| 摘要 |
PURPOSE:To reduce the number of parts and to detect tracking error with the stable three-beam method by modulating integrally a holographic grating, a diffraction grating, a lens, etc., with plastics, a glass, or the like. CONSTITUTION:A diffraction grating 2 is provided with a holographic grating face 3 on the side of a disk 7 and is provided with a diffraction grating face 4 having a diffraction grating part 4a and a lens part 4b on the side of a semi conductor laser light source 1. A diffraction grating which divides a luminous flux 9 from the semiconductor laser light source 1 to 0th-order light 9a for read of a pit signal on a disk 7 and defocusing and a pair of 1st-order light 10a and 11a for read of deviation of tracking is formed in the diffraction grating part 4a. The diffraction grating 4, the holographic grating 3, and optical means are molded integrally with glass or plastics. Thus, the number of parts is re duced and the tracking error signal is stably detected by the three-beam method. |
