Optical Solitons and Frequency Comb Generation - Abstract
Microresonator optical frequency comb devices is a disruptive technology in the area of precision spectroscopy and information processing rapidly entering into the application markets and generating a plethora of fundamental problems to address. One such problem is using materials with quadratic, $chi^(2)$, nonlinearity for the microresonator frequency comb generation and, within such devices, distinguishing between the $chi^(2)$ and Kerr effect induced frequency conversions. In this work 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.