Fig. 2 (a) reveals the output spectrum with 0.172 nm wavelength
spacing under 5 dBm BP power with 980 nm pump power of
90 mW. A total of 17 lasing lines in cluding 14 Stokes (7 odd-orders
and 7 even-orders) and 3 anti-Stokes lasing lines are obtained. The intra-cavity BP pre-amplification technique in the proposed configuration provides an efficient method to suppress the free-running cavity modes by injecting sufficient BP signal.