Optical waveguide device

An optical waveguide device, comprising:

• a first optical waveguide having:
• a first cladding;
• and a first core having a distal end portion exposed from the first cladding;
• a second optical waveguide having:
• a second cladding made of a same material as the first cladding;
• and a second core made of a same material as the first core, the second core having a distal end portion exposed from the second cladding;
• and
• an adhesive layer that adheres the first optical waveguide and the second optical waveguide to each other in a state where the distal end portion of the first core and the distal end portion of the second core have been arranged to partially overlap each other, wherein
• the adhesive layer is filled in between the first cladding and the second cladding to cover lateral surfaces of the distal end portion of the first core and of the distal end portion of the second core and has a refractive index closer to refractive indexes of the first cladding and the second cladding than to refractive indexes of the first core and the second core.