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Researchers at Harvard University in the US have made an optical antenna structure on graphene that can be tuned over a broad wavelength range. The device might find use in applications such as reconfigurable “metasurfaces”, adaptive optics and optoelectronics.

Conventional antennas are used to transmit radio or TV signals, but they can be made to work at optical frequencies if shrunk to the nanoscale. Nanoantennas possess "plasmonic modes" that can be tuned to resonate with the optical transitions in molecules nearby and it is these modes that increase the interaction between light and matter on sub-wavelength scales in the near field region of the antennas. However, although normal antennas are easy to tune, these nanodevices are not because of their small size.

Graphene, a monolayer of hexagonally arranged carbon atoms, comes into its own here. Its conductivity and optical constant can be tuned by simply applying a gate voltage applied to it. This is because the applied voltage changes the carrier (electron and hole) concentration in the material. Indeed, earlier this year, a team of scientists at Harvard, led by Federico Capasso, found that graphene placed in the nanogap of a dipole antenna acts as an electrically tuneable nanocircuit element and can therefore be used to control the resonance of the antenna.

Nano Tech Web: Optical nanoantenna goes wide wavelength

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