Grating-Coupled Surface-Emitters --- Highly Directional Outcouplers and Spatially Coherent Lasers

Doctoral thesis, 1997

This thesis deals with grating-coupled surface-emitting semiconductor lasers. The work is part of a larger effort that aims at developing semiconductor lasers with built-in beam-forming elements, which eliminate the need for external micro-optics. Such integrated light emitters have potential use in present and future applications because of increased functionality and simplified packaging. A grating-coupled surface-emitter consists of an integrated in-plane laser, that produces a spatially coherent guided wave, and a grating outcoupler, that diffracts the light out of the waveguide and shapes the emitted beam. The thesis covers two main aspects of such emitters: highly efficient outcouplers and spatially coherent broad-area lasers. We have theoretically and experimentally investigated two different methods to achieve high directionality in grating-outcouplers: blazed gratings and substrate reflectors. Outcoupling efficiencies of 84 and 94% have been measured for these two methods, respectively. This has produced overall laser efficiencies comparable to those of edge-emitters. An unstable-resonator laser design, aimed at producing a spatially coherent broad-area output, has been numerically modeled and experimentally investigated. The laser produces a 160-.my.m-wide coherent output with a nearly plane wavefront. Focusing and spot-array generating outcouplers have also been integrated with the laser.