Application: Design of sheathing for optical fibers. An optical fiber is made of a glass material with a thin plastic coating as shown in Figure 13.33. Both materials are transparent at the frequencies of interest. Relative permittivity of glass is 2.25 and that of the plastic material may be chosen as (1) 4.0 or (2) 2.0. The optical fiber operates in free space.
(a) Which coating is a better choice and why?
(b) Calculate the critical angle for propagation inside the glass material, based on your answer in (a).
(c) Suppose propagation is also allowed in the coating. What is now the answer to (a) and what is the critical angle for propagation?
