| 摘要 |
PURPOSE:To always execute stably an adjustment of a focus by adjusting a distance to an information storage medium of an optical means by a difference signal of outputs of two sets of opposed photodetecting parts. CONSTITUTION:The second photodetecting parts 40C, 40E of a photodetector 40 are connected to an adder 42, and the second photodetecting parts 40B, 40D are connected to an adder 44. Also, these adders 42, 44 are connected to a differential amplifier 46, this differential amplifier 46 is connected to a lens driving circuit and a focus detection is executed by the processing circuits. Also, the first photodetecting part 40A, 40B are connected to a differential amplifier 52 and an adder 54, respectively, and a tracking detection and an information reproduction are executed. That is to say, a distance to an information storage medium 14 of an objective lens 12 is detected by detecting by the differential amplifier 46 a difference between a signal added output signals of the photodetecting parts 40C, 40E by the adder 42, and a signal added output signals of the photodetecting part 40D, 40F by the adder 44. |
