L-band narrow linewidth Brillouin random fiber laser via distributed Rayleigh scattering in optical fibers

We proposed and experimentally demonstrated a tunable L-band narrow-linewidth Brillouin random fiber laser (BRFL) in a half-open ring cavity with Brillouin gain medium of 10-km single mode fiber (SMF) as well as distributed Rayleigh feedback provided by another 20-km SMF. With a low laser threshold of 6.8mW, the proposed laser can realize cavity-mode-free lasing resonance at a wavelength of 1576.08nm, indicating good single-frequency lasing operation. Compared with the Brillouin pump, the frequency noise (FN) of the proposed laser is significantly suppressed by around 30dB, benefiting from randomly distributed Rayleigh scattering along SMF. An ultra-narrow laser linewidth of 400.8Hz is also obtained with a pump/Stokes laser linewidth compression ratio of 87.5, which coincides with theoretical prediction. When the wavelength of the proposed laser is tuned from 1568.08nm to 1576.08nm, sub-kHz random lasers with cavity mode free lasing resonance achieves high optical signal-to-noise ratio (ONSR) operation. The proposed laser source with good tunability has great potentials for practical applications in future advanced optical communication and sensing.