ttering, the presence of signal-to- signal Raman power transfer, and Rayleigh backscattering. Consequently, there are many interactions within the fiber and the power propagation equations are normally very complicated. The pump powers to provide flattened gains can be predicted by appropriate use of Raman amplifier models, together with a suitable optimization procedure. Good agreement with experiment is possible. Thus, spectral profiles of over 100-nm bandwidth with subdeci- bel gain ripples have been achieved in DCF amplifier modules (Namiki, Emori, & Oguri, 2005), and in this sense the technique is successful. Unfortunately, multi-wavelength pumping creates several problems. As the number of pumps is increased, the gain spectrum becomes ever more sensitive to the launched pump powers and complicated control algo- rithms are required as a result. Moreover, the pump units are expensive and have demand- ing heat dissipation requirements. When multi-wavelength pumping is used with distributed amplification, high total powers are launched into the fiber transmission medium, raising potential concerns about the integrity of the fiber and, worse, about eye and skin damage to users. This aspect is considered further in the last section of the chapter, which discusses the benefits of distributed Raman amplification. Operation in Intermediate Saturation Line amplifiers are normally operated in intermediate saturation (Desurvire, 1994; Desur- vire et al., 2002; Srivastava & Sun, 2002). In WDM systems this is usually unavoidable if the required output powers are to be provided for the M channels. Multichannel operation with sufficient signal powers to cause saturation can be problematical for SOAs but beneficial for other amplifier types. In SOAs the conduction band has a lifetime of around 100 ps, which is comparable to the bit period of 10-Gbit/s operation; thus the population inversion can vary from one bit to another. (In contrast, EDFAs have ~10-ms metastable state lifetimes and, unless the data- rate is very low, t