We’re closer than ever to the kind of see-through projection screens that are a staple in science-fiction portrayals of the future.
Transparent screens could be the key to a lot of “augmented reality” applications, from shop window displays to smart glasses and car windshields (imagine if your GPS lit up, not on a tiny screen above you, but right in front of you).
We already have some ways to project images without totally blotting out a viewer’s vision. Take Google Glass, which doesn’t actually project images onto glass itself; it uses a miniature projector and a prism to focus an image directly on the retina of the person wearing the device. Other devices use organic light-emitting diodes, or OLEDs, sandwiched between two glass layers. OLEDs are a thin film that produces light in response to an electrical current.
Now, researchers at the Massachusetts Institute of Technology have come up with another option that they say is cheaper than current methods, using specially designed nanoparticles that interact with a single color on the visible spectrum. They describe the design in a paper published in the journal Nature Communications on Tuesday.
“This approach has attractive features including simplicity, wide viewing angle, scalability to large sizes and low cost,” MIT researcher Chia Wei Hsu and colleagues wrote.
The team made their transparent display by embedding silver-based nanoparticles just 62 nanometers wide (for comparison, a human hair is around 90,000 nanometers wide) in diameter into a transparent polymer sheet just two-hundredths of an inch thick. Ambient or projected light is made up of a variety of colors, and usually if something is transparent, it’s because all of those colors of light pass right on through the material. But the tiny nanoparticles the team designed are able to intercept blue light and bounce it back.
The result is a clear screen that allows all colors of light to pass through except blue, so you can project whatever monochromatic blue design you like.
"We are excited about our transparent display, but we are already thinking of the next challenges," senior author Marin Soljacic said in a statement. "In principle, we could implement a full-color display by embedding three types of nanoparticles, each scattering selectively red, green and blue.”
It may also be possible to design a single nanoparticle with multiple resonances, but with that design it might be more difficult to maintain the transparency of the screen.
"Think of all the surfaces covered by windows," Soljacic says. "It is a lot of space that is not fully used: When I stroll downtown and look at the glass of skyscrapers at night, or at the subway windows, I imagine all that we can project on them."
SOURCE: Hsu et al. “Transparent displays enabled by resonant nanoparticle scattering.” Nature Communications, Jan. 21, 2014.