Semiconductor optical device and method of manufacturing the same

A semiconductor optical device comprising:

• a substrate including an optical waveguide;
• a gain section formed of a compound semiconductor, having an optical gain, bonded to an upper surface of the substrate, and including a first mesa;
• and
• a first wiring line electrically connected to the gain section,
• wherein the first mesa of the gain section is optically coupled to the optical waveguide,
• the substrate includes a first layer, a second layer, and a third layer,
• a thermal conductivity of the first layer is higher than a thermal conductivity of the second layer,
• the second layer is stacked on the first layer,
• the third layer is stacked on the second layer and includes the optical waveguide,
• a recess is provided in the substrate at a position spaced from the first mesa, the recess being sunk from the upper surface of the substrate in a thickness direction of the substrate,
• the recess extends through the third layer to the second layer in the thickness direction, and
• the first wiring line extends from the first mesa of the gain section to the recess.