Optics researchers at the University of California, Berkeley have devised a way to squeeze light into tighter spaces than previously thought possible, potentially opening the door to new technology in the fields of optical communications, miniature lasers and optical computers.
The group, led by mechanical engineering professor Xiang Zhang Zhang, succeeded in compacting light to the extent that it could pass through 200 nm wide gaps. The research is not only significant because it could enable light to be compressed into smaller wires and lead to better optical communications, but it could represent 'an important step on the road to an optical computer', according to Rupert Oulton, a research associate in Zhang's group and lead author of the study. "This technique could give us remarkable control over light," added Oulton, "and that would spell out amazing things for the future in terms of what we could do with that light."
Similar to ic scaling, optical scaling, according to Zhang 'is the holy grail for the future of communications.' However, one goal that has alluded researchers until recently is the ability to compress light farther than its wavelength, down to the size of electron wavelengths, to force light and matter to cooperate.
The Berkeley researchers have been able to compress light beyond its wavelength using surface plasmonics, where light binds to electrons allowing it to propagate along the surface of metal. But the waves can only travel short distances along the metal before petering out.
Oulton had been working on combining plasmonics and semiconductors, and came up with an idea to achieve simultaneously strong confinement of the light and mitigate the losses. Oulton's hybrid optical fibre consists of a thin semiconductor wire placed close to a smooth sheet of silver. Simulations reveal that it enables the light to travel distances nearly 100 times greater than by conventional surface plasmonics alone.
According to the researchers, 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 hybrid system acts like a capacitor, storing energy between the wire and the 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.
Whilst the current study is theoretical, Oulton believes the construction of such a device will be straightforward. He says: "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."
Meanwhile, Oulton believes that the idea could be an important step in the eventual construction of an optical computer: "The construction of a compact optical transistor is currently 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."
Other authors of the study are Volker Sorger, Dentcho Genov and David Pile, all of Zhang's research group at UC Berkeley. Funding support for the study has come from the U.S. Air Force Office of Scientific Research, the National Science Foundation and the Department of Defense.
Adapted from material posted on ScienceDaily.