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One-atom-thick optical devices proposed

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Compiled by Photonics Spectra staff

One-atom-thick metamaterials that can now be made by controlling the conductivity of sheets of graphene could have wide applications in imaging, signal processing and telecommunications.

The study of metamaterials is based on the idea that devices can be designed so that their overall wave qualities rely not only on their material but also on the size, shape and pattern of irregularities – known as “inclusions,” or “metamolecules” – embedded within host media. Two university of Pennsylvania engineers said recently that by designing the properties of the inclusions, along with their shapes and densities, they achieved something that is not readily available in nature.

These unusual properties are generated from the manipulation of electromagnetic or acoustic waves. In this case, electromagnetic waves from the infrared spectrum were used. Changing the shape, speed and direction of these waves is a subfield of metamaterials known as “transformation optics.”

The research, which appeared in the June 10 issue of Science (doi: 10.1126/science.1202691), shows how transformation optics might be achieved using graphene – a lattice of carbon measuring a single atom thick.

By applying direct voltage to a sheet of graphene via a ground plate running parallel to it, scientists changed the conductivity of graphene to electromagnetic waves. Varying the voltage or the distance between the ground plate and the graphene alters the conductivity.

A graphene waveguide and splitter. Courtesy of the University of Pennsylvania.

In this marriage between graphene and metamaterials, the different regions of conductivity on the effectively two-dimensional, one-atom-thick sheet function as the physical inclusions do in three-dimensional versions. With a computer model, the scientists demonstrated a sheet of graphene having two different areas of conductivity – one that can support a wave and one that cannot. The boundary between the two areas acts as a wall that can reflect a guided electromagnetic wave on the graphene much as one would in a 3-D space.

Another example of the material’s potential involves three regions: one that can support a wave surrounded by two that cannot. This produces a “waveguide” that functions as a one-atom-thick fiber optic cable. A third example builds on this waveguide principle, adding another nonsupporting region to split the waveguide into two.

The engineers tamed the wave to make it move and bend according to their preference. This could allow for applications such as lensing and “flatland” Fourier transforms, a fundamental aspect of signal processing that is found in nearly every piece of technology with audio or visual components.

Photonics Spectra
Sep 2011
acoustic wavesAmericasCommunicationsconductive grapheneelectromagnetic wavesEM wavesflatland Fourier transformsgrapheneimaginginclusionslenseslensingmeta-moleculesmetamaterialsone-atom-thick metamaterialsopticsPennsylvaniaResearch & Technologysignal processingTech Pulsetelecommunicationstransformation opticsUniversity of Pennsylvania

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