Optical semiconductor resonator, optical semiconductor device, and optical module

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.