A new method for the reconstruction of refractive index profiles of optical waveguides from the intensity profile of the fundamental mode, as measured with near-field (NF) technique, is presented. In this procedure, an analytical expression of the index profile as function of some parameters such as the maximum index variation and depth is given. By a finite differences (FD) algorithm, the wave equation is solved in order to find the effective index and the intensity profile of the fundamental mode. The input parameters are then varied in order to minimize the difference between the measured intensity profiles and the calculated ones. An application of the method to the special case of planar Ti:Mg:LiNbO3 waveguides is presented.
Federico Caccavale, Francesco Segato, Ibrahim Mansour, and Massimiliano Gianesin, "A Finite Differences Method for the Reconstruction of Refractive Index Profiles from Near-Field Measurements," J. Lightwave Technol. 16, 1348- (1998)