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What is Hollow Core Fibre? BT Begins Trial to Explore ‘Revolutionary’ Potential

Ross Kelly


Hollow Core FIbre
BT hopes the trial will explore how optical fibre capabilities can be enhanced long-term.

BT has unveiled trials of a “revolutionary” new type of optical fibre, known as hollow core fibre, at its innovation labs in Adastral Park, Ipswich.

The trials are part of a collaborative project with Lumenisity, a Southampton University spin-out, and mobile vendor Mavenir.

BT researchers will carry out the trials at BT’s research and engineering campus using a 10-kilometre-long hollow core fibre cable provided by Lumenisity

The project will test a variety of use cases, including potential benefits for 5G networks and ultra-secure communications, like Quantum Key Distribution (QKD).

“We’re excited to begin trialling hollow core fibre and to discover the potential opportunities and benefits of deploying this technology in certain scenarios,” said Professor Andrew Lord, BT’s Head of Optical Network Research.

“This new type of fibre cable could play an important role in the future of the world’s communications infrastructure, heralding a step-change in capability and speed, to keep up with the demands for high-speed, low latency communications driven by 5G networks, streaming, and more,” Lord added.

What is hollow core fibre?

At present, networks across the world run on single-mode optical fibre which consists of solid strands of glass. The glass in these cables quickly carries information over long distances by channelling light from laser transmitters through the glass strands.

However, the nature of glass means that this light travels marginally slower inside the fibre than it would in air.

This new fibre has an air-filled central core, with an outer ring of glass, which guides the laser beam whilst maintaining the signal speed at very close to the ultimate speed of light.

BT said research into hollow core fibre presents an opportunity to explore how optical fibre capabilities can be enhanced in future.

Long-term, it is believed hollow core fibre could reduce signal delay caused by light travelling through glass by anywhere up to 50%.

The reduction in the delay of the light provided by hollow core fibre could potentially enable a variety of benefits, from high-frequency trading to lowering mobile network costs.


Working with Mavenir, BT said it has shown that using hollow core can increase the distance between street antennas and the back-end processing in exchanges.

Due to the low latencies, use of hollow core in the Radio Access Network (RAN) could also reduce mobile network costs by allowing more 5G antennas to be served from a single exchange or cabinet.

“The ability to extend the reach of fibre connected radios only further demonstrates the power of Open RAN and its Eco System,” according to John Baker, Mavenir’s senior VP of business development.

“This improvement will significantly increase the number of use cases that can be served from containerised cloud based Open RAN solution,” he added.

Ross Kelly

Staff Writer

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