Optical Communications Systems are very much essential part in our advanced fibre-based telecommunications and networks. They consists of a transmitter that encodes a message into an optical signal, a channel that carries the signal to its destination, and a receiver that reproduces the message from the received optical signal. This book presents up to date results on communication systems, along with the explanations of their relevance, from leading researchers in this field. Its chapters cover general concepts of optical and wireless optical communication systems, optical amplifiers and networks, optical multiplexing and demultiplexing for optical communication systems, and network traffic engineering. Recently, wavelength conversion and other enhanced signal processing functions are also considered in depth for optical communications systems. The researcher has also concentrated on wavelength conversion, switching, demultiplexing in the time domain and other enhanced functions for optical communications systems. This book is targeted at research, development and design engineers from the teams in manufacturing industry; academia and telecommunications service operators/ providers. This book presents a high level technical overview of the emerging technologies of optical communications and networking systems. It is intended as an introduction to the field for optical communication systems or network professionals, such as higher degree research students, academics and design engineers. Although it is intended for professionals who already have some technical background, it is nevertheless relevant to anyone wishing to understand optical communication systems or networks.