| 摘要 |
PURPOSE: An optical disc device and a focus control method are provided to arrange the focus of information beam accurately on a specific mark layer even when an optical disc is inclined to the optical disc unit, by switching the reference focus control mode of the optical disc unit into the information focus control mode. CONSTITUTION: An optical disc device(1) comprises a reference light source, an information light source, an objective lens, a beam forming section, a reference beam receiving section, and an information beam receiving section. The reference light source projects reference beam to a reference layer(102) of an optical disc(100) so that a concentric or spiral reference track is formed. The information light source project information beam to reproduce information from a mark layer(101) in which an information track including recording marks which indicate information to make the information track correspond to the reference track of the reference layer is formed. The objective lens focuses the reference beam and the information beam. The beam forming section shapes the reference beam and the information beam entering the objective lens in order to make the distance between the focuses of the reference beam and the information beam and the distance between the reference layer and the mark layer in the optical axis direction of the information beam the same. The reference beam receiving section receives reference reflection beam that is the reference beam reflected off the reference layer of the optical disc. The information beam receiving section light receives information reflection beam that is the information beam reflected off the mark layer of the optical disc.
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