In this paper we drive a numerical model for a separate confinement heterostructure quantum well (SCH-QW) laser. The physical effects of deep level traps (DLTs) and carrier transport on the threshold current, transient response and wavelength chirp of a SCH-QW laser are modeled by means of finite difference method. This numerical model calculates the time-dependent variations of optical output phase, photon density and carrier densities in the SCH layer and QW region, self-consistently. These equations are also coupled with the trap density equation. The exact carrier dependence of the linewidth enhancement factor and the gain function for the QW laser are included in this model. ©2007 IEEE.