Normal-dispersion microcombs enabled by controllable mode interactions

We demonstrate a scheme incorporating dual-coupled microresonators through which mode interactions are intentionally introduced and controlled for Kerr frequency comb (microcomb) generation in the normal-dispersion region. Microcomb generation, repetition rate selection, and mode locking are achieved with coupled silicon nitride microrings controlled via an on-chip microheater. The proposed scheme shows for the first time a reliable design strategy for normal-dispersion microcombs and may make it possible to generate microcombs in an extended wavelength range (e.g. in the visible) where normal material dispersion is likely to dominate. Microcomb generation, repetition rate selection, and mode locking are achieved with coupled silicon nitride microrings constructed from single-mode waveguides. Mode interactions are controlled via an on-chip microheater for reliable microcomb initiation. The proposed scheme shows for the first time a reliable design strategy for normal-dispersion microcomb generation and may make it possible to generate microcombs in an extended wavelength range (e.g. in the visible) where material dispersion is likely to dominate.