Abstract
The problem of determining the refractive-index profile of graded-index waveguides from the distribution of effective indices is analysed. The most common WKB-based methods appear to be rather poor in recovering smooth profiles in the case of waveguides supporting a low number of modes. A routine for the recovery of smooth refractive-index profiles of potassium-exchanged waveguides is described, which exploits accurate in-depth concentration measurements performed by secondary ion mass spectrometry. The method allows the separation of the compositional and the stress contributions to the index change of the analysed waveguides.