Measured spectral linewidth of variable-gap cleaved-coupled- cavity lasers.

A variable-air gap 1.3micron C(3) semiconductor laser with the gap width set for optimum mode-suppression ratio (5000:1) has been used to achieve a measured linewidth as small as 1 MHz at 3 mW power output and 250 kHz at 10 mW, corresponding to a linewidth-power product of 2.5-3 MHz mW. Care was taken to suppress reflections to the laser. The previous best value (measured on the same equipment) for a C(3) laser with fixed gap of arbitrary length was 30 MHz mW; it was 15 MHz mW for a GRECC (GRIN-rod external coupled cavity) laser.