Boosting few-cycle soliton self-frequency shift using negative prechirp.

Soliton self-frequency shifting of light pulses in fibers is used for versatile tunable light sources. Few-cycle pulses of high soliton number offer unique advantages, in particular the rate of Raman frequency shift is extremely fast. However, their dynamics is complicated, which makes the optimization of the frequency shifting difficult and sometimes counter-intuitive. We performed a systematic experimental study of the effects of initial prechirp for different pulse energies (for two different fibers). We found that a negative prechirp around C=-0.75 is the most effective (C being the chirp parameter). With such prechirping we managed to cross the severe OH absorption bands of nonlinear photonic crystal fibers. The mechanism behind the effectiveness of the prechirp appears to be the power distribution between the products of soliton fission.