| 摘要 |
PROBLEM TO BE SOLVED: To provide the focus control method capable of increasing reliability of the focus control by allowing each focus error signal to coincide with respect to lands and grooves. SOLUTION: In an optical pickup, a main beam and a sub-beam are produced by diffracting the laser beam, and a track of the optical disk constituted of the lands and grooves is irradiated with convergence of the main beam, and also the border part between the guide area of the track of optical disk and this track is irradiated with convergence of the sub-beam, then the beam reflected by the optical disk is supplied to a photodetector. By a producing circuit, a sum signal SUM0 corresponding to the light quantity of the main beam and the focus error signal FE of the sub-beam are produced from the output signal of the photodetector. By the focus controller, an objective lens is moved based on the sum signal SUM0 so that the value of the focus error signal FE of the sub-beam reaches the value in the linear area from the value at the outside of the linear area of the sigmoid curve, and next, the objective lens is moved based on the above focus error signal FE.
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