Optical semiconductor device
An optical semiconductor device according to the present disclosure includes a semiconductor substrate, at least one semiconductor laser provided on the semiconductor substrate, an optical multiplexer/demultiplexer circuit provided on the semiconductor substrate, multiplexing or demultiplexing first output light of the semiconductor laser and outputting second output light and third output light, a first waveguide portion provided on the semiconductor substrate, and outputting the second output light from an end face of the semiconductor substrate, and a second waveguide portion including an optical amplifier amplifying the third output light and a reflecting portion and provided on the semiconductor substrate, wherein the reflecting portion includes a diffraction grating that reflects the third output light amplified by the optical amplifier to feed back to the semiconductor laser via the optical amplifier and the optical multiplexer/demultiplexer circuit, and the semiconductor laser and the reflecting portion form a resonator.
1 . An optical semiconductor device comprising:
a semiconductor substrate;
at least one semiconductor laser provided on the semiconductor substrate;
an optical multiplexer/demultiplexer circuit provided on the semiconductor substrate, the optical multiplexer/demultiplexer circuit being configured to multiplex or demultiplex first output light of the semiconductor laser and being configured to output second output light and third output light;
a first waveguide portion provided on the semiconductor substrate, the first waveguide portion being configured to output the second output light from an end face of the semiconductor substrate; and
a second waveguide portion including: an optical amplifier configured to amplify the third output light, and a reflecting portion, the second waveguide portion being provided on the semiconductor substrate,
wherein the reflecting portion includes a diffraction grating that is configured to reflect the third output light amplified by the optical amplifier to feed back to the semiconductor laser via the optical amplifier and the optical multiplexer/demultiplexer circuit, and
the semiconductor laser and the reflecting portion are configured to form a resonator.
2 . The optical semiconductor device according to claim 1 , wherein the second waveguide portion has a linear shape.
3 . The optical semiconductor device according to claim 1 , wherein a phase of an oscillation mode of the semiconductor laser is configured to match a phase of an oscillation mode of the resonator.
4 . The optical semiconductor device according to claim 1 , wherein the optical amplifier is configured to amplify the third output light so that a line width of the second output light becomes smaller compared to a case where the third output light is not amplified.
5 . The optical semiconductor device according to claim 1 ,
wherein the optical semiconductor device comprises a plurality of the semiconductor lasers,
the reflecting portion is an SG-DBR configured to have a plurality of reflection peaks, and
oscillation wavelengths of the plurality of semiconductor lasers are configured to match the plurality of reflection peaks of the SG-DBR.
6 . The optical semiconductor device according to claim 1 ,
wherein the optical semiconductor device comprises one semiconductor laser,
the reflecting portion is a DBR configured to have one reflection peak, and
an oscillation wavelength of the semiconductor laser is configured to match the reflection peak of the DBR.
7 . The optical semiconductor device according to claim 1 ,
wherein the optical semiconductor device comprises one semiconductor laser, and
the semiconductor laser is an SG-DFB configured to have a plurality of gain peaks,
the reflecting portion is a CSG-DBR configured to have a plurality of reflection peaks, and
the semiconductor laser is configured to output light of a wavelength that matches the plurality of reflection peaks among the plurality of gain peaks.
8 . The optical semiconductor device according to claim 7 , wherein the CSG-DBR includes a heater, and the plurality of reflection peaks can be adjusted by the heater.
9 . The optical semiconductor device according to claim 1 , wherein the second waveguide portion includes a light absorption portion that is provided on an opposite side of the optical amplifier with respect to the reflecting portion and configured to absorb light that has passed through the reflecting portion.
10 . The optical semiconductor device according to claim 1 ,
wherein the reflecting portion comprises:
a first clad layer provided on an upper surface of the semiconductor substrate;
a light confinement layer provided on an upper surface of the first clad layer;
a current block layer provided on both sides of the light confinement layer on the upper surface of the first clad layer; and
a second clad layer provided on an upper surface of the light confinement layer and an upper surface of the current block layer.
11 . The optical semiconductor device according to claim 9 ,
wherein the light absorption portion comprises:
a first clad layer provided on an upper surface of the semiconductor substrate;
an active layer provided on an upper surface of the first clad layer;
a current block layer provided on both sides of the active layer on the upper surface of the first clad layer; and
a second clad layer provided on an upper surface of the active layer and an upper surface of the current block layer.
12 . The optical semiconductor device according to claim 1 ,
wherein the second waveguide portion is substantially straight in plan view.
13 . The optical semiconductor device according to claim 1 ,
wherein the diffraction grating has a refractive index different from a refractive index of a clad layer in which the diffraction grating is provided.
14 . The optical semiconductor device according to claim 1 ,
wherein the reflecting portion is spaced from each end face of the semiconductor substrate in plan view.