“Our method is similar to the technique used to provide the computing capabilities of computers,” said assistant professor Linyou Cao. “In computers, an electric field is used to turn electric current on or off, which corresponds to logic 1 and logic 0. With this discovery, a light may be controlled to be strong or weak, spread or focused, pointing in one direction or others by an electric field.”
Cao and his team have developed a technique that allows the refractive index for visible light in some semiconductor materials to be changed by up to 60% – two orders of magnitude better than previously achievable. Specifically, the researchers worked with thin films of molybdenum sulphide, tungsten sulphide and tungsten selenide.
“We changed the refractive index by applying charge to 2D semiconductors in the same way one would apply charge to transistors,” Cao said. “Using this technique, we achieved significant, tunable changes in the index within the red range of the visible spectrum.”
The technique allows the refractive index to be tuned by any amount up to 60%, with the greater the applied voltage, the greater the change in refractive index. And, because the same techniques used in existing computational transistor technologies are being applied, the changes are dynamic and can be made billions of times per second.
“This is only a first step,” Cao concluded. “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.”
