Unidirectional emission of high-Q scarred modes in a rounded D-shape microcavity.

We propose a deformed microcavity laser, where a high-Q mode group emits unidirectionally. The cavity comprises three circular arcs and one linear section. To minimize diffraction effects from the boundary, three circular arcs and one linear section are tangentially connected. By adjusting the sizes and the positions of the two sub-circular arcs, unidirectionality is maximized. In an experiment with an InP based InGaAsP semiconductor microcavity laser, a lasing mode group localized on aperiod-7 unstable periodic orbit emits unidirectionally. In our resonance calculation, a high-Q factor is confirmed.