Effects of non-parabolicity and band-warping of the energy dispersion are entered in a quantum well laser simulator (MINILASE-II), which self-consistently solves Schödinger's equation, Poisson's equation, the drift diffusion equations, and the photon rate equations. An eight band k.p model is used to determine the electronic band structure for a strained-layer In.2Ga.8As/Al.1Ga.9As system. The k.p calculation is performed independently of the laser simulator, and exported to MINILASE-II in the form of a density of states and an energydependent averaged momentum matrix element. The results obtained for the gain and modulation response are compared to those obtained from a parabolic band model with a constant matrix element.