Optical waveguide element, optical modulator, optical modulation module, and optical transmission device

An optical waveguide device comprising:

• an optical waveguide composed of a protruding portion extending on a substrate;
• and
• a signal electrode that is formed on the substrate and controls light waves propagating through the optical waveguide, wherein
• the optical waveguide includes a Mach-Zehnder optical waveguide including two parallel waveguides having curved portions,
• the signal electrode includes two signal lines for transmitting a differential signal, each intersecting the two parallel waveguides at the curved portions, and
• in an intersection region, which is a region on the substrate where the two signal lines and the two parallel waveguides intersect each other, the two signal lines have different intersection clearances, which are clearances between portions intersecting the two parallel waveguides, and
• in the intersection region, at least one of the two signal lines has a signal propagation velocity faster than in a portion other than the intersection region or one of the two signal lines having a longer intersection clearance has a signal propagation velocity faster than an other signal line having a shorter intersection clearance.