Figure 10: (a) Maximum transmission distance achieved in the long-haul WDM transmission system employing cascaded FOPAs and end-to-end equalization versus length of fiber span. (b) Constraints on number of amplifiers (with end-to-end equalization) ensuring BER below and signal powers between −30 dBm and 10 dBm versus length of fiber span. The results are computed for , eight externally modulated channels with 0.4 THz spacing (193.8–196.6 THz). Total signal power is −3 dBm before multiplexing. Optical fiber has the attenuation factor 0.2 dB/km. The FOPAs are pumped by 1.5 W of 1537.6 nm pump light. FOPAs are made with 1 km DSF and pumped at 1537.6 nm with 1.5 W power. The zero-dispersion wavelength is 1537 nm, and the dispersion slope is 0.034 ps  . The nonlinear coupling coefficient is 1.8 . Maximum value of Raman-gain coefficient for DSF is 0.8  , at the temperature of 300 K.