Cambridge, Mass. - February 23, 2012 Engineers at Harvard have demonstrated a new kind of tunable color filter that uses optical nanoantennas to obtain precise control of color output.
Whereas a conventional color filter can only produce one fixed color, a single active filter under exposure to different types of light can produce a range of colors.
The advance has the potential for application in televisions and biological imaging, and could even be used to create invisible security tags to mark currency. The findings appear in the February issue of Nano Letters.
Kenneth Crozier, Associate Professor of Electrical Engineering at the Harvard School of Engineering and Applied Sciences (SEAS), and colleagues have engineered the size and shape of metal nanoparticles so that the color they appear strongly depends on the polarization of the light illuminating them. The nanoparticles can be regarded as antennassimilar to antennas used for wireless communicationsbut much smaller in scale and operating at visible frequencies.
"With the advances in nanotechnology, we can precisely control the shape of the optical nanoantennas, so we can tune them to react differently with light of different colors and different polarizations," said co-author Tal Ellenbogen, a postdoctoral fellow at SEAS. "By doing so, we designed a new sort of controllable color filter."
Conventional RGB filters used to create color in today's televisions and monitors have one fixed output color (red, green, or blue) and create a broader palette of hues through blending. By contrast, each pixel of the nanoantenna-based filters is dynamic and able to produce different colors when the polarization is changed.
The researchers dubbed these filters "chromatic plasmonic polarizers" as they can create a pixel with a uniform color or complex patterns with colors varying as a function of position.
To demonstrate the technology's capabilities, the acr
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