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An antenna for light
Closeup of carbon nanotubes. Photo courtesy of Zhifeng Ren
Boston College physicists, working with researchers from the U.S. Army Natick Soldier Center and private industry, have created a microscopic antenna that reacts to visible light in much the same way that radio antennas respond to radio waves. The device may have applications for the effort to more efficiently convert solar energy into electricity and could be useful in developing fiber optic wires capable of carrying data at speeds thousands of times faster than current broadband connections allow. The development was reported in the September 27 issue of
Applied Physics Letters
by lead authors Professor Kris Kempa and Yang Wang, a second-year doctoral student.
Light waves, like radio waves, are composed of oscillating electric and magnetic fields. To receive the full breadth of a wave's field, an antenna must be similar in size to the wavelength for which it is intended. Radio waves have tangible wavelengths of three to 300 meters. Visible light wavelengths measure .00000075 of a meter at most. "Nobody had tried [to build an antenna] in optical frequencies," Kempa told BC's
Chronicle.
"Nobody talks about antennas for light."
To make their antenna, the physicists mounted an array of highly conductive carbon nanotubes, measuring one-70th the width of a human hair, on a wafer of silicon. When the wafer was exposed to visible light, a current of electrons, oscillating at one million billion cycles per second, was detected.
Much work remains to be done on the antenna before it is of practical use, according to Kempa—including development of a valve to admit electrons and then trap them, allowing light energy to be retained. The research team's ultimate goal is to develop a more efficient solar cell. Conventional cells are, at most, 30 percent efficient at converting light to electricity. The team envisions solar cells that could be 80 percent efficient.
BC coauthors on the report were professor Zhifeng Ren; research associate Jakub Rybczynski; lecturer Andrzej Herczynski; Wenzhi Li, a former senior research scientist in Ren's lab; and Kempa's son, Thomas '04, now a Marshall Scholar at Cambridge University. The project was funded by the Natick Army Labs.
Mark Sullivan
Mark Sullivan is a senior staff writer for the Boston College
Chronicle.
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