| 摘要 |
PURPOSE:To attain signal detection, defocusing detection and track shift detection at the same time only by a main beam by providing the 1st and 2nd photodetectors in front of and behind the focal point of one light obtained by dividing a reflected beam from a record carrier. CONSTITUTION:Light from light source 1, penetrating half mirror 3, is reflected by deflecting mirror 4 and then focused on optical record carrier 6 by condenser lens 5. Then, the light reflected by record carrier 6 is focused by condenser lens 5 again into reflected beam 9, which forms an image again at point fa. Photodetector 12 is provided a constant distance before point fa, and photodetectors 10, 11 and 13 a constant distance behind it; and the outputs of photodetectors 12 and 13 photoreceiving the reflected beam 9 are differentially amplified to obtain defocusing signal 17 and the outputs of photodetectors 10 and 11 are also differentially amplified to obtain track-shift signal 16. |
