New way to control light with electric fields

Researchers from North Carolina State University have discovered a technique for controlling light with electric fields.

"Our method is similar to the technique used to provide the computing capabilities of computers," says Linyou Cao, an assistant professor of materials science and engineering at NC State and corresponding author of a paper on the work. "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. 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. 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."

Controlling light with electric fields is difficult. Photons, the basic units of light, are neutral -- they have no charge, so they usually do not respond to electric fields. Instead, light may be controlled by tuning the refractive index of materials. Refractive index refers to the way materials reflect, transmit, scatter and absorb light. The more one can control a material's refractive index, the more control you have over the light that interacts with that material.

"Unfortunately, it is very difficult to tune refractive index with electric fields," Cao says. "Previous techniques could only change the index for visible light by between 0.1 and 1 percent at the maximum."

Cao and his collaborators have developed a technique that allows them to change the refractive index for visible light in some semiconductor materials by 60 percent -- two orders of magnitude better than previous results. The researchers worked with a class of atomically thin semiconductor materials called transition metal dichalcogenide monolayers. Specifically, they worked with thin films of molybdenum sulfide, tungsten sulfide and tungsten selenide.

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