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UK's BT starts trials of new hollow-core optical fibre networks

Promises lower latencies, higher power thresholds

BT has started trials of hollow-core fibre optical networks to test if they can raise fixed-line speeds and produce mobile networks with lower latencies.

The telco is performing the trials at its R&D campus in Suffolk's Adastral Park and aims to deploy up to 10km of fibre. It also intends to test the suitability of hollow-core networks for other more niche tasks, such as Quantum Key Distribution (QKD).

BT is working with American OpenRAN vendor Mavenir, as well as Lumenisity — a startup spun out from the University of Southampton that specialises in hollow-core fibre networks.

Last September, Lumenisity raised £7.5m in a funding round, with the money earmarked for further R&D and new manufacturing facilities. BT has said it will use the company's CoreSmart hollowcore fibre.

What are hollow-core fibre networks?

Normal single-mode optical cables are built from hundreds — and sometimes thousands — of strands of ultra-pure silica glass. By contrast, the hollow-core cables created by Lumenisity have an empty centre, which is surrounded by a support structure consisting of several glass membranes and an outer jacket.

As light travels faster in air than it does when pushed through solid glass, latencies are reduced. Previous tests from the University of Southampton showed a reduction of 30 per cent, although BT said it believed they could drop further, up to 50 per cent.

Tests of early hollow-core cables have also shown lower levels of attenuation (power loss caused by the refraction of light), and an ability to withstand higher power levels, making them well-suited for use with lasers.

Although hollow-core fibre has yet to see any extensive real-world deployments, its use might provide BT with an edge in the face of newfound rivalry from alternative fibre networks (commonly known as altnets).

BT has said it plans to "build like fury" in the coming years, as its Openreach subsidiary rolls out FTTP connectivity to 25 million premises by the end of 2026. Naturally, this has come with no small assistance from the British tax payer.

This spurt has been driven by an aim to meet the government's target of extending gigabit-capable connectivity to 85 per cent of UK premises by the decade's halfway point. Altnets — like Community Fibre — will contribute to that push.

If widely deployed, the performance advantages of hollow-core fibre could make Openreach's product set more appealing, particularly to mobile network customers hoping to deliver on the low-latency promises of 5G.

Openreach is the largest provider of mobile backhaul services in the UK. Although Virgin Media holds second place, in recent years we've seen a trend for carriers to work with altnets, with Three UK's financial agreement with Cityfibre among the most immediate examples.

In a statement, Professor Andrew Lord, BT’s Head of Optical Network Research, said it would be "trialling hollow core fibre... to discover the potential opportunities and benefits of deploying this technology in certain scenarios."

"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," he added. ®

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