Light Efficiency in LC Projectors Nearly Doubled

A new polarization technology that nearly doubles the energy efficiency of liquid crystal (LC) projectors could result in smaller, lower-cost devices with longer battery lives and significantly lower heat levels.

All LC projectors use polarized light. Efficient light sources such as LEDs, however, produce unpolarized light. As a result, the light generated by LEDs must be converted into polarized light before it can be used.

Conventional methods for polarizing light involve passing the unpolarized light through a polarizing filter, but this process wastes more than 50 percent of the originally generated light. The bulk of the “lost” light is converted into heat, which is why traditional projectors require noisy cooling fans.

Researchers used new polarization grating-polarization conversion system technology to create a small picoprojector, seen here, which could be embedded in a smartphone, tablet or other device. (Image: ImagineOptix Corp.)

But now new technology developed at North Carolina State University enables approximately 90 percent of the unpolarized light to be polarized and, therefore, used by the projector. The research team demonstrated the technology in a small picoprojector it created.

The small single-unit assembly is composed of four immobile parts, which can be embedded in a smartphone, tablet or other device. The unpolarized light beam first passes though an array of lenses, which focus the light into a grid of spots. Next, the light passes through a polarization grating, which consists of a thin layer of LC material on a glass plate. The grating separates the spots of light into pairs with opposite polarizations. The light then passes through a louvered wave plate — a collection of clear, patterned plates that give the light beams the same polarization. Finally, a second array of lenses focuses the spots of light back into a single uniform beam of light.

Researchers have developed new technology to convert unpolarized light into polarized light, which makes projectors that use liquid crystal technology almost twice as energy efficient. The technology, seen here, is called a polarization grating-polarization conversion system.

“This technology, which we call a polarization grating-polarization conversion system, will significantly improve the energy efficiency of LC projectors," said Dr. Michael Escuti, an associate professor of electrical and computer engineering at the university. "The commercial implications are broad-reaching. Projectors that rely on batteries will be able to run for almost twice as long. And LC projectors of all kinds can be made twice as bright but use the same amount of power that they do now."

The new technology will also reduce the need for loud cooling fans and enable more compact designs because approximately only 10 percent of the unpolarized light is converted into heat — as opposed to the more than 50 percent light loss that stems from using conventional polarization filters.

The research was funded by ImagineOptix, a startup company co-founded by Escuti and Jason Kekas. It appeared online July 10 in Applied Optics.

For more information, visit: www.ncsu.edu