Patent ID: 7940630

Claim:
An optical pickup apparatus with a single beam system, comprising: a semiconductor laser for emitting a laser light; an objective lens for irradiating the laser light emitted from the semiconductor laser as a single beam onto an optical disc; a diffraction grating for dividing the laser light reflected from the optical disc; and a light detector for receiving the laser light divided by the diffraction grating, wherein the diffraction grating has five regions of a region 1 , a region 2 , a region 3 , a region 4 and a region 5 ; the region 1 and the region 3 are line-symmetrical to the region 2 and the region 4 of the diffraction grating with respect to a center line of the diffraction grating; the region 5 of the diffraction grating is formed line-symmetrically with respect to the center line and is formed on the center line; the regions 1 and 2 of the diffraction grating include portions which become narrower in width with the distance away from the center line, wherein the portions also become narrower in width in a light irradiated area of the diffraction grating with distance away from the center line; the portion of the region 1 defines boundaries between the regions 1 and 3 , and the portion of the region 2 defines boundaries between the regions 2 and 4 ; the portions of the regions 1 and 2 extend beyond the light irradiated area of the diffraction grating, so that when the portions of regions 1 and 2 are at a point of crossing an end of the light irradiated area of the diffraction grating, opposite straight edges of the portion of the region 1 are non-parallel to each other and opposite straight edges of the portion of the region 2 are non-parallel to each other; signals detected by the light detector from diffracted lights in the region 1 , the region 2 , the region 3 and the region 4 of the diffraction grating are outputted by the light detector; and the center line extends in parallel to a track direction of the optical disc.