Semiconductor optical device

A semiconductor optical device comprising:

• a substrate having a main surface including a first region and a second region adjacent to the first region;
• a spot-size converter disposed in the first region;
• and
• an optical detector disposed in the second region,
• wherein the spot-size converter includes a core layer and a first III-V compound semiconductor layer,
• wherein the core layer is disposed between the substrate and the first III-V compound semiconductor layer,
• wherein the optical detector includes a light absorbing layer, a second III-V compound semiconductor layer, and an insulating film,
• wherein the light absorbing layer is disposed between the substrate and the second III-V compound semiconductor layer,
• wherein the second III-V compound semiconductor layer is disposed between the light absorbing layer and the insulating film,
• wherein the light absorbing layer is optically coupled to the core layer,
• wherein the spot-size converter has a first end face connected to the optical detector and a second end face opposite to the first end face, and
• wherein the first III-V compound semiconductor layer is connected to the second III-V compound semiconductor layer and the insulating film at the first end face.