STL and Colt Complete Multi-Core Fiber Trial in London Metro Network

Trial demonstrates 800G transmission and validates multi-core fiber for high-capacity AI and cloud connectivity.

March 9, 2026

2 min read

Members of the STL and Colt Technologies teams collaborate during the successful trial of multi-core fiber, deployed in Colt's metro network within London.

STL announced the successful completion of a multi-core fiber (MCF) trial conducted with Colt Technology Services across Colt’s London metro optical network, demonstrating the technology’s potential to support next-generation connectivity for AI, cloud, and digital services.

The field trial marks an important step in validating multi-core fiber as a high-capacity optical networking solution capable of increasing transmission capacity while maintaining the same physical footprint as standard single-mode fiber.

Multi-Core Fiber Tested Across London Metro Network

The trial deployed STL’s Multiverse four-core multi-core fiber, which integrates four independent cores within the same cladding diameter as standard single-mode fiber. The fiber maintains a coating size of 250/200 micrometers while achieving high transmission capacity per fiber strand.

Testing took place across two Colt points of presence within the London metro network, covering distances of approximately 9 km and 63 km.

During the trial, the network achieved an 800-Gbps line rate, with validation performed for both 100GbE and 400GbE services.

Engineers conducted a full set of optical performance tests, including:

Chromatic dispersion (CD)
Polarization Mode Dispersion (PMD)
Crosstalk
Throughput
Optical time-domain reflectometer (OTDR) testing
Insertion loss and optical return loss (ORL)

According to the companies, the results demonstrated stable performance across the metro network environment.

Moving Multi-Core Fiber From Lab to Field Deployment

STL says the trial represents part of its broader effort to transition multi-core fiber from laboratory research into real-world network environments, including underground and duct-based infrastructure.

Buddy Bayer, Chief Operating Officer, Colt Technology Services, said: “As demand for network capacity surges, customers need more bandwidth without compromising security, performance, or sustainability. At Colt, we’re pushing the boundaries of optical networking, and this pilot marks a breakthrough across Europe and the USA. It demonstrates our commitment to delivering future-ready, sustainable networks that meet growing needs without costing the earth.”