Frequency characteristics of graded-index fibers

Frequency response of graded-index multimode fibers, whose index profile parameter alpha deviates from the optimum value, is investigated both theoretically and experimentally. The frequency response of the fiber with optimum alpha diverges periodically. However, that of the fiber with nonoptimum a does not exhibit periodic divergence but has periodic curvature changing points whose period is inversely proportional to the amount of alpha deviation. The period is about a fifth of the divergence period of the fiber with optimum alpha when the alpha deviation is 0.1. The optimum a difference between lambda = 0.82 and 1.27, microm is found to be 0.07 for GeO(2)-P(2)O(5)-doped silica fibers by measurement of frequency responses at these wavelengths.