Longitudinal mode control in 1.3 µm Fabry–Perot lasers by mode suppression

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Abstract
Localised reflections within the lasing filament of Fabry–Perot lasers cause spectral perturbations. Focused Ga+ 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 single mode Fabry–Perot lasers with 30 dB of mode suppression and stable with temperature over 30°C with an increase in threshold current of a few milliamps. The authors also report the appearance of an enhanced single spectral line below threshold. Modelling results show that an effective reflectivity can be allocated to the etched pit, and this is an order of magnitude below the cleaved facet reflectivity.