Channel waveguides in glass via silver-sodium field-assisted ion exchange

Multimode channel waveguides were formed by field-assisted diffusion of Ag+ ion from vacuum-evaporated Ag films, into a sodium aluminosilicate glass reported to yield high diffusion rates for alkali ions. Two-dimensional index profiles of channel waveguides formed by diffusion from a strip aperture were controlled by means of diffusion time, temperature, and electric field. The diffusion equation for diffusion through a strip aperture in the presence of a one-dimensional electric field was solved. Its solution was in agreement with measured concentration profiles:{C(x,y,t)}{C₀} = 1/2 \{ erf ({a - x}{2√Dt}) + erf ({a + x}{2√Dt})\}.1/2 \{ erfc ({y - yt}{2√Dt}) + e^{(yEy/D)} erfc ({y + yt}{2√Dt})\}Diffusion coefficients in this aluminosilicate glass were determined to beD =(2.41 × 10⁻¹³) ({m²}{s})).exp ({-3.1 × 10⁴J/mol}{RT})Diffusion coefficients were higher (between 150°C and 300°C) than those of a low-iron soda-lime silicate glass "standard" also studied, for which diffusion coefficients wereD =(3.28 × 10⁻¹³ ({m²}{s})).exp ({-3.6 × 10⁴}{RT} (J/mol))This difference in diffusion coefficients is due to the higher activation energy of diffusion in the soda-lime silicate glass. The Gladstone-Dale relation was used to calculate the maximum possible refractive index change via Ag+-Na+ ion-exchange for each type of glass. The maximum index change in the sodium aluminosilicate glass is found to be about 65 percent of that in the soda-lime silicate glass.