Patent ID: 7978590

Claim:
An optical pickup apparatus comprising: a light source for emitting light; a light-receiving section for receiving light and converting an optical signal included in the received light into an electrical signal; and an optical system that generates a main beam of zeroth-order diffraction light and sub beams of + first-order diffraction light and − first-order diffraction light by diffracting light emitted from the light source, applies the resultant main and sub beams to one of a plurality of recording layers constituting an optical recording medium, and directs reflected light from the optical recording medium toward the light-receiving section, the light-receiving section including: a first light-receiving element having four regions divided by a straight line extending in a direction of a tangent to a track formed on the optical recording medium and a straight line extending in a direction of a normal to the track, for receiving main-beam reflected light; a second light-receiving element and a third light-receiving element which are disposed individually on either side of the first light-receiving element in the direction of the normal and each have two regions divided by the straight line extending in the direction of the tangent, for receiving sub-beam reflected light; a fourth light-receiving element disposed between the first light-receiving element and the second light-receiving element, for receiving stray light reflected from, out of the plurality of recording layers, the one other than the recording layer irradiated with the main and sub beams; a fifth light-receiving element disposed between the first light-receiving element and the third light-receiving element, for receiving the stray light; and a sixth light-receiving element and a seventh light-receiving element disposed individually on either side of the first light-receiving element in the direction of the tangent, for receiving the stray light wherein the fourth light-receiving element and the fifth light-receiving element are so positioned that a distance between the first light-receiving element and the fourth light-receiving element differs from a distance between the first light-receiving element and the fifth light-receiving element, and wherein the sixth light-receiving element and the seventh light-receiving element are so positioned that a distance between the first light-receiving element and the sixth light-receiving element differs from a distance between the first light-receiving element and the seventh light-receiving element.