Interplay Between Cavity Solitons and Doubly Resonant Brillouin Lasing

Temporal cavity solitons (CSs) are ultra-stable self-sustaining light pulses circulating indefinitely within a resonator [1]. They are sustained through a balance between the anomalous chromatic dispersion, cavity loss, Kerr nonlinearity and a coherent drive, detuned relative to a cavity resonance. CSs have been demonstrated across various platforms, with fiber ring resonators [1] and integrated microcombs [2] being the most common. Recent studies have explored the interaction between CSs-based frequency combs and stimulated Brillouin scattering (SBS), with the aim of developing hybrid combs. SBS arises from photon scattering onto an acoustic wave generated by the beating between two mutually coherent counter-propagating beams. For a single beam, this interaction results in an ultranarrow backward gain, enabling the generation of a highly coherent Brillouin laser from a lower coherence source. The combination of Brillouin laser coherence and high bandwidth of CSs-based combs motivates the development of hybrid CS-Brillouin frequency combs. Recent developments include using a Brillouin laser driven by a low-coherence external pump to drive counterpropagating CSs within the same cavity, in both a singly resonant fiber resonator [3] and a doubly resonant microcomb [4]. Brillouin dual-comb sources have also been demonstrated to generate both backward and forward microcombs [5]. Brillouin-enhanced Kerr frequency combs were also unexpectedly observed in a Fabry-Perot fiber resonator [6].