Successful ‘twisted’ light tests mark progress towards OAM communications in cities

Successful ‘twisted’ light tests mark progress towards OAM communications in cities

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‘Twisted’ light could soon be used in a form of wireless high-capacity data transmission that may eventually make fibre-optics obsolete.

A new report penned by a team of physicists hailing from the UK, Germany, New Zealand and Canada describes how ‘optical angular momentum’ (OAM) could overcome issues with using twisted light across open spaces.

The report, which appeared in the journal Science Advances, explains that scientists can ‘twist’ photons - individual particles of light - by passing them through a special type of hologram, which isn't  too different to what you’d find on a credit card. This gives the photons a twist known as optical angular momentum.

Conventional digital communications use photons as ones and zeroes to carry information, but the number of intertwined twists in the photons means they can carry additional data, which is similar to adding letters alongside the ones and zeroes.

Because the twisted photons can carry additional information, this means that optical angular momentum can create much higher-bandwidth communications technology.

Optical angular momentum techniques have already been used to transmit data across cables. However, scientists have found it significantly more problematic to transmit twisted light across open spaces so far. Even the slightest changes in atmospheric pressures across open spaces can scatter light beams and cause information to be lost.

The researchers examined the effects on the phase and intensity of OAM carrying light over a real link in an urban environment to assess the viability of these modes of quantum information transfer.  

The test was carried out in an open space that measured 1.6km in length, with information passing over fields and streets and close to high-rise buildings in a bid to accurately simulate an urban environment and atmospheric turbulence.

The test revealed new challenges that need to be overcome before the systems can be made commercially available. It also fully characterised the effects of turbulent air on the phase of the structured light propagating over links of this length.

Dr. Martin Lavery, head of the Structured Photonics Research Group at University of Glasgow and the lead author on the research paper, said there is a real need to discover new methods of carrying information that can keep up with the huge uptake in data across the world.

“A complete, working optical angular momentum communications system capable of transmitting data wirelessly across free space has the potential to transform online access for developing countries, defence systems and cities around the world,” he commented.

“Free space optics is a solution that can potentially give us the bandwidth of fibre, but without the requirement for physical cabling.”

Dr Lavery added that the study marks significant progress towards realising cheaper and more accessible high-dimensional free space optics.

He believes the team can now re-think its approaches to channel modelling and the requirement placed on adaptive optics systems.

The work was carried out in partnership with researchers from the Max Planck Institute for the Science of Light and Institute of Optics, and the Universities of Otago, Ottawa and Rochester.


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