Optical information reading apparatus comprising a

专利名称：Optical information reading apparatus

comprising a diffraction grating memberhaving first and second portions

发明人：Shigeki Tsuji,Hikaru Nishihara申请号：US07/334563申请日：190407公开号：US05048000A公开日：19910910

摘要：An optical information reading apparatus for reading recorded information bydetecting the presence or absence of pits on an optical disk using a laser beam. The laserbeam converged a lens irradiates the optical disk in the form of light spots when in thein-focus state. A dividing line of a holographic grating used for detecting offset of thelens from the in-focus state and a dividing line of a photosensitive detector receiving alight diffracted by the holographic grating are adapted to as to be parallel to a radialdirection of the optical disk. Therefore, when a light spot formed on the optical disk byastigmatism of the lens assumes an elliptical shape, the light spot becomes an ellipsewhose long axis extends to the direction of the dividing line of the photosensitivedetector, so that no error signal is generated in the in- focus state.

申请人：SHARP KABUSHIKI KAISHA

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