Near-surface optical analysis of ion-exchanged glass waveguides

Results from our near-surface approach for inhomogeneous films are compared with those from the standard m-fine (or dark-line) technique in K+ and Ag+ ion-exchanged, graded-index waveguides. We focused our attention on the determination of the refractive index at the film-air interface, and we conclude, from fundamental reasoning as well as from experimental evidence, that the direct near-surface approach can provide higher accuracy than the usual extrapolation from the modal effective indices.