A Rewritable Screen That Stays On—Even When the Power Is Off

Let the power run down completely on your laptop, computer tablet, digital clock or other electronic devices, and the screen goes blank. Basically no power means no image.

That doesn’t have to be the case. A new optically rewritable LCD screen does not need its own power source. Plus, its images can appear in 3-D.

Once an image has been uploaded, the screen “does not need any power, of any kind,” to hold the 3-D image,” says Abhishek Srivastava, whose team of researchers developed the new screen at Hong Kong University of Science and Technology. Optics Letters published the team’s study on November 1, 2014.

So, how does the new LCD screen work?

LCD stands for liquid crystal display. Material in one or more layers of the display flow like liquid, but have a structure similar to crystals. In general, the material’s structure affects how much light it lets through. LCDs are in screens for many electronic devices.

As with other LCDs, the new screen makes pictures with pixels. Think of them as thousands of tiny dots. The more twisted the structure of the liquid crystal molecules is in a pixel, the more it lights up.

A dye in the top layer of Srivastava’s screen is sensitive to polarized blue light. A flash of that light makes the long molecular axis of the dye rotate in particular ways to form a 3-D image. Anchoring forces caused by the dye then hold the image in place until someone uploads a new one.

One advantage Srivastava notes is that the image is 3-D. Second, he says, “It needs less optical energy to update the image, and it is faster in comparison” to other LCD screens.

Beyond this, he says, “the image resolution can be extremely high,” although the LCD printer that uploads the image could be a practical limitation.

“Last but not least,” Srivastava says, “the power consumption is greatly reduced.”

The new screen could lower energy use for e-book readers, computers, power monitors and other electronic devices. The screen might also be used for rewritable credit cards or ID cards.

Other developments still need to take place before the screens make their way into computer devices, especially those with color and moving images. “Our technology is ready for the gray still image,” Srivastava says. “Hopefully full color might be available by next year.”

In any case, the study is a neat example of how physics, material science and engineering can come together to shine new light on technology.


Original journal source: J. Sun, et al. “Optically rewritable 3D liquid crystal displays.” Optics Letters. Vol. 39, p. 6209, Nov. 1, 2014.




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