Chapter 35, Problem 94P

Figure 35-57 shows an optical fiber in which a central plastic core of index of refraction n₁ = 1.58 is surrounded by a plastic sheath of index of refraction n₂ = 1.53. Light can travel along different paths within the central core, leading to different travel times through the fiber. This causes an initially short pulse of light to spread as it travels along the fiber, resulting in information loss. Consider light that travels directly along the central axis of the fiber and light that is repeatedly reflected at the critical angle along the core–sheath interface, reflecting from side to side as it travels down the central core. If the fiber length is 300 m, what is the difference in the travel times along these two routes?

Figure 35-57 Problem 94.