Multipath interference pops up when a transmitted signal takes two or more paths to reach the receiver. These paths can come from reflection, diffraction, or scattering off stuff like buildings, hills, or water. Each route is a bit longer or shorter, so the signals show up at. Multiband transmission is, nowadays, being implemented worldwide to increase the optical transport network capacity, mainly because it uses the already-installed single-mode fiber (SMF). 654E SMF, due to its attributes (e. When designing such systems, many mechanisms that degrade the transfer of infor-mation must be taken into account. Until the late 1990s, the main causes of signal degradation in transmission were fiber nonlinear ty and amplified. We use the power coupled-mode theory to study the interplay between multipath interference (MPI) and differential mode attenuation (DMA) in quasi-single mode (QSM) fibers. As optical networks move to higher speeds while reducing electrical conversions, optical effects such as multipath. Optical Multi-Path Interference Noise Mitigation for 56 Gb/s PAM4 IMDD Transmission System Chuanming Huang, Haiping Song, Mengfan Cheng, Qi Yang, Ming Tang, Deming Liu, and Lei Deng C.