A high-speed optical modulator based on Surface Plasmon-Polariton (SPP) at the hetero-junction of a metal-insulator-semiconductor (MIS) tunneling diode and including a phase-matching optical element, such as a prism or gold-lattice structure, is described. An investigation using the coupled mode theory shows that the applied bias across the hetero-junction changes the optical reflectance of an optically coupled MIS tunneling diode, such as a prism-coupled MIS tunneling diode or a gold lattice-coupled MIS tunneling diode, while the modulation efficiency achievable of the device depends on the thickness of the metal film used to construct the tunneling diode
