Low-threshold Sheet Optical Parametric Oscillator by Triply-resonant Cavity Phase Matching

Microcavity laser represents a novel type of integrated platform potentially allowing low-threshold and high-efficiency lasing behavior. Phase matching is a key parameter to achieve efficient lasing processes. Here we report a study on a triply-resonant phase-matching process in a sheet optical parametric oscillator. The oscillator contains an x-cut KTiOPO₄ crystal, and the triply-resonant phase-matching was achieved by temperature tuning of the cavity. The measured oscillation threshold is as low as 13 μJ at 243.6 °C temperature along with a slope efficiency of 17.5% at 65.3 °C. Experimental results show that under some temperatures, triply-resonant sheet optical parametric oscillator can realize a limited number of longitudinal modes (n ≤ 3). Our results represent the first observation of triply-resonant phase-matching process in an on-chip optical parametric oscillator, opening up the possibilities on future applications including quantum chips, vertical-cavity surface-emitting lasers and narrow-band two-photon sources.