Broadband optical frequency comb generation based on a dual-pumped Brillouin-erbium fiber laser

A dual-pump Brillouin-erbium fiber laser is proposed to produce a relatively flat broadband Brillouin comb, in which the two beam of CW lights with the different wavelength are simultaneously injected into a double-ring cavity consisting of a sub-fiber loop (SFL) and a main fiber cavity (MFC). A part of Stokes waves and backward Rayleigh scattered (RS) Brillouin pump (BP) lights generated from a highly nonlinear fiber (HNLF) in the MFC are fed back through the SFL to form laser oscillations in a half-open cavity. Meanwhile, another part of the generated Stokes waves and backward RS lights of the BP are injected to the HNLF through the MFC to generate laser oscillations. Moreover, in combination with the dual-light injecting, four-wave mixing, and stimulated Brillouin scattering are remarkably enhanced, as a result, more and flatter Brillouin comb lines were produced. Since the Brillouin frequency shift in the fiber is dependent on the pump wavelength, the frequency intervals generated at different wavelength locations will usually vary slightly depending on the pump wavelength. As a demonstration, a broadband Brillouin comb spanning over 80 nm was achieved. 443 comb lines within a 30-dB peak power variation, and 229 comb lines within a 20-dB peak power variation were initiated. Due to the combination of multiple mechanisms, the maximum peak variation of the generated Brillouin comb is only 0.414 dB, indicating that the proposed system is extremely stable.