Frequency combs in a microring optical parametric oscillator

Abstract

We report the soliton frequency comb generation in microring 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 LiNbO${}_3$ 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.