A method of manufacturing an optical device is disclosed. The method includes scanning along a curved path at a first surface of a glass plate with a laser beam directed orthogonally to the first surface to form a trench according to a pattern of a waveguide. The curved path is coincident with a longitudinal axis of the waveguide. The method further includes filling the trench with a material having an index different from that of glass to form the waveguide and, after filling the trench, depositing a cladding layer.