Novel way to transmit data via laser light

Much of modern life depends on the coding of information onto a means of delivering it. A common method is to encode data in laser light and send it through optic cables. The increasing demand for more information capacity demands that we constantly find better ways of encoding it.

Researchers at Aalto University’s Department of Applied Physics found a new way to create tiny hurricanes of light — known to scientists as vortices — that can carry information. The method is based on manipulating metallic nanoparticles that interact with an electric field. The design method, belonging to a class of geometries known as quasicrystals, was thought up by Doctoral Researcher Kristian Arjas and experimentally realised by Doctoral Researcher Jani Taskinen, both from Professor Päivi Törmä’s Quantum Dynamics group. The discovery represents a fundamental step forward in physics and carries the potential for entirely new ways of transmitting information.

Half order and chaos

A vortex is in this case like a hurricane that occurs in a beam of light, where a calm and dark centre is surrounded by a ring of bright light. Just like the eye of a hurricane is calm due to the winds around it blowing in different directions, the eye of the vortex is dark due to the electric field of bright light pointing to different directions on different sides of the beam.

Previous physics research has connected what kind of vortices can appear with how much symmetry there is in the structure that produces them. For example, if particles in the nanoscale are arranged in squares, the produced light has a single vortex; hexagons produce a double vortex and so on. More complex vortices require at least octagonal shapes.

Now Arjas, Taskinen and the team have unlocked a method for creating geometric shapes that theoretically support any kind of vortex.

“This research is on the relationship between the symmetry and the rotationality of the vortex, ie, what kinds of vortices can we generate with what kinds of symmetries. Our quasicrystal design is halfway between order and chaos,” Törmä said.

Good vibrations

In their study, the group manipulated 100,000 metallic nanoparticles, each roughly the size of a 100th of a single strand of human hair, to create their unique design. The key lay in finding where the particles interacted with the desired electric field the least instead of the most.

“An electrical field has hotspots of high vibration and spots where it is essentially dead. We introduced particles into the dead spots, which shut down everything else and allowed us to select the field with the most interesting properties for applications,” Taskinen said.

Image caption: The quasicrystal design enables theoretically any kind of vortex. Image credit: Jani Taskinen/Aalto University.

The discovery opens a wealth of future research in the very active field of topological study of light. It also represents the early steps for a powerful way of transmitting information in domains where light is needed to send encoded information, including telecommunications.

“We could, for example, send these vortices down optic fibre cables and unpack them at the destination. This would allow us to store our information into a much smaller space and transmit much more information at once. An optimistic guess for how much would be 8 to 16 times the information we can now deliver over optic fibre,” Arjas said.

Practical applications and scalability of the team’s design are likely to take years of engineering. The Quantum Dynamics group at Aalto, however, have their hands full with research into superconductivity and improving organic LEDs.

The group used the OtaNano research infrastructure for nano-, micro- and quantum technologies in their pioneering study.

The research was published early November in Nature Communications.

Top image caption: Tiny hurricanes of light could be used to transmit information. Image credit: Aalto University.