Patent ID: 7697394

Claim:
An optical pickup comprising: a laser light source which emits a laser light; a diffraction grating which diffracts the laser light beam emitted by the laser light source into at least three laser light beams; a beam splitter which reflects the at least three laser light beams; and a detector which detects a reflected light beam from an optical disk, wherein; the diffraction grating includes first, second and third areas, the first area is placed between the second and third areas and the second area has a periodic structure that is shifted from that of the third area by 180° in the phase of the periodic structure, the phase of the periodic structure of the first area is different from both of the phases of the periodic structure of the second area and periodic structure of the third area, and the detector includes first, second and third photoreceptor surfaces and signals from the first, second and third photoreceptor surfaces are combined by addition and/or subtraction.