al theory of the Fourier transform tells us that the abscissa of the pulse maximum (that in our model is the required arrival time) is given by -iG'(0) if G(w) is the moment generating function of its envelope, while the pulse variance is iG"(0). Thus, the differential delay can be written as (4.27) From Equation 4.27, it is evident that the delay is maximum for 0=0, that is, if the input pulses are launched along the PSPs, while it is minimum if the states along which the two input pulses are launched are inclined of /4 with respect to the PSPs. In this case, both the input pulses are equally distributed among the PSPs and no differential delay exists. The pulse spreading due to PMD can be evaluated starting from the definition iuopu( (4.28) Exploiting the properties of the moment generating function and starting from (4.26), the following expression is found for the pulse spreading: (4.29) Equation 4.29 confirms the fact that, if 0=0, that is, the input pulse is launched along a PSP, the pulse spreading is zero, while it is maximum if the pulse energy is equally divided between the PSPs at the fiber input. Equation 4.29, even if it gives a very insightful expression of the pulse spreading, does not permit immediately to evaluate it starting from fiber parameters. Technology for Telecommunications: Optical Fibers, Amplifiers, and Passive Devices However, the evaluation of the average value of the pulse spread during propagation along a PMD-affected fiber can be carried out starting from Equation 4.29 with a further step. We can imagine that the fiber link can be decomposed in several fiber pieces, each of which is completely independent from the others from a PSP point of view. Since the output PSPs of the jth fiber piece are completely independent from the input PSPs of the 1)th, the final pulse broadening is the sum of a great number of indepen- dent contributions. We can consider the average pulse spreading given by Equation 4.29 also as the time delay standard deviation, due to the fact that in the presence 