Fiber-Optic Communication Systems

A communication system transmits information from one place to another, whether separated by a few kilometers or by transoceanic distances. Information is often carried by an electromagnetic carrier wave whose frequency can vary from a few megahertz to several hundred terahertz. Optical communication systems use high carrier frequencies (~ 100 THz) in the visible or the near-infrared region of the electromagnetic spectrum. They are sometimes called lightwave systems to distinguish them from microwave systems whose carrier frequency is typically smaller by five orders of magnitude (~ 1 GHz). Fiber-optic communication systems are the lightwave systems that employ optical fibers for information transmission. Such systems were deployed worldwide during the 1980s and have revolutionized the field of communications. Indeed, optical communications coupled with microelectronics is believed to be a major factor in the advent of the so-called information age. The objective of this book is to describe fiber-optic communication systems in a comprehensive manner. The emphasis is on the fundamental aspects, but the engineering aspects are also discussed. The purpose of this introductory chapter is to present the basic concepts and to provide the background material. Section 1.1 gives a historical perspective on the development of optical communication systems. Section 1.2 presents the concepts, such as analog and digital signals, channel multiplexing, and modulation formats. Section 1.3 discusses relative merits of guided and unguided optical communication systems, whereas Section 1.4 describes the components of a fiberoptic communication system. The concept of channel capacity is discussed in Section 1.5.