| 摘要 |
PURPOSE:To execute three functions of defocusing, track deviation and reproduction without using excess components by arranging a photodetector near the center and the periphery of a condenser lens and detecting the output of the detector. CONSTITUTION:A circular inside photodetector 1 and a ring form outer photodetector 2 are arranged near the center and the periphery of the condenser lens 3 respectively. Through a constitution above, in detecting defocusing, when the optical disc 4 is at the focusing position, the reflected light is not made incident to both the photodetectors 1, 2. When the disc 4 is near the lens 3, much a light reaches the inner detector 1 and when the disc 4 is remote, much light reaches the detector 2, then the defocusing is detected by an electric signal by the difference of the quantity of light. Other functions are executed similarly. Thus, the three functions of the detection of out of focus, the track deviation and the reproduction are attained without using any excess component. |
