Diffraction gratings are used to manipulate light in everything from electronic displays to fiber-optic communication technologies. 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. A new grating was developed that expands that window to 40 degrees, allowing light to enter the grating from a wider range of input angles.
The liquid crystal (LC) polymer Bragg polarization grating (PG) for steering light allows for more light input and greater efficiency — a development that holds promise for creating more immersive augmented-reality display systems in which users would have a greater field of view.
In previous gratings in a comparable configuration, an average of 30 percent of the light input is being diffracted in the desired direction. The new grating diffracts about 75 percent of the light in the desired direction. This advance could also make fiber-optic networks more energy-efficient.
The grating achieves the advance in angular bandwidth by integrating two layers that are superimposed in a way that allows their optical responses to work together. 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.