Numerical simulation of nonlinear mode interactions in ridge-waveguide semiconductor lasers

Nonlinear perturbation of effective group index is calculated numerically in semiconductor ridge waveguide laser structures under an influence of a strong driving wave (mode). Model of nonlinear interaction of waves is used to obtain conditions for appearance of anomalous dispersion of modal index and also for inversion of the group index of guided waves (modes of the ridge-waveguide laser structures). Ranges around critically anomalous dispersion (CAD) points, where the effective group index passes zero value, are calculated numerically. CAD points form closed loops in graphs of detuning vs. driving wave intensity. These loops define ranges where superluminal propagation, as well as slowed reflection of probe wave can be obtained. Numerical simulations are performed for an InGaAs/AlGaAs/GaAs double quantum well (DQW) laser structure and also for a GaAs/AlGaAs separate confinement heterostructure. The threshold intensities for the appearance of CAD points, as well as the influence of relaxation rate and optical confinement on the appearance of superluminal regime are compared for the DQW and SCH structures.