Competition between spectral splitting and Raman frequency shift in negative-dispersion slope photonic crystal fiber

We report on the nonlinear behavior of high air-filling fraction solid-core photonic crystal fibers pumped with ultrashort pulses in the vicinity of a negative-slope zero-crossing of the group velocity dispersion. We observed dramatically different behavior when the pump wavelength lies in the normal or the anomalous dispersion range. When pumping at the zero-dispersion wavelength the combined effects of spectral splitting, self-phase modulation and soliton self-frequency shift result a “comma”-shape of the power-dependant spectra. This spectral feature is explained using a simple model.