| 摘要 |
PURPOSE:To attain the adjustment of a focal point properly by allowing a detector whose photodetecting face is split into four to receive a reflected beam from a recording medium and correcting the irradiated beam by means of a focus error signal and a tracking error signal formed based on a detecting signal so as to control the focus of the irradiated beam. CONSTITUTION:An adder 12a operates Ia+Ib, an adder 12b operates Ic+Id, an adder 12c operates Ia+Ic and an adder 12d operates Ia+Id. Since a subtractor 13a subtracts an output of the adder 12a from an output of the adder 12b, (c+ Id)-(Ia+Ib)=DELTAIf (focus error signal) is calculated, and similarly, a subtractor 13b calculates (Ib+Ic)-(Ia+Id)=DELTAIt (tracking error signal). An absolute value amplifier 14 takes the absolute value of the DELTAIt, and KDELTAIt is obtained with proper amplification. A subtractor 13c calculates DELTAIf-DELTAIt and a true focus error signal is obtained by subtracting tracking error information KDELTAIt included in the DELTAIf. Thus, the effect of the tracking error on the adjustment of the focus is eliminated, thereby allowing to attain proper focal point at all times. |
