| 摘要 |
To provide an optical disc drive that can shift the focal point steadily to a focus controllable range. An optical disc drive includes: an optical branching element for splitting light from a light source into main and sub-beams; a condenser element for condensing the main and sub-beams; a photodetector section including photodetectors to receive reflected portions of the main and sub-beams, each photodetector having photosensitive areas, each of which outputs a signal representing the intensity of light received there; and a computing section for generating a first focus signal, representing where the focal point of the main beam is located with respect to the storage layer, based on the reflected light of the main beam, and a second focus signal based on the reflected light of the main and sub-beams. The drive performs a first type of control to shift the focal point toward the storage layer, switches the first type into a second type based on a result of comparison to the first focus error signal and then performs a second type of control to make the focal point keep up with the storage layer.
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