| 摘要 |
An optical pickup comprises light sources for emitting light beams including first and second light beams of different wavelengths, an objective for focusing light beams, and a grating structure having a shape symmetrical with respect to the optical axis of the objective. The p-th order diffracted light (p is an integer except for zero) produced from the first light beam (for example, a blue light beam) by the grating structure is focused on an information layer of an optical disk (for example, a BD) corresponding to the first light beam by the focusing section of the objective and the grating structure. The q-th order diffracted light (q is an integer except for zero and q p) produced from the second light beam (for example, a red light beam or an infrared light beam) by the grating structure is focused on the information layer of an optical disk (for example, a DVD or CD) corresponding to the second light beam by the focusing section of the objective and the grating structure. Thus, by adequately using different order diffracted light beams, focusing with a reduced spherical aberration on any one of optical disks having different wavelengths and base thicknesses is realized.
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