Fiber optics: With fiber optics, light entering one side of a glass or plastic fiber of optical quality is transmitted to the other end by the process of total internal reflection. Light rays that strike the core at the acceptance angle are reflected back and forth inside the core and travel to the other end of the fiber in a zigzag path of successive reflections. In use, a single, large-diameter fiber is impractical because it lacks flexibility. To increase flexibility, a large number of small-diameter fibers are clustered together in a bundle. In order to prevent light leaking from one fiber to another, each is coated with a transparent sheath that has a lower refractive index than the fiber. The sheathing process protects the surfaces of the fiber and allows the bundle to be embedded into other materials without loss of light from the sides