Abstract
The propagation of solitons through an optical fiber, described by the perturbed Nonlinear Schrödinger's equation, is studied in this paper by the method of Multiple Scale Perturbation Expansion. Here, it is shown for the first time that, by introducing a new definition of the phase of soliton, one can obtain corrections to the pulse, in presence of the perturbation terms, where the standard soliton perturbation theory fails. This dynamically stable soliton is a very useful physical model in the optical soliton communication world. A comparison is made with results obtained by other methods along with numerical simulations.