Noise and longitudinal mode characteristics of /GaAl/As TS lasers with reduced facet reflectivities

The AM noise in operation of index-guided (GaAl)As lasers is found to be strikingly reduced by the antireflection (AR) coating of cavity facets. This effect is shown to result from the longitudinal multimode operation due to the reduced facet reflectivity. It is observed that the width of the envelope of a laser spectrum depends on the facet reflectivity as well as the laser output power. The AM noise in the low-frequency range of the reduced reflectivity lasers is shown to be nearly constant with respect to temperature change. In contrast, the AM noise in a laser without the AR facet coating is characterized by a number of spikes occurring over a wide temperature range.