Semiconductor optical amplifier, method for manufacturing same, and optical phase modulator

1. A semiconductor optical amplifier provided on a compound semiconductor substrate, the semiconductor optical amplifier comprising:

a plurality of optical amplification regions arranged in series;

a passive waveguide region provided between adjacent optical amplification regions; and

a first electrode and a second electrode provided on an upper surface of each of the adjacent optical amplification regions,

wherein the passive waveguide region electrically insulates the first electrodes of the adjacent optical amplification regions from each other, electrically insulates the second electrodes of the adjacent optical amplification regions from each other, and optically connects the adjacent optical amplification regions,

wherein the first electrode of a first of the adjacent optical amplification regions and the second electrode of a second of the adjacent optical amplification regions are connected so that the plurality of optical amplification regions are electrically connected in cascade, and

wherein power is fed at both ends of the plurality of optical amplification regions thereby driving the plurality of optical amplification regions.

2. The semiconductor optical amplifier according to claim 1 , wherein the passive waveguide region has a resistance value higher than a forward resistance value when an active layer waveguide in the plurality of optical amplification regions are driven.

3. The semiconductor optical amplifier according to claim 2 ,

wherein, on each of the adjacent optical amplification regions, the first electrode is provided on the upper surface to cover at least an upper part of the active layer waveguide, and

wherein, on each of the adjacent optical amplification regions, the second electrode is provided on the upper surface at a position apart from the active layer waveguide.

4. The semiconductor optical amplifier according to claim 3 ,

wherein, on each of the adjacent optical amplification regions, the first electrode is provided to extend from above the active layer waveguide to a portion of the upper surface on a side opposite to the second electrode with the active layer waveguide interposed between the second electrode and the first electrode, and

wherein the first electrodes and the second electrodes are provided to be reversely arranged between the adjacent optical amplification regions.

5. The semiconductor optical amplifier according to claim 1 ,

wherein each of the plurality of optical amplification regions has a different region length along an arrangement direction,

wherein an optical amplification region having the longest region length is arranged to be closest to a light incident end side of the semiconductor optical amplifier, and

wherein an optical amplification region having the shortest region length is arranged to be closest to a light emission end side of the semiconductor optical amplifier.

6. The semiconductor optical amplifier according to claim 1 , wherein each of the plurality of optical amplification regions include an active layer waveguide in a tapered shape in which a width of an active layer waveguide of an optical amplification region arranged closest to a light emission end side of the semiconductor optical amplifier is wider than a width of an active layer waveguide of an optical amplification region arranged closest to a light incident end side.

7. The semiconductor optical amplifier according to claim 1 ,

wherein, in the plurality of optical amplification regions, a light confinement coefficient of an active layer waveguide in at least one optical amplification region is different from a light confinement coefficient of an active layer waveguide in another optical amplification region, and

wherein an optical amplification region including an active layer waveguide having the smallest light confinement coefficient is arranged closest to a light emission end side of the semiconductor optical amplifier.

8. The semiconductor optical amplifier according to claim 7 , wherein the active layer waveguide having the smallest light confinement coefficient has the smallest thickness of the active layers.

9. The semiconductor optical amplifier according to claim 1 ,

further comprising a spot size converter including a transparent waveguide whose waveguide width is reduced in a reverse tapered shape with respect to a traveling direction of light, and

wherein the spot size converter is connected to a light emission end of the semiconductor optical amplifier.

10. A method for manufacturing the semiconductor optical amplifier according to claim 1 , the method comprising:

forming a multilayer film of a compound semiconductor including an active layer on the compound semiconductor substrate, and then removing the multilayer film in a region forming the passive waveguide region; and

forming a transparent waveguide to be butt-joint coupled with the active layer by butt joint growth in a region from which the multilayer film is removed to form the passive waveguide region.

11. A method for manufacturing the semiconductor optical amplifier according to claim 1 , the method comprising:

forming a multilayer film of a compound semiconductor including an active layer on the compound semiconductor substrate and then selectively implanting protons or helium ions into the multilayer film in a region in which the passive waveguide region is formed, and

forming an ion implantation region in the active layer and a multilayer film of the compound semiconductor above and below the active layer to form the passive waveguide region.

12. An optical phase modulator comprising:

a quadrature phase shift keying (QPSK) phase modulator configured to:

split incident light into a first demultiplexed light beam and a second demultiplexed light beam,

split the first demultiplexed light beam into a third demultiplexed light beam and a fourth demultiplexed light beam,

split the second demultiplexed light beam into a fifth demultiplexed light beam and a sixth demultiplexed light beam,

modulate at least one of the third demultiplexed light beam and the fourth demultiplexed light beam and then to multiplex the demultiplexed light beams to form I modulated light,

modulate at least one of the fifth demultiplexed light beam and the sixth demultiplexed light beam and then to multiplex the demultiplexed light beams to form Q modulated light,

multiplex the I modulated light and Q modulated light to generate QPSK modulated light; and

an output side semiconductor optical amplifier configured to amplify emission light of the QPSK phase modulator,

wherein the output side semiconductor optical amplifier includes the semiconductor optical amplifier according to claim 1 , and

wherein the QPSK phase modulator is provided on the same compound semiconductor substrate as that of the output side semiconductor optical amplifier.

13. The optical phase modulator according to claim 12 , further comprising an input side semiconductor optical amplifier provided on an optical input side of the QPSK phase modulator, the input side semiconductor optical amplifier configured to amplify incident light to input the amplified light into the QPSK phase modulator.

14. The optical phase modulator according to claim 13 ,

wherein power is supplied in parallel to the input side semiconductor optical amplifier and the output side semiconductor optical amplifier.

15. An optical phase modulator comprising:

a first optical phase modulator; and

a second optical phase modulator,

wherein the first and the second optical phase modulators are configured as the optical phase modulator according to claim 12 ,

incident light is split into beams and the beams are input to the first and second optical phase modulators, and

respective signal light beams are output from the first and second optical phase modulators.

16. The optical phase modulator according to claim 15 , further comprising an input side semiconductor optical amplifier configured to amplify incident light to input the amplified light into the first and the second optical phase modulators,

wherein power is supplied in parallel to the input side semiconductor optical amplifier and the output side semiconductor optical amplifier.

17. An optical phase modulator comprising:

a first optical phase modulator;

a second optical phase modulator; and

an input side semiconductor optical amplifier configured to amplify incident light to input the amplified light into the first and the second optical phase modulators,

wherein one of the first and the second optical phase modulators includes the optical phase modulator according to claim 12 ,

wherein emission light of the input side semiconductor optical amplifier is split into beams and the beams are input to the first and second optical phase modulators, and

wherein respective signal light beams are output from the first and second optical phase modulators.

18. The optical phase modulator according to claim 17 ,

wherein power is supplied in parallel to the input side semiconductor optical amplifier and the output side semiconductor optical amplifier.