Spontaneous period-one oscillation in a deformed square microcavity laser via degenerate-mode-splitting engineering

We experimentally demonstrate spontaneous period-one (P1) oscillation in a solitary semiconductor microlaser. By engineering degenerate-mode splitting in a deformed square microcavity with two circular vertices, two near-degenerate modes with opposite symmetries can interact nonlinearly via the carrier effect. When the mode-frequency interval is tuned close to the intrinsic relaxation-oscillation frequency, the internal-mode interaction gives rise to spontaneous P1 oscillation. In a deformed square microcavity laser with a side length of 26 μm and a circular vertex radius of 12 μm, the P1 oscillation yields comb-like optical spectra featuring approximately 10 lasing lines. Microwave signals corresponding to the oscillation frequency can be generated by optical heterodyne detection or directly extracted from the electrode of the microlaser. By adjusting the injection current of the laser, the microwave frequency is tunable in the ranges from 6.62 to 7.66 GHz and from 9.24 to 10.06 GHz. Our findings offer a new, to the best of our knowledge, way to generate stable periodic oscillations in a compact-size solitary microlaser.