| 摘要 |
PURPOSE:To reduce the crosstalk of a focusing error signal and a tracking error signal by computing the difference of the sum of the output of partition photodetectors being positioned at both ends of each of two partition detectors with an arithmetic means, and outputting it as the focusing error signal. CONSTITUTION:Assuming the values of the output signals of the partition photodetectors 25A-25C as A-C and that of the partition photodetectors 26A-26C as A'-C', a differential amplifier 31 outputs the focusing error signal with a value FES=(A+C)-(A'+C') in equation (2). Meanwhile, an adder 30 outputs the total sum (A+B+C+A'+B'+C') of the output signals as a reproducing information signal. Since a spot is made incident on only the partition photodetectors 25B, 26B in the center when focusing is obtained, the focusing error signal in equation (2) shows zero, and also, next equation SUM=(A+ C)+(A'+C') goes to zero when the focusing is obtained, which prevents the tracking error signal mixed (servo crosstalk) to the focusing error signal when the focusing is obtained. |
