The study and the analysis presented in this thesis consider a fiber-optic transmission system in which the signal is routed from the source to the destination using devices called ROADMs. These devices act as multiplexers, being able to select a certain wavelength and decide whether to let it pass or block it. However, they rely on Wavelength Selective Switches (WSS) that act like filters on the signal, impairing it on the frequencies at the edges. In particular, the larger the number of cascaded WSS, the greater the impact on the signal. To mitigate the impact of filtering on transmission, a promising solution consists in dividing the channel into subcarriers, each with the same spectral bandwidth , and adopt modulation techniques able to improve efficiency.