Single-longitudinal-mode narrow linewidth broadband tunable Brillouin random laser including dispersion compensation fibers

We propose and demonstrate a single-longitudinal mode (SLM) narrow linewidth broadband tunable Brillouin random laser, including two segment dispersion compensated fibers (DCFs), in which enough narrowband Brillouin gain provided by a 2-km-length DCF to overcome the cavity loss, and Rayleigh backscattering (RBS) provided by a 1-km-length DCF form a mirrorless open cavity to continuously compress the laser linewidth. Compared to ordinary single mode fibers, DCF has an enhanced stimulated Brillouin scattering gain coefficient and RBS coefficient, which is attributed to its small core diameter structure, making the laser more compact and stable. Stronger random feedback effectively lowers the laser threshold, and enough Brillouin gain for multiple amplifications in random mode makes SLM operations more accessible. The proposed laser is with a threshold of -11 mW and an optical signal-to-noise ratio (OSNR) of -55.75 dB, the 3-dB linewidth and linewidth compression ratio of the output laser reaches -550 Hz and -236, respectively. By changing the wavelength of the pump laser, the laser wavelength can be continuously tuned in a broad wavelength range, which is only limited by tunable range of Brillouin pump laser. The laser wavelength fluctuation of 0.02 nm and the OSNR fluctuation of about 3 dB in a 30-minute measure period, indicating that the laser is with a good stability.