Optical Pickup Apparatus

Abstract

An optical-pickup apparatus includes: a diffraction grating that a laser beam enters, the diffraction grating being configured to generate a main beam that is 0th-order light and sub-beams that are +1st-order diffracted light and −1st-order diffracted light; an objective lens to focus the main and sub-beams onto a signal-recording layer; a main-beam light-receiving portion that the main beam reflected by the signal-recording layer is applied to; and sub-beam light-receiving portions that the sub-beams reflected by the signal-recording layer are respectively applied to, each light-receiving area of the sub-beam light-receiving portions being smaller than a light-receiving area of the main-beam light-receiving portion, wherein a focusing-control operation is performed by a differential astigmatic method using the main beam applied to the main-beam light-receiving portion and the sub-beams respectively applied to the sub-beam light-receiving portions.

1 . An optical pickup apparatus comprising:
 a diffraction grating that a laser beam enters, the diffraction grating being configured to generate a main beam that is 0th order light and sub-beams that are +1st order diffracted light and −1st order diffracted light;   an objective lens configured to focus the main beam and the sub-beams onto a signal recording layer;   a main-beam light-receiving portion that the main beam reflected by the signal recording layer is applied to; and   sub-beam light-receiving portions that the sub-beams reflected by the signal recording layer are respectively applied to, each light-receiving area of the sub-beam light-receiving portions being smaller than a light-receiving area of the main-beam light-receiving portion,   wherein a focusing control operation is performed by a differential astigmatic method using the main beam applied to the main-beam light-receiving portion and the sub-beams respectively applied to the sub-beam light-receiving portions.   
     
     
         2 . The optical pickup apparatus of  claim 1 , wherein
 the main-beam light-receiving portion and the sub-beam light-receiving portions are arranged side by side in a tracking control direction, and wherein   a ratio of a length of the sub-beam light-receiving portions in the tracking control direction to a length of the main-beam light-receiving portion in the tracking control direction is set to 0.6 or more and less than 1.0.   
     
     
         3 . The optical pickup apparatus of  claim 2 , wherein
 a ratio between the length of the main-beam light-receiving portion in the tracking control direction and the length of the sub-beam light-receiving portions in the tracking control direction is set based on an amount of reduction in a light reception amount of the sub-beams associated with displacement in the tracking direction.   
     
     
         4 . The optical pickup apparatus of  claim 1 , wherein
 the main-beam light-receiving portion and the sub-beam light-receiving portions are arranged side by side in a tracking control direction, and wherein a ratio of a length of the sub-beam light-receiving portions in the tracking control direction to a length of the main-beam light-receiving portion in the tracking control direction is set to substantially 0.6.   
     
     
         5 . The optical pickup apparatus of  claim 1 , wherein
 a length of the sub-beam light-receiving portions in a direction orthogonal to a tracking control direction is substantially the same as a diameter of a spot having intensity that is 1/e 2  (e is the base of natural logarithms) relative to the maximum intensity of the sub-beams.   
     
     
         6 . The optical pickup apparatus of  claim 1 , wherein
 each shape of the sub-beam light-receiving portions is made similar to each shape of the sub-beams.   
     
     
         7 . The optical pickup apparatus of  claim 1 , wherein
 each of the sub-beam light-receiving portions is in an octagonal shape.   
     
     
         8 . The optical pickup apparatus of  claim 1 , wherein
 each of the sub-beam light-receiving portions is in a shape elongated in a tracking control direction.   
     
     
         9 . The optical pickup apparatus of  claim 1 , wherein
 a focus error signal is generated from signals obtained from the sub-beam light-receiving portions and the main-beam light-receiving portion.   
     
     
         10 . An optical pickup apparatus comprising:
 a diffraction grating that a laser beam enters, the diffraction grating being configured to generate a main beam that is 0th order light and sub-beams that are +1st order diffracted light and −1st order diffracted light;   an objective lens configured to focus the main beam and the sub-beams onto a signal recording layer;   a main-beam light-receiving portion that the main beam reflected by the signal recording layer is applied to; and   sub-beam light-receiving portions that the sub-beams reflected by the signal recording layer are respectively applied to, each light-receiving area of the sub-beam light-receiving portions being smaller than a light-receiving area of the main-beam light-receiving portion,   wherein, when a focus search is performed, a focusing control operation is performed by an astigmatic method using only the main beam applied to the main-beam light-receiving portion, and thereafter a subsequent focusing control operation is performed by a differential astigmatic method using the main beam applied to the main-beam light-receiving portion and the sub-beams respectively applied to the sub-beam light-receiving portions.   
     
     
         11 . The optical pickup apparatus of  claim 10 , wherein
 the main-beam light-receiving portion and the sub-beam light-receiving portions are arranged side by side in a tracking control direction, and wherein   a ratio of a length of the sub-beam light-receiving portions in the tracking control direction to a length of the main-beam light-receiving portion in the tracking control direction is set to 0.6 or more and less than 1.0.   
     
     
         12 . The optical pickup apparatus of  claim 11 , wherein
 a ratio between the length of the main-beam light-receiving portion in the tracking control direction and the length of the sub-beam light-receiving portions in the tracking control direction is set based on an amount of reduction in a light reception amount of the sub-beams associated with displacement in the tracking direction.   
     
     
         13 . The optical pickup apparatus of  claim 10 , wherein
 the main-beam light-receiving portion and the sub-beam light-receiving portions are arranged side by side in a tracking control direction, and wherein a ratio of a length of the sub-beam light-receiving portions in the tracking control direction to a length of the main-beam light-receiving portion in the tracking control direction is set to substantially 0.6.   
     
     
         14 . The optical pickup apparatus of  claim 10 , wherein
 a length of the sub-beam light-receiving portions in a direction orthogonal to a tracking control direction is substantially the same as a diameter of a spot having intensity that is 1/e 2  (e is the base of natural logarithms) relative to the maximum intensity of the sub-beams.   
     
     
         15 . The optical pickup apparatus of  claim 10 , wherein
 each shape of the sub-beam light-receiving portions is made similar to each shape of the sub-beams.   
     
     
         16 . The optical pickup apparatus of  claim 10 , wherein
 each of the sub-beam light-receiving portions is in an octagonal shape.   
     
     
         17 . The optical pickup apparatus of  claim 10 , wherein each of the sub-beam light-receiving portions is in a shape elongated in a tracking control direction. 
     
     
         18 . The optical pickup apparatus of  claim 10 , wherein
 a focus error signal is generated from signals obtained from the sub-beam light-receiving portions and the main-beam light-receiving portion.