Abstract: An optical waveguide device, ideally suited for use in conjunction with an overlying grating or electro-optic material, is comprised of a substrate, a waveguide core, and an over-cladding layer. The over-cladding layer has an optically flat outer surface. The thickness of the cladding layer over the waveguide core may range from zero to several microns, with thickness uniformity and repeatability within a few percent of the nominal thickness. The thickness control and flatness can be maintained over a large area, such that the waveguide devices can be mass produced on wafers. A process is provided for fabricating the optical waveguide device with a thin, flat, precisely-controlled upper cladding layer.