Semiconductor ring lasers with reflection output couplers

We report circular-cavity semiconductor ring lasers with 45° reflection output couplers that increase the lasing output power and slope efficiency twofold compared to lasers with Y-junction output couplers. These devices emit more than 3.5 mW of cw single-frequency output power at 100 mA ring current with slope efficiencies of 0.07 W/A. The increased output power and reduced spontaneous emission improve single-frequency side-mode rejection by up to 10 dB (to nearly 32 dB).