This is the most authoritative, complete source of test and measurement information for engineers who design and maintain fiber optic networks. This book presents measurement principles for characterizing all three basic components of a fiber optic communication system: the optical transmitter, fiber medium and optical receiver. It also covers system level measurements, and discusses the principles and limitations of current fiber optic testing equipment. It discusses testing to SONET/SDH international standards, and helps engineers choose the best approach to testing today's new erbium doped fiber amplifiers. The book provides detailed recommendations for understanding polarization states, and presents new methods for accurately characterizing the behavior of Wavelength Division Multiplexing (WDM) fiber systems. It includes detailed coverage of testing fiber in the local loop, using optical power meters and optical time domain reflectometers. It also reviews the latest state-of-the-art 10 Gb/s systems, and even faster systems on the horizon. The coverage is practical, helping professionals accurately measure and test fiber optic systems without becoming experts in theory. All fiber optic engineers working with communications applications.