The invention of the ruby laser in 1960 created a breakthrough in the use of light as a means of communication. This book provides an overview of the principles and technology of optical communication systems. The book begins with a historical background of optical communication and continues with fundamentals of light propagation in optical fiber and a description of optical transmitters, photodiodes, receivers and preamplifiers. This third edition is updated throughout and concludes with a chapter discussing current systems and future trends. With worked examples and end-of-chapter problem sets, the book is suited for adoption as a course text for advanced undergraduate and graduate students in optical science, applied physics and electronic engineering.