s. The material used as strength- ening fibers can range in scope from wire strands to Kevlar 4 to gel- filled sleeves. The top portion of Figure 3.2 illustrates a three-dimensional side view of a basic fiber-optic cable; the lower portion shows the cable with respect to a cross-sectional view. As progress was made in manufacturing fiber-optic cable, the basic cable design underwent several modifications. One popular modifica- tion was the use of a concentric buffer area to shield the core and cladding from damage; another modification involved the use of a con- centric strength material instead of a wire. Figure 3.3 is a cross-sectional view of this revision to the basic fiber-optic cable. Chapter Three Figure 3.2 The components of a basic fiber-optic cable. Jacket glass core cladding 3-dimensional view Jacket cladding Cross section view Light Flow in a Fiber The ability of light to flow down the core of a fiber-optic cable results from the fact that the core and cladding have different indices of refrac- tion. Let's discuss this topic. Index of Refraction The index of refraction of a material is the ratio of the velocity of light in a vacuum to that in a material. Thus, the index of refraction, commonly denoted in physics books as n, can be defined as n = cl V, where C is the speed of light in a vacuum and V represents the speed of light in a medium. Since V is always less than C, the index of refraction is a dimen- sionless number greater than one. Figure 3.4 illustrates the bending of light as it passes between two or more media that have different indices of refraction. In this example we will assume that the beam of light has a wavelength of 550 nm traveling while in air and arrives at the junction with the second material at an Understanding Optical Fiber angle of 40.0° (01) with the normal. The refracted beam is shown, forming an angle of 26.0° (02) with the normal. Without further information, it is possible to compute the index of refraction using Snell's law of refraction: n,sin 01 = n2sin O2 where n, 