OPTICAL HEAD, PHOTODETECTOR, OPTICAL INFORMATION RECORDING AND REPRODUCING DEVICE, AND FOCUS ERROR DETECTING METHOD

摘要

PROBLEM TO BE SOLVED: To provide an optical head, a photodetector, an optical recording and reproducing device and a focus error detecting method, which deal with plural kinds of recording media and also a land/groove recording system. SOLUTION: A main spot light receiving section 92 of a photodetector 9 of an optical head is divided into plural parts. An intermediate light receiving section 92M, which consists of four small light receiving sections 92Mw to 92Mz, is provided at a central region surrounded by four peripheral light receiving sections 92A to 92D. Focus error signals are obtained only from the output signals of the sections 92A to 92D to conduct focus control without using the output signals from the section 92M, that is located at a portion where intensity distribution among light converging spots is unstable. The portions in the head other than the element 9 have the same configuration as a conventional astigmatic method so as to maintain compatibility and good focus control having small track cross noise is conducted for a land/groove recording medium.