This book is an important resource elaborating recent developments achieved in fiber communications systems. It consists of a compilation of research works on the essential technologies and mathematical concepts underlying optical fiber communications and devices of our age. The book encompasses various topics like the topologies and architecture of these networks, PONs, WANs, LANs, secure optical communication among others. Therefore, it presents an all-inclusive overview on latest research trends and technologies associated with these topics. It integrates contributions by veteran scientists and academicians hailing from renowned universities and research centers associated with the fields of optical communications and photonics. This book will serve as a valuable reference with a wide spectrum of information about this field. It will appeal to practitioners and researchers engaged in the field of photonics and optical communications.