eat speed at which the compensator has to work. Even if traveling wave FFE/DFE compensators have been realized and demonstrated effective in compensating PMD at 40 Gbit/s [6], no electronic equalization has been real- ized on a serial signal at 100 Gbit/s. For this reason, optical PMD compensation has a particular importance at very high speed. As a matter of fact, due to the random nature of the PMD, the instantaneous perfor- mance of the system can be also completely ruined by PMD in the occasion of unfortunate fluctuations of the Jones matrix even if the average penalty is quite low. To understand this phenomenon, let us consider the PMD-related penalty as defined in Figure 6.12: it was evaluated by starting from the error probability for a specific value of Next Generation Transmission Systems the PMD broadening At and averaging with respect to At. It is clear that, while At fluctu- ates, the system can experience instantaneous values of the penalty either smaller or larger than the average value. To evaluate the impact of these fluctuations, generally, the so-called outage probabil- ity P is used, that is, the probability that the instantaneous value of the PMD-induced penalty is higher than the value used in the system design, or equivalently (assuming all processes ergodic), the percentage of time in which the PMD-induced penalty is higher than the design value. In order to approach the problem of reducing the outage probability, it is important to notice that when launching a pulse into a fiber link with PMD, the received pulse width depends on the launched state of polarization (SOP), and in particular on its position with respect to the input Principal States of Polarization (PSPs), following Equation 4.29. The effect of the launched polarization state on the pulse broadening is represented in Figure 9.11 [7] where the pulse spreading ratio is shown versus the normalized average pulse width a. The parameters B and a are defined as 3-1/2 (9.5) where Tin is the half width at half maximum of the input puls