Optical Fiber Communications 4th Edition by Gerd Keiser

Exercise 27

Consider a dielectric slab having a thickness d = 10 mm and index of refraction n 1 = 1.50. Let the medium above and below the slab be air, in which n 2 = 1. Let the wavelength be = 10 mm (equal to the thickness of the waveguide).
( a ) What is the critical angle for the slab waveguide
( b ) Solve Eq. (2.26 b ) graphically to show that there are three angles of incidence that satisfy this equation.
( c ) What happens to the number of angles as the wavelength is decreased