Simple Polarimetric Approach to Direct Measurement of the Near-Surface Refractive Index in Graded-Index Films

In the standard M -line method for the characterization of graded-index films, an analytical curve is fitted to the waveguide mode measurements and extrapolated to provide the refractive index in the zero-depth limit. Here we review our polarimetric approach to a direct near-surface measurement, which complements the M -line method. Also, we present its new and more straightforward version, which is applicable to existing samples and does not require masking before ion exchange.