Optical Pickup

Abstract

An optical pickup includes a light source, an objective lens, a diffraction grating that divides an optical beam reflected from a predetermined information layer, into a plurality of optical beams, and a detector having a plurality of photo-receivers to receive a plurality of optical beams. The diffraction grating has a predetermined region for dividing from a signal light beam a region including a central portion of a spot which the signal light beam will form on the diffraction grating. A distance from a central section of the detector to that of a spot center photo-receiver on the detector, the spot center photo-receiver being provided to receive the optical beams formed by division in a predetermined region of the diffraction grating, is equal to or greater than a spot radius of the unwanted light beams entering the predetermined region of the diffraction grating, on the detector.

What is claimed is: 
     
         1 . An optical pickup that reproduces information from an optical disc having at least two information layers, the optical pickup comprising:
 a light source that emits an optical beam;   an objective lens that converges the optical beam upon a predetermined information layer from which desired information is to be reproduced in the optical disc;   a diffraction grating that divides the optical beam reflected from the predetermined information layer of the optical disc that is to be used for the reproduction, into a plurality of optical beams according to region of the optical beam;   a detector that includes a plurality of photo-receivers for receiving the plurality of optical beams; wherein:   the detector includes, as the plurality of photo-receivers, a plurality of photo-receivers for generating a tracking control signal, a focusing control signal, and a reproduction signal:   the detector is disposed at a position where is converged an optical beam that has not been divided by and has passed through the diffraction grating; and wherein, if the position at which the optical beam passed through the diffraction grating is defined as a central section of the detector, the optical beam reflected from the predetermined information layer of the optical disc that is to be used for the reproduction is defined as a signal light beam, and the optical beams reflected from the other information layers of the optical disc are defined as unwanted light beams;   the diffraction grating includes a predetermined region to divide from the signal light beam a region including at least a central portion of a spot which the signal light beam will form on the diffraction grating;   the detector includes a spot center photo-receiver to receive the optical beam divided in the predetermined region of the diffraction grating; and   a distance from a central portion of the spot center photo-receiver to that of the detector is equal to or greater than a spot radius of the unwanted light beams on the detector that have been admitted into the predetermined region of the diffraction grating.   
     
     
         2 . The optical pickup according to  claim 1 , wherein:
 if a vector connecting the central section of the detector and the photo-receiver is defined as a direction vector, the photo-receivers arranged outside the detector in order to generate the tracking control signal and the reproduction signal have a shape longer in a direction parallel to the direction vector, than in a direction vertical thereto.   
     
     
         3 . The optical pickup according to  claim 2 , wherein: the photo-receivers for generating the tracking control signal and the reproduction signal have a shape that includes at least a square region measuring at least 24 μm per side. 
     
     
         4 . The optical pickup according to  claim 1 , wherein: the spot center photo-receiver is disposed at a distance of at least 818 μm from the central section of the detector.