Patent ID: 7940631
Filing Date: 2011-05-10
Classification: G11B

Abstract:
1. An optical pickup device for recording information onto an optical information recording medium and reading and erasing information recorded on the optical information recording medium, comprising: a light source; a diffraction grating for separating a light beam emitted from the light source into at least three light beams; and a photodetector for receiving the separated light beams reflected from the optical information recording medium, wherein the diffraction grating is divided into a first region, a second region, and a third region having periodic structures with different phases by a first dividing line and a second dividing line that extend in a first direction parallel to a tangential direction of a track of the optical information recording medium, the second region is located between the first region and the third region and is divided into a first sub-block, a second sub-block, a third sub-block, and a fourth sub-block by a third dividing line extending in the first direction and a fourth dividing line extending in a second direction that crosses the first direction, the first sub-block and the second sub-block are located adjacent to each other in the second direction, and the third sub-block and the fourth sub-block are located adjacent to each other in the second direction, the first sub-block and the third sub-block are located adjacent to each other in the first direction, and the second sub-block and the fourth sub-block are located adjacent to each other in the first direction, the respective periodic structures of the first sub-block and the fourth sub-block have a same phase and the respective periodic structures of the second sub-block and the third sub-block have a same phase, the periodic structures of the first sub-block and the fourth sub-block have a phase difference of approximately 180 degrees from the periodic structures of the second sub-block and the third sub-block, the periodic structure of the first region has a phase difference of approximately 90 degrees from the periodic structure of each sub-block of the second region, and the periodic structure of the first region has a phase difference of approximately 180 degrees from the periodic structure of the third region.