Thepropagationoffemtosecondlaserpulseswithwavelengthsof1550nm,1064nm,800nmand700nm,respectively,whichareinthenormaldispersionregionofthenano-structuredphotoniccrystalfiber(N-PCF)withinterestingbroadbandnormaldispersionandhighlynonlinearproperties,isstudied.Fortheeffectofchirpvariationmainlyinducedbygroupvelocitydispersion(GVD)andself-phasemodulation(SPM),afterpropagationoverashortlength,thewavebreakingoccurs.Namely,oscillatorystructuresarepresentednearpulseedgesandsidelobesappearinthepulsespectrum.Inthecaseof800nm,afterthepropagationof20mm,asuperflatspectrumisobtained.Thebandwidthofthesuperflatspectrumisassociatedwiththedispersionlengthandthenonlinearlength.BychoosingN-PCFandlaserpulsewithappropriateparameters,abroadbandsuperflatspectruminashortlengthcanbeachieved.
