Influence of Ag+-Na+ ion-exchange equilibriumon waveguide index profiles

The Ag⁺-Na⁺ ion-exchange process in a soda-lime silicate glass was studied at 330° as a function of composition of AgNO₃-NaNO₃ melt, mixing condition, and exchange time. The concentration profile of silver in glass was measured by atomic absorption spectroscopy and SEM technique. The surface index change and the index profile were determined from mode index measurement. Ion-exchange was modeled by an ion-diffusion limited process in the glass with an equilibrium chemical reaction at the melt-glass interface. A large value of 75 for the equilibrium constant at low-silver melt concentrations (<10^-2 mole fractions) shows that uptake of silver in glass varies in highly nonlinear fashion with the melt concentration. The results provide boundary conditions necessary for solution of the diffusion equation and design of single-mode waveguides