Effect of Higher-Order Terms on Nonlinear Schrödinger Dark Solitons in Optical Fibres

We solve the nonlinear Schrödinger equation with higher order terms, which describes the propagation of femtosecond pulses in optical fibres, by means of a direct perturbation method for dark solitons. An exact dark-soliton solution of the higher order nonlinear Schrödinger equation is found, provided that parameters satisfy certain conditions. The soliton’s velocity with the high order effects as well as the formula for calculation of the first-order correction representing the perturbation-induced radiative field is presented.