Patent EP-2264706-A2 (EP)
Inventor: KADOWAKI SHIN-ICHI
IPC: G11B7/133
Filed: 2003-08-25
Abstract: An optical information apparatus, comprises 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 diffraction 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. The apparatus further comprises a tracking error signal generator generating a tracking error signal for irradiating a desired track with a beam. Guide grooves are formed on the optical recording medium, the optical recording medium has tracks for recording information, arranged substantially at a constant pitch, and the tracks are provided on the guide grooves or between the guide grooves. 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 respectively 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, and 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. An amplitude of the first 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, due to a fact that a track in which information is not recorded is adjacent to a track in which information is recorded or that a pitch of the track formed on the optical recording medium is partially different from the pitch tp. The first push-pull signal is generated using a polarity or amplification coefficient k different from that of an arithmetic operation for obtaining an ordinary push-pull signal with respect to a region in a vicinity of a center of the main beam. The second push-pull signal is generated using a polarity or amplification coefficient k different from that of an arithmetic operation for obtaining an ordinary push-pull signal with respect to a region in a vicinity of respective centers of the first sub-beam and the second sub-beam. A differential arithmetic operation is performed with respect to the first push-pull signal and the second push-pull signal to generate the tracking error signal.