Method of forming waveguide lens having refractive index distribution

Abstract

A method of forming on a substrate a waveguide lens having a predetermined distribution of refractive index, for converging or diverging light rays which propagate through a two-dimensional waveguide formed on a surface of the substrate. The method includes a step of forming a film of a diffusion metal having a constant thickness, a step of removing local portions of said film, by using a mask so that a density of the removed local portions of the film per unit area is continuously varied, and a step of effecting thermal diffusion of the remainder of the film into the substrate. Alternatively, the method includes a step of forming a mask having a multiplicity of separate openings whose density per unit area is continuously varied, a step of exposing a multiplicity of separate exposed areas of the substrate aligned with the separate openings to a material which serves to change a refractive index of the substrate, and a step of moving the material from the surface of the substrate into its interior.