| 摘要 |
Disclosed are an optical head, a photodetector, an optical recording and reproducing apparatus and a focus error detecting method, which can be adapted to a plurality of kinds of recording media and a land/groove recording system. A photoreceiving part for the main spot in a photodetector in an optical head is divided into a plurality of parts. An intermediate photoreceiving part consisting of four small photoreceiving parts is provided in a central area surrounded by four peripheral photoreceiving parts. Without using an output signal from the intermediate photoreceiving part positioning in an area where the intensity distribution is unstable in a converged light spot, a focus error signal is obtained only from output signals from the peripheral photoreceiving parts and a focusing control is performed by using the focus error signal. While maintaining compatibility by constructing the other parts of the optical head except for the photodetector in a manner similar to the case of the conventional astigmatism method, an excellent focusing control which does not cause much track crossing noise can be performed also on a land/groove recording medium.
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