Optical Gain and Gain Suppression of Quantum-Well Lasers with Valence Band Mixing

The effects of valence band mixing on the nonlinear gains of quantum-well lasers are studied theoretically for the first time. Our analysis is based on the multiband effective-mass theory and the density matrix formalism with intraband relaxation taken into account. The gain and the gain-suppression coefficient of a quantum-well laser are calculated from the complex optical susceptibility obtained by the density matrix formulation with the theoretical dipole moments obtained from the multiband effective-mass theory. The calculated gain spectrum shows that there are remarkable differences (both in peak amplitude and spectral shape) between our model with valence band mixing and the conventional parabolic band model. The shape of the gain spectrum calculated by our mode) becomes more symmetric due to intraband relaxation together with nonparabolic energy dispersions and is closer to the experimental observations when compared with 1) the conventional method using the parabolic band model and 2) the multiband effective-mass calculation without intraband relaxation. Both give quite asymmetric gain spectra. Optical intensity in the GaAs active region is estimated by solving rate equations for the stationary states with nonlinear gain suppression. Then we calculate the mode gain for the resonant mode including the gain suppression, which results in spectral hole burning of the gain spectrum.