Patent ID: 7460456
Filing Date: 2008-12-02
Classification: G11B

Abstract:
1. A radial slaving method for a device for reproducing information from an optical disc, in which the information stored on the disc in the form of alterations arranged along predetermined tracks of the disc is explored by a laser beam, which converges at a spot on the optical disc and results in a beam emerging from the disc by reflection or transmission, the device being equipped with a multi-photodiode far-field detection system for detecting the emergent light beam, the method comprising: combining read signals of the photodiodes of the detection system so as to form four read subsystems having two pairs of subsystems, the subsystems of each pair being arranged on either side of a first axis parallel to the image of the axis of the track being explored and having photodiodes of a four-quadrant detector, the pairs of subsystems being arranged on either side of a second axis perpendicular to the first axis, the first and second axes being axes of symmetry for the detection system, wherein combining the read signals of the photodiodes takes the difference between the read signals of two subsystems belonging to different pairs in order to form a read signal along a first diagonal of the detection system and a read signal along a second diagonal of the detection system; and phase-comparing the signals obtained by each of the two subsystems in order to obtain a radial error signal substantially proportional to the radial tracking, said step of phase-comparing the read signals along the first and second diagonals and performing a cross-correlation between each read signal of one diagonal and the signal of the other diagonal, to which a predetermined delay is assigned.