Longitudinal mode control in Fabry-Perot lasers

Localised reflections within the lasing filament of Fabry-Perot lasers cause spectral perturbations. Focused Ga/sup +/ ion beam etching can be used to form steep walled pits of submicron size in the lasing filament which give rise to localised reflections with minimal rises in threshold current. Control of both position and depth enables one to sculpture the modal envelope so as to form singlemode Fabry-Perot lasers with 30 dB of mode suppression, temperature stable over 30/spl deg/C with an increase in threshold of a few milliamps. Modelling results show an effective reflectivity can be allocated to the etched pit and this is an order of magnitude below the cleaved facet reflectivity.