North Carolina State University (NC State) researchers have developed a new technology to steer light that attains greater light input and efficiency. This development may lead to augmented reality display systems boasting next-gen immersion.
Diffraction gratings are used to handle light in many applications ranging from fiber-optic commination systems to electronic 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, professor of electrical and computer engineering at NC State, and corresponding author of the research. “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,” Escuti adds.
According to NC State Ph.D. student Xiao Xiang, and lead author of the research, 30 percent of light input is being diffracted in the intended direction on average with previous gratings. When in a comparable configuration, the team’s new grating system increases that figure to 75 percent.
Angular bandwidth is advanced by integrating two layers, which are superimposed in a special configuration that promotes cooperative optical responses. The first layer captures 20 degrees of angular bandwidth with its molecules arranged in a “slant.” The second layer carries a different slant arrangement, and captures an adjacent 20 degrees of angular bandwidth.
The liquid crystal molecules’ smooth pattern variation creates the higher efficiency, since the orientation affects the phase of light—the mechanism in charge of light redirection.
“The next step for this work is to take the advantages of these gratings and make a new generation of augmented reality hardware,” says Escuti.
Check out the paper, “Bragg polarization gratings for wide angular bandwidth and high efficiency at steep deflection angles,” published in Scientific Reports, to learn more.