Optical pick-up apparatus with tracking error detection by detection of amount of light in fan field

摘要

An optical pick-up apparatus for reading and/or writing information from and/or on an optical record medium including a semiconductor laser, an objective lens projecting a laser beam onto the optical record medium, a hologram optical element having a first hologram for diffracting the laser beam onto a first pair of photodetectors to derive a focusing error and a second hologram for diffracting the laser beam onto a second pair of photodetectors to derive a tracking error. Each of the photodetectors of the second pair has light receiving regions which are divided along a division line substantially parallel with a diffracting direction of the second hologram which introduces astigmatism into the diffracted beams. A large tracking error signal can be detected stably on the basis of a distribution of an amount of light in a far field by the push-pull method.