Researchers from the University of Michigan say that a new type of colour filter could significantly increase the energy efficiency of liquid-crystal displays (LCDs).
The best LCDs today only emit about eight per cent of the light produced by their back lights. This means that they drain batteries in portable electronics and ramp up electricity bills in businesses and homes.
Normally, LCDs use several layers of optical devices to colourise, polarise, and shutter light from a back light, and inefficiencies emerge at every step. Now researchers at the university have made an optical film that promises to boost the overall efficiency of LCDs by more than 400 per cent--so that 36 per cent of light makes it through. The film colours and polarises the light that passes through an LCD more efficiently than conventional components can.
The colour filter is a three-layer sandwich of an insulating material in between two layers of aluminium; the entire stack is less than 200 nanometres thick and is etched with periodic slits, like a grate. The distance between the slits and their width determines the colour they'll produce when illuminated by a white back light. This is because the grating patterns are on the same size scale as the wavelength of visible light.
In a research paper published in the journal Nature Communications, the Michigan researchers, led by L. Jay Guo, professor of electrical engineering and computer sciences, show that they can make a rainbow of colours using such a filter.
As well as being more efficient, the filter is also simpler to make than current LCDs, says Guo. It is possible to create red, blue, and green sub-pixels by patterning gratings of differing widths side by side in a single manufacturing step. Conventional LCDs use pigments to define the red, green, and blue sub-pixels that filter light from the back light.
The Michigan researchers are now focused on making the filters "production worthy," or compatible with the machinery used to mass-produce displays, says Guo.