An optical waveguide for guided an incident light is formed on a substrate having
an electro-optic effect. A first buffer layer is formed to cover an upper surface
of the substrate. A conductive film is formed above the first buffer layer. A center
electrode and a ground electrode are formed for applying a voltage in order to
induce an electric field in the optical waveguide. A second buffer layer is formed
between the conductive film and at least one of the center electrode and the ground
electrode. The conductive film is formed to be present on at least a part below
the ground electrode. A light guided through the optical waveguide is modulated
by changing a phase by a voltage applied to the optical waveguide. Thereby, a thermal
drift can be effectively restricted so that an optical modulation device having
excellent electric characteristics can be realized.
