Artificial-muscle diffraction grating

Manuel Aschwanden and Andreas Stemmer of ETH Zürich in Switzerland molded a soft, electroactive polymer into a shape resembling a microscopic pleated window shade and bonded it onto a prestretched elastic polymer. The result is an artificial muscle that contracts when a voltage is applied. With no voltage, the grating’s lines are spaced 1 µm apart. But when a voltage is applied to the ETH device, the line spacing can change by up to a whopping 32%—compared with less than 1% for tunable gratings made of hard materials. When white light strikes a diffraction grating, different wavelengths fan out at different angles; a small aperture placed within the fan can isolate any of the colors. Changed line spacing means changed angles, and a different color sweeps across the aperture. With different voltages, the test device isolated different wavelengths over a range of 139 nm starting at 446 nm, as shown in the figure. The researchers envision replacing the fixed red, green, and blue light-emitting elements in each pixel of a display screen with two or more tunable diffraction gratings, which would make available the full range of colors that the human eye can perceive. Tunable diffraction gratings are routinely used in fiber-optic telecommunications and video projectors. The new technology could exploit newly developed white LED lights. (M. Aschwanden, A. Stemmer, Opt. Lett. 31 , 2610, 2006 http://dx.doi.org/10.1364/OL.31.002610 .)