| 摘要 |
PURPOSE:To position plural spots on the same track by providing a trapezoid prism on an optical path, and making the ladder type prism rotative around the optical path. CONSTITUTION:Beams made incident on a trapezoid prism 10 is refracted by an incident surface, reflected by the underside of the surface, further refracted by an emitting surface, the trapezoid prism 10 is rotated around a center axis by theta, and thus an image is turned by 2theta. Concerning spots 21 and 22 formed by semiconductor lasers 3 and 4, when the spot 22 deviates to the right on an optical disk 1, and the trapezoid prism 10 is turned around the optical axis 20 by theta/2, the spots 21 and 22 are positioned on the same track. If the two spots do not exist on the objective track, a galvanomirror 29 is driven by a galvanomirror actuator 11, the two spots are shifted in parallel, and their positions can be regulated on the same track. |
