Abstract

Broad-area (BA) semiconductor lasers can provide high power coherent laser beams. However, the optical output of these lasers has a short coherence length and contains several transverse modes, which can cause degradation of the far field pattern. We report near-single-mode oscillation of a cw, 76 μm wide, BA double-heterostructure diode laser with output power up to 100 mW. Mode selection was achieved by using a self-injection-locking technique. The external cavity was formed by using a mirror in front of the BA laser, and an étalon was positioned in between. The results were obtained at feedback levels of about 5% of the output power. By slightly tilting the étalon, it behaved like a scanning Fabry-Perot resonator and selection of the different longitudinal modes of the laser was possible. This technique is applicable to other types of semiconductor lasers. Indeed, we obtained similar results with a cw multimode visible diode laser. In that case, feedback was provided by phase conjugation with a BaTiO₃ crystal. Coherence properties and far field patterns will also be presented.

© 1992 Optical Society of America