| 摘要 |
A beam emitted from a beam source is irradiated on an optical disc. A part of the reflected beam from the optical disc is incident on a four-piece prism, while the remaining part of the reflected beam is incident on a second sensor. The reflected beam incident on the four-piece prism is split into four beams outgoing in different directions so that they are incident on the first optical sensor. The first optical sensor is provided with first and second optical sensor elements, and the first optical sensor element that has received two beams of four beams split by the four-piece prism outputs a signal for producing a focus error signal. A plurality of operational amplifiers generate a focus error signal based on the signal output from the first optical sensor element. On the other hand, the second optical sensor element that has received two beams of a plurality of beams divided by the prism outputs a signal for generating an RF signal. An RF head amplifier generates an RF signal based on the signal output from the second optical sensor element.
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