Signal detection system for use in an optically reproducing apparatus

In a signal detection system for use in an optical reproducing apparatus in which a light beam emitted from a light source is made incident by means of an objective lens upon a record medium having recorded thereon an information signal along one or more tracks and in which the light beam modulated by the information signal and collected by the objective lens is received by a light detector arranged in a far field of the track and comprising four light receiving regions divided about an optical axis of the incident light beam in orthogonal directions, one direction being in parallel with a track direction and the other direction being perpendicular to the track direction, the improvement comprising:

• means for deriving a first sum S.sub.5 of output signals S.sub.1 and S.sub.3 from diagonally aligned light receiving regions and a second sum S.sub.6 of output signals S.sub.2 and S.sub.4 from remaining diagonally aligned light receiving regions;
• means for deriving a sum signal S.sub.7 of the first and second sums S.sub.5 and S.sub.6 and a difference signal S.sub.8 between the first and second sums S.sub.5 and S.sub.6 ;
• means for generating sampling pulses at predetermined zero cross points of said sum signal S.sub.7 ;
• means for sampling said difference signal S.sub.8 by said sampling pulses to generate sampled values and holding the sampled values;
• and
• means for processing the sampled values to derive a tracking error signal representing the amount and direction of deviation of the light spot with respect to the track in a direction perpendicular to the track direction.