Controlling light has potential for optical effects

Researchers from North Carolina State University (NC State) have developed a method to control light using electric fields. Based around a property of single-layer semiconducting metal compounds, the technique is able to change the direction, intensity and focus of a light beam.

Linyou Cao, co-author of a paper on the research in the American Chemical Society journal Nano Letters, explained that the technique is similar to that used to write information into computer memory. “In computers, an electric field is used to turn electric current on or off, which corresponds to logic 1 and logic 0, the basis of binary code,” he said. “With this new discovery, a light may be controlled to be strong or weak, spread or focused, pointing one direction or others by an electric field."

Photons — the basic unit of light — do not carry any electric charge, and therefore cannot be influenced directly by electric fields. Instead, the technique works by changing the optical properties of materials that interact with photons. The team used atomic monolayers of semiconducting compounds known as transition metal dichalcogenides; specifically, molybdenum sulphide, tungsten sulphide and tungsten selenide.

"We changed the refractive index by applying charge to two-dimensional semiconductor materials in the same way one would apply charge to transistors in a computer chip," Cao said. "Using this technique, we achieved significant, tunable changes in the index within the red range of the visible spectrum." Refractive index is a measure of how much material can change the direction of light passing through it.

Unlike previous techniques, which could only change refractive indices by between 0.1 and 1 per cent, the NC State team’s technique affects changes up to 60 per cent. The change is in direct proportion to the applied current, and because it is achieved by the same transistor technologies used in computing, the refractive changes can be made billions of times per second.

“We think that, just as computers have changed our way of thinking, this new technique will likely change our way of watching. For instance, it may shape a light into arbitrary patterns, which may find applications in goggle-free virtual reality lenses and projectors, the animation movie industry or camouflage," Cao said. “This is only a first step. We think we can optimise the technique to achieve even larger changes in the refractive index. And we also plan to explore whether this could work at other wavelengths in the visual spectrum."

The team is now looking for commercial partners to develop applications for their discovery.