包远志毕业外文翻译Word文件下载.docx
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Keywords:
fiberlaser;
doubleclad;
photoniccrystalfiber;
Yb3+
Foreword:
Comparedwithconventionalfiberlasersolid,gaslasers,fiberlasershavemanyuniqueadvantages,suchasgoodbeamquality,smallsize,lightweight,maintenance-free,air-cooled,easyoperation,lowoperatingcost,underindustrialenvironmentlong-termuse;
andhighprecision,highspeed,longlife,energysaving,inparticular,canintelligent,automated,flexible.Therefore,ithasreplacedthetraditionalYAG,CO2lasersinmanyareas.
However,theconventionalfiberlaser,fiberopticalwaveguideduetostructurallimitations,thenumericalapertureissmall,lowcouplingefficiency,andtomaintainsingle-modecoresmallsize,easyoperationconditionsathighpowernonlinearopticaleffectsandthermalinjuryproblem,theoutputpowerisverylimited.
Fiberfamilyappearedinthe1990sanewmember-aphotoniccrystalfiber（PhotonicCrystalFiber,PCF）,duetoitsflexiblestructure,especiallythosewithlargemodearea,whilemaintainingthesuperiorcharacteristicsofunlimitedsinglemodeeffectivelyovercomeshortcomingsofthetraditionalfiberlasers,sopeoplestartedtoshiftattentiontothephotoniccrystalfiberlasers.
One.Thebasicprincipleofthefiberlaser
Thecurrentdevelopmentofrareearthdopedfiberlasersusedmainlyfiberasthegainmedium.Fiberlaserworksbyapumplightthroughthemirror（orraster1）entersthedopedfiber,theabsorptionofthephotonenergyleveltransitionofrareearthionsoccurs,and"
inversion"
oftheparticlesafterinversionintheformofradiationwillthentransitionsfromtheexcitedstatebacktothegroundstateafterrelaxation,whiletheenergyreleasedintheformofphotons,（2orraster）outputofthelaserbythereflectingmirror2,asshowninFigure1.
Rareearthdopedfiberisusuallydouble-cladfiber（Doub-le-CladFiber,DCF）.SuchanopticalfibershowninFigure2,theoutercladding,theinnercladdingandadopedcoreofthecomposition,therefractiveindexoftheoutercladdingrefractiveindexlessthantheinnercladdingrefractiveindexlessthantheinnercladdingrefractiveindexofthecore,soastoconstitutedoublelayerwaveguidestructure.Dopeddouble-cladfiberisakeycomponentconstitutingfiberlasers,fiberlasersroleinthemainare:
1）toconvertthelaserpumppoweroftheworkingmedium;
2）withotherdevicestogetherformthelasercavity.Itsworkingprincipleis:
thepumpinjectedintotheopticalfiberthroughtheopticalcouplingorendside,theoutercladdingismuchlowerthantheinnercladdingofthefiber,theinnercladdingcanbetransmittedsothatthemultimodepumplight.Morecross-sectionaldimensiongreaterthantheinnercorecladding,thewavelengthofthelaserlightgeneratedbytheinnercladdingandacoredopedwithrareearthionsconstituteaperfectsinglemodeopticalwaveguidewiththesametimeitconstitutesthecladdingofthetransmissionpowerofthepumplightmodewaveguide.Suchpowermaybecoupledtoamultimodepumplightintothecladding,amulti-modepumplighttransmittedalongthefibercorethroughtheprocessseveraltimesandabsorbedbecausetherareearthionsinthecoreisexcitedtoproducehighpowersignallaseroutput.WorksshowninFigure2.
Currently,thefiberlaserresearchfocusedonseveralaspectsofhighpowerfiberlasers,narrowlinewidthfiberlasers,multi-wavelengthfiberlasers,ultrashortpulsefiberlasers,Ramanfiberlasersandphotoniccrystalfiberlasers.Thefollowinghighlightsthenextphotoniccrystalfiberlasers.
Two.Photoniccrystalfiberlasers
1photoniccrystalfiber
Photoniccrystalfibers（photoniccrystalfiber,pCF）conceptwasfirstproposedbytheP.St.J.Russelletalin1992,andin1996thefirstsuccessfulproductionofthesampleinthelaboratory,heisbasedonphotoniccrystalslocalelectronicsmadeextraordinaryability,heisaxiallyalignedwiththeuniformquartzfiber.Fromtheendfaceofthisopticalfibercladdingisorderedtwo-dimensionalphotoniccrystal,whichisacorestructureoftheperiodicdestructionofcladdingdefect,thelightcanpropagateinthedefect.Thisdefectmaybeasolidsiliconcanbeairholes.Herearesometypicalschematicphotoniccrystalfiber[2]:
Figure3severaltypicalphotoniccrystalfiber
Photoniccrystalfibertransmissionmechanismcanbeclassifiedaccordingtotheirtypephotoniccrystalfiberbandgap（PBG-PCF）andrefractiveindexguidingphotoniccrystalfiber（TIR-PCF）categories.
