This book provides a comprehensive account of fiber-optic communication systems. The 3rd edition of this book is used worldwide as a textbook in many universities. This 4th edition incorporates recent advances that have occurred, in particular two new chapters. One deals with the advanced modulation formats (such as DPSK, QPSK, and QAM) that are increasingly being used for improving spectral efficiency of WDM lightwave systems. The second chapter focuses on new techniques such as all-optical regeneration that are under development and likely to be used in future communication systems. All other chapters are updated, as well.About the Author: GOVIND P. AGRAWAL is a professor at the Institute of Optics at the University of Rochester and a Fellow of both the Optical Society of America and the Institute of Electrical and Electronics Engineering. He is also a Senior Scientist at the Laboratory for Laser Energetics. Dr. Agrawal is author or coauthor of more than 300 research papers, book chapters, and monographs.