Light-polarizing system could mean big things for tiny projectors
By Ben Coxworth
July 16, 2012
Liquid crystal video projectors could be getting smaller, more energy-efficient, and less expensive. Currently, such devices require polarized light for the projection of images. Unfortunately, conventional LEDs only produce unpolarized light. While an optical filter is typically used to polarize it, the polarization process wastes over 50 percent of the original light, converting it into heat instead of allowing it to pass through. That heat, in turn, must be dissipated using a noisy, power-consuming fan. Now, however, researchers have created a new polarizing system that allows almost 90 percent of the LED light to be converted to usable, polarized light.
Developed by a team from North Carolina State University and ImagineOptix Corporation, the system consists of a single unit, which is itself made up of four parts – an array of lenses, a polarization grating, a louvered wave plate, and a second array of lenses.
When a single beam of unpolarized light passes through the first lens array, it gets split into a grid of focused spots. Those spots then pass through the grating, which is a glass plate coated with a thin layer of liquid crystal material. This causes the spots to be grouped into pairs, in which each of the two spots are oppositely polarized.
All of those pairs then pass through the louvered wave plate – this is actually a series of clear, patterned optical plates that “corrects” the difference between the spots, so that they all have the same polarization. The second array of lenses then combines all the spots back into a single beam of now-polarized light, for use by the projector.
“This technology, which we call a polarization grating-polarization conversion system (PGPCS), will significantly improve the energy efficiency of LC [liquid crystal] projectors,” said NC State’s Dr. Michael Escuti. “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 the projectors won’t require as much in the way of cooling fans, it would follow that they could also be made more compact. Already, the team has used the PGPCS technology to built a prototype picoprojector, that could conceivably be incorporated into a smartphone or tablet. A paper on the research was published last week in the journal Applied Optics.
Source: North Carolina State University
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