This book presents a descriptive account on various latest advances in the field of optical communication systems. These systems are extremely essential for all types of networks and telecommunications. They comprise of a transmitter which encodes the message into an optical signal, a channel which carries the signal to its destination, and a receiver which reproduces the message from the received optical signal. This book provides updated results on communication systems, with elucidations on their relevance, provided by veteran researchers in this field. It encompasses fundamental concepts of optical and wireless optical communication systems, optical multiplexing and demultiplexing for optical communication systems, optical amplifiers and networks, and network traffic engineering. Lately, wavelength conversion and other advanced signal processing functions have also been studied in detail for optical communications systems. The book emphasizes on wavelength conversion, demultiplexing in the time domain, switching and other optimized functions for optical communications systems. It is primarily aimed at assisting in advancement and research for a wide range of readers including design engineer teams in manufacturing industry, academia and telecommunications service operators/providers.