Abstract: Formation of an optical modulator in an optical rib waveguide configuration in an epitaxial semiconductor layer is facilitated by using an electrode cladding (electrically conducting-optically transparent) layer for contacting the rib portion of the epitaxial layer. The electrode cladding layer is essentially a polycrystalline compound semiconductive material of suitably low refractive index and is advantageously characterized by a relatively high (0.4 to 1.0 volt or more) heterojunction potential barrier height at the epitaxial layer. The electrode cladding layer results in relatively low optical waveguide cladding loss as well as good electrode contact, thereby facilitating the application of a modulating electric field into the epitaxial rib waveguide during operation. The electrode cladding layer can also serve as a mask for controllably forming the rib portion with a predetermined rib height in the epitaxial layer.