Patent ID: 8023368

Claim:
A tilt sensor for detecting the tilt of a given optical disk by getting a light beam, emitted from a light source, converged by an objective lens toward a data storage layer of the optical disk and by sensing the intensities of the light beam, consisting of multiple light rays diffracted by at least one track on the data storage layer, the tilt sensor comprising: a photodetector having a photosensitive plane and detecting the light beam in a plurality of areas and outputting a plurality of detection signals representing the intensities of the light beam detected in the respective areas; and a tilt detector for generating a tilt error signal, including information about the tilt of the optical disk, based on the detection signals, wherein the light beam forms a beam spot on the photosensitive plane, the light beam including: (1) a +first-order light area, in which zero-order and +first-order light rays, diffracted by the track, are superposed one upon the other, (2) a −first-order light area, in which the zero-order light ray and a −first-order light ray are superposed one upon the other, and (3) a zero-order light area, which is sandwiched in a gap between the +first-order and the −first-order light areas, said zero-order light area including the zero-order light ray and not including the +first-order light ray and the −first-order light ray, wherein an opaque area is provided in a light path of the zero-order light area, and the photodetector generates the detection signals except for light rays that have entered the opaque area, wherein the opaque area is provided for neither the +first-order light area nor the −first-order light area, wherein the opaque area has a width W 1 , as measured perpendicularly to a direction into which the track extends, narrower than a width W 2 of the gap between the +first-order light area and the −first-order light area, wherein the photosensitive plane includes a first-division area and a pair of second-division areas that sandwiches the first-division area between themselves, the first-division area being provided so as to receive parts of the light beam corresponding to respective central portions of the +first-order and −first-order light areas, each of the first-division and second-division areas being split into two areas to detect the light beam corresponding to the +first-order light area and the −first-order light area, respectively, and wherein the tilt detector generates two push-pull signals for the first and second-division areas of the photodetector and senses a phase difference between a waveform modulated by a track associated with one of the two push-pull signals and another waveform modulated by the same track associated with the other push-pull signal.