Abstract
The multiple-scale perturbation analysis is used to study the perturbed optical solitons that are governed by the Nonlinear Schrödinger's equation, with dual-power law nonlinearity. We have considered the perturbations due to nonlinear damping and saturable amplification. A new definition of the phase of the soliton is introduced that captures the corrections to the pulse where the standard soliton perturbation theory fails.