Optical semiconductor device, optical subassembly, and optical module

1. An optical semiconductor device comprising:

a semiconductor substrate;

a plurality of mesa stripes, which are arranged side by side on the semiconductor substrate, and each of which includes an active layer and a diffraction grating, the diffraction grating extending up to a back end surface of each of the plurality of mesa stripes;

a plurality of electrodes, each of which is electrically connected to an upper surface of a corresponding one of the plurality of mesa stripes, having a pad portion for wire bonding;

a plurality of waveguides, each of which is optically connected to the active layer of a corresponding one of the plurality of mesa stripes, and that fan out from the plurality of mesa stripes,

wherein a first electrode of the plurality of electrodes connected to one or more first mesa stripes, of the plurality of mesa stripes, crosses one or more of the plurality of waveguides,

wherein the first electrode wraps around a tip of a second electrode, of the plurality of electrodes, on at least three sides, and includes a diagonal cut along a direction of the plurality of waveguides that fan out,

wherein the diagonal cut is configured to avoid overlap with the plurality of waveguides,

wherein the second electrode is connected to a second mesa stripe of the plurality of mesa stripes,

wherein the tip of the second electrode extends outward in a direction parallel to the waveguide, and

wherein the one or more first mesa stripes are configured to be between one or more second mesa stripes, of the plurality of mesa stripes; and

a reflective film provided at back end surfaces of the plurality of mesa stripes and having a reflectivity of 30% or more,

wherein a center-to-center distance at back end surfaces of two mesa stripes at both ends of the plurality of mesa stripes is 150 μm or less, and

wherein at least two mesa stripes, of the plurality of mesa stripes, are configured to be driven at the same time.

2. The optical semiconductor device of claim 1 , further comprising:

an array device in which a plurality of distributed feedback lasers are integrated,

the plurality of distributed feedback lasers each including a corresponding one of the plurality of mesa stripes.

3. The optical semiconductor device of claim 2 , wherein output beams emitted from the plurality of distributed feedback lasers have a wavelength in a 1.3-μm band.

4. The optical semiconductor device of claim 1 , further comprising:

a plurality of modulators, each of which is provided in front of a corresponding one of the plurality of waveguides.

5. The optical semiconductor device of claim 1 , further comprising:

a plurality of optical amplifiers, each of which is provided between a corresponding one of the plurality of mesa stripes and a corresponding one of the plurality of waveguides.

6. The optical semiconductor device of claim 1 , further comprising:

a dummy mesa stripe provided outside of each of the two mesa stripes at both ends of the plurality of mesa stripes.

7. The optical semiconductor device of claim 1 , wherein at least one waveguide, of the plurality of waveguides, has a bent portion with respect to an extending direction of a corresponding one of the plurality of mesa stripes.

8. The optical semiconductor device of claim 1 , wherein at least one adjacent pair of waveguides, of the plurality of waveguides, has portions that extend outward as viewed from a beam exit direction compared with an adjacent pair of mesa stripes corresponding to the at least one adjacent pair of waveguides.

9. The optical semiconductor device of claim 8 , wherein the at least one adjacent pair of waveguides has a longer center-to-center distance at front end surfaces of the at least one adjacent pair of waveguides than at back end surfaces thereof.

10. An optical sub-assembly, comprising:

the optical semiconductor device of claim 1 ;

a plurality of wires wire-bonded to the plurality of electrodes; and

a driver configured to output an electric signal for driving the optical semiconductor device.

11. The optical sub-assembly of claim 10 , wherein at least one waveguide, of the plurality of waveguides, has a bent portion with respect to an extending direction of a corresponding one of the plurality of mesa stripes.

12. The optical sub-assembly of claim 10 , wherein at least one adjacent pair of waveguides, of the plurality of waveguides, has portions that extend outward, as viewed from a beam exit direction, compared with an adjacent pair of mesa stripes corresponding to the at least one adjacent pair of waveguides.

13. An optical module, comprising an optical sub-assembly, wherein the optical sub-assembly comprises:

the optical semiconductor device of claim 1 ;

a plurality of wires wire-bonded to the plurality of electrodes; and

a driver configured to output an electric signal for driving the optical semiconductor device.

14. The optical module of claim 13 , wherein at least one adjacent pair of waveguides, of the plurality of waveguides, has portions that extend outward, as viewed from a beam exit direction, compared with an adjacent pair of mesa stripes corresponding to the at least one adjacent pair of waveguides.

15. The optical semiconductor device of claim 1 , wherein a first portion of the first electrode wraps around the second electrode, and

wherein the first portion of the first electrode overlaps a portion of the one or more waveguides.

16. The optical semiconductor device of claim 1 , wherein the first electrode is configured to avoid overlap with the second electrode.

17. The optical semiconductor device of claim 1 , wherein the diagonal cut is configured to be on a corner of the first electrode.

18. The optical semiconductor device of claim 1 , wherein the first electrode and the second electrode are configured to be adjacent each other along the direction of the plurality of waveguides.

19. The optical semiconductor device of claim 1 , wherein the tip of the second electrode overlaps a waveguide of the plurality of waveguides.

20. The optical semiconductor device of claim 1 , wherein the diagonal cut is configured to be on a corner of the first electrode that is different from another corner that is adjacent to the tip of the second electrode.