Optical control device

An optical control device comprising:

• a sheet-like substrate which has an electro-optical effect and has a thickness of 10 μm or less;
• an optical waveguide formed on the sheet-like substrate;
• and configured as a ridged optical waveguide;
• a control electrode for controlling light passing through the optical waveguide,
• wherein the control electrode is comprised of a first electrode and a second electrode which are arranged so as to interpose the sheet-like substrate so that the first electrode includes a coplanar electrode which is composed of at least a signal electrode and a ground electrode and the second electrode is configured to include at least a ground electrode so that an electric field is applied to the optical waveguide of the signal electrode of the first electrode and the ground electrode of the second electrode;
• wherein a low dielectric constant layer, which has a width at least larger than that of the signal electrode of the first electrode and is formed at least over an entire length of the signal electrode, is formed on a lower portion of the sheet-like substrate and the second electrode,
• wherein a relation of d2<∈2/∈1×d1 is satisfied, where ∈2 is a dielectric constant of the low dielectric constant layer, d2 is a thickness of the low dielectric constant layer, ∈1 is a dielectric constant of the sheet-like substrate, and d1 is a thickness of the sheet-like substrate.