# Frequency combs in a microring optical parametric oscillator

## TL;DR

This paper demonstrates soliton frequency comb generation in microring optical parametric oscillators with both $ ext{chi}^{(2)}$ and Kerr nonlinearities, revealing a power-dependent transition between different comb regimes.

## Contribution

It introduces the first analysis of comb generation in microring OPOs considering simultaneous $ ext{chi}^{(2)}$ and Kerr effects, identifying a critical power for regime transition.

## Key findings

- Identification of a critical power for regime transition.
- Observation of comb generation influenced by both nonlinearities.
- Analysis based on a LiNbO$_3$ toroidal resonator geometry.

## 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.