Book excerpt: This book discusses the role of optical networks in 3G, 4G, 5G and beyond. The authors discuss the evolution of the technologies, the research involved, and the applications with respect to optical communication systems. In addition, the book provides in-depth knowledge of broadband connectivity for future generation networks. More focus is given towards the front-, mid- and back- hauling of 5G and beyond. The authors present architecture for broadband connectivity and explain its potential in 5G and beyond applications. This book includes several architectures based on Hybrid Fiber-Wireless; Next Generation Passive Optical Networks Stage 1 and 2; millimeter wave over fiber; sub-THz wave over fiber; millimeter/sub-THz wave over multicore fiber; 6G fronthaul; 6G backhaul; GMPLS networks, and massive MIMO sub-Thz antenna. The contributors provide supplementary material such as simulations, analysis and experiments.