A widely tunable single-wavelength Brillouin fiber laser (BFL) incorporating a bismuth-based erbium-doped fiber (Bi-EDF)
is proposed. The 52 cm-long highly erbium-doped Bi-EDF provides broadband gain extending from the C-band (1525-1565
nm) to the L-band (1565-1625 nm). In experiment, the BFL operates in a range from 1555 nm to 1632 nm, which is the
widest to the best of our knowledge. The proposed BFL is an attractive narrow linewidth laser source on the L-band, which
has many potential applications, such as in slow light, coherent communication, and interferometric sensing.