the only nonlinearities that are present are those related to fiber propagation, which generally can be considered small. Thus in a first approximation optical dispersion compensation can work on a linear channel. On the other hand, if dispersion is to be compensated after the detection via an electronic circuit, one compensator per channel is needed; moreover, the photodiode square detec- tion law creates a strong nonlinearity in the channel before the electronic compensator. Nevertheless, electronic dispersion compensation has several attractive characteristics, SO that it is nowadays almost always present in high-performance systems. The cost of electronic circuits is not SO high, SO that from a cost point of view, having one compensator for each channel is not a big problem. On the other hand, per channel compensation allows accurate management of the dispersion slope and of the polariza- tion mode dispersion (PMD), which is not possible using a compensator that processes all the wavelength channels due to the fact that the bandwidth of the principal states of polarization (PSPs) is generally smaller than the wavelength extension of the multiplexed comb. Moreover, using more complex algorithms, electronic compensation can cope also with nonlinear distortion [68,70]. Electronic compensators can be divided into three categories [56]: electronic post- compensators (EPCs), electronic pre-compensators (EBCs), and electronic pre-distortion circuits (EPDs): EPCs are circuits located at the receiver that try to eliminate intersymbol interference caused by dispersion and, just in case, nonlinear effects by processing the photocurrent. EBCs on the contrary are located at the transmitter and distort the signal before modu- lation onto the carrier to simulate the transit through a virtual dispersion compensation device. Once the modulated signal is built and transmitted through the fiber, the pre- distortion is compensated by the fiber dispersion and ideally the signal arrives undis- torted at the receiver. The case of E