Modal dispersion in a fiber occurs because propagating rays travel different distances in arriving at the output. Consider the rays travelling in the fiber (see figure below) from A to B at two different paths:
(a) determine the ratio between the shortest (central ray or path ''2'') and the longest (Path ''1) rays and
(b) the time delay between the shortest and longest rays. Assume the originating rays on both paths occur at the input center of the fiber (point A), length L=1 km, n core=1.46 and n clad=1.45. θC in the figure corresponds to the critical angle.
