Patent ID: 7394745
Filing Date: 2008-07-01
Classification: G11B

Abstract:
1. An optical pickup device for writing data or reading data recorded on an optical disk, said optical pickup device comprising: a laser light source for emitting a laser beam for writing data or reading data; photodetectors having light-receiving portions for respectively receiving a laser beam reflected by recording surfaces of a plurality of layers of the optical disk; and an optical system for guiding to the optical disk the laser beam emitted from the laser light source, and guiding to the photodetectors the laser beam reflected by the optical disk; said optical system having: a half mirror for reflecting or transmitting a laser beam emitted from the laser light source, and transmitting or reflecting the light reflected from the optical disk; a collimator lens for converting the laser beam reflected or transmitted by the half mirror into parallel light; an object lens for condensing the laser beam converted to parallel light by the collimator lens onto the recording surfaces of the optical disk, having a curvature or refractive index that varies by steps in the radial direction, and comprising a multifocal lens for focusing on recording surfaces of the optical disk; and a diffraction grating for diffracting a part of the laser beam transmitted through the half mirror and guiding the laser beam to at least one of the light-receiving portions; wherein the object lens condenses the laser beam emitted from the laser light source onto the recording surfaces of the optical disk, and the diffraction grating guides light reflected by the recording surfaces to a plurality of light-receiving portions, so as to simultaneously read or write data to the recording surfaces, and the diffraction grating being spatially separated from the half mirror.