Optical pick-up head, optical information apparatus, and optical information reproducing method

An optical pick-up head, comprising:

• a light source emitting a light beam;
• a diffraction unit receiving the light 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, assuming that Tn−2, Tn−1, Tn, Tn+1, and Tn+2 represent tracks irradiated with the main beam when the main beam is scanned in a direction orthogonal to the tracks, and the main beam is placed at a center of the track Tn, the first sub-beam is placed between the tracks Tn−2 and Tn−1, and the second sub-beam is placed between the tracks Tn+1 and Tn+2.

A method for reproducing optical information using

• an optical pick-up head including:
• a light source emitting a light beam;
• a diffraction unit receiving the light beam emitted from the light source to generate a plurality of diffracted beams composed of a 0th order diffracted light beam and 1st or higher order diffracted light beams;
• a condensing unit receiving the plurality of 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, and
• a tracking error signal generator generating a tracking error signal for irradiating a desired track with a beam,
• wherein the photodetector has a plurality of light-receiving portions,
• the plurality of beams are radiated to positions different in a direction orthogonal to the tracks,
• the tracking error signal generator performs a differential arithmetic operation with respect to the signals output from the light-receiving portions to generate a push-pull signal,
• the optical recording medium has tracks arranged substantially at a constant pitch, and an average of the pitch is tp, and
• when an amplitude of the push-pull signal obtained at the pitch tp when the light beam is scanned in a direction orthogonal to the tracks of the optical recording medium is changed at a pitch different from the pitch tp, the change in the amplitude of the push-pull signal is reduced by manipulating a signal obtained from the plurality of beams.

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;
• wherein the light-receiving portions do not receive light in the vicinity of a center of the first sub-beam and light in the vicinity of a center of the second sub-beam;
• 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,
• the tacking 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 tacking 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.