The present invention relates to optical devices and, more particularly, to optical waveguide devices in which characteristics of a light signal are modulated or changed in accordance with an applied electric field. Conventionally, in such devices, such as, for example, a Mach-Zehnder modulator, DC drift problems, as are well known within the art, must be surmounted if the optical device is to meet minimum performance criteria. Suitably the present invention provides a layer of an oxide of silicon, preferably substantially, free of metallic impurities, where the ratio of oxygen to silicon is greater than 2 and is preferably greater than or equal to 2.2.