Semiconductor optical integrated circuit
A semiconductor optical integrated circuit includes: a semiconductor substrate; a light reflecting portion and a gain region, on the semiconductor substrate; a first optical waveguide connecting the reflecting portion and the gain region; and a second optical waveguide in conjunction with the first optical waveguide and having a larger optical absorptance than the first optical waveguide.
1. 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.
2. The semiconductor optical integrated circuit according to claim 1 , wherein light emitted from at least one of the gain regions and reflected at one of the first and second optical Y couplers is absorbed by the third waveguide portion.
3. The semiconductor optical integrated circuit according to claim 1 , wherein at least one of the first and second Y optical couplers includes a diffraction grating reflecting light passing through one of the first optical waveguide portions.
4. The semiconductor optical integrated circuit according to claim 1 , wherein each of the first and second Y optical couplers includes an MMI optical coupler.
5. The semiconductor optical integrated circuit according to claim 1 , wherein at least one of the first and second Y optical couplers includes an end face of the semiconductor substrate.
6. The semiconductor optical integrated circuit according to claim 1 , wherein the first and second gain regions include an optical amplification portion amplifying light passing therethrough and emitting amplified light, and the second optical waveguide portions are connected to respective light outlet portions of the optical amplification portions.
7. The semiconductor optical integrated circuit according to claim 1 , wherein at least one of the first and second gain regions and the second optical waveguide portions include an element separate from the semiconductor substrate, and the element is fixed on one of the semiconductor substrate and a quartz substrate.
8. The semiconductor optical integrated circuit according to claim 1 , wherein the third optical waveguide portions are optical amplifiers.