Patent ID: 8483022
Filing Date: 2013-07-09
Classification: G11B

Abstract:
1. An optical head device comprising: a laser light source for emitting laser light; an objective lens for collecting the laser light which travels toward an optical disc and collecting reflection light which has been diffracted by an information track on the optical disc; a diffraction element for diffracting the reflection light which is collected by the objective lens; an optical element for providing the reflection light with astigmatism; a photodetector for receiving the reflection light; and an objective lens actuator for receiving a drive signal from an external device and shifting the objective lens, in an amount corresponding to a value of the drive signal, at least in a radial direction of the optical disc; wherein the diffraction element includes: a first diffraction area including a whole of an area which is irradiated with overlap of a zeroth-order beam of the reflection light and positive/negative first-order beams of the reflection light; and a second diffraction area including an area which is irradiated with the zeroth-order beam of the reflection light and not irradiated with the positive/negative first-order beams of the reflection light and without including the first diffraction area; wherein the photodetector includes: a first light receiving section including a plurality of light receiving surfaces for receiving a first light beam which is the zeroth-order beam of the diffraction light generated by the first diffraction area and the second diffraction area, the plurality of light receiving surfaces being adjacently arranged at least in the direction corresponding to the radial direction; and at least one of a second light receiving section and a third light receiving section, the second light receiving section including a plurality of light receiving surfaces for receiving a second light beam which is a positive first-order beam of the diffraction light generated by the second diffraction area and the plurality of light receiving surfaces being adjacently arranged in the direction corresponding to the radial direction, the third light receiving section including a plurality of light receiving surfaces for receiving a third light beam which is a negative first-order beam of the diffraction light generated by the second diffraction area and the plurality of light receiving surfaces being adjacently arranged in the direction corresponding to the radial direction.