Optical device

An optical device, comprising:

• a substrate;
• and
• at least two optical waveguides formed on the substrate and facing a multiplexed portion on the substrate in a light propagation direction,
• wherein
• the at least two optical waveguides comprise a first optical waveguide and a second optical waveguide, the first optical waveguide being adjacent to the second optical waveguide,
• the first optical waveguide and the second optical waveguide are each configured to be multiplexed at the multiplexed portion,
• a first surface of the first optical waveguide faces a first surface of the second optical waveguide,
• a second surface of the first optical waveguide faces away from a second surface of the second optical waveguide, and
• in a cross section perpendicular to the light propagation direction, an angle formed between the substrate and the first surface of either the first optical waveguide or the second optical waveguide, is set to α, and an angle formed between the substrate and the second surface of either the first optical waveguide and the second optical waveguide, is set to β, satisfying α<β, wherein α≤90°, and β≤90°.