Guided modes in graded index optical fibers

A new approach to optical propagation in graded index fibers, based on local tracking of evanescent waves, is developed. The theory furnishes the high-frequency asymptotic expansion of the modal field and yields explicit tractable expressions for the expansion coefficients. When tested for the parabolic profile, the asymptotic series generated by the method is found to agree term by term with the known exact result. The method is then applied to polynomial profiles for which exact solutions are not available.