| 摘要 |
PURPOSE:To attain satisfactorily automatic focusing despite of the generation of shift on an axis by providing a means which detects a position shift between the otpical axis of the irradiated laser light and the center axis of a photodetector by said photodetector and then shift the photodetector based on the detection output. CONSTITUTION:The variance is sometimes produced between the optical axes of the laser light 2 (shown by solid lines and the center axis of a photodetector 11 when a lens 4 is driven for tracking of the light 2. Under such conditions, the light quantity irradiated to photodetecting surfaces 11b and 11d changes. Therefore a differential amplifier 16 which uses the outputs of the surfaces 11b and 11d as two inputs is activated to deliver the error component between both surfaces 11b and 11d. This error output is amplified by an amplifier 17 and applied to a piezoelectric element 18. Then the detector 11 to which an end of the element 18 is attached is driven in the tracking direction to obtain the coincidence between the optical axis of the light 2 and the center axis of the detector 11. In this case, the element 18 uses a lamination type one and the detector 11 can be shifted with the expansion/contraction of each piezoelectric element in its thickness direction. |
