 power (W) Technology for Telecommunications: Optical Fibers, Amplifiers, and Passive Devices The loss of the fiber at the signal wavelength is 0.472 dB/km, the length of the gain fiber is 5.64km, and the Raman gain coefficient is 13.5 dB/(W km). For the EDFA curve, it is assumed that the amplifier is forward pumped by a 1480nm pump. The passive loss in the EDFA is assumed to be 0.15 dB/m and the length of the coil (20m) is optimized to give maximum signal output power when pumped with 750 mW of 1480 nm pump for 20 mW of input power. The definition of the amplifier efficiency n is given by the following equation: (4.83) where Ps,out, Psin are the signal output and input powers, respectively Ppin is the total pump input power (adding all the used pumps if the case) G is the amplifier gain It is clear that the efficiency of EDFA is limited by the pump saturation for high values of the pump, while the efficiency of the Raman amplifier does not have this limitation. As a consequence, a threshold pump power exists above which, at least in the booster application, the Raman efficiency becomes higher than the EDFA one. After verifying that the Raman efficiency allows designing functional amplifiers hav- ing their own advantages, as in the case of EDFAs, the pumping configuration has to be selected. This point for Raman amplifiers is even more critical than for EDFAs since a certain degree of gain flatness can be achieved by an effective pumping scheme. Even if it was proposed to pump Raman amplifiers with broadband pumps to achieve gain flatness [67], the most practical solution is to use several pumps, often propagating along the Raman fiber in both the directions. Besides the issues related to the amplification efficiency, when this is the case, and to the optimization of the pumping scheme, Raman concentrated amplifiers are also limited by another important factor: the presence of spurious noise contributions besides ASE noise. As a matter of fact, the global noise factor of a Raman amplifier cannot be foreseen cor- 