《光纖理論與技術(shù)》

《光纖理論與技術(shù)》哈爾濱工程大學(xué)理學(xué)院光子科學(xué)與技術(shù)研究中心2007年3月第十一章：發(fā)展無限的新型光纖

特種光纖光子晶體光纖特種光纖保偏光纖

摻稀土元素光纖

雙包層光纖

倏逝場(chǎng)光纖

多芯光纖

紅外光纖

納米光纖保偏光纖幾何形狀引起高雙折射

高雙折射橢圓芯保偏光纖結(jié)構(gòu)剖面示意圖

保偏光纖應(yīng)力誘導(dǎo)高雙折射

保偏光纖摻稀土元素光纖

摻稀土元素光纖是采用某種工藝技術(shù)將釹、鉺和釔等稀土元素離子單獨(dú)或混合摻入光纖芯中而制成的。目前主要是摻雜到光纖纖芯中的，但亦有同時(shí)摻雜到光纖包層中去的。其摻雜濃度可從1PPm到0.25w%的寬廣范圍內(nèi)變化。

纖芯中摻雜稀土元素有

Er、Yb、Nd、Tm、Pr、Er/Yb、Ho等纖芯直徑～4mm，NA0.1

包層直徑～125mm，形狀為圓形摻稀土元素光纖

摻稀土元素光纖用這種摻雜光纖可以獲得四方面的應(yīng)用：(1)激光光纖與光纖放大器；(2)基于吸收、熒光的分布溫度傳感；(3)增大菲爾德常數(shù)；(4)提高克爾效應(yīng)及非線性光學(xué)系數(shù)。

雙包層光纖

雙包層光纖及其工作原理

纖芯中摻雜稀土元素有：

Er、Yb、Nd、Tm、Pr、Er/Yb、Ho等單模光纖：纖芯小4mm，NA0.1

纖芯結(jié)構(gòu)分類大芯多模光纖：纖芯大（>30mm），NA大大模面積（LMA）：纖芯大（>30mm），NA小（<0.1）內(nèi)包層光纖芯外包層保護(hù)層激光輸出泵浦光雙包層光纖

內(nèi)包層形狀圓形（同心、偏心）

方形、矩形、、六邊形、星形和D形

圓形偏心內(nèi)包層圓形同芯內(nèi)包層雙包層光纖

矩形內(nèi)包層星形內(nèi)包層方形內(nèi)包層D形內(nèi)包層六邊形內(nèi)包層雙包層光纖

雙包層光纖用包層泵浦的光纖激光特種光纖

倏逝場(chǎng)光纖

主要用途：倏逝場(chǎng)光纖生化傳感器

電光克爾效應(yīng)調(diào)制器

多芯光纖

主要用途：密集型光纜光子器件用于圖像傳遞的傳像光纖

紅外光纖方形中空光纖芯紅外光纖

納米光纖第十一章：發(fā)展無限的新型光纖

特種光纖光子晶體光纖ContentsIntroductionWhatisphotoniccrystalfiber?WorkingprincipleofPCFStructuresofphotoniccrystalfiberCharacteristicsofcrystalfiberFabricationofcrystalfiberApplicationsWhatwehavedone?ConclusionsIntroduction

Photoniccrystalfibers(PCFs)wasfirstdemonstratedin1996andhasgeneratedmuchattentionsincethen.PCFsareopticalfibersthatemployamicrostructuredarrangementoflow-indexmaterialinabackgroundmaterialofhigherrefractiveindex.Thebackgroundmaterialisoftenundopedsilicaandthelowindexregionistypicallyprovidedbyairvoidsrunningalongthelengthofthefiber.GrowthtrendofpublicationsPublicationpaperscitedbySCIfrom19962003330+?Whatisphotoniccrystalfiber?

Photoniccrystalfibers,alsoknownasmicrostructuredfibersareabrandnewrangeofopticalfibersofferingsignificantnewpossibilitiesandfunctionalitywithintelecommunicationsandopticalcomponentsingeneral.

Twocategoriesphotoniccrystalfiber

PCFsmaybedividedintotwocategories,highindexguidingfibersandlowindexguidingfibers.Similartoconventionalfibers,highindexguidingfibersareguidinglightinasolidcorebytheModifiedTotalInternalReflection(M-TIR)principle.

Thetotalinternalreflectioniscausedbythelowereffectiveindexinthemicrostructuredair-filledregion.

Workingprincipleofcrystalfiber

Lowindexguidingfibersguidelightbythephotonicbandgap(PBG)effect.ThelightisconfinedtothelowindexcoreasthePBGeffectmakespropagationinthemacrostructuredcladdingregionimpossible.

ThestrongwavelengthdependencyoftheeffectiverefractiveindexandtheinherentlylargedesignflexibilityofthePCFsallowsforaholenewrangeofnovelproperties.Suchpropertiesincludeendlesslysingle-modedfibers,extremelynonlinearfibersandfiberswithanomalousdispersioninthevisiblewavelengthregion.

