New technique to compress light opens doors to optical computing

August 1st, 2008 - 11:43 am ICT by IANS  

Mountain View (California), Aug 1 (IANS) Scientists at the University of California, Berkeley have devised a way to squeeze light into tighter spaces than ever thought possible, potentially opening doors to new technology in the fields of optical communications, miniature lasers and optical computers. The university said in a statement that a group of UC Berkeley researchers led by mechanical engineering professor Xiang Zhang had devised a way to confine light in incredibly small spaces on the order of 10 nanometres or about 100 times thinner than current optical fibres. The width of a human hair is about 60,000 nanometres.

“This technique could give us remarkable control over light,” the statement said quoting Rupert Oulton, lead author of the study that will be published in the August issue of Nature Photonics and is currently available online.

Just as computer engineers cram more and more transistors into computer chips in the pursuit of faster and smaller machines, researchers in the field of optics have been looking for ways to compress light into smaller wires for better optical communications.

Not only would compressed light make possible smaller optical fibres, but it could lead to huge advances in the field of optical computing, according to the study. Compressing light further than its wavelength is a challenging task as light doesn’t want to stay inside a space that small.

Berkeley researchers squished light beyond these limits using surface plasmonics, where light binds to electrons allowing it to propagate along the surface of metal. But the light waves could only travel short distances along the metal before petering out due to losses. They then tried out their idea of combining plasmonics and semiconductors and found it worked.

The group’s theoretical “hybrid” optical fibre consists of a very thin semiconductor wire placed close to a smooth sheet of silver.

Their computer simulations showed that not only could the light compress into spaces only tens of nanometres wide, but it could travel distances nearly 100 times greater in the simulation than by conventional surface plasmonics alone. Instead of the light moving down the centre of the thin wire, as the wire approaches the metal sheet, light waves are trapped in the gap between them, the researchers found.

The research team’s technique works because the hybrid system acts like a capacitor storing energy between the wire and the metal sheet, the scientists reported.

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.

Though the current study is theoretical, the construction of such a device should be straightforward, according to the researchers. The problem lies in trying to directly detect the light in such a small space. No existing devices 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.

The university statement said the hybrid technique of confining light could have huge ramifications. It brings light closer to the scale of electrons’ wavelengths, meaning that new links between optical and electronic communications might be possible.

This idea could be an important step on the road to an optical computer, a machine where all electronics are replaced with optical parts. The technique for compacting light and linking plasmonics with semiconductors might help construction of compact optical transistors, the building blocks of an optical computer, the researchers said.

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