Broadband bidirectional Brillouin-Raman random fiber laser with ultra-narrow linewidth

We present a Brillouin-Raman random fiber laser (BRRFL) with full-open linear cavity structure to generate broadband Brillouin frequency comb (BFC) with double Brillouin-frequency-shift spacing. The incorporation of a regeneration portion consisting of an erbium-doped fiber and a single-mode fiber enables the generation of broadband BFC. The dynamics of broadband BFC generation changing with the pump power (EDF and Raman) and Brillouin pump (BP) wavelength are investigated in detail, respectively. Under suitable conditions, the bidirectional BRRFL proposed can produce a flat-amplitude BFC with 40.7-nm bandwidth ranging from 1531 nm to 1571.7 nm, and built-in 242-order Brillouin Stokes lines (BSLs) with double Brillouin-frequency-shift spacing. Moreover, the linewidth of single BSL is experimentally measured to be about 2.5 kHz. The broadband bidirectional narrow-linewidth BRRFL has great potential applications in optical communication, optical sensing, spectral measurement, and so on.