BT has conducted the world’s first trial of quantum key distribution (QKD), a method of ultra-secure communications, over hollow core fibre cable. The company commenced trials of a new type of optical fibre – Nested Anti-Resonant Nodeless Fibre (NANF) hollow core fibre – earlier this summer at the BT Labs in Ipswich.
The trials tested the potential benefits of deploying this technology for a variety of scenarios, including secure communications. The trials used cable developed and manufactured by Lumenisity to address the need for high-speed transactions and bandwidth increases in advanced communications systems.
In the latest trial, BT researchers worked with Lumenisity, a Southampton University spin out, to operate a QKD system using commercial equipment over a 6-kilometre-long Lumenisity CoreSmart cable with a hollow, air-filled centre. The trial revealed potential benefits such as reduced latency and no appreciable crosstalk.
Professor Andrew Lord, BT’s head of optical network research, said, “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. 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.”
In most optical fibre communications, high-speed signals are sent over a solid piece of glass using different wavelengths of light to deliver high-capacity transmissions. 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. The effect is similar to having a whispered conversation next to an orchestra – it can be hard to hear the other person’s voice over the music.
Hollow core fibre doesn’t have internal material – it’s filled with only air – so there is less light scattering and less crosstalk between channels, even at a single photon level. This clearer separation makes 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.