A study of spatial phenomena in semiconductor lasers: Beam filamentation and optical feedback effects

In an effort to improve the performance of high-power semiconductor lasers to meet the demands of applications, this thesis contains work studying the issues which limit their performance: beam filamentation and spatial feedback effects.;Through computer simulations, we investigate the role of three nonlinear mechanisms which can lead to filamentation, and determine the stability boundaries of the material parameters for which the device will not exhibit filamentary tendencies. We use an analytic theory to verify these findings, and to predict the spatio-temporal nature of the filaments through an analytic expression for the gain, in which contributions of the various mechanisms can clearly be seen. We experimentally verify the spatio-temporal characteristics of the filaments, discover effects of the stripe width and transitions to chaos, and discuss how to compare the relative severity of filamentation among different devices.;We propose a new method of controlling filamentation using below-bandgap semiconductor nonlinearities. With simulations, we determine under what conditions this imposed nonlinearity can counteract the carrier-induced self-focusing inside the active region. We fabricate a prototype device using new epitaxial layers containing the below-bandgap nonlinearities, and compare the performance of these new devices to a control set.;In studying the spatial effects of optical feedback, we use Fresnel diffraction theory to derive an expression for the field that is reflected back into the laser. This result is applied to our computer model and used to explore the effects of feedback on narrow-stripe, broad-area, and tapered-stripe semiconductor lasers. Re-examining feedback in narrow-stripe devices through experiments and analytic theory, we investigate the coupling effects between the narrow waveguide and the feedback field, and the changes in the operating characteristics of the laser due to this coupling. We experimentally examine the beam quality of high-power tapered-stripe devices under feedback, paying particular attention to the degradation of the far-field intensity pattern and the issue of filamentation. Finally, we measure the effects of feedback on the spatial distribution of the laser field in broad-area semiconductor lasers, specifically investigating the modification of filamentation due to a lateral displacement in the feedback field with respect to the laser facet.