| 摘要 |
PROBLEM TO BE SOLVED: To provide a high-performance focal error detection device of very small focal shifting, and an optical pickup device. SOLUTION: The focal error detection device of an optical pickup including a aberration correction lens group includes a diffraction optical element designed to selectively diffract light having an outer diameter smaller than an optical beam diameter after aberration correction by the lens group and passing through an annular part around the optical axis of the optical beam within a plane perpendicular to the optical axis of the beam, and carries out focal error detection by using the light diffracted by the diffraction optical element. The annular part includes a part in which residual light ray aberration after aberration correction by the lens group is smallest. COPYRIGHT: (C)2004,JPO
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