| 摘要 |
<p>PURPOSE:To reduce abberation and to improve detection accuracy by forming the front surface of a planar optical member as a prism surface, and forming the rear surface as the surface of a Fresnel lens. CONSTITUTION:Surface parts 11a and 11c of linear multiple prisms are formed at the front surface of a planar optical member 11. The prism surface parts 11a and 11c are symmetrical with respect to an optical axis O - O' and formed at the same angle. Fresnel-lens parts 11d, 11e and 11f are formed at the rear surface. Photodetectors 12, 13 and 14 are arranged at the rear side of the Fresnel lens parts. In this constitution, the luminous fluxes from detecting regions 15a, 15b and 15c are transmitted through the prism-surface parts 11a and 11c or the flat surface part 11b and inputted into the Fresnel lens parts substantially along the optical axis. Therefore, the light is inputted into the photodetectors 12, 13 and 14 without generating large abberation. The detection accuracy of the presence or movement of an object in the regions 15a, 15b and 15c can be enhanced.</p> |
