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1、AnalysisofPhotonicCrystalFibers(PCF)inOptiFDTDIntroductionInthepast10years,photoniccrystalfibers(PCF)haveattractedmuchscientificandcommercialinterest.TheresearchanddesignworkforPCFstartsfromaccuratemodalanalysisofthefiber.Oncethemodesarefound,allofthePCFprop
2、ertiessuchasloss,dispersion,andcutoffcanbedetermined.TherearegeneralthreetypesofPCF:holeyfiber(HF),field-confinedholyfiber(FCHF)andHole-AssistedLight-guideFiber(HALF),asshowninfigure1.InOptiFDTD,themodesolveriscombinedwiththeFDTDenginesothatFDTDsimulationcan
3、usethemodalfieldasinputdirectly.Inadditiontothisintegratedmodesolver,OptiFDTDalsoprovidesanindependentmodesolvertoallowusertosolveandstudythemodeoutsideofanFDTDcalculation.ThePCFmodesolvierwillmainlybeusedasanindependentmodesolver.Modalanalysisrequirestwomai
4、nsteps:(1)Createthelayout(2)CalculatethemodesWewillusewaveguidelayoutdesignertodefinethePCFlayout,andthenconvertthelayouttoarefractiveindexdistributionfile.Themodesolverwillloadintheindexdistributionfileandperformthemodeanalysis.Someusersmaywanttoscanthewave
5、lengthtofindoutthecutoffwavelength,orwanttoscanthelayoutparameters.AllofthisispossiblewithOptiFDTDThefollowingsectionwilldemonstratehowaphotoniccrystalfibercanbeanalyzedinOptiFDTD.Sample1---PhotonicCrystalFiber---HoleyFiberThemostcommonPCFisHoleyFiberasshown
6、infigure1(a),thecladdingregionconsistsofahexagonalarrayofair-holes;Onemissingair-holedefinesthecoreregion.Thereallayoutmayhavemorelayersofairholes,butitissufficienttomodelonlythree[2]layerssincethemodeiswellconfined.Tobesafe,herewetakefivelayersforthemodesol
7、ving.WeusethePBGarrayeditortodefinethehexagonalairhole.Tomakethecorecenterinthesimulationdomain’scenter,weneedtodrawagraph(seefigure2)sothatthedetaildimensioninformationcanbemarked.Suchagraphcanmakethelayoutcreationeasier,soitishighlyrecommended.Xan=1.46ox=5
8、.5*a*sin(60)Z(orY)o-x=5.5*a*sin(60)PBGDomainOriginz=11*aFigure2FivelayersholeyfiberPleasenote:Forthisfivelayerholeyfiber(a)Thebackgroundmaterialrefractiveindexn=1.46(b)HexagonalAirhole,periodica