Patent ID: 7158452
Filing Date: 2007-01-02
Classification: G11B

Abstract:
1. An optical disc unit for an optical disc having at least one information recording layer and at least one protective layer formed on respective ones of the at least one information recording layer, comprising: reflective surface detection means for detecting a reflective surface; focus control means for performing focus control to the reflective surface such that a distance between a focal point of an optical beam applied to the optical disc and the reflective surface is within a predetermined error limit; shift means for shifting the position of the focal point in a direction perpendicular to the optical disc; and control means for controlling the focus control means and the shift means, wherein the control means controls the shift means such that the focal point of the optical beam shifts toward the protective layer until a surface of the protective layer is detected by the reflective surface detection means, the control means controls the focus control means to perform focus control to the surface of the protective layer when the surface of the protective layer is detected, the control means controls the shift means to release the focus control to the surface of the protective layer and shifts the focal point of the optical beam toward the information recording layer until a surface of the information recording layer is detected by the reflective surface detection means, the control means controls the focus control means to perform focus control to the surface of the information recording layer when the surface of the information recording layer is detected, and a feedback gain of the focus control to the surface of the information recording layer is changed from a feedback gain of the focus control to the surface of the protective layer based on a reflectance of the surface of the protective layer and a reflectance of the surface of the information recording layer.