Apparatus for reading and/or recording a trackwise arranged optical information structure

Claim 1

An apparatus for reading and/or recording a trackwise arranged optical information structure in a record carrier, which information structure comprises information areas alternating with intermediate areas in the track direction, which apparatus comprises radiation source, an objective system for focussing a beam produced by the radiation source to form a radiation spot on the information structure, and a tracking error detection system for generating a tracking signal containing information on the magnitude and the direction of a deviation between the centre of the radiation spot and the central axis of a track, which detection system comprises a beam-splitting element which is arranged in the path of the beam from the record carrier to form two sub-beams, and four radiation-sensitive detectors arranged along a line transverse to the effective track direction, of which the first detector and the second detector cooperate with a first sub-beam and of which the third detector and the fourth detector cooperate with the second sub-beam, and an electronic circuit for processing the detector signals to form the tracking signal, characterized in that the electronic processing circuit comprises elements for forming a tracking signal which is defined by: S.sub.r,1 =(S.sub.1 -S.sub.2)+(S.sub.3 -S.sub.4) where S 1 , S 2 , S 3 and S 4 are the output signals of the first, the second, the third and the fourth detector respectively.

Claim 2

An apparatus for reading and/or recording a trackwise arranged optical information structure in a record carrier, which information structure comprises information areas alternating with intermediate areas in the track direction, which apparatus comprises radiation source, an objective system for focussing a beam produced by the radiation source to form a radiation spot on the information structure, and a tracking error detection system for generating a tracking signal containing information on the magnitude and the direction of a deviation between the centre of the radiation spot and the central axis of a track, which detection system comprises a beam-splitting element which is arranged in the path of the beam from the record carrier to form two sub-beams, and four radiation-sensitive detectors arranged along a line transverse to the effective track direction, of which the first detector and the second detector cooperate with a first sub-beam and of which the third detector and the fourth detector cooperate with the second sub-beam, and an electronic circuit for processing the detector signals to form the tracking signal, characterized in that the electronic processing circuit comprises elements for forming a tracking signal which is defined by: S.sub.r,1 =(S.sub.1 -S.sub.2)+(S.sub.3 -S.sub.4) where S 1 , S 2 , S 3 and S 4 are the output signals of the first, the second, the third and the fourth detector respectively.