| 摘要 |
PURPOSE:To obtain a track error signal with a high SN ratio by comparing the output sum of divided photodetecting areas with each other. CONSTITUTION:Photodetectors 19a-19d are formed on both the sides of a photodetector 19e for reading out information from an information track, the photodetectors 19a, 19b having respectively two-divided photodetecting areas are irradiated with one sublight flux 91' out of two light flux 91', 92' and the photodetectors 19c, 19d are irradiated with the other sublight flux 92'. At that time, the centers of circular spots of the sublight flux 91', 92' are arranged on respective boundaries between the photodetectors 19a, 19b and 19c, 19d. The sum of outputs from the photodetectors 19a, 19c is detected by an adder 20 and the sum of output signals from the photodetectors 19b, 19d is detected by an adder 21. A difference between output signals from the adders 20, 21 is detected by a subtractor 22 to tain a focus error signal. Consequently, the detecting sensitivity of the focus error signal can be improved. |
