Linewidth Measurement of a Single Longitudinal Mode AlGaAs Laser with a Fabry-Perot Interferometer

Interferometric measurement of the linewidth has been carried out on a single longitudinal mode AlGaAs/GaAs double heterostructure laser by using a Fabry-Perot interferometer with spacers of 30 cm, 3.2 m, and 10 m. The full width at half maximum was estimated to be less than 1 MHz when the current level exceeds 1.15 times the threshold, which was near the estimated theoretical limit.