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Graphene finding promises ultrafast electrical-to-optical conversion

Technology News |
By Rich Pell

The work reported in the journal Nature Communications, shows this new way of converting electricity into visible radiation is highly controllable, fast, and efficient so it could open new graphene usages.

“Graphene has this ability to trap light, in modes we call surface plasmons,” says MIT postdoc and the paper lead author Ido Kaminer. Plasmons are a kind of virtual particle that represents the oscillations of electrons on the surface. The speed of these plasmons through the graphene is “a few hundred times slower than light in free space,” he says.

This effect coincides with another of graphene’s exceptional characteristics: electrons pass through it at very high speeds, up to a million meters per second, or about 1/300 the speed of light in a vacuum. That meant that the two speeds were similar enough that significant interactions might occur between the two kinds of particles, if the material could be tuned to get the velocities to match.

That combination of properties suggested the possibility of using graphene to produce the opposite effect: to produce light instead of trapping it, and the researchers’ theoretical work shows that this can lead to a new way of generating light. With an analogy to the shockwave of sound when one breaks the sound barrier, when the electrons’ approach the light speed in graphene, they somehow break the ‘light barrier’, yielding a shockwave of light trapped in two dimensions.

The illustration depicts the process of light emission from a sheet of graphene, represented as the blue lattice on the top surface of a carrier material. The light-coloured arrow moving upwards at the centre depicts a fast-moving electron (going faster than light) that generates a shock wave, ejecting plasmons in two directions (shown as red wavy lines). Courtesy of the researchers.

This microscale, fast, and tuneable plasmon-based approach to emitting light may take off in new fields of application such as on-chip photonics.

“If you want to do all sorts of signal processing problems on a chip, you want to have a very fast signal, and also to be able to work on very small scales,” says Kaminer, hinting that using light instead of flowing electrons as the basis for moving and storing data could push operating speeds six orders of magnitude higher than what is used in electronics.

Rather than having to design complex opto-coupling interfaces where optical losses hinder efficiency, graphene could be used to emit and confine the beams at the same time. Next on the researchers’ roadmap is to create a working proof-of-concept of their theoretical findings.

For more, see the paper “Efficient plasmonic emission by the quantum Cerenkov effect from hot carriers in graphene.”

Visit the MIT at www.mit.edu

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