Abstract: An integrated optical waveguide includes a substrate, a waveguide under-cladding layer disposed on the substrate, and a waveguide core, having top and sidewall surfaces, disposed on the under-cladding layer. A glassy surface smoothing layer disposed on the waveguide core top surface and sidewall surfaces and has a refractive index, relative to a refractive index of the waveguide core, that enables guided optical transmission through the waveguide core and the glassy surface smoothing layer. In fabrication of the optical waveguide, a waveguide under-cladding layer is formed on a substrate and a waveguide core having sidewall surfaces and a top surface is formed on the under-cladding layer. A liquid suspension comprising particles of a glassy material is applied on the top and sidewall surfaces of the waveguide core. The applied liquid glassy particle suspension is heated to form a glassy surface smoothing layer on the waveguide core top surface and sidewall surfaces.