pers [22]. An estimation of the possible perfor- mance of a third order PMD compensator is reported in Figure 9.16 [22]. When compared to a relevant gain passing from a first to a second order compensator, the gain achieved when passing from a second to a third order component is not SO pronounced while it is paid with a sensible increase in the complexity. Thus it is possible to conclude that system design should try as much as possible to use second order compensator (if optical com- pensation is needed) and passing to third order compensators only if it is really needed. 9.2.4 Other Limiting Factors 9.2.4.1 Fiber Nonlinear Propagation Increasing the signal bandwidth has essentially no impact both on Brillouin (at least if the carrier is maintained in the spectrum) and on Raman effects. Telecommunication Networks No compensation First order Second order FIGURE 9.16 Estimation of the possible performance Third of a third order PMD compensator. (After order Kim, S., IEEE J. Lightwave Technol., 20(7), 1118, 2002.) =<T>/T0 While the impact of Cross Phase Modulation (XPM) and Four Wave Mixing (FWM) can be managed by a suitable channel spacing and residual dispersion, SPM depends on the individual channel and can become the dominant nonlinearity and the system limiting factor besides PMD. In this case also, the reduction of the signal bandwidth occupancy seems to be the only way to go to reduce SPM impact besides the possibility of an effective electronic compensation via some kind of coherent detection or of signal predistortion (compare Chapter 5). 9.2.4.2 Timing Jitter Due to the very short bit time, timing jitter assumes a particular importance in 100 Gbit/s serial systems. We can decompose the jitter into three factors: 1. Transmission jitter 2. Detection clock jitter 3. Propagation jitter The transmission jitter depends on the fluctuations of the transmitter clock that causes the center instant of the pulses sent to the modulator to fluctuate randomly around the average value. This problem can be faced with a c