Observation of tuning properties in a continuous- wave doubly resonant backward optical parametric oscillator

Doubly resonant optical parametric oscillators (OPOs) under continuous-wave (CW) pumping are particularly notable for their low threshold and narrow linewidth. Backward OPOs (BOPOs) realized through backward quasi-phase matching, which exhibit unique tuning properties compared with conventional forward OPOs, have been demonstrated under pulsed pumping. In this work, a doubly resonant BOPO was implemented in a semi-monolithic cavity under CW pumping, and its tuning properties were characterized. By tuning the pump wavelength, the forward and backward waves exhibited tuning rates of 1.02 and -0.02, respectively. Adjusting the crystal temperature resulted in tuning rates of 3 GHz/K and -3 GHz/K for the forward and backward waves, respectively. This research establishes the BOPO as a promising candidate for applications in the field of CW OPOs.