An optical waveguide is provided. The optical waveguide includes: a layered structure including: a first cladding layer; a second cladding layer; and a core layer that is sandwiched between the first cladding layer and the second cladding layer, wherein an inclined surface is formed on at least one longitudinal end of the layered structure; and an outer cladding layer that seals at least a portion of the inclined surface corresponding to the core layer, wherein a refractive index of the outer cladding layer is smaller than that of the core layer.