Modulational instability and frequency combs in whispering-gallery-mode microresonators with backscattering

We introduce the first-principle model describing frequency comb generation in a whispering-gallery-mode microresonator with the backscattering-induced coupling between the counterpropagating waves. The elaborated model provides deep insights and an accurate description of the complex dynamics of nonlinear processes in such systems. We analyze the backscattering impact on the splitting and reshaping of the nonlinear resonances and demonstrate backscattering-induced modulational instability in the normal dispersion regime and subsequent frequency comb generation. We present and discuss features of the soliton comb dynamics induced by the backward wave.