Envelope Function Calculations of Linear and Nonlinear Optical Gains in a Strained-Layer Quantumwell Laser

In this article, we study theoretically the linear and the nonlinear optical gains of strained-layer InGaAs-AlGaAs quantum well lasers with band mixing effects taken into account. Effects of the biaxial compressive strain of the InGaAs-AlGaAs quantum well on the band structure are investigated by solving for the Pikus-Bir Hamiltonian. The biaxial compressive strain separates the HH and the LH subbands by pulling down the HH subbands and pushing away the LH subbands from the valence band edge. Since the C-HH transition is dominated by the TE polarization we expect that the TE mode gain would be substantially larger than the TM mode gain in the strained InGaAs-AlGaAs quantum well. The gain and the gain-suppression coefficient of a strained quantum well laser are calculated from the complex optical susceptibility obtained by the density matrix formalism. Optical output power is calculated by solving the rate equations for the stationary states with nonlinear gain suppression. The calculated L-I characteristics show reasonable agreement with the experimental data.