Dynamic Interplay Between Kerr Combs and Brillouin Lasing in Fiber Cavities

Highly coherent frequency combs are of crucial importance for optical synthesis and metrology, spectroscopy, laser ranging, and optical communications. Kerr combs, generated via cascaded nonlinear frequency conversion in a passive optical cavity, typically offer high repetition rates, which is essential for some of these applications. Recently, new ways of generating Kerr combs combining Kerr and Brillouin effects have emerged with the aim of improving some performances, especially in the fiber cavity platform. Direct coherent pumping is replaced by lasing on specific cavity modes, offering easily adjustable repetition rates, and enhanced coherence by Brillouin purification. In this study, such a scheme is implemented and investigated in a non-reciprocal cavity. Highly coherent combs are demonstrated by finely controlling bi-chromatic Brillouin lasing and the Kerr comb parameters. A suitable numerical model is introduced to account for the interplay between Brillouin scattering, Kerr effect, and cavity resonant feedback. Quantitative agreements with experiments reveal the importance of the pump lasers detuning in setting the comb's properties, through the mode pulling effect. This phenomenon, along with multi-mode lasing that impedes the coherence, is not studied in previous fiber-based demonstrations. These limitations are discussed, and several scaling laws are devised. Kerr comb generation is investigated in a bi-chromatic Brillouin fiber laser. A numerical model is proposed to analyze the interplay between Brillouin scattering, Kerr effect, and cavity resonant feedback. The observations highlight some key parameters and provide scaling laws for these systems, which help understand previous experimental results. Benefits and limitations of the scheme are discussed.image