| 摘要 |
PURPOSE:To detect a track shift stably, by making a part of a reflected ray from an optical disk incident onto a photodetector through a convex cylindrical lens. CONSTITUTION:A part of a reflected ray from an optical disk 4 is made incident to a photodetector 26 through a convex cylindrical lens 23. Light 11b used for detecting a track shift is in a state that light of a position deflected in the lengthwise direction of a tracking guide against an optical axis of an objective lens 17 has been extracted. As for an image formation pattern of the tracking guide reflected in an elliptical bean spot 11b' on the photodetector 26, the lengthwise direction of a shadow 30 of a diffracted pattern is a direction indicate with an arrow A. When an optical head 3 moves in the direction crossing the tracking guide, the shadow 30 moves in the direction as indicated with an arrow B, therefore, a difference between a photodetector 26c and 26d, or 26e and 26f becomes a track shift signal. |
