Homemade 20 kW Yb-Doped Double-Cladding Fiber for Tandem Pumping
CHINESE JOURNAL OF LASERS-ZHONGGUO JIGUANG（2022）
Abstract
Objective With the development of Yb-doped fiber lasers the output power of asingledomesticfiberhasreachedthe10kWlevelWiththeincreaseoflaseroutputpowerthethermaleffectproblemoftraditionaldirectpumpingisdifficulttobesolvedeffectivelyOwingtothelowquantumdeficitandhighbrightnessthetandempumpingemployingYb-dopedfiberlasersasthepumpingsourcecaneffectivelyreducethisthermalissueandachieveahighoutputpowerwhichisanimportanttrendintheresearchofhigh-powerfiberlaseramplificationBecauseofthemuchlowerabsorptioncoefficientat1018nmthanthatat976nmthetandempumpingconfigurationneedsalongergainfibertosufficientlyabsorbpumplightwhichinturninducesaseverernonlineareffectbringinginmorechallengesinfiberlasersIn2018theDepartmentofPrecisionInstrumentsofTsinghuaUniversityreportedtheuseofadomesticgainfiberproducedbyChinaElectronicsTechnologyCroupCorporationNo46ResearchInstitutetoachievea3000WlaseroutputbasedontandempumpingInMay2021theChinaAcademyofEngineeringPhysicsCAEPusedthehomemadeYb-dopedactivefibertorealizethelaseroutputof20kWbyusingthetandempumpingmethodToachieveahigheroutput-powerhereahighlyYb-dopeddouble-claddingfiberisproposedusedfortandempumpingMethodsTheYb-dopeddouble-claddingfiberpreformispreparedbytheimprovedchemicalvapordepositionMCVDmethodcombinedwiththesolutiondopingtechniqueBasedontheexistingtechnologythekeyprocessisimprovedandoptimizedThroughthedesignoffibercorecomponentsandtheoptimizationofthemulti-layerdepositiontechnologythedopingconcentrationandtheuniformdistributionofYbionsareimprovedThebackgroundlossofanYb-dopedfiberunderhighdopingconcentrationiseffectivelyreducedTherefractiveindexdistributionoftheimprovedfiberisshowninFig3andthedopedelementdistributionintheimprovedfibercoreis ResultsandDiscussionsThecrosssectionoftheYb-dopeddouble-claddingfiberisshowninFig5andthemainfiberparametersareshowninTable1ThediametersofthecoreandinnercladdingoftheYb-dopeddouble-claddingfiberare47 mu mand400 mu mrespectivelyThefiberhasamoreuniformdistributionofYbionsalargerabsorptioncrosssectionandahigherabsorptioncoefficientThenumericalapertureofthefiberis0069046andthefiberhasinnercladdingabsorptionofapproximately072dBmat1018nmFig6Basedontheimprovedfiberanall-fibermasteroscillatorpoweramplifierisbuiltFigure7showstheexperimentalsetupInthepoweramplifyingstagea33mlonggainfiberispumpedbya1018nmfiberlaserWhenthepumplaserpowerinjectedintheamplifierstagereaches2456kWthelaserpoweroutputof2088kWat1080nmisobtainedandthesystemslopeefficiencyis827%afterremovingtheresidualpumplightFig8InadditiontheoutputlaserspectrumhasnotypicalStokespeaksandthe3dBbandwidthoftheoutputlaserismeasuredtobe21nmFig9TothebestofourknowledgethismarksthehighestresulteverreportedforhomemadeYb-dopeddouble-claddingfibersbasedontandempumpingConclusionsTandempumpingisoneofthemaintechnicalapproachestorealizehighpowerfiberlasersBycombiningtheimprovedchemicalvapordepositionmethodwiththesolutiondopingtechniquewehavefabricatedanYb-dopeddouble-claddingfiberThroughthedesignoffibercorecomponentsandtheoptimizationoftherodmakingprocesstheuniformityoftherefractiveindexofthehighlydopedfibercoreisimprovedThelaserperformanceofthefiberisdemonstratedbyanall-fibermasteroscillatorpoweramplifyinglasersystemAsforthe1081nmfiberlaserbasedontandempumpinga2088kWlaseroutputat1080nmwithahighstimulatedRamanscatteringrejectionratiohasbeenachievedwithan827%slopeefficiency This is the highest power achieved for the domesticfiber based on tandem pumping
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Key words
fiber optics,Yb-doped double-cladding fiber,vapor phase,liquid phase doping,tandem pumping
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