North Carolina State University engineering and physics researchers have created a new technology that steers light in a way that results in more light input and greater efficiency. This development is promising for even more immersive augmented reality (AR).

This photo shows a one-inch diameter Bragg polarization grating diffracts white light from an LED flashlight onto a screen placed nearby. Source: Michael Escuti, NC State UniversityThis photo shows a one-inch diameter Bragg polarization grating diffracts white light from an LED flashlight onto a screen placed nearby. Source: Michael Escuti, NC State University

In the past diffraction gratings have stopped development of this new technology. Diffraction gratings are used to manipulate light in everything electronics, including AR displays.

"Until now, state-of-the-art diffraction gratings configured to steer visible light to large angles have had an angular acceptance range, or bandwidth, of about 20 degrees, meaning that the light source has to be directed into the grating within an arc of 20 degrees," says Michael Escuti, a professor of electrical and computer engineering at NC State and corresponding author of a paper on the work. "We've developed a new grating that expands that window to 40 degrees, allowing light to enter the grating from a wider range of input angles. The practical effect of this — in augmented-reality displays, for example — would be that users would have a greater field of view; the experience would be more immersive."

The newest grating is significantly more efficient than the methods used in the past.

"In previous gratings in a comparable configuration, an average of 30 percent of the light input is being diffracted in the desired direction," says Xiao Xiang, a Ph.D. student at NC State and lead author of the paper. "Our new grating diffracts about 75 percent of the light in the desired direction."

As well as improving the overall quality of VR systems, the new developments could also make the fiber-optic networks more energy efficient.

The newest grating uses two integrated layers that are attached in a way that allows optical responses to work together. One layer has molecules arranged at a “slant” so it was able to capture 20 degrees of angular bandwidth. The other layer has a different slant that captures the adjacent 20 degrees of angular bandwidth.

The high efficiency stems from a smoothly varying pattern in the orientation of liquid crystal molecules in the grating. The pattern is what affects the phase of the light. This is the mechanism that is responsible for directing where the light goes.

"The next step for this work is to take the advantages of these gratings and make a new generation of augmented-reality hardware," Escuti says.

The paper on this technology was published in Scientific Reports.