[1] [1] Hansen P B, Eskildsen L, Stentz A J et al.. Rayleigh scattering limitations in distributed Raman pre-amplifiers. IEEE Photon. Technol. Lett., 1998, 10(1):159～161

[3] [3] Wan P,Conradi J. Impact of double Rayleigh backscatter noise on digital and analog fiber systems. J. Lightwave Technol., 1996, 14(3):288～297

[4] [4] Zhang W, Peng J, Liu X et al.. An analytical expression of equivalent noise figure for distributed fiber Raman amplifiers with Rayleigh scattering. Opt. Commun., 2001, 198(1～4):231～236

[5] [5] Haus H A. The noise figure of optical amplifiers. IEEE Photon. Technol. Lett., 1998, 10(11):1602～1604

[6] [6] Chinn S R. Analysis of counter-pumped small-signal fibre Raman amplifiers. Electron. Lett., 1997, 33(7):607～608

[7] [7] Wan P, Conradi J. Double Rayleigh backscattering in long-hual transmission systems employing distributed and lumped fibre amplifiers. Electron. Lett., 1995, 31(5):383～384

[8] [8] Lewis S A E, Chernikov S V, Taylor J R. Characterization of double Rayleigh scatter noise in Raman amplifiers. IEEE Photon. Technol. Lett., 2000, 12(5):528～530