Compact hybrid resonant-optical reflector lasers with very narrow linewidths

Lasers with submegahertz linewidths have importance in various applications, such as in coherent optical communications, interferometric sensors, and resonant-optical gyroscopes. For several years our laboratory has investigated a hybrid Bragg reflector laser with typical linewidths of less than 1 MHz and a narrowest linewidth of 100 kHz. The narrow line results from operating the laser at the steeply rising edge of the Bragg reflection. Understanding this mechanism led to the development1 of resonant-optical reflectors (RORs), integrated-optical elements capable of providing feedback with a reflection spectrum even sharper than previously obtained. We report hybrid ROR laser linewidths as narrow as 7.1 kHz.