Multi-comb patterns in normal-dispersion integrated silicon nitride microresonators via multi-frequency self-injection locking of a DFB diode laser

Self-injection locking of a diode laser frequency to a mode of a microresonator has proven to be an effective and robust technique of laser stabilization and Kerr microcomb generation. Here, we demonstrate and investigate a regime of multi-frequency self-injection locking (MF-SIL) of a single-frequency DFB diode laser. We show that in the normal group velocity dispersion (GVD) microresonator, MF-SIL enables the generation of different platicon-like multi-comb patterns. It is revealed that in this regime several narrow pump laser lines can appear and excite frequency combs independently, which leads to the generation of multi-comb patterns with a larger number of spectral components and enhanced pump-to-comb conversion efficiency. We study dynamics and conditions of multi-microcomb generation comparing it with single-platicon generation. These findings reveal new features of the laser-microresonator nonlinear interaction that are enabled by improvements in the fabrication of the photonic integrated circuits with high Q-factors.