| 摘要 |
An optical pickup apparatus includes a diffraction grating having a grating constant that is entirely uniform. The duty ratio referred to as L/G duty that is the ratio between a land L and a groove G and defined by the expression UG duty (%)=L/(L+G)x100 is continuously changed in the direction orthogonal to grating grooves of the diffraction grating. For example, the L/G duty ratio is set close to 50% in a central portion of the diffraction grating while the duty is set close to 100% in an outer peripheral portion of the diffraction grating. Accordingly, the number of components of the optical pickup is reduced while loss in light quantity in recording and reproduction can be minimized.
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