Patent ID: 7978586

Claim:
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 dividing line of a first direction that is a straight line extending in a 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 and a second sub-block having the periodic structures with different phases by a dividing line of a second direction that is a straight line extending in a direction parallel to a radius direction of the optical information recording medium, the periodic structure of the first sub-block has a phase difference of approximately 180 degrees from the periodic structure of the second sub-block, the periodic structure of the first region has a phase difference of approximately 90 degrees from the periodic structure of the first sub-block, and the periodic structure of the first region has a phase difference of approximately 180 degrees from the periodic structure of the third region.