Book excerpt: Optical Communications in the 5G Era provides an up-to-date overview of the emerging optical communication technologies for 5G next-generation wireless networks. It outlines the emerging applications of optical networks in future wireless networks, state-of-the-art optical communication technologies, and explores new R&D opportunities in the field of converged fixed-mobile networks.Optical Communications in the 5G Era is an ideal reference for university researchers, graduate students, and industry R&D engineers in optical communications, photonics, and mobile and wireless communications who need a broad and deep understanding of modern optical communication technologies, systems, and networks that are fundamental to 5G and beyond. - Describes 5G wireless trends and technologies such as cloud radio access networks (C-RAN), massive multiple-input and multiple-output (MIMO), and coordinated multipoint (CoMP) - Gives an insight into recent advances on the common public radio interface (CPRI), the evolved CPRI (eCPRI), and the open radio access networks (O-RAN) interface - Presents X-haul technologies and how transportation technologies can satisfy the mobile network requirements - Describes recent technological advances in access, aggregation, metro, data center, backbone, and undersea optical networks - Discusses the vision and use cases of the 5th generation fixed network (F5G) to help realize a fully connected, intelligent world for the benefit of our global society