Patent ID: 8126301

Claim:
An optical waveguide comprising: a first clad layer formed on a semiconductor substrate; a first core layer formed on the upper side of the first clad layer with the use of a semiconductor material the refractive index of which is higher than that of the first clad layer; and a second clad layer formed on the upper side of the first core layer with the use of a material the refractive index of which is lower than that of the first core layer, wherein the width of the first core layer is defined based on the width of an unoxidized semiconductor material sandwiched between oxide films the parts of which are thermally oxidized, the thickness of the first core layer is defined based on the thickness of an unoxidized semiconductor material sandwiched between the first clad layer and an oxide film the part of which is thermally oxidized, and at least the input/output portion of the optical waveguide has a tapered waveguide portion where both of the width and the thickness of the first core layer monotonically decrease or both of the width and the thickness monotonically increase with respect to the propagation direction of light.