An optical device includes a core formed on a substrate, a first source electrode and a second source electrode formed in contact with both side surfaces of the core interposed between the first source electrode and the second source electrode, and a drain electrode formed in contact with an upper surface of the core. The core, the first source electrode, and the second source electrode together form a plasmonic waveguide. The first source electrode and the second source electrode are Schottky coupled to the core.