Patent ID: 6339567
Filing Date: 2002-01-15
Classification: G11B

Abstract:
An optical information reproducing apparatus for reading recorded information by having a light spot trace an information track having a sequence of information pits by which information is recorded on an information medium, comprising:a light source emitting a light beam; a photo-electric converter including first, second, third, and fourth optical detectors; an optical system passing the light beam from the light source to the photoelectric converter via the information medium; said first, second, third, and fourth optical detectors converting the light beam into electrical signals, said first, second, third, and fourth optical detectors being situated in a far-field of the information pits in separate quadrants of an imaginary X-Y coordinate system, whose origin is disposed on an optical axis of the optical system and whose X-axis effectively extends in the track tangential direction and whose Y-axis effectively extends transversely to the track tangential direction, said first and second optical detectors being disposed on one side of the Y-axis, said third optical detector being disposed on the other side of the Y-axis, and disposed diagonally with respect to the first optical detector, and said fourth optical detectors being disposed on the other side of the Y-axis, and disposed diagonally with respect to the second optical detector; first, second, third, and fourth phase adjusters respectively adjusting the phase of each of the outputs from the first, second, third, and fourth optical detectors; a phase difference detector selectively detecting the phase difference between a first sum signal obtained by adding the output of the first phase adjuster and the output of the second phase adjuster, and a second sum signal obtained by adding the output of the third phase adjuster and the output of the fourth phase adjuster, and the phase difference between a third sum signal obtained by adding the output of the first phase adjuster and the output of the third phase adjuster, and a fourth sum signal obtained by adding the output of the second phase adjuster and the output of the fourth phase adjuster; an offset correction learning unit adjusting the first, second, third, and to fourth phase adjusters in accordance with the output of the phase difference between the first and the second sum signals from the phase difference detector, so as to eliminate the phase difference; and a tracking controller obtaining the tracking error signal information from the output of the phase difference between the third and fourth sum signals from the phase difference detector.