Patent ID: 7460448

Claim:
An optical information apparatus, comprising: an optical pick-up head including: a light source emitting a light beam; a diffraction unit receiving a beam emitted from the light source to generate a plurality of diffracted beams composed of a 0th order diffracted light beam and a 1st or higher order diffracted light beam; a condensing unit receiving the plurality of diffracted beams from the diffraction unit and condensing the beams onto an optical recording medium; a beam splitter receiving the plurality of beams reflected from the optical recording medium and splitting the beams; and a photodetector receiving the beams split by the beam splitter and outputting signals in accordance with amounts of the received light beams, wherein the 0th order diffracted light beam generated in the diffraction unit is set to be a main beam, and two 1st or higher order diffracted light beams generated in the diffraction unit are set to be a first sub-beam and a second sub-beam, the photodetector has a plurality of light-receiving portions, and the main beam, the first sub-beam, and the second sub-beam are received by the plurality of light-receiving portions, respectively; and a tracking error signal generator generating a tracking error signal for irradiating a desired track with a beam, wherein the optical recording medium has tracks arranged substantially at a constant pitch, an average of the pitch is tp, when the main beam is placed on the track, the first sub-beam and the second sub-beam are placed between the tracks, the tracking error signal generator performs a differential arithmetic operation with respect to signals output from the light-receiving portion receiving the main beam to generate a first push-pull signal, performs a differential arithmetic operation with respect to signals output from the light-receiving portions receiving the first sub-beam and the second sub-beam to generate a second push-pull signal, and performs a differential arithmetic operation with respect to the first push-pull signal and the second push-pull signal to generate the tracking error signal, in a case where an amplitude of the first push-pull signal obtained at the pitch tp is fluctuated when the light beam is scanned in a direction orthogonal to the tracks of the optical recording medium.