COMPATIBLE OPTICAL PICKUP FOR RECORDING/PLAYING

摘要

PURPOSE: A compatible optical pickup for recording/playing is provided to detect focus error signals in which groove influence with respect to land groove type optical disc for carrying out the servo control for DVD-RAM, thereby using a single photodetector for information signal or error signal detection for both DVDs and CDs. CONSTITUTION: The first and second light sources respectively project first and second light(21a,22a) having different wavelength. An objective lens is designed optimally for the wavelength of the first light and the thickness of a first optical disc(20a). The diffraction is mounted on a light path between the light path converter and the objective lens, and has first and second holograms and a polarization conversion layer. The first and second holograms respectively have a first diffraction area having a wide width in the tangential direction of a recording medium, and second to fifth diffraction areas positioned outside the first diffraction area, so that the first and second light reflected from the optical discs are divided into five light areas. The photodetector has first to fifth light receiving parts for receiving the first and second light diffracted in the first to fifth diffraction areas.