Yb-doped large-pitch fibres effective single-mode operation

Light:Science&Applications(2012)1,e8;doi:10.1038/lsa.2012.8ß2012CIOMP.Allrightsreserved2047-7538/12

http://www.77cn.com.cn/lsa

ORIGINALARTICLE

Yb-dopedlarge-pitchfibres:effectivesingle-modeoperationbasedonhigher-ordermodedelocalisation

¨rgenOtto1,TinoEidam1,2,CesarJauregui1JensLimpert1,2,3,FabianStutzki1,FlorianJansen1,Hans-Ju

¨nnermann1,2,3andAndreasTu

Rareearth-dopedfibresareadiode-pumped,solid-statelaserarchitecturethatishighlyscalableinaveragepower.Theperformanceof

pulsedfibrelasersystemsisrestrictedduetononlineareffects.Hence,fibredesignsthatallowforverylargemodeareasathighaveragepowerswithdiffraction-limitedbeamqualityareofenormousinterest.Ytterbium-doped,rod-type,large-pitchfibres(LPF)enableextremefibredimensions,i.e.,effectivesingle-modefibreswithmodesizesexceeding100timesthewavelengthoftheguided

离开

radiation,byexploitingthenovelconceptofdelocalisationofhigher-ordertransversemodes.Thenon-resonantnatureoftheoperating

无比的

principlemakesLPFsuitableforhighpowerextraction.Thisdesignallowsforanunparalleledlevelofperformanceinpulsedfibrelasers.

Light:Science&Applications(2012)1,e8;doi:10.1038/lsa.2012.8;publishedonline27April2012

Keywords:higher-ordermodedelocalisation;high-powerfibrelasersandamplifiers;photonic-crystalfibre;verylargemodearea

配置

INTRODUCTION

Diode-pumped,solid-statelasershavebeenutilizedinnewapproachesinareasrangingfromfundamentalsciencetoindustrial

典型

production.Thecanonicalarchitectureoftheactivemediumisarod,typicallyofcrystallinematerial,dopedwithrareearthions.Suchcon-ventionalrod-typelasershavebeenpushedtoveryhighpowerlevels.However,thebeamqualityoftheemittedlightdegradeswithincreas-ingpower;therefore,theotherwiseexcellentfocusabilityofthebeamislost.Thereasonsforthisdegradationareso-calledthermo-opticalproblemscommonlyreferredtoasthermallensingandthermallyinducedbirefringence.Tomitigatetheseproblems,novelsolid-statelaserarchitectures,suchasthethin-disk,1theinnoslab2andthefibreconcept,3havebeendeveloped.Alloftheseconceptsreducethermo-opticalissuesduetotheirspecificgeometry.Amongthem,fibrelasers

名誉

havethereputationofbeinghighlyefficientsourceswithexcellentpower-independentbeamquality.Moreover,fibresofferunique光纤的优点

properties:(i)theheatthatisgeneratedbythelaserprocessisdistrib-utedoveralonglength;(ii)thelargeratioofthesurfacetoactivevolumeleadstooutstandingheatdissipation;and(iii)mostimpor-定义保护

tantly,awaveguidestructuredefinesthebeamqualityandshieldstheradiationfromexternalperturbations.Consequently,ytterbium-dopedfibrelaserswithdiffraction-limitedcontinuous-waveoutputpowersashighas10kWhavebeendemonstrated.4However,theperformanceoffibrelasersystemsisgenerallylimitedbynonlineareffectsduetothetightconfinementofthelightoverlonginterac-tionlengthsinthefibres.Nonlineareffectscandestroythetemporal,spectralandspatialcharacteristicsofthelaseremission,particularly

13

inthepulsedregime,andthiswouldhaveadetrimentalinfluence

减少定向的

onthetargetedapplication.5Themosteffectivemitigationstrategyisthescalingofthemode-fieldarea(MFA),whichallowsforadra-maticreductionoftheguidedintensity.TheeffectiveMFAcanbedefinedas

ÂÐÐÃ2

I(x,y)dxdy

ð1ÞAeff~I(x,y)dxdywhereI(x,y)istheintensitydistributionofthebeam.Theeffectivemode-fielddiameter(MFD),whichwillbeemployedinthefollowingconsiderations,canbedefinedfromequation(1)as

p

ð2ÞMFD~2Aeff=p

ScalingtheMFAofafibreunavoidablyleadstothefibrecoresup-连贯的叠加portingseveralmodes.However,thecoherentsuperpositionofdiffer-然而丆不同

enttransversemodescaninduceseverespectralmodulations,beam横切模式的

叠加能够导

qualitydegradationsandareductioninthepointingstability.Inother致严重的频words,mostoftheoutstandingpropertiesoffibre-basedlasersystems谱调制丆光

束质量下降canbelost.

和稳定性的

Hence,tremendouseffortshavebeenmadetodesignlarge-mode-降低areafibres,i.e.,fibreswithmodesizesbeyondthesingle-modelimitofconventionalstep-indexfibres,whichisapproximately15mm(atawavelengthof1mm).Mostoftheseapproachesallowforeffective

区别

single-modeoperation,achievedbyincludingdiscriminationmechanismsforthehigher-ordermode(HOM)inthefibredesign.突出的Prominentstate-of-the-arttechniquesforeffectivesingle-mode

InstituteofAppliedPhysics,AbbeCenterofPhotonics,Friedrich-Schiller-Universita¨tJena,07745Jena,Germany;2HelmholtzInstituteJena,07743Jena,Germanyand

FraunhoferInstituteforAppliedOpticsandPrecisionEngineering,07745Jena,GermanyCorrespondence:ProfessorATu¨nnermannorProfessorJLimpert,InstituteofAppliedPhysics,AbbeCenterofPhotonics,FriedrichSchillerUniversityJena,Albert-Einstein-Str.15,07745Jena,Germany

E-mail:andreas.tuennermann@iof.fraunhofer.de;jens.limpert@uni-jena.deReceived:16February2012;Accepted:25March2012

Yb-dopedlarge-pitchfibers

JLimpertetal

2

operationinstep-indexfibresincludematchedexcitation,6HOMdiscriminationbybending7andresonantfilteringofHOMs.8,9

Thetechniqueofmodematchingisbasedonthecarefulinjectionoftheseedradiationsothatonlythefundamentalmodeofthefibreis

适配器

excited.6Bulkopticsandfibre-basedmodeadapterscanbeemployedforthispurpose.Thisapproachcanbeusedforalltypesoffew-modefibresanditalwaysresultsinanimprovementintheoperationbeha-viour.However,withgrowingMFAs,excitingonlyonemodebecomesincreasingdifficult,mainlyduetothecollapseoftheeffective-indexahexagonalarrayofairholes.Dependingonthesurroundingregion,threemainapproachesforeffectivesingle-modeoperationarepossi-ble.First,anendlessperiodicstructurewithasingledefectformingthecorecanbetheoreticallyconsidered.Thisstructurecanbeanalyticallydescribed,andsingle-modeconditionsbasedontheeffectiveV-para-metercanbedefined.10However,everyrealfibrewithfinitedimen-sionsdeviatesfromthisapproximation;therefore,thisapproach …… 此处隐藏：22352字，全部文档内容请下载后查看。喜欢就下载吧 ……