Continuous-wave whispering-gallery optical parametric oscillator based on CdSiP2

Continuous-wave (cw) optical parametric oscillators (OPOs) are ideally suited for applications, for example high-resolution spectroscopy, that need coherent sources combining narrow-linewidth emission with good wavelength tunability. Here, we demonstrate for the first time cw OPOs based on a millimeter-sized whispering gallery resonator (WGR) made of cadmium silicon phosphide (CdSiP2). By employing a compact laser diode at 1.57-mm wavelength for pumping, a cw OPO with wavelength tunability from 2.3 mm to 5.1 mm is realized based on such a resonator. The oscillation thresholds are in the milliwatt range. The maximum total power conversion efficiency reaches more than 15%. The intrinsic quality factor at 1.57 mm is determined to be 3.5 × 106. This work suggests that CdSiP2 is a very promising alternative for constructing mid-infrared parametric devices.