Patent ID: 6400664
Filing Date: 2002-06-04
Classification: G11B

Abstract:
An optical head comprising:a semiconductor laser which emits light; a light-converging optical system which converges light emitted from the semiconductor laser onto an optical disk having a periodic structure in a radial direction of the optical disk to form at least one focused spot on the optical disk, the periodic structure including information tracks; means for generating a plurality of reflected light beams from the at least one focused spot on the optical disk, the reflected light beams including at least one first reflected light beam having an intensity distribution which varies with a first polarity when the periodic structure crosses the at least one focused spot on the optical disk, and at least one second reflected light beam having an intensity distribution which varies with a second polarity opposite to the first polarity when the periodic structure crosses the at least one focused spot on the optical disk, wherein a variation in the intensity distribution of the at least one first reflected light beam when the periodic structure crosses the at least one focused spot on the optical disk is substantially inverted with respect to a variation in the intensity distribution of the at least one second reflected light beam when the periodic structure crosses the at least one focused spot on the optical disk; an optical detection system which detects the at least one first reflected light beam and the at least one second reflected light beam, and outputs detection signals in response to the detected at least one first reflected light beam and the detected at least one second reflected light beam; and an electrical circuit which generates respective focus error signals and respective tracking error signals for the at least one first reflected light beam and the at least one second reflected light beam from the detection signals output from the optical detection system, adds the focus error signals of the at least one first reflected light beam to the focus error signals of the at least one second reflected light beam to produce a focus error signal for the optical head so that variations in the focus error signals of the at least one first reflected light beam and the at least one second reflected light beam caused by the variations in the intensity distributions of the at least one first reflected light beam and the at least one second reflected light beam cancel each other out, amplifies the tracking error signals of the at least one first reflected light beam with a first gain, amplifies the tracking error signals of the at least one second reflected light beam with a second gain, a ratio of the second gain to the first gain being proportional to a ratio of a total amount of light in the at least one first reflected light beam to a total amount of light in the at least one second reflected light beam when one of the at least one focused spot is centered on one of the information tracks, and takes a difference between the amplified tracking error signals of the at least one first reflected light beam and the amplified tracking error signals of the at least one second reflected light beam to produce a tracking error signal for the optical head.