| 摘要 |
PURPOSE:To improve the light transmission efficiency and to make a light spot having a high intensity image-form in very small size on the disk, by independently receiving each reflected ray from the disk of the main beam and the subbeam at each split part of the three-split photodetector. CONSTITUTION:This device is equipped with a collimater lens 12 for converting a divergent ray from the laser beam source 1 to a parallel ray, an objective lens 4 which is of a smaller aperture than that of the lens 12 and condenses the parallel ray on a disk 5, a side face trapezoidal prism 9 which is placed between the lens 12 and 4, and splits the parallel ray to the main beam and two subbeams, a half-mirror 3 which is placed between the lens 4 and the prism 9, and separates the reflected ray from the disk 5, and a three-split photodetector 7 for detecting the reflected ray from the mirror 3. And, the reflected rays coming from the main bean and two subbeams are detected independently by each split part of the detector 7. |
