External cavity laser with high-sidemode suppression ratio using grating-assisted directional coupler

We propose and demonstrate, for the first time, a method to improve the sidemode suppression ratio (SMSR) of an external cavity laser (ECL) with a grating-assisted directional coupler as an external mirror. The ECL consisting of a Fabry-Pe/spl acute/rot laser diode and a grating-assisted coupler exhibited single-longitudinal-mode oscillation at Bragg wavelength with a high SMSR of 60 dB without any additional devices.