Sagnac-Lyot梳狀濾波器有效長度的數(shù)量為。如圖3a所示，Sagnac-Lyot濾波器的唯一特性是旋轉(zhuǎn)兩個片段偏振軸22.5°可以產(chǎn)生一個的一階濾波器。濾波器片段使用Newport公司PM光纖，折射率為。實驗中搭建了兩個獨立的濾波器：1）一個由=9.4m，=3.76m，=1.88m組成的三元濾波器。這種濾波器應用于Lyot和Sagnac-Lyot結(jié)構(gòu)中。由=5.65m，=11.31m，=3.77m，=1.88m組成的四元濾波器可用作的順序Sagnac-Lyot濾波器。使用一個相干光源（Calmar公司飛秒激光器）和一個摻鉺光纖放大器中的ASE作光源，Lyot和Sagnac濾波器的傳輸光譜可以用光學頻譜分析儀測量。圖1b，2b和3b顯示了三種濾波器測量的傳輸光譜。旋轉(zhuǎn)光纖片段各邊上的半波片可以得到不同的波長間隔。各濾波器波長間隔的數(shù)量為13、4、2，和理論值都一致。典型的插入損耗為4dB。插入損耗主要是由于偏振控制器中光纖環(huán)半徑小，產(chǎn)生了明顯的彎曲損耗，并且保偏和非保偏光纖的接合也會產(chǎn)生損耗。內(nèi)在損耗可以通過弄直偏振控制光纖測量，其值為1.5dB。部分損耗來自于保偏與非保偏焊接。消光比的數(shù)值從16dB到12dB不等。濾波器響應間隔非常平坦（<0.04dB）和一致。圖1Lyot濾波器結(jié)構(gòu)圖2Sagnac-Lyot濾波器圖3二階Sagnac-Lyot濾波器4、結(jié)論我們證明了一個新的頻道間隔可調(diào)諧的全光纖梳狀濾波器。這種濾波器可以用于一個在多波長激光器中，并且為激光器設(shè)計了提供極高的靈活性。我們同時證明了Lyot濾波器和Sagnac-Lyot濾波器。其中Lyot濾波器只需要少量光纖片段就能提供大量波長間隔數(shù)量。（例如四段濾波器提供40個波長間隔）另外，Sagnac-Lyot濾波器的可調(diào)諧功能獨立于輸入偏振態(tài)。測量的插入損耗的典型值為4dB，消光比為15dB。使用低損耗偏振控制器和改善保偏與非保偏光纖的熔接技術(shù)可以降低插入損耗值。外文原文二：TunableAll-FiberBirefringenceCombFilters1.IntroductionTunableopticalcombfiltershavebeendemonstratedtobeusefulinthedevelopmentofmultiwavelengthlasersourcesforwavelengthdivisionmultiplexing(WDM)opticalfibercommunicationsystems.SuchfiltershavebeenimplementedusingfiberBragggratings,high-birefringencefibersandFabry-Perotresonators.1Inallthesecases,thechannelspacingofthecombfilterfunctionisfixedandinthecaseofthefiberBragggrating,thespectralextentislimited.Inthispaperweexperimentallydemonstrateatunablecombfilterwithadjustablechannelspacingwithlowinsertionloss,largeextinctionratioandcanbemadepolarizationinsensitive.Thisfiltercaneasilybeimplementedintoafiberlaserconfigurationformulti-wavelengthoperation.2.BasicTuningConceptAbasicLyotfiberfiltercanbeconstructedbyplacingahigh-birefringencefiber(PMfiber)betweentwopolarizerswiththefast-axisofthefiberrotated45degreesrelativetothepolarizeraxis.2ThewavelengthdependentphasedifferencebetweenthetwoaxesofthePMfiberproducesasinusoidalwavelengthdependentfiltertransmissionfunctionasgivenbyEquation1,whereisthefiberbirefringenceandisthelengthofthefiber.ThewavelengthspacingisdeterminedbytheseparationofthetransmissionpeaksasgivenbyEquation2.（1）（2）ThewavelengthspacingcanbetunedbychangingthelengthofthePMfiberbutisnotpracticalforthedynamicwavelengthspacetuning.Inrecentwork,wehavedemonstratedamethodtoeffectivelychangethefiberlengthindiscretestepsbyusingaLyotfilterbasedontwo-segmentsofPMfiber.3Inthisconfiguration,thefibersegmentsareplacedbetweentwopolarizersandeachsegmentisrotatedindependently.Theeffectivelengthischangedbyrotatingeachsegmentsuchthatthefastaxisiseither+45,0,or–45degreesrelativetothepolarizeraxis.Thenumberofpossiblewavelengthspacingsincreaseswithincreasingnumberoffibersegments.Thenumberofwavelengthspacingsfora2-segment,3-segmentand4-segmentLyotfilteris4,13,and40,respectively.Hereweextendthisworkfromatwo-segmentLyotfiltertoathree-segmentLyotfilterandthreeandfour-segmentSagnac-Lyotfilters.Thisworkdemonstratestheuniquefilteringpropertiesofmulti-segmentedbirefringencefilters.3.FilterTransmissionMeasurementsFibercombfiltersareimplementedbytwomethods:1)standardLyotbirefringencefilterusinginlinefiberpolarizersand2)theSagnac-LyotfilterusingaSagnacinterferometerconfigurationwitha50:50coupler.Figures1a–3ashowtheexperimentalsetupsforbothconfigurations.FiberhalfwaveplatesareusedoneachsideofaPMfibersegmenttoeffectivelyrotateits’axis.TheSagnac-Lyotfilterhasonlytwovalidrotationangles,+45°and–45°.Therefore,theeffectivelengthsfora2-elementSagnac-Lyotcombfilterareand.Ingeneral,thenumberofeffectivelengthsforannth-elementSagnac-Lyotcombfilterisgivenby.AuniquepropertyoftheSagnac-Lyotfilteristheabilitytocreateaorderfilterbyrotatingthepolarizatio