| 摘要 |
An optical system has a prism for deforming a sectional shape of a laser beam reflected on an optical disc into an ellipse, and a photodetector comprising a pair of detector elements disposed side by side in a direction perpendicular to the tangential direction of the disc. The elliptic beam is irradiated on the photodetector to form an elliptic spot thereon, so that the major axis of the elliptic beam spot is perpendicular to the tangential direction, and the area of the elliptic beam spot is larger than that of the photodetector.
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