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 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 lightwave systems that employ optical fibers for information transmission | Fiber-Optic Communications Systems Third Edition. Govind P. Agrawal Copyright 2002 John Wiley Sons Inc. ISBNs 0-471-21571-6 Hardback 0-471-22114-7 Electronic Chapter 1 Introduction 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 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 lightwave systems that employ optical fibers for information transmission. Such systems have been deployed worldwide since 1980 and have indeed revolutionized the technology behind telecommunications. Indeed the lightwave technology together with microelectronics is believed to be a major factor in the advent of the 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 issues are also discussed. The purpose of this introductory chapter is to present the basic concepts and to provide the background material. Section gives a historical perspective on the development of optical communication systems. In Section we cover concepts such as analog and digital signals channel multiplexing and modulation formats. Relative merits of guided and unguided optical communication systems are discussed in Section . The last section focuses on the building blocks of a fiber-optic communication system. Historical Perspective The use of light for communication purposes dates back to antiquity if we interpret optical communications in a broad sense 1 . .
