| 摘要 |
In an optical head unit, a shift of a laser beam is corrected by a parallel flat plate such that the center of an intensity distribution of the laser beam incident on an objective lens with a greatest numerical aperture among at least two objective lenses coincides substantially with the optical axis of the objective lens with the greatest numerical aperture. The parallel flat plate is disposed in an optical path of the laser beam traveling toward the lens such that a predetermined angle is defined between a surface of the parallel flat plate and the laser beam. Thereby, optical disks with different recording densities can be reproduced with high precision, without influence of the shift of the beam.
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