hird based on IM and complete link electronic pre-compensation with single-stage EDFA amplification. 6.3.4.1 Single-Span Systems with Intensity Modulation and All Raman Amplification A system based on all Raman amplification tries to leverage on the specific characteristics of Raman amplifiers: low global noise factor and distributed amplification in the DCF (Table 6.11). This last characteristic, in particular, helps to maintain a low peak power along the link contributing to take nonlinear effects under control. Due to the fact that nonlinear effects pose at the end the final limitation to the system reach, they need a careful consideration. In all the following reasoning we will assume to have a link around 250km long. The attenuation of 250 km of SSMF is on the order of 63 dB, a formidable amount of attenuation to be compensated. In order to achieve a high Raman amplification efficiency, we will divide the DCF part at the transmitter and part at the receiver. The power injected per channel into the fiber at the end of the DCF located at the trans- mitter determines practically the amount of nonlinear effects, since Raman amplification from pumps located at the transmitter only happens into the DCF since the pumps are extracted at the DCF end. Being SPM and XPM critical, RZ modulation is mandatory, even if this means having a big optical bandwidth accepting more ASE noise on the detector. To make a trade-off between robustness to ISI and ASE noise power, we will select a duty cycle of 40% that means that the Gaussian pulse at the transmitter has a full width at 1/e equal to 40 ps. We assume also to leave a residual dispersion of about ps/nm and to pre-chirp at the modulator the pulses with the same pre-chirp used to plot Figure 6.9. Telecommunication Networks TABLE 6.11 Parameters Values for the All Raman Single Span Intensity Modulation and Direct Detection System Channel Speed 10 Gbit/s Optical bandwidth of the DWDM comb Extended C band Modulation Duty cycle Number of channels Channel spacing 100 GHz Transmi