Planar waveguide refractive-index profiling using modal intensity distributions

The intensity distributions of optical modes in planar waveguides were examined using a conventional near-field scanning apparatus. A new method is given, where the mode penetration depths are used for refractive-index profiling. The method was experimentally tested using planar optical waveguides fabricated with silver-sodium ion exchange into soda-lime glass. The observation of the modal intensity distributions was also used to ease the propagation constant measurement and to examine the waveguide quality, including the scattering and modal cross-coupling properties.