Novel processing methods for production of high-refractive index contrast and low loss optical waveguides are disclosed. In one embodiment, a “channel” waveguide is produced by first depositing a lower cladding material layer with a low refractive index on a base substrate and a refractory metal layer. Then, an etch mask layer is deposited on the refractory layer, followed by selective etching of the refractory metal layer with a dry-etch tool with high selectivity to the etch mask layer. Then, the refractory metal layer is oxidized to form an oxidized refractory metal region, and a top cladding layer made of a second low refractive index material to encapsulate the oxidized refractory metal region. In another embodiment, a “ridge” waveguide is produced by using similar process steps with an added step of depositing a high-refractive-index material layer and an optional optically-transparent layer.