Stokes microcombs in silicon nitride microresonators

TL;DR

This paper reports the first observation of Stokes microcombs in silicon nitride microresonators with normal dispersion, demonstrating controllable switching between Kerr and Raman combs, and revealing complex nonlinear interactions.

Contribution

It introduces the first observation of Stokes microcombs in silicon nitride microresonators with normal dispersion and explores controllable switching between Kerr and Raman combs.

Findings

Observation of Stokes microcombs in silicon nitride resonators.

Demonstration of on-chip stimulated Raman frequency combs.

Numerical model confirms Raman-induced platicon formation.

Abstract

Silicon nitride microresonators have become an ubiquitous platform for cutting-edge photonics applications. Improvement in silicon nitride fabrication techniques, providing ultra-high quality-factor values up to $10^7$, has opened up new possibilities for nonlinear effects realizations in such structures. Here we report for the first time to our knowledge on the observation of the Stokes microcombs in silicon nitride on-chip microresonators exhibiting normal group velocity dispersion. Moreover, using different pump schemes, namely, a tunable laser with an isolator and a stabilized diode laser, we demonstrate on-chip stimulated Raman frequency combs including dark-pulse Raman states. We reveal a complex interplay between Kerr and Raman nonlinearities and elaborate effective method of controllable switching between predominantly Kerr-comb and predominantly Raman-comb operation. We prove the Raman-induced platicon formation by numerical model which shows perfect agreement with experimental results. These findings are of special importance for silicon nitride photonics and provide a basis for novel photonic devices.