| 摘要 |
PURPOSE:To improve the asymmetricity and nonlinearity of a focus position error signal by combining in total 4 kinds of output signals obtained from each detection part of each 2-split photodetector so as to obtain the focus position error signal. CONSTITUTION:When a recording medium 1 approaches an objective lens 2 from the focusing position, a reflected luminous flux passing through the lens 2 is diverged and passes through a beam splitter 5 and then converged by a spot lens 6. The luminous flux not reflected by a reflector 10 in the said luminous flux is converged at a point P and made incident in a photodetector 8 as a diverged light again. On the other hand, the luminous flux reflected in the reflection plate 10 is made incident in a photodetector 11 and when the photodetector 11 does not exist, the light is focused at a point P'. In this case, 4 kinds of output signals obtained by photodetection sections 8a, 8b, 11a, 11b of the photodetectors 8, 11 are used and the combination of (A-B)-(C-D) is used as the focus error signal, then the asymmetricity and nonlinearity of the signals obtained at the photodetectors 8, 11 are remarkably improved and the sensing sensitivity of the focus error is improved. |
