Patent ID: 7535814

Claim:
An optical pickup device, comprising: a first semiconductor laser emitting a light beam having a first wavelength; a second semiconductor laser placed in parallel with the first semiconductor laser and emitting a light beam having a second wavelength different from the first wavelength; a diffraction grating for separating one of the light beam with the first wavelength and the light beam with the second wavelength into at least three light beams; an object lens for causing each of said at least three light beams separated by the diffraction grating to converge and causing said at least three light beams to form at least three separate convergence spots on a recording surface of an optical information recording medium; and a photodetector for receiving light beams respectively reflected from said at least three convergence spots on the optical information recording medium, wherein the diffraction grating is partitioned into at least five areas each having a given periodic structure, said at least five areas include a first area, a second area adjacent to the first area in a first direction, a third area adjacent to the first area and the second area in a second direction, a fourth area defined with the third area sandwiched between the fourth area and the first area and a fifth area adjacent to the fourth area in the first direction and defined with the third area sandwiched between the fifth area and the second area, a phase of the periodic structure of each of the first and fifth areas is ahead of a phase of the periodic structure of the third area by substantially 90°, and a phase of the periodic structure of each of the second and fourth areas is behind a phase of the periodic structure of the third area by substantially 90°.