Theory of multicolor soliton microcombs

Abstract

We present a general theory of multicolor soliton microcombs. These frequency combs require engineered dispersion and have an optical spectrum consisting of multiple spectral windows, centered at distinct frequencies. Our theory is based on a multiple-scale approach applied to the Lugiato-Lefever equation, and provides a framework to investigate different pumping configurations. For multi-frequency pumping, we predict a decreasing pumping threshold as the number of spectral windows increases due to an enhanced effective nonlinear parameter. However, comb formation does not require multi-frequency pumping and can emerge even with a single driving field. Our theoretical predictions are in excellent agreement with numerical simulations.