Patent ID: 7733934

Claim:
An optical waveguide comprising: a substrate having upper and lower surfaces; a common electrode disposed on the lower surface of the substrate; a semiconductor laser section having a lower cladding layer, a first core layer, and an upper cladding layer, sequentially laminated on the upper surface of the substrate in a mesa stripe, wherein at least part of the upper cladding layer extends outwardly from, beyond, and transverse to both sides of the mesa stripe with a substantially planar first surface, and a laser electrode, wherein laser light is generated in the first core layer in response to an electrical signal applied across the common electrode and the laser electrode; an intermediate section located adjacent to the semiconductor laser section on the upper surface of the substrate, and having the lower cladding layer, a second core layer, and the upper cladding layer sequentially laminated on the substrate, wherein the second core layer is connected to the first core layer in the mesa stripe, and at least parts of the lower cladding layer, the second core layer, and the upper cladding layer extend outwardly from, beyond, and transverse to both sides of the mesa stripe with a substantially planar third surface; and an optical modulator section located adjacent to the intermediate section on the upper surface of the substrate, so that the intermediate section is sandwiched by the semiconductor laser section and the optical modulator section, the optical modulator section having the lower cladding layer, the second core layer, and the upper cladding layer sequentially laminated on the upper surface of the substrate, and a modulator electrode, wherein the second core layer absorbs the laser light generated in the first core layer in response to an electrical signal applied across the common electrode and the modulator electrode, wherein at least part of the lower cladding layer extends outwardly from, beyond, and transverse to both sides of the mesa stripe in the optical modulator section with a substantially planar second surface, the first surface is farther from the upper surface of the substrate than is the second surface, and the third surface decreases in distance from the upper surface of the substrate, in the intermediate section, from the first surface toward the second surface.