| 摘要 |
The focus is moved from a first layer (L 0 ) to a second layer (L 1 ) of a double-layered optical disk by stopping a control loop operation and applying acceleration pulses for an interlayer jump to a two-axis electromagnetic actuator. Here, switching timing between acceleration and deceleration for an interlayer jump is generated based on the rate of change of a SUM signal obtained from a light-sensitive element ( 27 ), the SUM signal is distinguished by a specific threshold TH, and an S-shaped error signal is distinguished by thresholds THH and THL with different positive/negative level, thereby performing a pull-in operation of focus control. In addition, at the time of the interlayer jump, a liquid crystal element ( 23 ) for correcting the spherical aberration is optimized in advance for the cover layer thickness of the target layer L 1.
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