| 摘要 |
PURPOSE:To obtain a focus error signal and tracking error signal by photodetecting the return luminous flux from a recording medium with plural photoelectric elements and detecting the output differences of photoelectric elements arrayed in the longitudinal direction of the straight image at the time of focusing and in the direction orthogonal with said direction, respectively. CONSTITUTION:The luminous flux emitted from a laser diode is projected through a beam splitter and an objective lens onto the recording medium and the return luminous flux from the recording medium is reflected by the beam splitter so as to enter the photodetecting system. The incident luminous flux on the photodetecting system is separated to the two luminous fluxes to sandwich the optical axis by a wedge prism 15. The separated luminous fluxes form the images respectively on photodetectors 17 divided to 8 parts via a cylindrical lens 16. The two straight images intersecting orthogonally with the tracking direction (shown by an arrow IV in the figure) and formed on the detectors 17 at the time of focusing of the luminous flux. The focus error signal is obtd. by detecting the output difference of the photoelectric elements arrayed in the longitudinal direction of the straight images and the tracking error signal is obtd. by detecting the output difference of the photoelectric elements arrayed in the direction orthogonal with the longitudinal direction of the straight images, respectively with high sensitivity. |
