Semiconductor optical device

A semiconductor optical device comprising:

• a first optical waveguide including a first section, a second section, and a third section aligned in that order in a waveguiding direction;
• a second optical waveguide including a fourth section, a fifth section, and a sixth section aligned in that order in the waveguiding direction;
• an input optical coupler connected to one end of each of the first optical waveguide and the second optical waveguide;
• and
• an output optical coupler connected to the other end of each of the first optical waveguide and the second optical waveguide,
• wherein the first, second, and third sections of the first optical waveguide, the fourth, fifth, and sixth sections of the second optical waveguide, the input optical coupler, and the output optical coupler each include a first cladding layer composed of an n-type semiconductor and a core layer disposed on the first cladding layer, the core layer being composed of an undoped semiconductor,
• the second section of the first optical waveguide and the fifth section of the second optical waveguide each include an intermediate semiconductor layer disposed on the core layer and a second cladding layer disposed on the intermediate semiconductor layer, the second cladding layer being composed of an n-type semiconductor,
• the first and third sections of the first optical waveguide, the fourth and sixth sections of the second optical waveguide, the input optical coupler, and the output optical coupler each further include a third cladding layer on the core layer,
• at least one of the third cladding layers included in the first and third sections of the first optical waveguide, the fourth and sixth sections of the second optical waveguide, the input optical coupler, and the output optical coupler includes a first cladding section disposed on the core layer and a second cladding section disposed on the first cladding section, and
• the second cladding section is composed of a semi-insulating semiconductor.