| 摘要 |
PURPOSE:To improve the reliability of a self-diagnostic system by switching the position of a reflection plate located outside the optical path of laser beams or located to block the optical path. CONSTITUTION:One half of the reflected light beams from a direct read after write type optical disk 6, which are reflected by a polarizing beam splitter 3, are reflected by a split mirror 8 and are made incident on a tracking a error detection light receiving element 9. The remaining half of the reflected light beams are made incident on a focusing error detection light receiving element 10. A tracking error signal is obtained based on the difference between the light receiving signals from the two light receiving surfaces of the element 9 and a focusing error signal is obtained based on the difference of light receiving signals of the element 10. Reproduction signals from the disk 6 are obtained based on the sum of light receiving signals of the element 10. A reflection plate 11, whose reflection surface 11a is set against a quarter wave length plate 4, is placed right front of an objective lens 5 so as to insert into or to take out from the optical path. By doing this, a suitable self-diagnostic is performed when a semiconductor laser element is driven at a recording level and a highly reliable self-diagnostic is executed. |
