| 摘要 |
An optical pickup device for optically reproducing an information recorded on a recording medium of a magneto-optical disc or a write-only-read-many optical disc, includes a semiconductor laser, an objective lens for converging the laser light emitted by the laser on the recording medium, a photo-detector for detecting a light reflected from the recording medium, a beam splitter for leading the emitted light from the laser to the objective lens and for leading said light reflected by the recording medium to the photodetector, a first phase plate disposed between the beam splitter and the objective lens, a second phase plate disposed between the beam splitter and the photo-detector, and a rotator for rotate the first phase plate in such a manner than the beam splitter forbids to transmit the light reflected by the recording medium into the laser in a case where the recording medium is said write-only-read-many optical disc, and that the beam splitter allows to transmit the light reflected by the recording medium into the laser in a case where the recording medium is the magneto-optical disc.
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