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Breakthrough Airguide Photonics research on the transmission of high-power laser light over long distances published in prestigious journal

Published: 30 May 2022
Illustration
Hollow-core fibres with record-low propagation losses

Breakthrough research by Southampton's Airguide Photonics programme into the development of hollow-core fibres with record-low propagation losses and exceptional power-handling properties has been published in the prestigious Nature Photonics journal.

The research focuses on the transmission of kilowatt power laser beams over kilometre-scale fibre lengths, while preserving a practically ideal, single-mode beam quality.

This transmission is impossible in conventional optical fibres as the very high laser intensity interacts with the glass and quickly compromises the beam integrity, meaning single-mode kilowatt power levels can typically only be transmitted over a few tens of metres in conventional fibres.

The paper Kilowatt-average-power single-mode laser light transmission over kilometre-scale hollow-core fibre uses nested antiresonant nodeless fibres (NANFs) that have been under development at Southampton's Optoelectronics Research Centre (ORC) for several years.

Southampton's Dr Hans Christian Mulvad, who led the high-power transmission experiments, said: "The enabling technology behind our breakthrough is the development of hollow core fibres with record-low propagation losses. Since the laser beam propagates within a hollow core, instead of a solid glass core as in a conventional fibre, the detrimental non-linear interactions with the glass are virtually eliminated. This allows very high-power levels to be transmitted without any detrimental effect on the beam quality.

"Also, the low loss is essential for an energy efficient transmission, allowing the bulk of the laser source power to be delivered at the fibre output even after a kilometre.

"Recent breakthroughs have seen the propagation loss reduced to record-low levels, comparable to established fibres at near-infrared telecom wavelengths and even lower in the visible range of the spectrum. It is one of these record-low loss NANFs, operating in the near-infrared, which is employed in this work.

"This fibre enabled us to demonstrate transmission of a kilowatt single-mode laser beam over one kilometre, with a total power loss of only 20 per cent. We have also performed detailed numerical simulations showing that the fibre may support even higher power levels and longer transmission lengths, underlining the superior performance of NANF over conventional fibres for single-mode power delivery."

The innovative research has the potential to be used in a range of applications in industry, as well as lead to new scientific opportunities.

Hans Christian added: "A single-mode, diffraction-limited beam has essential properties: it can be focused to the smallest possible spot size, or it can be transmitted in free-space with the least divergence. As a consequence, single-mode lasers are already widely used in industry where they enable high-precision manufacturing, remote processing, and 'wobble-welding' for battery production.

"However, until now, the very limited power delivery range of conventional fibres has implied close proximity between the laser source and workpiece. The advent of low-loss NANF and long-range power delivery may simplify laser manufacturing in large factories by separating lasers and the required water-cooling from the work area, enabling the sharing and distribution of laser power.

"It could also enable single-mode power delivery to distant and hazardous locations supporting applications such as the remote optical powering of electrical devices, laser processing tasks in radioactive environments, or even underground/undersea drilling.

"NANFs present fundamentally new possibilities relative to conventional fibres and we believe that new and surprising applications may emerge."

The research team is now planning to extend their work into demonstrating even higher power levels and longer fibre lengths, engaging with industrial partners to bring the technology closer to real-life applications.

Hans Christian added: "We are very excited to have our work accepted for publication in such a highly regarded and widely read journal as Nature Photonics.

"Our paper is the result of significant efforts and contributions from all members of the team, and finally having it published in this journal is a highly rewarding experience.

"We are looking forward to seeing how it will be received by a wider audience and are hoping it will lead to interest and useful feedback from both industry and other researchers in the community to help us improve and further advance our work, possibly leading to new collaborations and interesting new research directions."

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