Effect of the cladding on pulse broadening in graded-index optical waveguides

The WKB analysis is extended to take into account the discontinuity in index profile shape that occurs at the core-cladding boundary of graded-index optical waveguides. The presence of the cladding introduces a large correction to the delay times of the highest 5% of the guided modes and greatly increases the predicted rms pulse broadening of a parabolic profile fiber. Using a model of differential mode attenuation, it is shown that these highest order modes are very susceptible to attenuation. A small degree of waveguide irregularity restores the low pulse broadening originally predicted for a parabolic fiber.