| 摘要 |
In the present invention, by utilizing the difference between the polarization directions of an optical beam and a reflected optical beam, a neutral density filter part of a variable filter in an optical pickup reduces the light amount of the optical beam and directs the optical beam to the objective lens, and directs the reflected optical beam to a photodetector being a photodetection unit with slight change in the light amount of the reflected optical beam. When reducing a transmitted beam, which is the optical beam transmitted by diffracting the optical beam using a diffraction grating, the irradiation positions of first-order optical beams being diffracted±first-order optical beams on the recording layer of an optical disc are dispersed.
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