| 摘要 |
PURPOSE:To perform optical reading with high accuracy with a small-sized and easily adjustable optical system consisting of a less number of parts by executing focus control and tracking control in accordance with the photodetected outputs divided to >=4 parts by using a multi-division beam splitter. CONSTITUTION:The beam from a light source 1 is made incident on a recording medium 5 via a multi-division beam splitter 2 for quadrisection, etc., a rectangular prism 3 and an objective lens 4. The light reflected therefrom is deflected in the direction approximately parallel with the track direction and is emitted in the direction intersecting orthogonally with the incident light by the splitter 2. The exit light is detected by a quadrisection photodetector 6 which is in the track direction and within the plane inclusive of the optical axes of the lens 4 and the prism 3 and has the 1st dividing line for dividing the luminous flux by half in parallel with the optical axes of the lens 4 and the prism 3 and the dividing line parallel with the 1st dividing line for dividing the respectively divided light in two regions having an equal quantity of light. The focus control and tracking control are executed with high accuracy by the simple and easily adjustable optical system consisting of a less number of parts in accordance with the difference between the prescribed photodetection outputs. |
