Apparatus for optically reproducing signals recorded on a rotating

Abstract

An optical apparatus reproduces an information signal recorded as pits along track turns of a rotating recording medium. At least one kind of reference signal is recorded along and overlapping the lateral edges of the adjacent track turns of the information signal. A light source projects a first light beam onto the surface of the recording medium to simultaneously reproduce the information and reference signals. A detector responds to reflections of the projected light which includes and reproduces the information signal and the reference signal. The optical system is controlled so that the center of the light beam coincides with the centerline of the track. A circuit separates the reference signal from the total reproduced signal and produces a tracking control signal in response thereto. The optical system also projects a second light beam onto the recording medium and its reflected component is used for focus control. The depth of focus of the objective lens is substantially equal to or less than two times the pit depth, so that the focussing point of the reproduction light beam coincides with the upper surface of the rotating recording medium or the bottom surface of the pits. Thereby resulting in fine reproduction without introducing second-order harmonic distortion.