Patent ID: 7177337

Claim:
A semiconductor optical integrated circuit comprising: a semiconductor substrate; first and second Y optical couplers having respective reflectances R 1 and R 2 , each of the first and second Y optical couplers having a single input and first and second outputs; a first optical branch connecting the first outputs of the first and second Y optical couplers together, optically; and a second optical branch connecting the second outputs of the first and second Y optical couplers together, optically, wherein each of the first and second optical branches includes a gain section having a gain A, and respective optical wave guides coupling the first and second outputs of the first and second Y optical couplers to respective gain regions, each optical waveguide including first and second optical waveguide portions sandwiching a third optical waveguide portion which has an absorbance L, larger than absorbance of the first and second optical waveguide portions, wherein A·L·R 1· R 2<1.