| 摘要 |
PURPOSE:To simplify the structure of an optical system and to attain ease of adjustment by splitting a photodetection section of a reflected light from a recording medium into an outer peripheral sensor and a center sensor of a light spot and detecting a focusing error of the recording medium from an output difference of both the sensors. CONSTITUTION:The photodetector section 25 consists of the circular outer peripheral sensor 27 and the the circular center sensor 28 sharing the center and having different size, they are connected respectively to a differential amlifier 26 and detect a signal independently. Then a reflected light from a recording medium 23 is collected to the photodetection section 25 to form a circular spot 29 and when no focusing error is caused to the recording medium 23, the center sensor 28 and the outer peripheral sensor 27 are set so that an output difference in the differential amplifier 26 causes a 0 signal. Since the rate of area of the light spot applied to the two-split photodetector 25 is detected and the focusing error is detected in this way, the structure of the optical system is simplified and the adjustment is attained easily. |
