| 摘要 |
PURPOSE:To detect the variance of the quantity of light on the surface of an optical information recording medium by providing a second photodetector which detects the luminous flux from a semiconductor laser in a position equivalent to the optical information recording medium passing an objective lens and outputs the detection signal to a control circuit at the time of non-operation. CONSTITUTION:A second photodetector 13 is provided which detects the luminous flux from a semiconductor laser 3 in the position equivalent to an optical information recording medium 1 passing an objective lens 7 and outputs the detection signal at the time of non-operation. Driving of the semiconductor laser 3 is controlled by this detection signal to correct an influence of dirt or the like of the objective lens so that the actual intensity of a light on the optical information recording medium 1 is controlled to be a desired value for reproducing, recording, or erasing. Since the second photodetector 13 performs the detecting operation at the time of the stand-by state, it is arranged in such position that it does not hinder the essential operation. Thus, the variance of the quantity of light due to dirt or the like of the objective lens is detected. |
