Strip-loaded semiconductor ring lasers employing multimode interference output couplers

Abstract
Strip-loaded semiconductor ring lasers were successfully fabricated in the GaAs/AlGaAs material system. The radius was 400 μm and a 2×2 3 dB multimode interference coupler 320 μm long was used to extract the output signal. Devices operated continuous wave at 140 mA threshold current with a differential quantum efficiency of 7% per output, which we believe is the highest value reported to date for lasers of this type.