Novel type of micromachined retroreflector

This paper reports on the manufacturing of a novel type of retroreflecting sheeting material. The geometry presented has high reflection efficiency even at large incident angles, and it can be manufactured at low cost through polymer replication techniques. The paper consists of two parts. A theoretical section outlining the design parameters and their impact on the optical performance, and secondly, an experimental part comprising both manufacturing and optical evaluation for a candidate retroreflecting sheet material in traffic control devices. Experimental data show that the retroreflecting properties are promising. The retroreflector consists of a front layer of densely packed spherical microlenses, a back surface of densely packed spherical micromirrors, and a transparent spacer layer with a thickness equal or not equal to the focal length of the lens. The master structures for the lens and mirror sides of the retroreflector were produced by thermal reflow of photoresist pads on silicon wafers. The silicon master structures were transferred into metallic counterparts by electroforming. The casting of the retroreflector was then done in a cavity being limited by the respective mould inserts for the lens and mirror sides.