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Energy-efficient polarising filter yields brighter images

Posted: 24 Nov 2014     Print Version  Bookmark and Share

Keywords:University of Utah  polarising filter  mobile device  LCD 

A team of engineers from the University of Utah has come up with a polarising filter that lets in more light, boasting potential to be used in manufacturing mobile device displays that last much longer on a single battery charge and cameras that can shoot in dim light. The electrical and computer engineering researchers developed the filter by etching a silicon wafer with nanoscale pillars and holes using a focused gallium-ion beam.

Polarisers are indispensable in digital photography and LCDs, but they block enormous amounts of light, wasting energy and making it more difficult to photograph in low light.

The novel concept in light filtering from the University of Utah can perform the same function as a standard polariser but allows up to nearly 30 per cent more light to pass through, said Rajesh Menon, an electrical and computer engineering associate professor form the university. The study is being published in November's issue of Optica, a recent journal from The Optical Society.

Rajesh Menon

Menon holds up a piece of silicon that has been etched with microscopic pillars and holes to create a polarised filter. He leads a team of researchers that developed a polariser that can allow more light to pass through than conventional polarisers.

Sunlight as well as most ambient light emits half of its energy as light polarised along a horizontal axis and the other half along a vertical axis. A polariser typically allows only half of the light to pass because it's permitting either the horizontal or vertical energy to go through, but not both. Meanwhile, the other half is reflected back or absorbed, but the resulting image is much darker. Polarisers are widely used by photographers, for example, to reduce glare in the image. They also are used in LCDs to regulate what light passes through to create images on the screen.

Research team that developed the innovative polarising filter

(left to right) Menon; graduate student Bing Shen; and Utah Nanofab senior optical engineer, Randy Polson, are part of the research team that developed the polariser, which could lead to LCDs for smartphones and tablets that last longer on a battery charge and cameras that can take better pictures at low light.

"When you take a picture and put the polarised filter on, you are trying to get rid of glare," stated Menon. "But most polarisers will eliminate anywhere from to 60 to 70 per cent of the light. You can see it with your eyes."

Yet with Menon's polariser, much of the light that normally is reflected back is instead converted to the desired polarised state, he noted. The researchers have been able to pass through about 74 per cent of the light, though their goal is to eventually allow all of the light to pass through.

LCDs on devices such as smartphones and tablets have two polarisers that ultimately throw away most of the light when working with the liquid crystal display. "If one can increase that energy efficiency, that is a huge increase on the battery life of your display. Or you can make your display brighter," Menon said.

Menon's team validated their concept using a polariser that is only 20 x 20um and tested with only infrared light. But they plan to increase the size of the filter, use it with visible light, and figure out a way to make it more cost effective to manufacture. Menon said the first marketable applications of this technology could be available in five to 10 years. The technology also could be a boon for photographers who want to bring out more detail in their pictures while shooting in low-light situations and for scientists using microscopes and telescopes to visualise obscure phenomenon.

The study was funded by NASA, the U.S. Department of Energy and the Utah Science Technology and Research economic development initiative (USTAR). The paper was co-authored by University of Utah electrical engineering graduate student Bing Shen, along with graduate student Peng Wang and Utah Nanofab senior optical engineer Randy Polson.

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