| 摘要 |
A data recording and playback device to perform focusing control on each recording layer of a multi-layer recording medium having a plurality of recording layers. The data recording and playback device includes a focus control device having a focusing movement device to set a position of a light spot, which illuminates a data recording medium having a plurality of recording layers, with respect to a direction perpendicular to the data recording medium. A focus error signal forming device forms a focus error signal based on a relative displacement of the position of the light spot set by the focusing movement device and the recording surface of the medium. A position signal forming device forms a position signal based on a displacement of the focusing movement device in a direction perpendicular to the recording medium surface, the position signal forming device having a detection range wider than that of the focus error signal forming device. A control device forms a control signal at the time of a focus jump operation to move the light spot from a recording layer to a target recording layer based chiefly on the position signal, and forms a control signal to control the focusing movement device at the time of a focusing operation to move the light spot to follow a target recording layer based chiefly on the focus error signal.
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