The stable output spectrum with a wavelength spacing of 0.082 nm is displayed in Fig. 2 (b) under 12 dBm BP power with 980 nm pump power of 90 mW. It is noted that 16 Stokes lasing lines show up and none of the anti-Stokes lines are observed owing to the low BP power. The peak power is about 21 dBm with the OSNR of 18 dB. At the high 980 nm pump power,free-running cavity modes cannot be suppressed due to the high EDFA gain. Therefore, the measured OSNR decreases under the lower BP
power, and the peak noise around floor region is severely distorted as shown in Fig. 2(b).