Numerical techniques are developed to study the output spectra and to solve the coupled mode rate equations for InxGa1−xAs/Al0.3Ga0.7As quantum well lasers. The optical properties of the laser are calculated from a 4×4k⋅pband structure which includes the effects of strain. We find that the side modes are severely suppressed in the strained laser. Large signal switching of the laser is also studied and the role of strain is identified in the device response. If the laser is switched from the off state to a state of given photon density in thelasingmode, then the strained system exhibits a faster time response. If, however, the laser is switched from the off state to a state of giventotalphotondensity, then the strained system has a slower time response.