Single-frequency coupled asymmetric microcavity laser

Single-mode lasing from a coupled asymmetric microcavity is achieved. By coupling two size mismatched circular microrings to form a coupled asymmetric microcavity, multi-whispering-gallery modes are successfully suppressed and single-frequency laser emission is robustly obtained. Moreover, the laser emits in four directions, and each beam has a divergence of only $6.6°$. It is demonstrated further that this single-frequency coupled microcavity laser can be easily integrated with planar lightwave circuits. We provide an easily accessible approach to achieve a single-frequency laser from microcavity lasers operating on whispering-gallery modes.