Researchers from Spain's CIC nanoGUNE, in collaboration with ICFO and Graphenea (also in Spain) have shown that a nanoscale metal rod on graphene (acting as an antenna for light) can capture infrared light and transform it into graphene plasmons, analogous to a radio antenna converting radio waves into electromagnetic waves in a metal cable.
Pablo Alonso-González, who performed the experiments at nanoGUNE, highlights some of the advantages offered by the antenna device: "The excitation of graphene plasmons is purely optical, the device is compact and the phase and wavefronts of the graphene plasmons can be directly controlled by geometrically tailoring the antennas. This is essential to develop applications based on focusing and guiding of light”.
nanoGUNE's Nanodevices group fabricated gold nanoantennas on graphene provided by Graphenea. The Nanooptics group then used the Neaspec near-field microscope to image how infrared graphene plasmons are launched and propagate along the graphene layer. In the images, the researchers saw that, indeed, waves on graphene propagate away from the antenna, like waves on a water surface when a stone is thrown in.
The wavelength of light captured by a graphene layer can be shortened by a factor of 10 to 100 compared to light propagating in free space. As a consequence, this light propagating along the graphene layer - called graphene plasmon - requires much less space.
“We introduced a versatile platform technology based on resonant optical antennas for launching and controlling propagating graphene plasmons, which represents an essential step for the development of graphene plasmonic circuits”, said team leader Rainer Hillenbrand.
Altogether, the experiments show that the fundamental and most important principles of conventional optics also apply for graphene plasmons, or "squeezed" light propagating along a one-atom-thick layer of carbon atoms. Future developments based on these results could lead to extremely miniaturized optical circuits and devices that could be useful for sensing and computing, among other applications.