Single envelope equation modelling of multi-octave comb arrays in microresonators with quadratic and cubic nonlinearity

TL;DR

This paper uses the single envelope equation to numerically analyze multi-octave optical frequency comb generation in nonlinear microresonators, revealing phase-matched quadratic processes and modulation instabilities that produce diverse comb structures.

Contribution

It introduces a comprehensive numerical model for multi-octave combs in resonators with quadratic and cubic nonlinearities, highlighting phase-matching and instability effects.

Findings

Quadratic and cubic nonlinearities enable multi-octave comb generation.

Phase-matched quadratic processes activate at low power in lithium niobate resonators.

Modulation instabilities lead to coupled comb arrays and pulse trains.

Abstract

We numerically study, by means of the single envelope equation, the generation of optical frequency combs ranging from the visible to the mid-infrared spectral regions in resonators with quadratic and cubic nonlinearities. Phase-matched quadratic wave-mixing processes among the comb lines can be activated by low-power continuous wave pumping in the near infrared of a radially poled lithium niobate whispering gallery resonator (WGR). We examine both separate and co-existing intra-cavity doubly resonant second-harmonic generation and parametric oscillation processes, and find that modulation instabilities may lead to the formation of coupled comb arrays extending over multiple octaves. In the temporal domain, the frequency combs may correspond to pulse trains, or isolated pulses.