Optical pickup capable of detecting thickness variation of recording medium, and/or capable of compensating for spherical aberration caused by thickness variation of recording medium

摘要

An optical pickup is provided,, in which a light beam division and detection unit (65) is used to determine variation in thickness of a recording medium (50). The light beam division and detection unit (65) is arranged for dividing a light beam passed back through an objective lens (57) and an optical path changer (55) after having been reflected from a recording medium (50). The unit (65) is constructed as a single photodetector having a divided configuration, or a light beam divider (160) and a plurality of photodetectors (165a,b), which can detect divided light beam portions, taking into account variation in the intensity distribution of light caused by thickness variation of the recording medium. The optical pickup allows detection of variation of thickness of the recording medium without a need to install an astigmatism lens at the light receiving side of the optical pickup. Spherical aberration caused by thickness variation of the recording medium can be corrected by driving a spherical aberration compensation element (75) or a collimating lens (53) along the optical axis according to the detected thickness variation signal using an actuator.