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Ruffled electrons could introduce a new information technology

PR13(07)

Tue, 22 May 2007

Getting light and electronics to talk to each other is one of the biggest challenges for telecommunications. Signals are sent over long distances as light pulses travelling through optical fibres, but the information at the sending and receiving ends is typically handled and manipulated by electronic circuits. Translating between light and electricity is rather cumbersome, and limits the size, speed and capacity of today’s telecommunication technology. Now Chris Phillips and co-workers at Imperial College London have proposed a new way to couple light and electronics. The work will be described by team member Jonathan Plumridge on 12 April at the Condensed Matter and Materials Physics conference, organised by the Institute of Physics.

The Imperial researchers say that electron waves called plasmons, which are formed at the surface of conducting materials like metals, are ideal for creating a transaction between light beams and electronic circuits, because they are directly affected by light. Shining light onto the material’s surface can ruffle the electrons into plasmon waves, and the plasmons can in turn alter a light beam, allowing two-way interconversion of light-borne and electron-borne signals.

But the key to turning this idea into a new information technology – plasmonics – is to be able to tune the properties of a plasmon by design. To do this, the researchers use a so-called quantum metamaterial: a material built up from small engineered components, in this case alternating layers of two semiconductors each just a few nanometres (millionths of a millimetre) thick. The stack of layers produces a curious material that behaves like a metal, supporting plasmons at the surface, parallel to the layers, but is rather like a collection of ‘artificial atoms’ perpendicular to the layers.

The plasmons on the top and bottom surfaces of this metamaterial become ‘tied’ together, and this enables them to move as waves over very long distances through the layers, whereas most plasmon waves get damped down after a short distance. So the metamaterial acts like a kind of ‘plasmonic fibre’ comparable to the optical fibres that bear light signals over long distances. And crucially, the plasmon can be turned ‘on’ and off’ by applying an electrical field to the metamaterial, which means that plasmonic devices could act as switches, rather like the transistors that supply the key components of logic circuits in today’s computer chips.

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