Polarizability, Volume Expansion and Stress Contributions to the Refractive Index Change of Cu+-Na+ Ion Exchanged Waveguides in Glass

The refractive index of optical waveguides formed by electric field assisted Cu+-Na+ ion exchange in two types of glass is measured. Assuming, as in a previously published work, that the observed refractive index increase is solely due to polarizability changes, the difference in electronic polarizability between Cu+ and Na+ ions is determined by applying the Lorentz–Lorenz equation to the data. In our work, the concentration of exchanged ions, which is a necessary input to the Lorentz–Lorenz equation, is determined by combining optical data and electrical data obtained during the exchange. Values for the electronic polarizability difference are in agreement with that in the literature. However, when a correction is made, taking into consideration the measured volume expansion and stress in the glass, the calculated electronic polarizability difference is shown to increase by 19%.