Researchers have achieved record-breaking data speeds of 450 terabits per second over a standard fibre-optic network in London.

To put that in perspective, the fastest widely available consumer connection in the UK is 1Gbps, which is roughly 450,000 times slower than the connection achieved by the team from the National Institute of Information.

The 450Tbps data rates achieved during the experiment surpasses previous records of 402 Tbps and 430 Tbps, set in 2024 and 2025 over laboratory fibres.

Unlike those earlier demonstrations, the new experiment used real, already-installed fibres from the UK National Dark Fibre Facility (NDFF) and is therefore the closest demonstration to date of how the full capacity of existing fibre infrastructure could be unlocked, potentially paving the way for the next generation of networks needed to support AI services and beyond-5G mobile systems.

The NDFF is fundamentally based on the same fibre-optic technology delivering internet to homes and businesses across the UK. But because it’s a ‘dark’ network, it provides researchers with raw, unlit fibre-optic cables that allows them to plug their own custom-built prototypes, lasers and amplifiers directly into the physical glass strands. 

To achieve the record-breaking speeds, the team introduced new optical-amplifier technologies that support ultra-wideband signals. Conventional commercial systems use up to about 10THz of bandwidth, covering the C- and L-bands. The new system uses the O-, E-, S-, C- and L-bands together, more than quadrupling the available bandwidth to a record 42.4THz. 

The signal was sent over 39km of fibre, most of it running underground, between the UCL campus and the Telehouse data centre in London Docklands, and back again. 

Crucially, because the speeds were achieved using the kind of standard cabling already deployed, it could avoid the need to dig up London’s streets and lay six to nine times more physical fibre-optic cables to match the speeds. Instead, the technology proves you can just swap out the equipment at either end to get the same massive jump in data capacity.

New ultra-high-capacity optical-fibre technologies will be essential for communications beyond 5G. To keep deployment costs and timelines manageable, they need to be compatible with the fibre infrastructure already in the ground.