Inverse Algorithm With Built-In Spatial Filter to Obtain the 2-D Refractive Index Profile of Optical Waveguides From the Propagating Mode Near-Field Profile

We propose a modified inverse regularization algorithm for computing the 2-D refractive index profiles of integrated-optic waveguides from measured near-field data. The algorithm involves embedding of a spatial mean filter to remove impulses and high frequency noises from the near-field intensity as well as from its second derivative. The proposed filtering scheme is built-in to the inverse algorithm and does not require extra computation for filtering. The effectiveness of the proposed method is demonstrated by reconstructing the refractive index profile of a single mode lithium niobate channel waveguide from the propagating mode near-field intensity pattern.