Walk-off-induced modulation instability, temporal pattern formation, and frequency comb generation in cavity-enhanced second-harmonic generation

TL;DR

This paper develops a mean-field model for cavity-enhanced second-harmonic generation, revealing how temporal walk-off induces a new quadratic modulation instability that leads to frequency combs and complex temporal patterns.

Contribution

It introduces a novel mean-field equation capturing the full dynamics, highlighting the role of walk-off in generating previously unknown nonlinear behaviors and frequency combs.

Findings

Identification of a new quadratic modulation instability

Numerical simulations match experimental frequency comb observations

Prediction of rich temporal pattern formation due to walk-off

Abstract

We derive a time-domain mean-field equation to model the full temporal and spectral dynamics of light in singly resonant cavity-enhanced second-harmonic generation systems. We show that the temporal walk-off between the fundamental and the second-harmonic fields plays a decisive role under realistic conditions, giving rise to rich, previously unidentified nonlinear behaviour. Through linear stability analysis and numerical simulations, we discover a new kind of quadratic modulation instability which leads to the formation of optical frequency combs and associated time-domain dissipative structures. Our numerical simulations show excellent agreement with recent experimental observations of frequency combs in quadratic nonlinear media [Phys. Rev. A 91, 063839 (2015)]. Thus, in addition to unveiling a new, experimentally accessible regime of nonlinear dynamics, our work enables predictive modeling of frequency comb generation in cavity-enhanced second-harmonic generation systems.