Patent ID: 8045432

Claim:
An optical disc apparatus comprising a radiation light source, a diffraction grating formed on a diffraction grating surface, an objective lens, light diverging means and detectors, wherein light emitted from the radiation light source passes through the diffraction grating and is separated into transmitted light a, +1st order diffracted light b, and −1st order diffracted light c; the transmitted light a, the +1st order diffracted light b, and the −1st order diffracted light c are collected through the objective lens on tracks of a signal plane of the optical disc in a partially overlapped state; light reflected by the tracks of the signal plane passes through the objective lens and is incident upon the light diverging means, and the light diverging means is split into four areas by a straight line passing through the center of the objective lens and parallel to the direction of rotation of the optical disc and a straight line that intersects that straight line at a right angle; depending on the location of the light incident upon the light diverging means, light corresponding to the transmitted light “a” diverges into four light components a 1 , a 2 , a 3 and a 4 , which are respectively incident upon light detection regions A 1 , A 2 A 3 and A 4 on the light detectors, light corresponding to the +1st order diffracted light “b” diverges into two light components b 1 and b 2 , which are respectively incident upon light detection regions B 1 , B 2 on the light detectors, and light corresponding to the −1st order diffracted light “c” diverges into two light components c 1 and c 2 , which are respectively incident upon light detection regions C 1 , C 2 on the light detectors; the light detection regions A 1 and A 2 are aligned in parallel to the direction of rotation of the optical disc, the light detection regions A 3 and A 4 are located outside the light detection regions A 1 and A 2 in the direction of the rotation of the optical disc, while sandwiching the light detection regions A 1 and A 2 in the radial direction of the optical disc, the light components a 1 and a 2 are located diagonally to each other on the light diverging means, and the light components a 3 and a 4 are located diagonally to each other on the light diverging means; and a tracking error signal associated with the tracks of the optical disc is generated by combining signals detected in the light detection regions A 1 , A 2 , A 3 , A 4 , B 1 , B 2 , C 1 , and C 2 .