Book excerpt: The phenomenal growth in Internet traffic has lead to a huge increase in demand for data transmission capacity on a worldwide level. As a result, wavelength division multiplexing (WDM) technology emerged, which makes it possible to transmit a large number of optical channels on a single optical fiber. An equally significant development occurred in optical networks, where switching and routing of signals takes place in the optical domain. This technology places special demands on the optical sources (lasers) used in the system. This text offers a description of the optical sources (equipment and devices) designed to meet these demands. Sources for DWDM Systems is intended for the engineers and graduate students working on optical networks. There is currently a nearly explosive interest in optical networks and the components required for such networks, but there is presently no single work which covers the variety of optical sources which may be used. This book will cover a particular component, tunable lasers, which is the next "big thing" in DWDM. The primary market are engineers developing tuneable lasers for optical networks, as well as graduate students enrolled in the optical engineering curriculum, especially: optical communication, semiconductor lasers, optical networks, and/or components for optical networks.