Method and device for optical reading out of the information of a recording eger opening tra

摘要

A tracking mirror reflects monochromatic divergent light toward a rotating record disc provided with an engraved spiral track. The reflected light is focussed, as an optical spot, on the track by a collecting lens. Light reflected from and diffracted by the track is focussed onto an optical detector in a diffraction pattern including a principal maximum and bilaterial secondary maxima. The optical detector detects the principal maximum to form a reproduced signal and differentially detects the secondary maxima to produce a tracking signal. The mirror along with the lens and optical detector unit is moved in response to the tracking signal to cause the optical spot to follow the track.