Optical memory system providing improved focus detection and control by detecting reflected beam diameter variations at spaced predetermined locations in the system

摘要

An optical storage system is disclosed having improved focus detecting and controlling apparatus which is responsive to a reading laser beam reflected from an optical medium so as to provide a focus error signal having a high gain in the immediate vicinity of the in-focus position along with a wide capture range. Focus detection is achieved based on determining the difference between the diameters of the beams applied to a pair of photosensitive elements located so that the diameters of the beams applied thereto are indicative of the quality of focusing of the reading beam on the optical medium.