Swiss develop optical circuit based on silver atom

Swiss scientists have created a digital circuit at the atomic level. It is an optical modulator that can function on the basis of a single silver atom. The switch does not yet work quickly and is difficult to make, but the scientists want to improve that.

The research team of the Eidgenössische Technische Hochschule in Zurich speaks of the smallest integrated optical switch to date. The modulator is even smaller than the wavelength of the light it uses, something team leader Juerg Leuthold, a professor of Photonics and Communication, never thought possible until recently.

The modulator consists of two small plates, one of silver and one of platinum. They are placed on an optical light path made of silicon, where they are only a few nanometers apart. The silver plate also has a protrusion right next to the platinum, leaving a tiny passage. The researchers then direct light with a fiberglass to the passageway on the light path.

Under the influence of light, plasmons are formed at the interface of the silver and platinum. The collective vibration of the electrons oscillates at the frequency of light, but with a much smaller amplitude. This allows the electron oscillations to pass through the small passage, and at the other end can be converted back into optical signals.

In order for the system to switch, a voltage must be applied to the silver plate. This causes a single silver atom, or at most a few atoms, to move towards the tip of the passageway and connect the silver and platinum plate together, allowing an electric current to pass through. As soon as the voltage is reduced, the atom returns and the passage is clear again for the plasmons. This creates an on and off switch that can be used millions of times by subsequent researchers.

“This allows us to make a digital circuit, like a transistor,” says Leuthold. The switch works at room temperature but still functions slowly for a modulator: at megahertz level or lower. In addition, the production of the system succeeds only one in six times. The team now wants to work towards terahertz-level use and improve the lithography process. A practical elaboration should be ready within a few years.

The research of the ETH Zurich has been published in Nano Letters under the heading Atomic Scale Plasmonic Switch.