Modeling of diode laser cavity under the condition of above-threshold operation

A menu-driven computer program is developed for numerical simulations of diode lasers. Three-dimensional structures of typical single-mode lasers are considered. A beam propagation method being employed for the wave (Helmholtz) equation leads to the so-called round-trip operator which is non-linear due to gain saturation and thermal effects. Thus, the main problem for numerical modelling of lasing is the eigen-value problem for the round-trip operator. Special iterative procedure is applied for calculation of a lasing mode under the assumption of potential instability. A large size 3D numerical mesh is employed to discretize a set of equations describing the propagation of two counter-propagating waves using Fade approximation, lateral diffusion of charge carriers within a quantum well, and thermal conductivity. To calculate the injection electric current, at which additional lasing modes appear, the numerical code incorporates a subroutine that calculates a set of possible competing modes using gain and index variations produced by the oscillating mode. The corresponding linear eigen-problem is solved by the Arnoldi method. If all higher-order modes have eigen-values of amplitude less than 1 then the oscillating mode is stable, else we have the unstable mode. Results of numerical simulations for typical experimental conditions will be presented.