Day of optical communications nears

a very thin semiconductor wire placed close to a smooth sheet of silver. “It’s really a very simple geometry, and I was surprised that no one had come up with it before,” Oulton said. Oulton ran computer simulations to test this idea. He found that not only could the light compress into spaces only tens of nanometers 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 center 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, Oulton said, 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. “Previously, if you wanted to transmit light at a smaller scale, you would lose a lot of energy along the path. To retain more energy, you’d have to make the scale bigger. These two things always went against each other,” Zhang said. “Now, this work shows there is the possibility to gain both of them.” Even though the current study is theoretical, the construction of such a device should be straightforward, Oulton said. 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.

Oulton believes 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. “We are pulling optics down to the length scales of electrons,” Oulton said. “And that means we can potentially do some things we have never done before.” This idea could be an important step on the road to an optical computer, a machine where all electronics are replaced with optical parts, Oulton said. 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, the researchers said.