Frequency combs in a microring optical parametric oscillator

We report the soliton frequency comb generation in micro-ring optical parametric oscillators operating in the down-conversion regime and with the simultaneous presence of the chi((2)) and Kerr nonlinearities. The combs are studied considering a typical geometry of a bulk LiNbO3 toroidal resonator with the normal group velocity dispersion spanning an interval between the pump and the down-converted signal. We have identified critical power signaling a transition between the relatively low pump power predominantly chi((2)) combs and the high pump power ones shaped by the competition between the chi((2)) and Kerr nonlinearities. (C) 2019 Optical Society of America