Unless you look closely, the colors in a pixel are indistinguishable: the eye sees a single combined, or composite, color. 

The fundamental colors in each pixel are fixed. Only their amounts can change, by adjusting the brightness of the color elements. 

That way, existing displays can reproduce most visible colors, but not all. For example, they don’t faithfully reproduce the blue hues of the sky or sea.

The new technology’s developers, Manuel Aschwanden of the Swiss Federal Institute of Technology in Zurich, Switzerland, and colleague Andreas Stemmer, plan to overcome such limitations by changing the fundamental colors themselves, not just their brightness. 

To get different colors, they used an optical trick called diffraction. When white light hits a pattern of equally spaced grooves on a surface, called a diffraction grating, the light spreads out into its component colors. The effect is similar to the way light spreads out when it goes through a prism, or reflects off a CD.

The colors coming out of a diffraction grating fan out at different angles. In Aschwanden’s setup, the grating is a rubbery, ultra-thin membrane, with one side molded into a shape resembling microscopic pleated window shades. 

It also has the feature of doubling as an “artificial muscle,” a substance that contracts in the presence of a voltage. As the membrane stretches or relaxes, the incoming light “sees” the grooves spaced closer or tighter. This changes the angles of the colors. 

A desired color can then be isolated by passing its light through a hole. The color can be changed by altering the voltage so that different parts of the spectrum pass through the hole. The artificial muscles enable the “fan” of colors to move enough that the isolated light beam can change from one end of the spectrum to the other, Aschwanden said.

To create composite colors, each pixel would use two or more diffraction gratings. This way, a display could produce the full range of visible colors, he claimed. 

Getting the full range requires a source of “true” white light to begin with, he added—rather than a mere combination of red, green and blue that looks white to human eyes, and that is typically used for white. For this purpose, he said, the technology could exploit a new generation of white lights recently developed using devices known as light-emitting diodes.

Though Aschwanden and Stemmer have so far only what they call a proof of concept, it demonstrates the technology’s feasibility, Aschwanden claimed; with enough investment, it could turn into consumer products. 

“Once you have one pixel, it doesn’t take too long to develop a new product,” he said. 

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