Nanoparticles that control the flow of light could mean a faster, cheaper internet

Imagine a window with an image etched into its surface, but when you walk around the other side, the image is entirely different.

Although it sounds impossible, that’s essentially what researchers at the Australian National University (ANU) have achieved, with tiny translucent slides that can show two separate images, at the same time, when viewed from opposite sides. .

In one experiment, for example, scientists created a slide showing the Australian continent on one side and the Sydney Opera House on the other.

The advance in the field known as “nonlinear optics” could have applications in photonic computing – using visible light or infrared instead of electric current to perform numerical calculations.

These new light-based devices could eventually lead to a faster and cheaper internet, the researchers said.

Their research was published today in Nature Photonics.

How it works?

As you may have noticed, light generally travels the same path forward and backward through a material like glass or water.

To change that, the researchers created tiny glass slides coated with cylinder-shaped nanoparticles, each particle so small that 12,000 of them could fit in the cross-section of a human hair.

ANU physicist Sergey Kruk hopes to see applications in computing.(Supplied: ANU)

Each cylinder controlled the flow of light like traffic signs directing traffic, said ANU physicist and co-author Sergey Kruk.

“We were able to introduce an asymmetry in the way light travels,” he said.

“So when the light propagates forwards and when it propagates backwards, we get completely different results.”

The technical name for these “traffic signs” is “nonlinear dielectric resonators”.

The cylinders were made of two layers of silicon and silicon nitride. Each layer had a different index of refraction – a measure of how fast light travels through a medium, and therefore the material’s light-bending ability.

The different refractive indices of air and water, for example, explain why a spoon in a glass of water looks bent.

These cylinders could be positioned to be “light” or “dark” only for the rear or front directions, or “light” or “dark” for the front and rear.

Asymmetric Parametric Image Generation
Nanoparticles have been arranged to form images ⁠—in this case, the Sydney Opera House and a map of Australia.(Provided: Sergey Kruk et al)

By arranging these four types of cylinders into patterns, Dr. Kruk and his colleagues from China, Germany and Singapore were able to form images.

“Basically, slides are made up of individual pixels,” Dr. Kruk said.

“And we can put those pixels together in any pattern you like.”

Light-Based Computing

Benjamin Eggleton, director of the Sydney Nano Institute, called the research “significant” and a “fundamental finding”.

“This is a heroic fundamental breakthrough,” said Professor Eggleton, who was not involved in the research.

The most obvious application, he said, was “nano-photonic components” for computing.

A The key element in electronic computing and the complex architecture of microchips is the diode which allows electrical current to flow in only one direction.

Photographs (top and bottom right) of opposite sides of one of the nanotechnology slides
Photographs (top and bottom right) of opposite sides of one of the nanotechnology slides.(Provided: Sergey Kruk et al)

In photonics, or light-based computing, a diode is called an isolator.

The current harvest of Insulators are relatively large and complicated, but ANU’s research could lead to much smaller and simpler designs, Professor Eggleton said.

Photonic circuits, or optical computing, have been dubbed the future of computing because they can be smaller than electronic circuits, operate at higher speeds, use less power, and generate less heat.

Many leading companies commercializing quantum computing technology rely on photonic circuits,” Professor Eggleton said.

“And on those circuits, you’ll need those insulators.”

Faster internet?

Dr. Kruk has also seen applications in photonic circuits.

This could ultimately lead to faster and cheaper internet, he said.

Two years ago, for example, researchers built a clocked photonic circuit 44.2 terabits per second on 76 kilometers of optical fibers installed between two university campuses in Melbourne.

By comparison, that’s around 1 million times faster than the average Australian broadband download speed.

Physicists are just beginning to understand how intense light interacts with the structure of materials at the nanoscale, Dr Kruk said.

At this point in technological development, we’ve gotten incredibly good at controlling electric currents, and we’re not so good at controlling beams of light.

This [research] perhaps a first convincing step towards the establishment of a very sophisticated control of the traffic of the light beams.

“[This is] similar to a very sophisticated control of the traffic of electric currents, which we began to establish perhaps in the middle of the 20th century.”

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