Optical Fibers The phenomenon of total internal reﬂection, responsible for guiding of light in optical ﬁbers, has been known since 1854 . Although glass ﬁbers were made in the 1920s –, their use became practical only in the 1950s, when the use of a cladding layer led to considerable improvement in their guiding characteristics –. Before 1970, optical ﬁbers were used mainly for medical imaging over short distances . Their use for communication purposes was considered impractical because of high losses (∼ 1000 dB/km). However, the situation changed drastically in 1970 when, following an earlier suggestion , the loss of optical. | 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 2 Optical Fibers The phenomenon of total internal reflection responsible for guiding of light in optical fibers has been known since 1854 1 . Although glass fibers were made in the 1920s 2 - 4 their use became practical only in the 1950s when the use of a cladding layer led to considerable improvement in their guiding characteristics 5 - 7 . Before 1970 optical fibers were used mainly for medical imaging over short distances 8 . Their use for communication purposes was considered impractical because of high losses 1000 dB km . However the situation changed drastically in 1970 when following an earlier suggestion 9 the loss of optical fibers was reduced to below 20 dB km 10 . Further progress resulted by 1979 in a loss of only dB km near the spectral region 11 . The availability of low-loss fibers led to a revolution in the field of lightwave technology and started the era of fiber-optic communications. Several books devoted entirely to optical fibers cover numerous advances made in their design and understanding 12 - 21 . This chapter focuses on the role of optical fibers as a communication channel in lightwave systems. In Section we use geometrical-optics description to explain the guiding mechanism and introduce the related basic concepts. Maxwell s equations are used in Section to describe wave propagation in optical fibers. The origin of fiber dispersion is discussed in Section and Section considers limitations on the bit rate and the transmission distance imposed by fiber dispersion. The loss mechanisms in optical fibers are discussed in Section and Section is devoted to a discussion of the nonlinear effects. The last section covers manufacturing details and includes a discussion of the design of fiber cables. Geometrical-Optics Description In its simplest .