"Until now, 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 Professor Michael Escuti of NC State. "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," continues Prof. Escuti.
"In previous gratings in a comparable configuration, an average of 30% of the light input is being diffracted in the desired direction," adds Xiao Xiang, lead author. "Our new grating diffracts about 75% of the light in the desired direction."
According to NC State, the advance could also make fibre-optic networks more energy efficient.
The new grating achieves the advance in angular bandwidth by integrating two layers, which are superimposed in a way that allows their optical responses to work together, explains the researchers. One layer contains molecules that are arranged at a ‘slant’ that allows it to capture 20 degrees of angular bandwidth. The second layer is arranged at a different slant, which captures an adjacent 20 degrees of angular bandwidth.
The higher efficiency stems from a smoothly varying pattern in the orientation of the liquid crystal molecules in the grating. The pattern affects the phase of the light, which is the mechanism responsible for redirecting the light.
"The next step for this work is to take the advantages of these gratings and make a new generation of augmented-reality hardware," Prof. Escuti concludes.
