New observations could lead to 'twisted' light free space communication

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On 26 October, researchers published findings on newly observed challenges of using ‘twisted’ light as a form of wireless, high-capacity data transmission in urban environments that could one day render fibre-optical communication obsolete.

The work, published in Science Advances, will enable new approaches to be taken by researchers in adaptive optics to address the observed challenges, which could to lead fibre optics being replaced by free space optics as a functional mode of communication in urban environments and remote sensing systems.

The new challenges were observed over a 1.6km free space link in Erlangen, Germany. (Credit: Lavery et al.)

‘Free space optics is a solution that can potentially give us the bandwidth of fibre, but without the requirement for physical cabling,’ said lead author Dr Martin Lavery, head of the Structured Photonics Research Group at University of Glasgow. ‘This study takes vital steps forward in the journey towards high dimensional free space optics that can be a cheaper, more accessible alternative to buried fibre optics connections.’

Twisted light refers to photons that have been given optical angular momentum (OAM) after having passed through a special type of hologram. This additional property enables photons to represent more than just the conventional ones and zeroes of digital communication – the number of twists in a photon can also be interpreted as a type of value – allowing them to carry additional data and deliver much higher bandwidth communication.

‘In an age where our global data consumption is growing at an exponential rate, there is mounting pressure to discover new methods of information carrying that can keep up with the huge uptake in data,’ said Lavery. ‘A complete, working OAM 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.’

While OAM techniques have already been used to transmit data across cables, transmitting twisted light across open spaces has been significantly more challenging to date. Even simple changes in atmospheric pressures across open spaces can scatter light beams and cause the spin information to be lost.

The team of physicists, based in the UK, Germany, New Zealand and Canada, therefore examined these effects on the phase and intensity of OAM when sending light over a free space link in an urban environment, in order to assess the viability of this transfer of quantum information. 

The link, which was in Erlangen, Germany, was 1.6km in length and passed over fields and streets and close to high-rise buildings to simulate an urban environment and the atmospheric turbulence that can disrupt information transfer in space.

The field tests allowed the researchers to characterise the effects of turbulent air on OAM and revealed new challenges, such as the fragility of shaped phase fronts, that must be overcome before twisted light can be used commercially. The observations could lead to new research into adaptive optics and OAM that could overcome these difficulties when using twisted light in open spaces.

‘With these new developments, we are confident that we can now re-think our approaches to channel modelling and the requirement places on adaptive optics systems,’ commented Lavery. ‘We are getting ever closer to developing OAM communications that can be deployed in a real urban setting … We want to start a conversation about the issues that need to be addressed and how we are going to move towards the resolution.’

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