| 摘要 |
PURPOSE:To eliminate an ineffective part of a photodetecting part for detecting an RF signal, and to maintain a high level of the RF signal, for forming separately the photodetecting part for detecting the RF signal and a photodetector for detecting a focus. CONSTITUTION:Laser light which is made incident to a disk passes through a lambda/4 plate two times when going and returning, the plane of polarization of return light is rotated by 90 degrees, and it is made incident to a detector 21. Five photodetecting faces 22-25 and 26 are formed on the detector 21. The photodetecting part 22 is used for detecting an RF signal, and photodetects a spot (a) of main light. The photodetecting parts 23, 24 are used for tracking-servo, and photodetect spots (b), (c) of auxiliary light, respectively. Also, the photodetecting parts 25, 26 are used for detecting a focus, and photodetect spots (d), (e) of auxiliary light. Not only the photodetecting parts 23, 24 but also the photodetecting part 22 are constituted of a single photodetector, therefore, an ineffective part is eliminated, and a loss of about a half can be eliminated. Accordingly, sensitivity of the photodetecting part 22 becomes large, and a large level of the RF signal can be maintained. |
