Refractive Index Profiling Of Single-mode Graded-Index Planar Optical Waveguides

The refractive index (RI) distribution profile in a waveguide (WG) is one of the main WG characteristics. The characteristics of the modes and the transmission are mostly dependent on their refractive index profiles (RIP). Determination of RIP of the graded-index WG can provide much useful information in the fabricating process. By now, many methods have been developed to solve this problem of multi- and few-mode WG such as ellipsometric method, inverse WKB method, and interferometric method, of which inverse WKB method has been widely used for its clear physical meaning and simple calculation process. However, WKB is a proximate method, the accuracy of the result is dependent on the RIP of the graded-index WG But there is no effective method to examine the single-mode WG for lacking enough information.In this paper, an inverse analytic transfer matrix (IATM) method is presented to reconstruct the RIP of the single-mode graded-index WG. In this method, we use the surface plasma resonance (SPR) to obtain the near surface RI and combine both mode types to reconstruct the RIP of the graded-index WG. We demonstrate with numerical and experimental results that the method can reconstruct the RIP of the single-mode graded-index WG to a good accuracy.