| 摘要 |
PURPOSE:To improve the precision of auto-tracking servo and auto-focusing servo by providing a means, which limits a spatial frequency component, in the optical path between an information recording medium and a photodetector which obtains a tracking control signal. CONSTITUTION:The reflected light from an information recording medium 5 passes an objective lens 4 and a beam splitter 3 and is made incident on a halfmirror 8 and passes a condenser lens 6 and reaches a photodetector 71 which detects an RF signal and a focusing control signal. Meanwhile, the transmitted light cuts only a high spatial frequency component by a one-dimensional optical low-pass filter 9 and reaches a photodetector 72 through the condenser lens 6 to perform the tracking control. By this constitution, the modulated wave of a tracking servo signal is raised and that of an auto-focusing servo signal is reduced to improve the precision of auto-tracking servo and auto- fucusing servo. |
