Shape of things to comeDay of optical communications nears

Published 31 July 2008

New technique to compress light could open doors for optical communications; scientists at the University of California-Berkeley have devised a way to squeeze light into tighter spaces than ever thought possible, opening doors to new technology in the fields of optical communications, miniature lasers, and optical computers

Optics researchers succeeded previously in passing light through gaps 200 nanometers wide, about 400 times smaller than the width of a human hair. A group of UC Berkeley researchers led by mechanical engineering professor Xiang Zhang devised a way to confine light in incredibly small spaces on the order of 10 nanometers, only five times the width of a single piece of DNA and more than 100 times thinner than current optical fibers. “This technique could give us remarkable control over light,” said Rupert Oulton, research associate in Zhang’s group and lead author of the study, “and that would spell out amazing things for the future in terms of what we could do with that light.”

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, said Zhang, senior author of the study, which will be published in the August issue of Nature Photonics and is currently available online. “There has been a lot of interest in scaling down optical devices,” Zhang said. “It’s the holy grail for the future of communications.” Not only would compressed light make possible smaller optical fibers, but it could lead to huge advances in the field of optical computing. Many researchers want to link electronics and optics, but light and matter make strange bedfellows, Oulton said, because their characteristic sizes are on vastly different scales. However, confining light can actually alter the fundamental interaction between light and matter. Ideally, optics researchers would like to cram light down to the size of electron wavelengths to force light and matter to cooperate.

The researchers run into a brick wall, however, when it comes to compressing light farther than its wavelength. Light doesn’t want to stay inside a space that small, Oulton said. They have squished light beyond these limits using surface plasmonics, where light binds to electrons allowing it to propagate along the surface of metal. The waves, however, can only travel short distances along the metal before petering out. Oulton had been working on combining plasmonics and semiconductors, where these losses are even more pronounced, when he came up with an idea to achieve simultaneously strong confinement of the light and mitigate the losses. His theoretical “hybrid” optical fiber consists of