| 摘要 |
The optical disc drive reads and/or writes data from/on an optical disc having an information storage layer. In an optical disc drive 100 , light from a light source 3 is focused by a focusing section 1 , and each of the peripheral and non-peripheral part of light reflected by the information storage layer is received by a photodetector 4 . Then, for each part of light, the drive 100 generates a focus signal and a light quantity signal, and normalizes the focus signal based on the light quantity signal. As a result, it is possible to generate a spherical aberration signal according to a quantity of spherical aberration produced at the focusing position of the light. Hence, the signal is not affected by defocusing and thus it is possible to precisely detect a spherical aberration caused by an uneven thickness of the disc and to detect a spherical aberration with high accuracy.
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