| 摘要 |
A diffraction grating is constituted such that directions of diffraction are disposed asymmetrically with respect to the optical axis, by causing light subjected to aperture restriction to have a difference of one half wavelength in the optical path length by making use of the fact that the difference in the optical path length experienced by the light passing through a diffraction element varies depending on the wavelength. With this constitution of the diffraction grating, aperture restriction is applied to both the light focused on an optical disk and the light reflected from the optical disk, thereby achieving an optical pickup that is capable of recording/reproducing information on/from optical disks of different types by using a single objective lens. The optical pickup prevents unnecessary light from entering a photodetector and enables the production of diffraction elements at a low cost.
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