| 摘要 |
An optical disk unit capable of correcting a spherical aberration without using special patterns is provided. Also provided is an aberration correcting method used for such an optical disk unit. An objective lens 7 is moved along an optical axis by a predetermined distance from an in-focus position in a first direction, and then, is moved by the predetermined distance from the in-focus position in a second direction that is opposite to the first direction. In each of the objective lens moved states, a random signal having a plurality of amplitudes and periods is reproduced from an optional area of an information recording layer 12 of an optical disk 11. A servo circuit 10 extracts a specific portion having a specific amplitude or period from the reproduced random signal in each of the objective lens moved states, finds a first amplitude value and second amplitude value in the specific portions, and controls an aberration corrector 6 so that the difference between the first amplitude value and the second amplitude value approaches zero.
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