| 摘要 |
PURPOSE:To eliminate difficulty in attaining the positioning accuracy and miniaturization of optical system by executing a side spot formation by a diffraction grating and the focusing control of an objective lens by a reflecting light intensity comparison from a side spot. CONSTITUTION:Two side spots 17a and 17c out of optical spots 17a (c) of three branching lights by a diffraction grating 16 for detecting a focus are used for focus detection. A side spot 17a is at the position of an optical disk 6 closer than a spot 17c, a signal recorded at the optical disk 6 is detected by respective light detecting elements 13a (c), and then, the modulation of a signal detected by a detecting element 13a is larger than that of the spot 17c by the side spot 17a. At this time, the position of a main spot at the intermediate position of the side spot is the one dislocated from an optical disk position. Consequently, when the modulation of the detecting signal by the side spot is made equal, the position of a main spot 17b becomes the focusing condition. Thus, the device is made small and the adjustment is facilitated. |
