| 摘要 |
PURPOSE:To easily adjust an optical system, and to raise the detection sensitivity and the detection accuracy by detecting a focal shift of an optical spot focused to the surface of a recording medium, by a shift from an expected value of a time interval in case when the focus has been adjusted exactly. CONSTITUTION:A laser beam from a semiconductor laser 2 is irradiated to the surface of an optical recording carrier 7 through a deflecting splitter 4, a 1/4 wavelength plate 5, a luminous flux lens 6, etc., a reflected light from the carrier 7 is applied to a photodetector 8 from the splitter 4, and a distribution of an optical intensity of a field of the reflected light is detected. A point where the distribution of this optical intensity becomes maximum is detected by a differential amplifier 9 and a differentiator 10 and applied to a comparator 11. A pulse signal outputted from this comparator 11 is inputted to a synchronizing pulse generating circuit 12 and a pulse width comparing circuit 13. Next, a time interval in which an optical intensity difference becomes maximum is detected, and when a laser luminous flux has been focused to the surface of the carrier 7, a shift of an expected value of an estimated time interval, and a detected time interval is detected, and an optical system can be adjusted easily. |
