| 摘要 |
PURPOSE:To obtain the S-shaped characteristic curve with no dependence on the width of a dividing line of a photodetector, by using two cylindrical lenses to form two caustic curves and providing a 2-split photodetector for detection of focus error signal between those two caustic curves. CONSTITUTION:The sectional form of the light beam reflected by an optical disk 11 and passed through an objective lens 13 is substantially circular. the half of the light beam is reflected by a total-reflection mirror knife 14 and made incident on the 1st 2-split photodetector 15. While the other half of the light beam is made incident on the 2nd 2-split photodetector 18 via the 1s and 2nd cylindrical lenses 16 and 17. Thus a tracking error signal can be obtained from the output difference between photodetecting parts 15a and 15b of the photodetector 15 in an optical recording or reproducing mode. While a focus error signal is obtained from th output difference between photodetecting parts 18a and 18b of the photodetector 18. |
