Dispersion characteristics of diffused channel waveguides

A variational method is used to calculate dispersion curves for channel waveguides fabricated by masked diffusion. Composition profiles for the waveguides are obtained by numerical solution of the diffusion equation, assuming that the diffusant concentration in the unmasked region of the substrate surface is constant during the diffusion process. A linear dependence of refractive index change on diffusant concentration is assumed. The dependence of the number of guided modes on mask gap width and diffusion depth is determined as an aid to the design of modulators and switches for integrated optics.