Abstract

Conventional broad area (BA) diode lasers tend to oscillate on several lateral modes as the injection current is increased above threshold, causing a spatial coherence degradation and a far field pattern broadening. We present numerical simulations of BA diode lasers with smooth spatial filtering at the output facet. The spatial filtering takes place only in the direction parallel to the junction and is provided by an output facet having a laterally varying reflectivity profile. Beam characteristics and discrimination against high-order lateral modes of the laser devices are calculated with the beam propagation method and Prony algorithm. An output facet with a Gaussian reflectivity profile favors the fundamental lateral mode. Discrimination between the two lowest-order modes increases significantly with narrow reflectivity profiles. The Gaussian facet slightly broadens the far field distribution of the fundamental mode. However, multimode oscillation is inhibited and the beam coherence is preserved higher above threshold. The threshold current increase is compensated by the crossing of the L-I curves, yielding a better wall-plug efficiency at high drive levels for broad area lasers with a Gaussian output facet.

© 1989 Optical Society of America