We extend the well-known inverse Wentzel-Kramer-Brillouin (WKB) method for refractive-index profiling of graded-index planar waveguides. We demonstrate, with numerical examples and experimental results, that the refractive-index profile of a graded-index planar waveguide can be calculated from effective indexes measured with different external refractive indexes. With this technique, single-mode and two-mode waveguides can be profiled easily to a good accuracy.
Kin Seng Chiang, Chi Lai Wong, Sin Yip Cheng, and Hau Ping Chan, "Refractive-Index Profiling of Graded-Index Planar Waveguides from Effective Indexes Measured with Different External Refractive Indexes," J. Lightwave Technol. 18, 1412- (2000)