In the past few years, the use of erbium-doped fiber amplifiers has increased the capacity of fiber optics transmission systems by more than a hundred-fold. These amplifiers allow for the amplification of transmission signals in all optical ways without the need for electronic processing of the signal, which limits the capacity of optical systems. With the recent explosive growth in optical transmission networks, the fiber amplifier has become an essential building block for these networks. Understanding it provides great insight into today's high-capacity fiber networks, their design, and their future evolution.Erbium-Doped Fiber Amplifiers has been written by early pioneers in the development of fiber amplifier technology and optically amplified systems. The book guides the reader from the most fundamental aspects of fiber amplifiers all the way to system design and applications. The fundamental chapters address the important aspects of noise theory, design, and understanding of optically amplified systems. The coverage is such that the book will be of interest to researchers, practitioners, and students new to the field.The book can be read as a sequence of linked chapters which build on each other. Since each chapter is relatively self-contained, the reader can also jump in at the desired point of interest and refer to other chapters as needed. Many figures are used to present concepts in an intuitive and understandable way. Numerous references are provided for the reader wishing to delve further into any of the topics covered. With the continued soaring demand for optical transmission networks, the book provides an important base for understanding the technicalunderpinnings of such networks.