Optical waveguide device, and optical modulation device and optical transmission apparatus using same

An optical waveguide device comprising:

• a substrate on which an optical waveguide is formed;
• and
• a control electrode disposed next to the optical waveguide on the substrate, wherein a thickness of the substrate is 1 μm or less,
• the optical waveguide is a rib type optical waveguide whose height is 70 percent or less of the thickness of the substrate,
• an end portion of the control electrode facing to the rib type optical waveguide is positioned in a first recess portion of the substrate that forms the rib type optical waveguide,
• a dielectric layer that covers the rib type optical waveguide is provided,
• a second recess portion that is further recessed from a shallowest position of the first recess portion is provided in a part of the first recess portion at a base part of the rib type optical waveguide,
• the dielectric layer is disposed in the second recess portion and continuously formed between the rib type optical waveguide and the control electrode, the second recess portion includes an inclined surface that becomes shallower towards the control electrode from the rib type optical waveguide, and an inclination angle formed by the inclined surface with respect to a plane parallel to an entire surface of the substrate is 20 degrees or less, and
• a depth of a deepest position of the second recess portion based on the shallowest position of the first recess portion is 0.07 μm or less.