| 摘要 |
<p>It is possible to provide an optical disc device capable of surely focusing on a target layer of a plurality of layers constituting an optical disc. Control is made to focus the target layer in the state that spherical aberration caused by a device material thickness up to the target layer is corrected. If a layer other than the target layer is erroneously focused, a spherical aberration is generated since the device material thickness is different and the level of the signal to be outputted and the balance are greatly shifted. By using this shift, it is detected that a layer other than the target layer is erroneously focused. As the signal for detection, it is possible to use an addition signal, a tracking error signal, a reproduction signal, and the like. Moreover, by using these general-purpose signals, it is possible to perform detection by using the conventional circuit without requiring a special circuit. When an erroneous focusing is detected, the operation for focusing the target layer is tried again.</p> |
