Conversion of chirp in femtosecond fiber compressors

Various optical fibers have been used efficiently for femtosecond pulse compression purposes including different photonic crystal fibers with varying core diameters. The phenomenon of chirp conversion is reviewed in these compression fibers and its effect in femtosecond applications is analyzed. Measurements with large-mode-area photonic crystal fibers show that the input group delay dispersion of the pulse is considerably reduced by fiber nonlinearities, by about a factor of ten. The mechanism of chirp reduction is understood by an interplay of self-phase modulation with initial chirp within the fiber. In practice, the reduction of chirp observed here allows for compressing the spectrally broadened intense pulses by ultra-broadband dispersive multilayer mirrors of quite moderate dispersion.