Shining New Light On Optical Computing

Practical optical computing is like unicorn hunting to researchers. It promises all sorts of wonderful effects like superfast speeds and less waste heat. But messing about with photons instead of electrons posed challenges that seemed insurmountable, especially the limit on the size of the conduit needed to carry it. Researchers at the University of California at Berkeley have come up with a way to at least partially overcome this hurdle by compressing light to fit inside spaces formerly thought impossible.

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, [Berkeley research assistant]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. But the waves 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 a very thin semiconductor wire placed close to a smooth sheet of silver.

Using their new technique, the researchers say they can compress the size of a light beam to fit through a gap only ten nanometers wide. As you bring the scale of optical signals down to the size of electrons moving through a wire, you get closer to making a practical compact optical computer a possibility.