2.Photoniccrystalfiber
（1）Asnosinglemode,large-mode-area
Theso-called"
nosinglemode（EndlesslySingleMode）"
thatis,thefibercut-offwavelengthisveryshort.Standardsinglemodefibercladdingrefractiveindexvarieswithwavelengthisverysmall,whenthetransmissionwavelengthisshorter,thevalueofvbecomeslargefiber,singlemodefiberwaveguidetransmissionconditionswillnolongerbe:
PCFcladdinginashort-wavelengthlighttransmissionbecauseitcanbettertoavoidthespreadofairholes.Therefractiveindexofthecladdingsothatshort-wavelengthlightcorrespondingtotherefractiveindexofthematrixmaterialiscloser,sothatVcandecreasetheamountofchange,theopticalfiberremainssinglemodetransmissionconditions,goodshortwavelengthlighttransmissioninthecoreconstraints.Therefore,reducingthecorediameterisnotnecessary,onlythedutycycleoftheappropriatedesignofthecladdingd/A（disthediameteroftheairholesinthecladding,Aisthecenterairholespacing）,PCFsinglemodecanbeachievedwithoutthetransmission,whichisPCFUnlikeordinaryopticalfiberwithauniqueadvantage.
Inthecaseofsingle-modetransmissiontomeettheincreasedsubstitutionofairholesPCFcoremandrelrealnumber,wecanachievemuchlargerthantheconventionalfibercorearea,largemodearea（1argemodearea,LMA）isdesignedtoreducefiberthepowerdensityofthecore,toimprovethethresholdofthenonlinearopticaleffect,whichhaswideapplicationinhighpowerlasertransmission.
（2）ahighnumericalapertureandlightgatheringcapabilityprimarilyonfibernumericalapertureNA,sincetheairholesdisposeddutyflexibility,PCFcladdingcanbeachievednotonlythelowrefractiveindexdifferencebetweenthecore,large-mode-areadesigncorePCF:
canalsobecoatedlayer/alargerefractiveindexdifferencebetweenthecoredesignedtoachievehighNAofthemultimodecoreorinnercladding.Althoughthestructureofairholesinthetransmissionsignalwillcausesignaldistortion,butthehighNAPCFtogatherandtransmithighpowerveryfavorable,andthereforehasveryimportantapplicationswherehighpowercladding-pumpedfiberlasersandamplifiersaspects.OnthebasisofahighNAPCFensureefficientcouplingofthepumplight,whichallowstheuseofsmallinnercladdingdesign,thepumplightandsignallighttoimprovethecross,thelightabsorptionefficiencyofthepumpincreases.
（3）anomalousdispersionanddispersioncharacteristicscontrolleddispersioncharacteristicsofthematerialdispersionzerovacuum,air,materialdispersionisalsoverysmall,whichmakesphotoniccrystalfiberdispersionisveryspecial,photoniccrystalfiberdispersionisstronglydependentonthecladdingairholesthesize,shapeandarrangement,sincetheopticalfiberdesignflexibility,aslongastheratioofthechangeinporesizeandporespacingcaneasilycontroltheamountofdispersionphotoniccrystalfiber,thefiberchromaticdispersionreachedatotaldistributionofhope.（4）non-lineareffectsandbirefringenceeffects
Nonlineareffectscanbereducedtoachievemodeareafibercanbeadjustedbyvaryingtheeffectivespacingoftheairholes
Modearea,at1.5μmwavelengthadjustmentrangeisabout1~800μm2,ifasuitablenonlinearmaterialfillingtheholesintheair,itwillsignificantlyimprovethenonlineareffectsinphotoniccrystalfibers.
Excellentbirefringenceeffectforpolarizationmaintainingfiber,thebirefringenceeffectisstronger,theshorterthewavelength,thepolarizationstateofthelighttransmittedmaintainedbetter.Inphotoniccrystalfiber,onlyneedtodestroysectionalcircularsymmetryofphotoniccrystalfiber,itconstitutesatwo-dimensionalknot
Structurecanbeformedtherebypreparingahighlybirefringentphotoniccrystalfiberwithhighbirefringencepolarizationmaintainingfiber.Comparedwithconventionalpolarizationmaintainingfiber,highbirefringencephotoniccrystalfiberwithpolarizationmaintainingfiberproductionprocessissimple,designflexibility,enablinghighbirefringence,isnotsensitivetotemperaturechanges,etc..
IncorporationinphotoniccrystalfibercoreREE,canbemadeoffiberlasers;
takeadvantageofphotoniccrystalfibermodefieldcharacteristicscanbeflexiblydesignedtochangetheinteractionbetweentheconductionmodeandtheactivemedium,canbemadesuitablefordifferentrequirementslaser.
3.basicprinciplesofphotoniccrystalfiberlasers
Double-cladphotoniccrystalfiberlasersandotherconventionallasers,justascomposedofthreebasicparts:
apumpsource,thegainmediumand
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