Effect of initial chirp on supercontinuum generation by femtosecond pulse in photonic crystal fibers

The numerical simulations with the method of split-step Fourior were presented to investigate the effect of initial chirp on supercontinuum generation in photonic crystal fibers. According to the fiber length, the evolution of pulse in photonic crystal fibers was divided into three stages: initial broadening stage, dramatic broadening stage and saturation broadening stage. By discussing the differences in evolution of the chirp pulse and non-chirp pulse in each stage, we find that the initial chirp only affects the spectrum at the initial broadening stage and the dramatic broadening stage, and the chirp is profitable for spectrum broadening when beta(2) C 0. In the saturation broadening stage, chirp does not affect the spectrum anymore. If we want to broaden the spectrum by using chirp pulse we must choose a right fiber length, and output the pulse in the dramatic broadening stage. These conclusions provide significant reference for supercontinuum generation in photonic crystal fibers with chirp pulse.