Abstract

Stimulated Brillouin scattering (SBS) is the first nonlinear effect to be triggered when a powerful continuous wave laser interacts with a nonlinear waveguide. This effect is further exacerbated in resonators due to the multiple round trips in the cavity. SBS has proven to be extremely interesting for building ultra-stable microwave photonic synthesizers [1], to trigger broadband cavity solitons [2], or to balance thermo-optical effects to obtain ultra-stable sources [3]. Whatever the cavity architecture, the only requirement is to obtain a spectral overlap between the SBS gain (νB = 10 GHz, ∆ν = 50 MHz), and the cavity resonances. This condition is automatically verified in fiber ring cavities, which have free spectral ranges (FSRs) typically between 1 and 100 MHz, or can be met by fine-tuning the cavity lengths in microresonators with FSRs in the GHz range [2-3]. In this paper we evidence an original mode-locking phenomena to generate a stable Brillouin Kerr frequency comb in fiber Fabry Perot resonators. The surprising feature of our work is illustrated in Fig. 1 (a). While there is a spectral overlap between the 8^th cavity resonance (dashed lines) and the SBS gain curve (red curve) at 9.416 GHz, we observed a Brillouin Kerr frequency comb with a line-to-line spacing equals to 10.593 GHz (exactly 9 times the cavity FSR, blue line in Fig. 1 (a)) where there is no spectral overlap.

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