Engineers at Harvard University’s School of Engineering and Applied Science (Cambridge, MA, USA) have developed a new kind of color filter whose output depends on the polarization of incoming light.
Kenneth Crozier, an Associate Professor of Electrical Engineering at Harvard, and his colleagues created the active color filters using arrays of metallic optical nano-antennas that are tailored to interact with light at visible frequencies through the excitation of localized surface plasmons (LSPs).
This interaction maps the polarization state of incident white light to visible color. Similarly, it converts un-polarized white light to chromatically polarized light.
To demonstrate the technology's capabilities, the acronym LSP was created. With un-polarized light or with light which is polarized at 45 degrees, the letters are invisible (gray on gray).
In polarized light at 90 degrees, the letters appear a vibrant yellow color with a blue background, and at 0 degrees the color scheme is reversed. By rotating the polarization of the incident light, the letters then change color, moving from yellow to blue.
The researchers envision several kinds of applications for the filters -- using the color functionality to present different colors in a display or camera, showing polarization effects in tissue for biomedical imaging, and integrating the technology into labels or paper to generate security tags that could mark money and other objects.
Seeing the color effects from current fabricated samples requires magnification, but large-scale nano-printing techniques could be used to generate samples big enough to be seen with the naked eye.
It might also be feasible to build a television using the nano-antennas, but that would require a great deal of advanced engineering.
More information on the technology is available here.
-- by Dave Wilson, Senior Editor, Vision Systems Design
