Abstract

Solid-state, electric field assisted, film diffusion (Ag⁺ - Na⁺) in glass substrates has been investigated for the fabrication of passive, integrated, optical waveguides. A new corrosion based mechanism is proposed that couples the oxidation of silver metal to silver oxide by the glass substrate, and the subsequent diffusion of silver ions within the silver oxide layer into the glass substrate. At high electric fields and/or high temperatures, the growth rate of the interfacial, silver oxide film limits the formation of mobile silver ions and constrains the diffusion of silver into the glass. This new mechanism is able to correctly predict the dopant distribution profile under those conditions and also under conditions where a constant surface concentration approximation is appropriate (infinite oxide film). It also explains the characteristics of the experimentally observed current versus time curve during the field assisted, diffusion process. The formation of silver oxide at the interface was confirmed by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction analysis. This new mechanism provides a foundation for tighter control of refractive index profiles in glass or crystal substrates.

© 1993 Optical Society of America