WorkingprincipleofcrystalfiberM-TIRisanalogoustototalinternalreflectionknownfromstandardopticalfibers.Itreliesonahighindexcoreregion,typicallypuresilica,surroundedbyalowereffectiveindexprovidedbythemicrostructuredregion.Theeffectiveindexofsuchafibercan,inthesimplecase,beapproximatedbystandardastepindexfiber,withahighindexcoreandalowindexcladding.However,therefractiveindexofthemicrostructuredcladdinginPCFsexhibitsawavelengthdependencyverydifferentfrompuresilica-aneffectwhichallowsPCFstobedesignedwithacompletenewsetofpropertiesnotpossiblewithstandardtechnology.Stepindexfiber

WorkingprincipleofcrystalfiberPhotonic

crystalfiber

Asanexample,thestrongwavelengthdependenceoftherefractiveindexallowdesignofendlesslysingle-modedfibers,whereonlyasinglemodeissupportedregardlessofopticalwavelength.Furthermore,itispossibletoalterthedispersionpropertiesofthefibers,therebymakingitpossibletodesignfiberswithananomalousdispersionatvisiblewavelengths.Morecomplexindexstructurescanalsobeconstructedbyutilizingarrangementsofholesofdifferentsizeinvariousperiodicorunperiodicstructures.Inaddition,highlyasymmetriccorefiberscanbefabricatedtherebycreatingfiberswithveryhighlevelofbirefringence.

WorkingprincipleofcrystalfiberPhotonicbandgapfibersarebasedonphysicalmechanismsfundamentallydifferentfromtheM-TIRguidingfibers.Thebandgapeffectcanbefoundinnature,wherethebeautifulandbrightcolorsthatareseeninbutterflywingsaretheresultofnaturallyoccurringperiodicmicrostructures.TheSEMpictureatthelowerleftshowsthemicrostructureonabutterflywing.Thestructuresizeisintheorderofafewmicrons.

InaPBGfiber,thecoreiscreatedbyintroducingadefectinthePBGstructure(e.g.anextraairhole),therebycreatinganareawherethelightcanpropagate.

WorkingprincipleofcrystalfiberAsthelightcanonlypropagateatthedefectregion,alowindexguidingcorehasbeencreated.Thisisnotpossibleinstandardfibers,andthelowindexguidingofPBGfibersthereforeopensawholenewsetofpossibilities.Inthisway,itispossibletoguidelightinair,vacuumoranygascompatiblewiththefibermaterial.Especiallythepossibilityforguidinginairorvacuumhasattractedmuchattention,asitmightholdthekeytotransmissionfiberswithextremelylowlosses.

Workingprincipleofcrystalfiber

Thedifferentguidingmechanisms.(A)Conventionaltotalinternalreflection(TIR);thisoccurswhenthewavevectorcomponent

inthedirectionofpropagationliesintherangekn2

<

β

<

kn1.(B)PBGguidancewhenthelightisevanescentintheairregions;thiscanonlyoccurwhen

liesinthesamerangeasin(A);theprocessisoneoffrustratedtunneling,thatis,thecladdingresonatorsareoutofresonancewiththecorewaveguideandhencetunnelingisprevented.Workingprincipleofcrystalfiber

(C)PBGguidancewhenthelightispropagatinginallsubregionsofthefiber;thiscanonlyoccurwhenliesintherangeβ

<

kn2,theunderlyingmechanismbeingaBraggPBG.PBGPCFBasicexplanation

VectoranalysisofPCFfiberStructuresofcrystalfiberTypicalhoneycombbasedPCFstructureAir-guidingPCFLowbendloss:unnoticeable@3mmradiusLowFresnelreflection:<10-4ReducednonlinearitiesPotentialultra-lowlosstransmissionStructuresofcrystalfiberStructuresofcrystalfiber1.7μmCoreHighlyNonlinearFiberFEATURES:-Smallmodefieldarea

-Zerodispersioninthevisiblewavelengthrange

-Bendinginsensitive

APPLICATIONS:-Continuumgeneration

-Four-wavemixing

-Ramanamplification15μmCoreLargeModeAreaFiber

FEATURES:-Handlesveryhighpowerlevelswithoutnonlinearities

-Lowfiberloss

APPLICATIONS:-Highpowerdelivery

HighNumericalAperturePCFHighnumericalaperture(NA): upto0.7LargecoreareaLownonliearitiesDoubleCladdingPCFExtremelyhighNAforthepumpcore/innercladding.Largemodeareaforsignalmodesignal:highpowerdelivery,lownonlinearity,andagoodoverlapbetweenpumpingandsignalarea(highpumpefficiency)HighlyNonlinearPolarizationMaintainingFiber

FEATURES:-PolarizationMaintaining

-Smallmodefieldarea

-Zerodispersioninthevisiblewavelengthrange

-Bendinginsensitive

APPLICATIONS:-Continuumgeneration

-Four-wavemixing

-Ramanamplification

EndlesslySingle-ModeFiberEndlesslysingle-modelargemodeareaPCFcanhandleupto20timesmorepowerthanconventionalfiberandismadeentirelyfromun-dopedsilicaglass.EndlesslySingle-ModeFiberActualunitcellinthephotoniccrystalwithItscircularapproximation

