All LC projectors utilise polarised light. However, researchers say that efficient light sources, such as LEDs, produce unpolarised light. As a result, the light generated by LEDs has to be converted into polarised light before it can be used.
According to NC State researchers, the most common method of polarising light involves passing the unpolarised light through a polarizing filter. They claim that this process wastes more than 50% of the originally generated light, with the bulk of the "lost" light being turned into heat. This is a major reason that projectors get hot and have noisy cooling fans.
The new technology, demonstrated in a small pico projector and developed at NC State, allows approximately 90 percent of the unpolarised light to be polarised and, therefore, used by the projector
"This technology, which we call a polarisation grating-polarisation conversion system (PGPCS), will significantly improve the energy efficiency of LC projectors," said Dr. Michael Escuti, co-author of a paper describing the research and an associate professor of electrical and computer engineering at NC State.
"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."
Because only approximately 10 percent of the unpolarised light is converted into heat – as opposed to the more than 50 percent light loss that stems from using conventional polarisation filters – the new technology will also reduce the need for loud cooling fans and enable more compact designs.
The technology is a small single-unit assembly composed of four immobile parts. A beam of unpolarised light first passes through an array of lenses, which focus the light into a grid of spots. The light then passes through a polarisation grating, which consists of a thin layer of liquid crystal material on a glass plate. The polarisation grating separates the spots of light into pairs, which have opposite polarisations. The light then passes through a louvered wave plate, which is a collection of clear, patterned plates that gives the beams of light the same polarisation. Finally, a second array of lenses focuses the spots of light back into a single, uniform beam of light.
The paper, "Efficient and monolithic polarization conversion system based on a polarization grating," was published July 10 in Applied Optics. The paper was co-authored by Drs. Jihwan Kim and Ravi Komanduri, postdoctoral researchers at NC State; Kristopher Lawler, a research associate at NC State; Jason Kekas, of ImagineOptix Corp.; and Escuti. The research was funded by ImagineOptix, a start-up company co-founded by Escuti and Kekas.