ion of nonlinear propagation distortion has demonstrated very good results allowing very long reach and stabile EDFA- based systems to be realized without using in-line compensation [40] (see Chapter 4). Q factor (dB) Chirped RZ FIGURE 6.24 Q factor versus the spectral position of the considered channel in a long-haul system 4600km long with 64 channels and 50GHz spacing. System parameters are reported in Table 6.1. Spectral channel position (nm) Transmission Systems Architectures and Performances SN per BER = 10-4 (dB) 40 Gbit/s 10 Gbit/s Transmitted power per channel (dBm) FIGURE 6.25 Comparison between standard pre-compensation via DCFs and substitution of the first DCF at the transmit- ter with electronic dispersion pre-compensation. System parameters are reported in Table 6.1. (After Weber, C. et al., Optical Fiber Conference Proceedings, OFC 2009, IEEE, s.l., 2009.) The advantages of this technique are potentially very important: adaptive electronic pre-compensation can face effectively system parameters fluctuations due to tolerances and aging; it allows much simpler EDFAs to be deployed in-line, with an evident cost advantage. On the other hand, implementing compensation of nonlinear propagation requires com- plex algorithms to be implemented in a real-time signal processor with a very high sam- pling rate (50 GHz in the specific case). As an example of the performance of these classes of algorithms in Figure 6.26 [18], the SNo penalty is shown versus the power launched at the transmitter into the fiber. The considered system is a single channel 1200 km long system with 15 span of 80 km each. The transmission fiber is a standard SSMF fiber with D 17 ps/nm/km, a = 0.21 dB/km, Optical SN penalty (dB) Optical power launched into the fiber (dBm) FIGURE 6.26 SN, penalty versus launched power in a single-channel RZ IM-DD 1200 km long system with 15 span of 80km each using SSMF fiber with D 17ps/nm/km, x=0.21 dB/km, y=(1/(W km)). Dispersion is electronically pre- compensated via an adaptive algorithm, no optical