VariationofVeff

withΛ/λforvariousrelativeholediametersd/Λ.ThedashedlinemarksVeff

=

2.405,thecutoffVvalueforastep-ndexfiberChromaticDispersionAnomalousdispersionSupercontinuumGeneration Supercontinuumgenerationina75cmlengthofPCF.Thefiberispumpedwith100fs,680nmpulse.Thepulseenergyis~1nJ.Lossproperties3.2dB/kmat1550nm7.1dB/kmat850nm2kmlengthfiberMacro-bendinglosspropertiesHighlybirefringent

propertiesBeatlength=0.4mmAtwavelength1540nmFabricationofcrystalfiberFabricationofPCF,likeinconventionalfiberfabrication,startswithafiberpreform.PCFpreformsareformedbystackinganumberofcapillarysilicatubesandrodstoformthedesiredair/silicastructure.

FabricationofcrystalfiberThiswayofcreatingthepreformallowsahighlevelofdesignflexibilityasboththecoresizeandshapeaswellastheindexprofilethroughoutthecladdingregioncanbecontrolled.Thisisveryusefulforfabricationofe.g.polarizationmaintainingfiberswithhighlyasymmetriccoreregions,wheremultipleofthecapillarytubesisreplacedwithsolidsilicarods.

FabricationofcrystalfiberWhenthedesiredpreformisconstructed,itisdrawntoafiberinaconventionalhigh-temperaturedrawingtowerandhair-thinphotoniccrystalfibersarereadilyproducedinkilometerlengths.Throughcarefulprocesscontrol,theairholesretaintheirarrangementallthroughthedrawingprocessandevenfiberswithverycomplexdesignsandhighairfillingfractioncanbeproduced.FabricationofPCFFabricationofcrystalfiberFinally,thefibersarecoatedtoprovideaprotectivestandardjacketthatallowsrobusthandlingofthefibers.Thefinalfibersarecomparabletostandardfiberinbothrobustnessandsizeandcanbebothstripedandcleavedusingstandardtools.

ApplicationsofPCFFiberdeliveryofveryhigh-powerlight,single-modefromUVtoinfrared;2.Dispersioncompensation;3.Whitelight(supercontinuum)sources;4.Wavelengthconverters;5.Hollowtransmissionfibers;6.Multi-corefibercouplers;7.Pulseshapers;ApplicationsofPCFChemicalsensorswithlonginteractionlengths;9.Temperature-insensitivePMpigtails;Gyroscopefibers--athermal,andhighly

birefringent

11.Pressureandtemperaturesensors;HighAeffandPMfibersforsingle-mode

interconnects;13.Modeconverters

High-powerlightdeliveryWhite-lightsupercontinuumgenerationexperimentWhite-lightsupercontinuumgenerationPropagationlengths40cm,1.3m,and2.6mWavelengthconverterWavelengthconverterOutputspectrafordifferentvaluesofincidentpeakpowerThisfiberguidedpinklight

(core~14micronsindiameter)

Usingaircoreasthemediumalmostentirelyeliminatesopticalnonlinearitiessothenonlinearpowerthresholdcanbemorethan1000timeshigherthanthatofaconventionalfiber.HollowCoreBandgapFiberMulticorePCF

and

MulticorecouplerApplications:1.Strainsensor;2.Temperaturesensor3.PressuresensorDispersion

compensationPCFusingasgassensorTestingresultofacetylenegasAcousticwavelength-shiftmodulatorTwincorePCFfiberastemperaturesensor“Itriedtothinkofsomethingdifferent,somethingnobodyelsehadthoughtof”

-PhilipSt.JohnRussellTheideaofPhotoniccrystalfiberMicrostructuredfiberusedasanatomwaveguideCoaxialperiodicopticalfiberSegmentedcladdingfiberAirsuspendedcorefiberforproducingefficientevanescentfielddevicesWhatwehavedone?InventionpatentsaboutplasticphotoniccrystalfiberdesignResearchonmodefielddistributionanddispersioncharacteristicsofphotoniccrystalfiberSimulationofhighlybirefringentPCFSplicelossestimationofPCF/SMFAnalysisfortaperedphotoniccrystalfiberAnalysisofcombinationstructuredphotoniccrystalfibersHollowlyplasticphotoniccrystalfiberdesignandfabricationtechniqueBasicequationsCrosssectionofthePCFwithapitchof2.3ContourmapsoftheenergydistributionoffundamentalmodeThreedimensionalmodefielddistributionsEnergydistributionofcentralaxisVparameterofaPCFversusthenormalizedfrequencyEffectiveindexofaPCFversusthenormalizedfrequencyEffectiveindexofaPCFversuswavelengthDispersionasafunctionofwavelengthDispersionasafunctionofwavelengthPropagationconstantvsthewavelengthModelingofHighlyBirefringentPCF

Thecross-sectionofthePCFandelectricfieldvectorsofthey-polarizedfundamentalmode.

Dependenceofmodalbirefringenceonthesizeofholes.

Themodefielddiameterandhalfdivergenceangle

asafunctionofwavelengthforvariousd2/Λ.Thedashedandsolidli