Model a parabolic graded-index fibre with n(r) = n 1 [1 - r/a) 2 ] A for r a with n 1 = 1.5.

Model a parabolic graded-index fibre with n(r) = n ₁ [1 - r/a) ² Δ] A for r ≤ a with n ₁ = 1.5. a = 0.1 mm and Δ = 0.01, using the equivalent multiple-step approximation. Divide the radius into 10 equal parts, Consider a ray inside the fibre crossing the fibre axis at 5° with respect to that axis. Using the graph paper, plot the progress of the ray through the fibre until it tums back and re-crosses the fibre axis. (Angles can be magnified on the plot.) Ar what value of r/a will the ray tun back? Does it depend on the value of a?