Spontaneous soliton mode-locking of a microcomb assisted by Raman scattering

Abstract

We successfully control the interaction dynamics between optical parametric oscillation (OPO) and stimulated Raman scattering, leading to the generation of distinct frequency comb states in a microresonator. Through Raman-scattered photons, a Raman comb with a sech2 envelope is demonstrated having a broad RF beat note linewidth of several hundred kHz. Moreover, under a specific coupling regime, we successfully generate self-locked Raman single-solitons which is confirmed by a narrow RF beat note of 25 Hz. Remarkably, this spontaneous Raman soliton is deterministically generated through adiabatic pump frequency detuning without the requirement of external locking mechanisms. Additionally, we identify a frequency comb with an unconventional envelope that can be fitted with a Lorentzian x sech2 function, generated via an anti-Stokes process with respect to the Raman comb.