Device for optically tracking information

Abstract

A device for optically tracking information recorded on an optical disc wherein a photodetector is disposed on the optical axis of an optical system for guiding diffracted waves to the photodetector. The origin of a fictitious X-Y coordinate system at the photodetector is placed on the above-mentioned optical axis, X- and Y-axes of the coordinate system are made parallel to and perpendicular to an information track having the information pits on the rotating recording medium, and the photodetector is divided into four equal parts. A first summation signal indicating the sum of output signals from the four parts of the photodetector is converted into a binary signal, and a difference signal between second summation signals each indicating the sum of output signals from a pair of photodetector parts facing each other with the origin of the coordinate system therebetween is converted into another binary signal. A signal indicating a direction in which the light beam deviates from the information track, is formed on the basis of the above-mentioned binary signals, and a tracking signal indicating the deviation of the light beam from the information track is formed by full-wave rectifying the difference signal and modifying the rectified signal with the above-mentioned direction indicating signal.