A chirped photonic crystal fiber for ultrashort laser pulse delivery

Photonic crystal fibers have opened interesting new ways for guiding ultrashort laser pulses. Hollow-core fibers (HCF) enable guiding of short light pulses at significantly reduced nonlinearities, which avoids nonlinear distortions to the extent possible. The latest generation of these fibers exhibits remarkably low losses, which suggests HCFs as the ideal choice for femtosecond beam delivery. However, with their strongly resonant periodic cladding, HCFs display an awkward third-order dispersion characteristic, strongly distorting sub-100 fs pulses already after a few ten centimetres of propagation. This article demonstrates chirped photonic crystal fibers (CPCFs) as an alternative for guiding ultrashort pulses, widely avoiding the detrimental dispersion properties of HCFs with strictly periodic cladding. This chirped structure causes a nearly vanishing dispersion of a few fs²/mm in a broadband spectral range from 700 nm to 820 nm. The GVD measured with spectral interferometry and calculated values computed in a finite element simulation are compared.