| 摘要 |
<p>An optical information reading apparatus for reading recorded information by detecting the presence or absence of pits (1061) on an optical disk (104) using a laser beam converges the laser beam by a lens (103b) to irriadiate the same on the optical disk in the form of light spots (105) in the in-focus state. A dividing line (107) of a holographic grating (102) used for detecting offset of the lens from the in-focus state and a dividing line of a photosensitive detector (108) receiving a light diffracted by the holographic grating are adapted so as to be parallel to a radial direction of the optical disk. Therefore, when a light spot formed on the optical disk by astigmatism of the lens assumes an elliptical shape, the light spot becomes an ellipse whose long axis extends to the direction of the dividing line of the photosensitive detector, so that no error signal is generated in the in-focus state.</p> |
