Patent ID: 8385169
Filing Date: 2013-02-26
Classification: G11B

Abstract:
1. An optical disc drive comprising: an optical head device comprising: a motor for rotating the optical disc; and a control device for controlling operations of the optical head device and the motor; wherein the objective lens comprises a diffraction lens that diffracts the laser light emitted from the plurality of light sources, such that a laser light, emitted from the plurality of light sources, having a longer wavelength increases a focal length of the objective lens on the optical axis at a side of the optical disc, and such that a focal point of the converged laser light is positioned on the optical axis of the objective lens, wherein, when the control device outputs a command to replay signals, the control device (i) causes a first laser light to be initially emitted from one light source of the plurality of light sources emitting the laser light of different wavelengths before determining a type of a pre-replayed optical disc, and (ii) determines a type of the optical disc based on signals obtained from the optical head device as a result of the first laser light initially emitted, while moving, via the objective-lens actuator, the objective lens in the direction of the optical axis of the objective lens, wherein a wavelength of the first laser light (i) maximizes an air-equivalent length between the focal point converged by the objective lens and a surface of the objective lens, and (ii) is a longest wavelength of the different wavelengths of the laser light emitted by the plurality of light sources, wherein, when no information recording layer is found as a result of a searching for the information recording layer by moving the objective lens toward the optical disc beyond a given distance in the direction of the optical axis of the objective lens after the surface of the optical disc is found, the searching for the information recording layer from near the surface of the optical disc is restarted, and wherein a number of times that the searching is performed is limited.