A survey of optical techniques with an emphasis on frequency control (phase stability) aspects

An introductory survey of fiber-optic techniques for signal transmission is given. The intensity modulation/direct detection technique, the most widely used approach at present, is discussed. A brief discussion of the erbium-doped fiber-optical amplifier and its impact on long-distance signal transmission is given, followed by a discussion on a coherent technique and its requirements on laser linewidth and frequency stability. The author also discusses recent developments in narrow linewidth lasers, laser frequency stabilization, and generation of microwave signals using coherent mixing of two laser beams