Optical modulators are described having a Mach-Zehnder interferometer and a pair of RF electrodes interfaced with the Mach-Zehnder interferometer in which the Mach-Zehnder interferometer comprises optical waveguides formed from semiconductor material. The optical modulator also comprises a ground plane spaced away in a distinct plane from transmission line electrodes formed from the association of the pair of RF electrodes interfaced with the Mach-Zehnder interferometer. The ground plane can be associated with a submount in which an optical chip comprising the Mach-Zehnder interferometer and the pair of RF electrodes is mounted on the submount with the two semiconductor optical waveguides are oriented toward the submount. Methods for forming the modulators are described.