| 摘要 |
PURPOSE:To maintain always the specified exit light quantity of an objective lens even if the position of the objective lens fluctuates in a focusing direction. CONSTITUTION:Two pieces a pair of photodetectors 6a, 6b are disposed in proximity to both sides in the tracking direction of at least the aspherical objective lens 3. These photodetectors detect the light proportional to the incident light quantity on the objective lens. The exit output of a semiconductor laser 1 is controlled by the output signal of these photodetectors. |
