A multi-wavelength Brillouin fiber laser of switchable frequency spacing based on a bi-directional ring cavity

A multi-wavelength Brillouin fiber laser (MW-BFL) of switchable frequency spacing is proposed and experimen-tally demonstrated. This MW-BFL comprises a ring cavity that includes a piece of 20-km-long single-mode fiber as the gain medium for Brillouin amplification. The switchability of wavelength spacing is implemented by adjusting the Brillouin pump (BP) coupling ratio into the ring cavity of a bi-directional pumping scheme, as the outputs of single and double Brillouin shifts are achieved with either a 50/50 coupler or a 99/1 coupler, respectively. A total of 11 lasing Stokes lines with single Brillouin shifts and 9 lasing Stokes lines with double Brillouin shifts have been observed when the BP power is set at 0 dBm. Both Brillouin lasers are wavelength-tunable, and the tuning ranges are 16 and 10 nm for the single-and double-spaced outputs, respectively.