| 摘要 |
PURPOSE:To miniaturize a device, to thin in type, and to lighten in weight, by detecting dislocation between the optical axis of an objective lens, and that of a laser beam of light from a semiconductor laser by detecting a beam of light position from a deflecting element made incident on a position detecting photodetector by the said photodetector. CONSTITUTION:The outputs divided into two of photoreceiving parts A' and B are inputted to a subtractor 22, and an output difference (Pb-Pa) can be found. A position detecting photodetector 16 is mounted at a focusing moving body 14, and a deflecting element 20 has a width enough to project the spot of a laser beam possible to detect. When the optical axis of an objective lens 12, and that of the laser beam of light coincide, it goes to (Pb-Pa)=0. and when a lens holder 11 is moved in a tracking direction with the objective lens 12, the difference of the output signals of those photoreceiving parts A and B goes to Pb-Pa>0, or Pb-Pa<0. Thus, it is possible to detect the dislocation between the optical axis of the objective lens 12, and that of the laser beam of light from the value of the difference (Pb-Pa) of the output signals. In such a way, it is possible to make the device into the miniaturization, the thin type, and the lightening.
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