Optical Pickup and Optical Disc Apparatus

Abstract

When recording/reproducing an optical disc having a recording layer of multi-layer structure, an unwanted optical beam reflected from a recording layer other than a target layer for recording/reproduction is incident on a photodetector to cause an unwanted disturbance component to leak to a detection signal, giving rise to a degradation in the quality of a tracking control signal. In an optical pickup apparatus, for suppression of the degradation, an optical element is mounted having a diffraction area for diffracting part of the optical beam and light receiving planes for sub-optical beams are provided each of which has a light shielding zone or dead zone of a predetermined width on its central sectioning line.

1 . An optical pickup apparatus comprising:
 a laser light source;   a beam splitting element for splitting a laser beam emitted from said laser light source into a main optical beam and sub-optical beams;   an objective lens which is arranged in an actuator capable of moving it in a predetermined direction and is adapted to focus the main optical beam and sub-optical beams on said disc;   an optical element having a diffraction area for diffracting part of the main optical beam and sub-optical beam which are reflected at said optical disc; and
 a photodetector for receiving said main optical beam and sub-optical beams, 
 wherein said photodetector includes: 
 a light receiving plane for main optical beam on which said main optical beam is incident; and 
 light receiving planes for sub-optical beams on which said sub-optical beams are incident, each of said light receiving planes for sub-optical beams being halved by a sectioning line vertical to a direction corresponding to the radial direction of said optical disc and having on and near said sectioning line a light shielding zone for blocking light. 
   
   
   
       2 . An optical pickup apparatus according to  claim 1 , wherein said optical element is disposed in said actuator and a polarization diffraction grating is formed in the diffraction area. 
   
   
       3 . An optical pickup apparatus according to  claim 1  further comprising a ¼ wavelength plate interposed between said objective lens arranged in said actuator and said optical element. 
   
   
       4 . An optical pickup apparatus according to  claim 1 , wherein the light shielding zone provided in said light receiving plane for sub-optical beam has, in a direction corresponding to the radial direction of said optical disc, a width which amounts to a value within a range of 20% to 40% of the diameter of a focused light spot of said sub-optical beam irradiated on said light receiving area for sub-optical beam. 
   
   
       5 . An optical pickup apparatus according to  claim 1 , wherein the light shielding zone provided in said light receiving plane for sub-optical beam has, in a direction corresponding to the radial direction of said optical disc, a width which amounts to a value within a range of 20 μm to 40 μm. 
   
   
       6 . An optical pickup apparatus according to  claim 1 , wherein said light receiving plane for main optical beam is divided into eight divisional areas by a sectioning line parallel to a direction corresponding to the radial direction of said optical disc and by three sectioning lines vertical to the direction corresponding to the radial direction, said three sectioning lines being first, second and third sectioning lines of which the second one is intermediate of the first and third sectioning lines. 
   
   
       7 . An optical pickup apparatus according to  claim 6 , wherein said main light receiving plane for main optical beam is first divided into three divisional areas by two sectioning lines vertical to a direction corresponding to the radial direction of said optical disc (first and third sectioning lines) and is then halved, at each of the divisional areas excepting the central one of said three divisional areas, by a single sectioning line substantially parallel to the direction corresponding to the radial direction of said optical disc, thereby being divided into five divisional areas in total. 
   
   
       8 . An optical pickup apparatus according to  claim 6 , wherein said light receiving plane for main optical beam is divided into six divisional areas by two sectioning lines vertical to a direction corresponding to the radial direction of said optical disc (first and third sectioning lines) and by a sectioning line parallel to the direction corresponding to the radial direction of said optical disc. 
   
   
       9 . An optical pickup apparatus according to  claim 6 , wherein the spacing between the first and third sectioning lines on said light receiving plane for main optical beam is substantially equal to the width the light shielding zone provided in said light receiving plane for sub-optical beam has in a direction corresponding to the radial direction of said optical disc. 
   
   
       10 . An optical pickup apparatus according to  claim 7 , wherein the spacing between the first and third sectioning lines on said light receiving plane for main optical beam is substantially equal to the width the light shielding zone provided in said sub-light receiving plane for sub-optical beam has in a direction corresponding to the radial direction of said optical disc. 
   
   
       11 . An optical pickup apparatus according to  claim 8 , wherein the spacing between the first and third sectioning lines on said light receiving plane for main optical beam is substantially equal to the width the light shielding zone provided in said sub-light receiving plane for sub-optical beam has in a direction corresponding to the radial direction of said optical disc. 
   
   
       12 . An optical pickup comprising:
 a semiconductor laser light source;   a beam splitting element having the function to split a laser optical beam emitted from said semiconductor laser source into a main optical beam and sub-optical beams;   an objective lens for focusing the main optical beam and each of the sub-optical beams on a predetermined recording layer provided in an optical information recording medium; and   a photodetector for receiving reflections of the main optical beam and sub-optical beams from said recording layer independently to detect predetermined signals,   wherein said photodetector includes a light receiving plane for main optical beam on which said main optical beam is incident and which is divided into four divisional areas by two mutually substantially orthogonal sectioning lines, light receiving planes for sub-optical beams on which the sub-optical beams are incident and each of which is divided into two divisional areas by at least one sectioning line, and a strip-shaped light shielding zone or dead zone provided on and near the sectioning line provided for said light receiving plane for sub-optical beam and having a predetermined width so as to completely block the incident light.   
   
   
       13 . An optical pickup according to  claim 12 , wherein the light shielding zone or dead zone provided in said light receiving plane for sub-optical beam has a minor side width amounting to a value within a range of 20% to 40% of the diameter of a focused light spot of said sub-optical beam irradiated on said light receiving area for sub-optical beam. 
   
   
       14 . An optical pickup apparatus according to  claim 12 , wherein the light shielding zone or dead zone provided in said light receiving plane for sub-optical beam has a minor side width amounting to a value within a range of 20 μm to 40 μm. 
   
   
       15 . An optical pickup comprising:
 a laser light source;   a splitting element for splitting a laser beam emitted from said laser source into a main optical beam and sub-optical beams;   an objective lens for focusing the main optical beam and sub-optical beams on a predetermined recording layer of an optical disc;   a photodetector for receiving reflections of the main optical beam and sub-optical beams at said optical disc; and   light shielding means for blocking a predetermined output from said photodetector,   wherein said photodetector includes a light receiving plane for main optical beam and light receiving planes for sub-optical beams and said light shielding means blocks a predetermined output from each of said light receiving planes for sub-optical beams.   
   
   
       16 . An optical pickup according to  claim 15 , wherein said light shielding means covers and conceals a portion on said light receiving plane for sub-optical beam to block the predetermined output. 
   
   
       17 . An optical pickup according to  claim 15 , wherein said light shielding means neglects an output from a portion on said light receiving plane for sub-optical beam to block the predetermined output.