BT Trials New Hollow Core UK Fibre Optic Cable at its Labs

BT has announced that they’ve begun trials of a new type of hollow core optical fibre cable at their BT Labs R&D facility in Adastral Park (Ipswich), which could in theory be more resistant to damage, while also delivering better performance (e.g. latency) for future broadband ISP and mobile connectivity services.

At present most conventional single-mode optical fibre cables work to guide laser light through solid glass cores, which need to be extremely transparent in order to avoid signal loss. Nevertheless, even the clearest of fibres will still have a slight loss over distance (akin to around 0.142 decibel per kilometre) and solid glass fibres struggle to carry very high-power transmissions, especially in short pulses.

Some years ago (2013 example) we began reporting on the development of a new type of optical fibre cable – hollow core fibre – that could put right some of these problems. Essentially, these cables have an air-filled central core (i.e. light travels faster through the air than glass), with an outer ring of glass to help guide the laser beam. Since then the technology has continued to be refined.

According to BT, such cables have the “potential to reduce the latency, or signal delay, caused by the light travelling through glass, by up to 50%.” Naturally, the operator is keen to trial this, and so they’ve teamed up with Lumenisity, a Southampton University spin out company, and Open Radio Access Network (O-RAN) mobile vendor Mavenir.

The trial involves a 10km long hollow core fibre cable provided by Lumenisity (CoreSmart® hollowcore). Working with Mavenir, BT has shown that using such cables 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 one exchange or cabinet. High-Frequency Trading (HFT) is another area that may benefit.

Professor Andrew Lord, BT’s Head of Optical Network Research, said:

“We’re excited to begin trialling hollow core fibre and 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.”

Just to be absolutely clear, this does NOT mean that BT will in the near future task Openreach with having to replace all of today’s optical fibre cables. Indeed, we aren’t even close to maximising the capability of existing optical fibres in the local access network (e.g. those used for Fibre-to-the-Premises (FTTP) broadband), which may well exist for many decades or possibly longer.

However, we could see such hollow core fibres potentially being deployed as part of future / new core network links, or for providing backhaul style capacity over longer distances etc. The technology is still developing and so BT’s trial is all about testing different use cases and seeing how it performs.