Optical pickup having a plurality of photodetectors divided into four regions used to obtain both focus and tracking error signals

摘要

An optical pickup comprises: first and second semiconductor lasers ( 11, 14 ); a hologram element ( 17 ) for diffracting light reflected by an optical information recording medium ( 9 or 12 ); and a plurality of photodetectors ( 18 - 23 ). The hologram element ( 17 ) has two or more different diffraction regions. The plurality of photodetectors ( 18 - 23 ) are provided away from the first and second semiconductor lasers ( 11, 14 ) at both sides thereof along an extended line of a line between light emission positions of the first and second semiconductor lasers ( 11, 14 ). The diffracted light generated from the light beam of the first wavelength ( 10 ) by the hologram element ( 17 ) and the diffracted light generated from the light beam of the second wavelength ( 13 ) by the hologram element ( 17 ) are collected at substantially the same position at one side, and part ( 18, 19 ) of the plurality of photodetectors ( 18 - 23 ) are provided at the position. Signals obtained from the photodetectors ( 18 - 23 ) at the both sides are used to obtain a focus error signal and a tracking error signal.