Light compression method could enable optical computers

The new method has been devised by scientists at the University of California, Berkeley, and improves on work from other researchers who previously have passed light through gaps 200 nanometres wide.

In theory, it is able to confine light in spaces on the order of 10 nanometres -- more than 100 times thinner than current optical fibres -- and could lead to huge advances in the field of optical computing.

Confining light could alter the fundamental interaction between light and matter in accordance with Einstein’s famous formula, ‘E=mc^2’, which could enable interactions between electronics and optics.

“There has been a lot of interest in scaling down optical devices,” said mechanical engineering professor Xiang Zhang, who is the senior author of the study.

“It's the holy grail for the future of communications,” he said.

The new method compresses light using surface plasmonics, where light binds to electrons allowing it to propagate along the surface of metal.

Normally, these light-electron waves can only travel short distances along the metal before petering out.

However, the University of California researchers have suggested a ‘hybrid’ optical fibre that consists of a very thin semiconductor wire placed close to a smooth sheet of silver and acts as a capacitor that stores energy between the wire and metal sheet.

As the light travels along the gap, it stimulates the build-up of charges on both the wire and the metal, and these charges allow the energy to be sustained for longer distances.

This finding flies in the face of the previous dogma that light compression comes with the drawback of short propagation distances, Zhang said.

Even though the current study is theoretical, researchers expect the construction of such a device should be straightforward.

The problem lies in trying to directly detect the light in such a small space -no current tools are sensitive enough to see such a small point of light. But Zhang's group is looking for other ways to experimentally detect the tiny bits of light in these devices.

Ideally, optics researchers would like to cram light down to the size of electron wavelengths to force light and matter to cooperate.

This idea could be an important step on the road to an optical computer, which is a machine where all electronics are replaced with optical parts.

The construction of a compact optical transistor currently is a major stumbling block in the progress toward fully optical computing, and this technique for compacting light and linking plasmonics with semiconductors might help clear this hurdle, the researchers said.

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