| 摘要 |
An optical pickup apparatus comprising: a diffraction grating including a first grating for diffracting a first laser light beam, and a second grating for diffracting a second laser light beam which is shorter in wavelength than the first laser light beam, the diffraction grating being disposed in a common optical path for guiding the first laser light beam and the second laser light beam to an optical disc; and a photo detector including in a first light receiving area, a main light receiving unit, a front sub-light receiving unit, and a rear sub-light receiving unit that receive reflected light beams, which are reflected by the optical disc, of a main beam, of a front sub-beam, and of a rear sub-beam, respectively, the first laser light beam being diffracted by the diffraction grating into the main beam, the front sub-beam formed in front of the main beam, and the rear sub-beam formed at the back of the main beam, wherein the first grating is set such that the front sub-light receiving unit and the rear sub-light receiving unit in the first light receiving area are disposed at positions which substantially avoid unnecessary diffracted light beam spots which are generated by projecting to the first light receiving area unnecessary diffracted light beams, the unnecessary diffracted light beams being generated by the second grating from the first laser light beam.
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