Patent ID: 6407966
Filing Date: 2002-06-18
Classification: G11B

Abstract:
Apparatus for determining the focus of a light beam from a reflective medium having at least one or more track, comprising:a prism for receiving the light beam and outputting optical beams; and a photodetector having subdetectors, two adjacent subdetectors forming a first pair, the other two adjacent subdetectors forming a second pair, wherein the prism projects the optical beams onto the photodetector such that one of the optical beams is projected on at least one subdetector of the first pair of the subdetectors, and another of the optical beams is projected on at least one subdetector of the second pair of the subdetectors, wherein the amount of light projected on the subdetectors indicates the focus of the light beam with respect to the reflective medium, the subdetectors are arranged in quadrants, the quadrants being aligned with an on-track axis and a cross-track axis, wherein the optical beams from the prism are substantially vertically aligned along a beam axis, wherein the beam axis of the prism is rotated with respect to the on-track axis and the position of the light beam with respect to at least one of the tracks, one of subdetectors of each pair receives more light than the other subdetector of that pair when in focus, one of the optical beams is projected asymmetrically onto the subdetectors of the first pair of subdetectors, and the other optical beam is projected asymmetrically onto the subdetectors of the second pair of subdetectors, and the apparatus further including a summary block recovering the output of the photodetectors and generating an FES signal, a TES signal and an RDS signal.