| 摘要 |
PURPOSE:To make the alignment of the optical axis of an information reading beam of light, by detecting relative change between electrical signals of the position detecting electrodes of a first optical detector when it is in focus and the electrical signals outputted from those of the first optical detector when it is out of focus. CONSTITUTION:The optical detectors 20 and 21 are arranged so as to sandwich the optical detector 16, and also, the output terminals 23 and 24 of the position detecting electrodes 18 and 19 of the optical detector 16, the output terminal 25 of the optical detector 20, the output terminal 26 of the optical detector 21, and a substrate terminal 27 are arranged respectively. And the relative change between the electrical signals outputted from the position detecting electrodes 18 and 19 of the optical detector 16 when an objective lens is in focus with an information recording disk and the electrical signals outputted from those of the optical detector 16 when it is out of focus with the information recording disk is detected. In such a way, it is possible to make the alignment of the optical axis of the information reading beam of light.
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