Type II microcomb generation in a filter-driven four wave mixing laser

TLDR: In this paper, a well-known route to comb generation starts from the modulation instability (MI) of the pump, which generates coherent lines spaced by more than one free spectral range of the microcavity.

Abstract: Optical frequency combs in microresonators [1] or microcombs have generated significant attention in recent decades. Specifically, microcombs can be generated by resonantly coupling a powerful CW laser light in a microcavity, inducing multiple frequency oscillation by parametric generation. A well-known route to comb generation starts from the modulation instability (MI) of the pump. MI generates coherent lines spaced by more than one free spectral range of the microcavity [2]. This kind of optical spectrum is generally referred to as a Type I comb [3], and it is usually coherent. Type II combs are generated at higher powers, and consist of a cascaded generation from the original Type I comb. Usually such combs are incoherent [3]. Similar spectra with coherent properties are also observed during the interaction of multiple cavity solitons [4].