| 摘要 |
An optical disk device of a simple structure using an optical pickup alone as read mechanism for detecting a thickness of the substrate of an optical disk. The optical disk device (1) carries out the focus search by moving the focal point of a laser beam emitted through an objective lens in a direction along the thickness of the optical disk in a region covering both the substrate surface and the recording layer, (2) converts S-shaped wave forms produced in a focus error signal FES from a two-piece photo-diode when the focal point passes through the substrate surface and recording layer, respectively into a digital signal CPout, and (3) detects a pulse interval of the digital signal CPout, by means of an MPU. Since the MPU detects the number of pulses of the digital signal CPout, the optical disk device can also detect the number of the recording layers.
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