Fabrication of optical waveguides in soda‐lime glass by field‐assisted potassium ion migration and the index‐profile formation process

Abstract

AbstractAn optical waveguide was formed by thermal diffusion or field‐assisted thermal diffusion of potassium ions (K+) into a soda‐lime glass. The refractive index profile could be estimated precisely by the diffusion equation. Assuming that the exchange between the potassium ions and the sodium ions in the glass takes place, the diffusion equation was derived. Next, the mutual diffusion coefficient was obtained by the measuring the potassium ion density profile by an x‐ray microanalyzer. Using the result, it was shown that the diffusion process of potassium ions in a glass matches the model for the diffusion equation, unlike the case of silver diffusion. In addition, it was also shown that in the case of fieldassisted thermal diffusion, the potassium density profile in the glass can be obtained by numerically solving the diffusion equation using the measured values of the diffusion coefficient and current density. Also, the refractive index profile can be obtained for an arbitrary diffusion time and temperature. This indicates that the waveguide of graded‐index through step‐index types can be fabricated by diffusing potassium ions.