| 摘要 |
PURPOSE:To facilitate the manufacture of an optical splitter and to make the error detection exact by providing a prism part and a non-prism part dividing a signal into two by the optical splitter whose reflected axis is made coincident with the boundary between both the parts and outputting a signal through the photodetection by a photodetector. CONSTITUTION:The optical splitter 9 has the prism part 9a and the non-prism part 9b and the boundary 9c of both the parts is arranged vertically on an optical axis. When an information recording medium 6 and an objective lens 5 are in the focused position, a light spot appears at each split band of light receiving faces 8a, 8b and 8c, 8d of the split type photodetector 8 and no focus error signal is detected. When the medium 6 and the lens 5 are not focused, the light spot appears in a semi-circular form at the inner or the outer side of the split band. Thus, the focus error is detected by operating a photodetection signal in response to the light receiving quantity of the detector 8. Thus, the splitter is formed easily and the focus error signal with high reliability is obtained. |
