| 摘要 |
PURPOSE:To facilitate size reduction and resolution improvement by atilizing light converging effect based upon the diffraction and interference f a 1-dimensional Fresnel zone plate in the presence of parallel and coherent luminous flux. CONSTITUTION:Light from the light emission surface of a laser diode 11 is collimated by a collimator lens 12 into parallel luminous flux, which illuminates a code plate 13. Tracks 16a-16d are drawn on the code plate 13 and binary code patterns consisting of the 2-dimensional Fresnel zone plate are drawn on the tracks 16a-16d; and the light is cut off in shield zones and transmitted in other zones, and transmitted light illuminates a mask 14. The mask 14 has slit parts, and the light is transmitted through the parts and cut off by the remaining part, so that the transmitted light illuminates a photodetecting element 15. For the purpose, the binary code patterns on the code plate 13 and the distance of the element 15 are made coincident with the focal length of the 1-dimensional Fresnel zone plate to obtain the converging effect based upon the diffraction and interference of the linear Fresnel belt plate, and projection image of binary code patterns on adjacent tracks are clearly discriminated, so track intervals are reduced to facilitate the size reduction and resolution improvement. |
