BT tests quantum key distribution across hollowcore fiber cable

BT has announced results of the latest in its series of application tests of hollow-core fiber cable. The test saw a channel of quantum key distribution (QKD) traffic as well as a channel of standard traffic transmitted across a 6-km hollowcore fiber cable provided by Lumenisity Ltd. The trial is significant in that QKD is particularly susceptible to crosstalk from other channels, and this trial showed that hollowcore fiber could be used to transmit QKD wavelengths in the presence of conventional traffic.

Cathy White, a researcher at BT, explains that QKD traffic is encoded at the level of a single photon, making crosstalk from nearby channels a potentially significant issue on standard fiber. For this reason, QKD traffic often is transmitted on its own fiber. In the tests at BT Labs, the QKD channel and the conventional channel were spaced on opposite sides of the C-Band when transmitted across the hollowcore fiber, but the power of the conventional channel was as high as +9 dBm. White says the only significant crosstalk detected at such high optical power levels was in the standard single-mode fiber patch cords.

White says that the Nested Anti-Resonant Nodeless Fibre (NANF) technology developed at the University of Southampton and used in Lumenisity’s CoreSmart cable shows significant promise in terms of providing an attenuation performance similar to standard single-mode fiber cable. She noted that the cable tested showed more loss than she would like to see in real-world applications, but that the University of Southampton has published work that indicates this issue can be addressed.

BT’s tests of the hollowcore fiber cable’s accommodation of QKD follows similar research into the technology’s applicability to 5G networks and 400ZR optical transport scenarios (see “BT testing hollowcore fiber for 5G support” and “Lumenisity, BT drive 400ZR DWDM transmission over hollowcore fiber”). Hollowcore fiber is interesting in that the use of a hollow core promises lower latency and better resistance to nonlinear effects than standard single-mode fiber.

“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 Professor Andrew Lord, BT’s head of optical network research via a press release. “We’ve proven a range of benefits that can be realized by deploying hollowcore fiber for quantum-secure communication. Hollowcore fiber’s low latency and ability to send QKD over a single fiber with other signals is a critical advancement for the future of secure communications.”

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