| 摘要 |
PURPOSE: To eliminate useless diffracted light and to improve an error signal detecting accuracy in an optical pickup device composed of in such a way that a light beam is transmitted through a hologram element twice to go and return. CONSTITUTION: Diffraction gratings 22A and 22B bisected in the vicinity of an optical axis are provided on the hologram element, and these diffraction gratings 22A and 22B are blazed in the opposite direction to each other and also in approximately the same direction as the track direction of a recording medium. Then, 0-th order light and e.g. +1st order light of the light beam are generated by one diffraction grating 22A, and 0-th order light and e.g. -1st order light of the light beam by the other diffraction grating 22B to form three beams on the recording medium, so that overlapping of diffracted light on a photodetector is reduced or eliminated, and hence useless diffracted light can be eliminated. |
