This book is intended for people interested in the future of telephone, data, video, and internet communication, and to graduate students, scientists, designers, development engineers, and technicians who want to learn more about dense wavelength division multiplexing (DWDM). The readers working in the field of telecommunications, such as components and systems designers, may find useful references along with the text. I hope this book will also be useful to scientists and engineers working in the field of optics, spectroscopy, optronics, electro-optics, and micro/nano technology who would be willing to offer their expertise to solve some of the still-open problems in telecommunications. Conversely, this book may help them to apply to different fields some of the tremendous progress and investments already made in the optical telecommunication field. Perhaps this book will be also useful to marketing managers who want to get information and prospects on the future of optical networks.