| 摘要 |
PURPOSE:To obtain an information signal and error signal from a single beam and to enable detecting of a displacement in focus over a wide range, by a method wherein a photo detector is placed on a line passing an optical axis, and a photo detector, collecting remaining light bundle not intercepted by aforesiad photo detector, is arranged. CONSTITUTION:A beam splitter 9 is placed above a collecting lens 10 collecting reflection light from an information recording surface 11, and a convex lens 12, converging the reflection light, in turn, is located. Two photo detectors 13 and 14 are situated on an optical axis 15 of the lens 12 such that a converging point 16 is positioned between the photo detectors 13 and 14, and the photo detector 14 is positioned so that it collects beam not intercepted by the photo detector 13. For example, if each collecting surface of the photo detectors 13 and 14 is divided into 3 parts and outputs A-F corresponding to an irraditing light amount are obtained from each division collecting surface, a focus is regulated by an output (A+B)-(C+D) of a differential amplifier 24, a tracking control is performed by an output (A+D)-(B+C) of a differential amplifier 25, and an information signal is obtained by the output (A+B+C+D+E+F) of an adder 23. |
