Fit method to determine the refractive index profile of planar surface waveguides

Abstract
We present a fit method, based on the WKB approximation, to find the refractive index profile of a planar graded-index waveguide from the evaluation of the positions of the turning points corresponding to each mode of the waveguide. Results are applied to recover numerically a given Gaussian profile and to determine the profile of a fabricated waveguide.