Patent ID: 8792756

Claim:
An optical semiconductor device comprising: an optical semiconductor element, wherein the optical semiconductor element has a mesa structure having a mesa width and including an active layer, and a burying layer coating side faces of the active layer; a first optical waveguide, wherein the first optical waveguide has a mesa structure having a mesa width and including a first optical waveguide layer, and having a layer structure different from the active layer of the optical semiconductor element, and a burying layer coating side faces of the first optical waveguide layer, wherein the mesa width of the first optical waveguide is narrower than the mesa width of the optical semiconductor element, and the optical semiconductor element is butt joined to the first optical waveguide; and separating channels extending along opposite sides of the active layer and of the first optical waveguide layer, in the burying layers of the optical semiconductor element and the first optical waveguide, and defining the mesa structures between the separating channels so that separations between the separating channels are the mesa widths.