Analysis of gain-induced waveguiding in stripe geometry diode lasers

Abstract

This paper analyzes two-dimensional waveguiding in stripe geometry diode lasers. Refractive index discontinuities guide the light by total internal reflection in the direction perpendicular to the p-n junction plane, but the guidance mechanism along the p-n junction and transverse to the propagation direction is that of gain variation. In the active region, the gain is a maximum under the pump stripe center and decreases to loss (optical absorption) in the unpumped region. This variation is modeled by three different functions for which analytic solutions are obtained. The first is the usual quadratic. The second, by choice of parameters, represents transition cases from quadratic to square gain profiles, which occur with increasing stripe width. The third is quadratic near stripe center and continuously decreases to a constant loss value in the unpumped region. We present mode patterns, laser threshold gains, and propagation constants for a variety of cases to illustrate the effects of laser length, stripe width, and active region thickness in these devices.