Evolution of dark solitons in the presence of Raman gain and self-steepening effect**Project supported by the National Natural Science Foundation of China (Grant No. 61167004) and the Natural Science Foundation of Inner Mongolia Autonomous Region, China (Grant No. 2014MS0104).

Abstract

Based on the equation satisfied by optical pulse that is a slowly varying function, the higher-order nonlinear Schrödinger equation (NLSE) including Raman gain and self-steepening effect is deduced in detail, and a new Raman gain function is defined. By using the split-step Fourier method, the influence of the combined effect between Raman gain and self-steepening on the propagation characteristic of dark solitons is simulated in the isotropic fiber. The results show that gray solitons can be symmetrically formed by high order dark soliton, however self-steepening effect will inhibit the formation mechanism through the phenomenon that gray solitons are produced only in the trailing edge of the central black soliton. Meanwhile, the Raman gain changes the propagation characteristic of optical soliton and inhibits the self-steepening effect, resulting in the broadening of pulse width and the decreasing of pulse offset.