Abstract

Recent developments of integrated photonic platforms have opened unique possibilities for on-chip generation of coherent and broadband frequency combs, both in normal and anomalous dispersion regimes via the generation of coherent nonlinear structures [1]. The potential role played by quasi-phase matching in dispersion engineering for this has remained an open question. As it happens, Si₃N₄ microresonator frequency combs typically employ waveguides with a large cross sections to reduce propagation loss and to reach anomalous dispersion. Coupling between transverse spatial modes can interfere with stable microcomb generation, so a narrow tapered mode ‘suppression’ section can be added to the microresonator in order to alleviate this issue [2] (Fig. 1(a)). In our experiment, we found that this tapered waveguide section provided precisely this quasi-phase matching between higher order of dispersion, leading to the emergence of Faraday Instability (FI) [3]. When combined with synchronous pulse-driving in a microresonator having normal dispersion on average [4], we observe FI combined with switching wave formation to generate ‘satellite’ switching wave microcombs.

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