BT advances hollow core fibre research with world’s first trial of quantum-secure comms

Three months after beginning trials of a potentially “revolutionary” optical fibre technology, BT claims to have achieved a milestone in the world’s first trial of quantum key distribution (QKD) over hollow core fibre cable.

Even as the current generation of fibre-optic networks is being marketed as “future-proofing” broadband communications, BT said it was looking ahead and exploring how the capabilities of optical fibre could be enhanced with the potential to reduce the latency, or signal delay, by up to 50%, surmounting the limitations of traditional fibre.

Networks across the world currently run on single-mode optical fibre, which consists of solid strands of glass. By contrast, the new type of network cable has a hollow, air-filled centre that runs the entire length of the cable with an outer ring of glass to guide the laser beam while maintaining the signal speed at very close to the ultimate speed of light.

BT claimed the reduction in the delay of the light provided by hollow-core fibre would enable various benefits, ranging from high-frequency trading to lowering mobile network costs.

Working with technology company Mavenir, BT said it had shown that using hollow-core fibre could increase the distance between street antennas and back-end processing in exchanges. It will test a variety of use cases, including potential benefits for 5G networks and ultra-secure communications, such as quantum key distribution.

The current trial involves conducting a method of ultra-secure communication and is based around a 6km cable provided by Southampton University spin-out company Lumenisity.

BT researchers said they had successfully operated a QKD system provided on loan by the EU OpenQKD project using a Lumenisity CoreSmart cable. The trial revealed potential benefits such as reduced latency and no appreciable crosstalk, which is the effect of a transmitted signal interfering with the transmission of another signal.

In QKD systems, quantum light is transmitted on a single photon channel, traditionally necessitating use of a separate fibre, due to crosstalk, an effect that causes the light from high-speed data channels to spread their wavelengths, interfering with a quantum signal carried over the same fibre, as the change in frequency can cause channels of light to leak into other channels.

“This is an exciting milestone for BT. We’ve proven a range of benefits that can be realised by deploying hollow core fibre for quantum-secure communication”

Given hollow core fibre doesn’t have internal material, there is less light scattering and less crosstalk between channels, even at a single photon level. BT said this clearer separation made it easier to deliver both a high-speed encrypted data stream and the faint quantum signal that carries the encryption key over the same fibre.

Lumenisity’s cable also demonstrated further benefits for the deployment of QKD as it meant commercial telecommunications equipment would not need to be optimised to send a data-encrypted key. This is regarded as critically important because the equipment can be used normally without modifications, an issue that BT said created added complications for sending secure signals over standard fibre.

“This is an exciting milestone for BT, accelerating the UK’s lead in quantum technologies that will play an important role in future communications systems globally,” said Andrew Lord, head of optical network research at BT. “We’ve proven a range of benefits that can be realised by deploying hollow core fibre for quantum-secure communication. Hollow core fibre’s low latency and ability to send QKD over a single fibre with other signals is a critical advancement for the future of secure communications.”

Tony Pearson, vice-president of sales and marketing at Lumenisity, said it was excited to be identifying new applications for its field-deployable CoreSmart cable solutions and working with the BT team on the first trial in the world of this kind.

“This milestone further accentuates not just the capability of our hollow core cable solutions, offering low latency and high bandwidth, but also demonstrates the potential CoreSmart has in new applications thanks to ultra-low non-linearity and dispersion across a broad spectrum, perfect for networks operated by our carrier partners.”