| 摘要 |
PURPOSE:To contrive the miniaturization and the improvement of the detection accuracy by installing a first and a second gratings by separating them by a talbo distance, and providing a condensing lens between them so that the whole light quantum for transmitting through a first and a second gratings is radiated onto a four-split photodetector. CONSTITUTION:The device is constituted so that the whole light quantum for transmitting through a first and a second gratings is radiated onto a four-split photodetector 11 by placing a condensing lens 10 between a first grating 8 and a second grating 9. Accordingly, a moire fringe made by a first and a second gratings is distinct since a first and a second gratings are separated by a talbo distance, and a beam of the moire fringe photodetected by the four- split photodetector 11 is made incident on the four-split photodetector 11 in a state that the whole light quantum is focused by condensing of a condensing lens 10. In such a way, an increase of the detection light quantum can be contrived without making an optical pickup device large in size at all. |
