Patent ID: 8472300
Filing Date: 2013-06-25
Classification: G11B

Abstract:
1. An optical head device comprising: a laser light source; an objective lens for focusing a light beam emitted from the laser light source onto an optical disc; a diffractive optical element for diffracting a returning light beam that has been reflected by the optical disc and has passed through the objective lens and outputting a transmissively diffracted light beam; and a photodetector for receiving the transmissively diffracted light beam; the diffractive optical element including a primary diffraction region disposed in a position where parts of ±1-order reflectively diffracted light beam components and part of a zero-order reflectively diffracted light beam component included in the returning light beam are incident, having a zero-order diffractive function and a ±1-order diffractive function, and secondary diffraction regions disposed outward of the primary diffraction region in a second direction orthogonal to a first direction, the first direction being the direction of a row formed by the zero-order reflectively diffracted light beam component and the ±1-order reflectively diffracted light beam components, in positions where a different part of the zero-order reflectively diffracted light beam component and different parts of the ±1-order reflectively diffracted light beam components are incident, having the zero-order diffractive function and the ±1-order diffractive function, the secondary diffraction regions including partial regions in which the incident different part of the zero-order reflectively diffracted light beam component and the incident different parts of the ±1-order reflectively diffracted light beam components partly overlap each other; and the photodetector including a main light-receiving section for receiving a zero-order transmissively diffracted light beam component that has passed through the primary diffraction region and the secondary diffraction regions, and a secondary light-receiving section for receiving one of ±1-order transmissively diffracted light beam components that have passed through the secondary diffraction regions; the secondary light-receiving section having at least two light-receiving surfaces.