A world record set on an existing London fiber connection has already been broken by the same international research effort.
In November 2025, researchers transmitted data at 300.28 terabits per second through an operational fiber link beneath London. Less than a year later, an expanded international team has increased that result to 450 Tbps.
The new figure represents an improvement of approximately 50 percent over the previous field deployed fiber record. More importantly, the team achieved it without replacing the optical fiber already installed beneath the city.
Who held the previous record?
The previous field deployed single mode fiber record was announced by University College London in November 2025.
UCL researchers Dr Jiaqian Yang and Romulo Aparecido reached 300.28 Tbps by using four optical transmission bands. The work was completed with Lightera, Japan’s National Institute of Information and Communications Technology and Keysight Technologies.
The experiment used a real fiber connection between the UCL campus and the Telehouse North data center in East London.
The two locations are approximately 19.5 kilometers apart. The signal travelled to the data center and returned through a second fiber, creating a total transmission route of 39 kilometers.
The 2025 experiment proved that operators could unlock additional capacity from existing fiber by using more of the available light spectrum.
The new record reaches 450 Tbps
The new experiment expanded the same concept and reached a combined transmission capacity of 450 Tbps.
Japan’s NICT worked with University College London, Aston University, the University of Bristol, Lightera Laboratories and Nokia Bell Labs.
The team transmitted information through five optical bands known as O, E, S, C and L. The previous 300.28 Tbps result used four major bands, while the new test added the E band and expanded the available transmission spectrum.
The system carried up to 1,273 individual wavelength channels across a total bandwidth of 42.4 terahertz. NICT describes this as the widest bandwidth ever transmitted through an optical fiber.
The result was presented at the 2026 Optical Fiber Communication Conference in Los Angeles and accepted as a postdeadline paper, a category used for significant research developments announced close to the event.
Why is the new record important?
Many optical transmission records are achieved with new or specially designed cables under controlled laboratory conditions.
This test used fiber that was already installed beneath London. The network included real connectors, splices and previous cable repairs, all of which can increase signal loss compared with an ideal laboratory cable.
The ability to reach 450 Tbps under those conditions suggests that existing metropolitan fiber networks may contain significantly more unused capacity than current commercial systems access.
Upgrading transmitters, receivers and optical amplifiers could allow network operators to carry more information without immediately replacing every underground fiber cable.
This is not a home download or upload speed
The 450 Tbps result should not be confused with an internet speed test performed on a home computer or smartphone.
The official research reports one combined transmission capacity. It does not provide separate consumer download and upload speeds.
The number represents data carried across 1,273 wavelength channels and processed after reception. It is the total potential capacity of a major network connection, not a broadband plan for one household.
At 450 Tbps, the theoretical data rate is equivalent to approximately 56.25 terabytes every second. Purely as a mathematical comparison, that would be enough capacity to carry a 100 GB game in less than two milliseconds.
A real game download could never reach that result because the server, storage system, router, local network and user device would all introduce additional limits. Network capacity would also be shared among many services and users.
What about Japan’s 1.02 petabit record?
A separate result announced in 2025 reached 1.02 petabits per second across 1,808 kilometers.
That experiment used a specially designed 19 core optical fiber and established a different record based on the combination of transmission capacity and distance.
The new 450 Tbps result does not replace the 1.02 petabit figure in every category. Its importance comes from achieving the fastest result on conventional single mode fiber that was already installed in a real metropolitan environment.
The two records measure different technological achievements and should not be presented as the same type of internet speed test.
When could the technology become available?
UCL estimates that commercial adoption for data center connections and internet backbone infrastructure could begin within approximately three to five years.
This does not mean households will receive 450 Tbps internet connections within that period. Early adoption would most likely focus on connections between large data centers and other critical parts of the global internet.
For gamers, stronger network backbones may eventually support larger downloads, cloud gaming, streaming services and data centers handling more simultaneous users.
The technology will not instantly reduce ping or remove every download bottleneck. However, it demonstrates how much additional capacity may still be available inside fiber networks that are already beneath major cities.
Previous Field Record: 300.28 Tbps
New Field Record: 450 Tbps
Increase: Approximately 50 percent
Distance: 39 kilometers
Location: London, United Kingdom
Fiber Type: Existing field deployed single mode fiber
Consumer Availability: Not available
Estimated Commercial Adoption: Three to five years for data center and backbone applications
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