<title>Analysis of near field data of diffused channel waveguides: an accurate method to obtain delta-n and the index profile</title>

Abstract

A simple and reliable method for obtaining the index profile and the value of (Delta) n of diffused planar and channel waveguides from the near-field scan data is presented. The method involves fitting of the Hermite-Gauss functions to the near-field scan data; the implicit assumption in case of channel waveguides being the separability of the field in its dependence of the two transverse coordinates (x and y). The coefficients of expansion are then used to obtain two 1D index profiles. These two profiles are then suitably combined to give the index profile and the value of (Delta) n of channel waveguides. The validity of the procedure is first tested on planar waveguides. Our simulations show that the method is very stable with respect random errors up to 15 - 20% in the intensity, and accurate estimated for (Delta) n can be reliably obtained. For diffused channel waveguides also, our simulation studies show that the method yields very good estimates for (Delta) n with typical errors being less than a few percent.