Self-injection-locked near-visible laser at 781 nm by frequency-doubling in a quasi-singly resonant high-Q micro-cavity

Based on a quasi-singly resonant plane-concave Fabry–Perot (FP) micro-cavity with a high Q-factor of 9.1 M and a volume of <0.12 mL, we have demonstrated self-injection-locked (SIL) second-harmonic generation (SHG) at near-visible frequencies. With an incident SIL pump power of 80 mW at 1561.8 nm, the maximum output SHG power at 780.9 nm reached 16.9 mW, achieving a high conversion efficiency of 21.1%. The intrinsic linewidth of the SIL pump laser was reduced from 1.1 MHz to about 130 Hz, and the corresponding linewidth of the SIL-SHG light was about 520 Hz as expected. Most importantly, high SHG efficiency was observed at any pump frequency of the corresponding FP resonant modes. Compared to the recently reported results of SIL-SHG using microring cavities, our SIL-SHG design with a quasi-singly resonant FP cavity offers higher conversion efficiency and output SIL-SHG power, along with a potential of continuous tunability of the SHG frequency. Thanks to its significantly larger mode-field volume, it can handle higher input power without incurring unwanted nonlinear effects.