Multiple output semiconductor ring lasers with high external quantum efficiency

The external quantum efficiency of semiconductor ring lasers has been significantly improved by introducing output couplers that couple more light out of the ring cavity. Improvements from 10% and 16% to 14% and 27% of a comparable single 2×2 MMI coupler device were achieved by using 3×3 multimode interference (MMI) couplers and dual 2×2 MMI couplers, respectively. A further increase to the value of 33% (or 2 times that of the previous devices) was obtained by AR coating the output facets of the dual 2×2 MMI coupler devices. These devices also provided four output beams as required in an integrated optical time domain multiplexing (OTDM) system.