[4] Zhou X,Birk M,Woodward S. Pump-noise induced FWM effect and its reduction in a distributed Raman fiber amplifier [J].IEEE Photonics Technology Lett.,2002,14(12): 1686-1688.

[5] Wong W S,Chen C J,Ho M C,et al. Phase-matched four-wave mixing between pumps and signals in copumped Raman amplifier [J].IEEE Photonics Technology Lett.,2003,15(2): 209-211.

[6] Pasquale F D,Meli F. New Raman pump module for reducing pump-signal four-wave-mixing interaction in co-pumped distributed Raman amplifiers [J].Journal of Lightwave Technology,2003,21(8): 1742-1748.

[7] Kung T T,Chang C T,Dung J C,et al. Four-wave mixing between pump and signal in a distributed Raman amplifier [J].Journal of Lightwave Technology,2003,21(5): 1164-1170.

[9] Forghieri F,Tkach R W,Chraplyvy A R. WDM systems with unequally spaced channels [J].Journal of Lightwave Technology,1995,13(5): 889-897.