| 摘要 |
The present invention provides an optical pickup apparatus which can prevent an offset to a focus signal and can satisfactorily correct spherical aberration generated by difference in substrate thickness while achieving the formation of a thinner type of the apparatus. In the present invention, a parallel flat plate for correcting spherical aberration generated by difference in thickness of a transmissive substrate to the first and second recording layers of an optical disk is arranged between a beam splitter and a collimator, and in addition, the spherical aberration is corrected by inserting and removing the parallel flat plate, or switching and inserting another parallel flat plate having a different thickness to an optical path.
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