Optical semiconductor resonator, optical semiconductor device, and optical module

1. An optical semiconductor resonator, comprising:

a waveguide which comprises a first area and a second area adjacent to the first area where an effective refraction index and a thickness vary in an optical axis direction of the wave guide; and

diffraction gratings formed along the optical axis direction of the waveguide,

wherein the effective refraction index in the first area is larger than the effective refraction index in the second area, and the thickness in the first area is larger than the thickness in the second area,

wherein a pitch at the adjacent diffraction gratings at a boundary between the first area and the second area is narrower than a plurality of pitches of the diffraction gratings that are formed in the first area and narrower than a plurality of pitches of the diffraction gratings that are formed in the second area, and

wherein a number of the diffraction gratings included in the first area is smaller than a number of the diffraction gratings included in the second area.

2. The optical semiconductor resonator according to claim 1 ,

wherein the pitches of the diffraction gratings in the first area are uniform and the pitches of the diffraction gratings in the second area are uniform.

3. The optical semiconductor resonator according to claim 1 ,

wherein the pitches of the diffraction gratings in the first area and the pitches of the diffraction gratings in the second area are uniform.

4. The optical semiconductor resonator according to claim 1 ,

wherein, in the first area, a pitch between the diffraction grating closest to the second area and the diffraction grading second closest to the second area is wider than the pitch at the adjacent diffraction gratings at the boundary between the first area and the second area and is narrower than the pitches of the diffraction gratings that are located farther from the second area.

5. The optical semiconductor resonator according to claim 1 ,

wherein the waveguide further comprises a third area adjacent to the second area where an effective refraction index and a thickness vary in the optical axis direction of the wave guide,

wherein the effective refraction index in the third area is smaller than the effective refraction index in the second area, and the thickness in the third area is smaller than the thickness in the second area, and

wherein a pitch at adjacent diffraction gratings at a boundary between the second area and the third area is narrower than the pitches of the diffraction gratings that are formed in the second area and narrower than a plurality of pitches of the diffraction gratings that are formed in the third area.

6. The optical semiconductor resonator according to claim 5 ,

wherein the number of the diffraction gratings included in the second area is smaller than a number of the diffraction gratings included in the third area.

7. The optical semiconductor resonator according to claim 5 ,

wherein an average of the pitches over the first area and the second area is shorter than an average of the pitches over the second area and the third area.

8. The optical semiconductor resonator according to claim 1 , further comprising:

a mesa stripe structure along the waveguide.

9. The optical semiconductor resonator according to claim 1 , wherein a difference in emission wavelength between a front end of the waveguide and a rear end of the waveguide is within ±2 nm.

10. An optical semiconductor device, comprising:

an optical semiconductor resonator; and

an optical modulator connected to the optical semiconductor resonator by a butt-joint structure,

wherein the optical semiconductor resonator includes:

a waveguide which comprises a first area and a second area adjacent to the first area where an effective refraction index and a thickness vary in an optical axis direction of the wave guide, and

diffraction gratings formed along the optical axis direction of the waveguide,

wherein the effective refraction index in the first area is larger than the effective refraction index in the second area, and the thickness in the first area is larger than the thickness in the second area,

wherein a pitch at the adjacent diffraction gratings at a boundary between the first area and the second area is narrower than a plurality of pitches of the diffraction gratings that are formed in the first area and narrower than a plurality of pitches of the diffraction gratings that are formed in the second area, and

wherein a number of the diffraction gratings included in the first area is smaller than a number of the diffraction gratings included in the second area.

11. The optical semiconductor device according to claim 10 , wherein, in the optical semiconductor resonator, the first area is closer to a connection portion connecting to the optical modulator than the second area.

12. The optical semiconductor device according to claim 11 ,

wherein, in the optical semiconductor resonator, the waveguide further comprises a third area adjacent to the second area where an effective refraction index and a thickness vary in an optical axis direction of the wave guide, and

wherein the effective refraction index in the third area is smaller than the effective refraction index in the second area, and the thickness in the third area is smaller than the thickness in the second area, and

wherein a pitch at the adjacent diffraction gratings at a boundary between the second area and the third area is narrower than the pitches of the diffraction gratings that are formed in the second area and narrower than a plurality of pitches of the diffraction gratings that are formed in the third area.

13. The optical semiconductor device according to claim 12 ,

wherein an average of the pitches over the first area and the second area is shorter than an average of the pitches over the second area and the third area.