| 摘要 |
PURPOSE:To control a focal point without any influence of a polarization state, by splitting reflected light from a recording carrier into two accroding to a polarization direction, and by photodetecting two kinds of split reflected light by a two-split photoelectric detector. CONSTITUTION:In addition to a two-split photoelectric detector 7, another two- split photoelectric detector is provided; and a beam 11 obtained by splitting a beam into two beams 11 and 12 by a polarizing beam splitter 5 is photodetected by the two-split photoelectric detector 7 through a condenser lens 6, and the other beam 12 is also photodetected by the two-split photoelectric detector 10 through a reflecting plate 8 and a condenser lens 9 to obtain the sum of the differential outputs of the two-split photoelectric detectors 7 and 10 at two places as a focusing control signal for a stop-down lens 9. Thus, stable focusing control is exercised without being influence by the polarization state of the reflected light. |
