Nanotechnology that bosses light around to make one-way images

The translucent slide is less than a thousandth of a millimetre thick. It’s not much bigger in width or length – about a tenth of a millimetre on each side. When infrared light shines on it from one direction, it lights up blue with a picture of the Sydney Opera House. But when it shines the opposite way, the image changes, becoming a tiny map of Australia.

According to the international team of researchers which made this slide, it’s much more than a microscopic curio. It represents an optical technology that could one day speed up our internet and communications – all because of the way it manipulates light.

The slide is a carefully arranged two-dimensional array of nanoparticles, each 12,000 times smaller than the width of a human hair.

“They’re made of two materials: silicon and silicon nitride,” says Dr Sergey Kruk, a researcher at the Australian National University’s Nonlinear Physics Centre, and lead author of a paper describing the research, which is published in Nature Photonics.

“[It’s] essentially the same materials that we use to produce computer chips – but these are not electronics. These are photonic.

“They don’t control electricity, they control light.”

The slides are made in a similar way to computer chips.

While the Opera House and Australia images are neat, the real novelty of the panel is its ability to show two completely different images based on the direction of light it’s receiving.

“The particles control the flow of light like road signs control traffic on a busy road by manipulating the direction in which light can, or can’t, travel,” says Kruk.

“Some particles allow light to flow from left to right only, others from right to left or the pathway might be blocked in either direction.”

This ability to block and allow light could be used in a number of different places.

“We are the thinking that it will be really great for controlling light in a way similar to how we control electricity,” says Kruk.

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Co-author Dr Lei Wang, a researcher from Southeast University in China, says: “In real-world applications these nanoparticles can be assembled into complex systems that would control the flow of light in a useful manner – such as in next-generation communications infrastructure.”

Kruk adds: “We exchange enormous amounts of information with the help of light. When you make a video call, say, from Australia to Europe, your voice and image get converted into short pulses of light that travel thousands of kilometres through an optical fibre over the continents and oceans.

“Unfortunately, when we use current light-based technologies to exchange information, a lot of parasitic effects might occur. Light might get scattered or reflected, which compromises your communication.

“By ensuring light flows exactly where it needs to flow, we would resolve many issues with current technologies.”

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