Characterization of planar optical waveguides formed by copper–sodium, electric field assisted, ion exchange in glass

Planar waveguides have been formed by the electric field assisted diffusion of copper ions from a metallic copper film into a borosilicate glass (Corning 7740). The waveguides have been analysed using conventional prism coupling techniques and have been compared with the electric field assisted diffusion of silver into the same glass type. The measured refractive index profiles for copper guides are shown to have nearly Fermi function shapes, which are consistent with the theory of field assisted ion diffusion in glass. It is shown, however, that the guide depth formed by copper or silver ions is larger than that predicted by calculations based on the nominal composition, possibly indicating that only a fraction of the sodium ions within the glass are mobile. Annealing experiments have been performed on the guides in order to determine the copper self-diffusion coefficient in the glass. The coefficients are extracted from the data by fitting a non-linear diffusion equation model of ion motion in glass to the experimental profiles.