Measurement of the refractive-index profile of planar waveguides by the use of a double Lloyd's interferometer

We present a nondestructive experimental method to measure monotonically varying refractive-index profiles of planar waveguides. The technique is a modification of the Lloyd's mirage setup proposed by Allman et al. [Appl. Opt. 33, 1806 (1994)] in order to have a reference phase distribution for the interference pattern. The theoretical calculations have been implemented to account for multiple reflections inside the sample. An application of the method to ion-exchanged glass waveguides is reported.