Apparatus for reading and/or recording a trackwise arranged optical information structure
AssigneeU.S. Philips Corporation
InventorAndreas J. M. Bressers
Life of this patent
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Abstract
An apparatus for reading and/or recording a trackwise arranged optical structure in a record carrier including a tracking-error detection system with a beam-splitting element and four detectors. The first detector and the second detector cooperate with a first of two sub-beams formed by the beam-splitting element, and the third detector and the fourth detector cooperate with the second sub-beam. It is demonstrated that for larger phase depths of the information details a very suitable tracking signal is obtained by adding the difference between the signals from the first and the second detector to the difference between the signals from the third and the fourth detector.
Claims4
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.sub.1, S.sub.2, S.sub.3 and S.sub.4 are the output signals of the first, the second, the third and the fourth detector respectively.
Dependencies are inferred from the claim text.