In this paper, we describe a detailed numerical investigation on the relative merits of gain flattened distributed Raman amplification (DRA) and discrete gain flattened amplifiers. We simulate a system with forty 40-Gb/s channels spaced at 100 GHz and compare the performance of three different modulation formats nonreturn-to-zero (NRZ), return-to-zero (RZ) and carrier-suppressed RZ (CS-RZ). Three types of amplifiers, multifrequency backward-and forward-pumped DRAs, and an idealized discrete gain flattened amplifier are examined for various signal powers and transmission distances. For the backward-pumped DRA, we also describe calculated tolerance limits imposed by incomplete dispersion slope compensation and polarization mode dispersion (PMD) level.
D. Dahan and G. Eisenstein, "Numerical Comparison Between Distributed and Discrete Amplification in a Point-to-Point 40-Gb/s 40-WDM-Based Transmission System With Three Different Modulation Formats," J. Lightwave Technol. 20, 379- (2002)