Modulation Instability Induced Frequency Comb Generation in a Continuously Pumped Optical Parametric Oscillator

TL;DR

This paper demonstrates the generation of optical frequency combs via second-order nonlinear effects in a continuously pumped optical parametric oscillator, revealing new dynamical regimes and coherence properties.

Contribution

It introduces a mean-field model for quadratic combs in OPOs, identifying novel modulation instability regimes and experimentally confirming comb formation.

Findings

Quadratic combs can be generated in OPOs around half the pump frequency.

New dynamical regimes induced by modulation instabilities were identified.

Simulated spectra show good agreement with experimental results and exhibit phase-locking.

Abstract

Continuously pumped passive nonlinear cavities can be harnessed for the creation of novel optical frequency combs. While most research has focused on third-order "Kerr" nonlinear interactions, recent studies have shown that frequency comb formation can also occur via second-order nonlinear effects. Here, we report on the formation of quadratic combs in optical parametric oscillator (OPO) configurations. Specifically, we demonstrate that optical frequency combs can be generated in the parametric region around half of the pump frequency in a continuously-driven OPO. We also model the OPO dynamics through a single time-domain mean-field equation, identifying previously unknown dynamical regimes, induced by modulation instabilities, which lead to comb formation. Numerical simulation results are in good agreement with experimentally observed spectra. Moreover, the analysis of the coherence properties of the simulated spectra shows the existence of correlated and phase-locked combs. Our results reveal previously unnoticed dynamics of an apparently well assessed optical system, and can lead to a new class of frequency comb sources that may stimulate novel applications by enabling straightforward access to elusive spectral regions, such as the mid-infrared.