Ultrashort soliton generation through higher-order soliton compression in a nonlinear optical loop mirror constructed from dispersion-decreasing fiber

A novel technique to generate ultrashort fundamental solitons is proposed and demonstrated numerically. The technique utilizes both the multisoliton pulse-compression effect and the switching characteristics of a nonlinear optical loop mirror constructed from dispersion-decreasing fiber. We show that, in contrast to the conventional soliton-effect pulse compression in which compressed pulses are always accompanied by broad pedestals, the proposed technique can completely suppress pulse pedestals, and the compressed pulses propagate like fundamental solitons. Unlike the adiabatic-compression technique based on dispersion-decreasing fibers that are limited to input pulse widths <5 ps, the proposed technique does not require the adiabatic condition and therefore can be used to compress long pulses by use of reasonable fiber lengths. Furthermore, the scheme is more tolerant of initial frequency chirps than the adiabatic-compression technique, and it is shown that positive chirps are beneficial to ultrashort soliton generation. The influences of higher-order effects such as Raman self-scattering and third-order dispersion on soliton generation are also investigated, and it is found that Raman self-scattering can significantly enhance pulse compression under certain conditions.