| 摘要 |
A pickup device comprises a diffraction grating (12) for branching a light beam exiting a semiconductor laser element into at least three light beams. The diffraction grating (12) is divided into three regions by a line extending in the direction parallel with the tangent of track of an optical information recording medium. A second region (12B) is divided into a first subblock (13) and a second subblock (14) by a line extending in parallel with the radial direction of the optical information recording medium. Phase difference between the first subblock (13) and the second subblock (14) is about 180 degrees, phase difference between a first region (12A) and the first subblock (13) is about 90 degrees, and phase difference between the first region (12A) and a third region (12C) is about 180 degrees.
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