| 摘要 |
PURPOSE:To simplify focus position detecting optical system and enable reproduction information signals of always good S/N to be obtained by introducing the convergent luuminous flux from recording medium to plural photo detectors by the use of a combination prism. CONSTITUTION:The laser ray from a generator 1 is projected as an information read beam on a disc 6 and the reflected light thereof is reflected by a beam splitter 4 and is entered to a combination prism 13. At the just focus time, it is received in a signal detecting photo detector 14 without loss. At the time other than just focus, the convergent position of the incident luminous flux to the prism 13 changes according to the fluctuations in the distance between the objective lens 5 and the recording information face of the disc 6 and the exit luminous flux of the prism 13 moves in the upward or downward direction of the bisected planes, thus while the fluctuations of the incident luminous flux to the disc 6 with respect to its optimum focus position is being detected by the differential signal of the bisected photo detector 15 or 16, the reading of the recording information signal is accomplished by the element 14. |
