| 摘要 |
PROBLEM TO BE SOLVED: To prevent the out of focus at a track jump while suppressing the number of pins of a chip of an optical pickup device. SOLUTION: Reflected light rays of light spots M, E, F, G and H with which a DVD-RAM 70 is irradiated are made incident on photodiodes 52M, E, F, G and H. The photodiodes 52M is quadrisected as known to A, B, C and D. The photodiode 52E is bisected to the array direction of the photodiodes and is bisected to a transverse direction only on the array direction G side to Ea, Eb and Ec. The photodiode 52F is bisected to the array direction and is bisected to the transverse direction only on the array direction H side to Fa, Fb and Fc. FEM=(A+C)-(B+D), FEE=Ea-Ec, FEF=FB-Fa, FES=FEE+FEF and FE=FEM+FES are set and the focus control of an objective lens 30 is executed by using FE for a focus error.
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