GÉANT has successfully completed a field trial that sets a new benchmark for long-haul optical networking: 3,403 km of terrestrial transmission at 400G using Cisco / Acacia 400G Ultra Long Haul (ULH) Quad Small Form Factor Pluggable Double Density (QSFP-DD) coherent pluggable optical modules.
Conducted on the GÉANT live production network in June 2025 and using commercially available technology, this trial represents one of the longest known reaches ever demonstrated on a terrestrial network using a 400G QSFP-DD coherent pluggable transceiver with a 24W power envelope, making it compatible with all existing 400G-capable routers. GÉANT intends to deploy this technology in the new Nokia router platform currently being deployed across its European backbone network.
Bram Peeters, Chief Network Services Officer for GÉANT, said “This significant milestone reaffirms our vision for the GÉANT network. We have been working on making our router and optical platform as open as possible, and now this trial demonstrates the capabilities of high capacity, cost effective, easily deployable pluggable solutions to bridge impressive distances and challenging optical links. These advancements, combined with our recent upgrades, ensure GÉANT is ready for the Terabit era”
From Lab to Field: Proven Confidence
Before deploying the system in the field, GÉANT conducted extensive lab testing in its internal optical testbed in Cambridge (UK), simulating realistic network conditions and validating optical characteristics of the Cisco / Acacia 400G ULH QSFP-DD coherent pluggable transceivers, particularly with regards to Optical Signal to Noise Ratio (OSNR) performance. These tests provided a high degree of confidence in the technology’s ability to perform under production constraints. The seamless transition from lab to field confirms the robustness and maturity of the Acacia 400G ULH solution.
Field Trial Details
The field trial route consisted of a path through London → Paris → Geneva → Frankfurt → Amsterdam → London, spanning a total of 3,403 km and passing through seven ROADM nodes and 42 in-line amplifier sites.
Not too long ago, this distance would have only been possible using traditional stand-alone DWDM transponders. The field trial ran over Nokia’s FlexILS open line system, employing both EDFA and Raman amplification. The infrastructure included a mix of G.652 and G.655 fibre, presenting varying dispersion and attenuation profiles. Notably, the path included a 240 km / 42 dB loss non-repeated subsea segment between the UK and the Netherlands, emphasising the solution’s ability to handle long spans with high loss, high noise and other non-linear impairments.
The system ran stable and error-free and with production grade optical performance margin, further confirming its suitability for real-world deployment within the GÉANT network (typical 1,000-2,000km range).
IP-Optical Convergence
The result supports a broader industry trend: the convergence of IP and optical layers through coherent pluggable transceivers, enabling simpler, cost-effective architectures for high-capacity services across extended distances.
This trial directly supports GÉANT’s network architecture to move towards IP-Optical convergence. By deploying coherent optics with QSFP-DD form factor directly in router ports, the network eliminates traditional DWDM transponders and the associated intermediate infrastructure and management. This architectural shift reduces energy consumption, simplifies design, and enables faster, more cost-efficient service activation. The result is a scalable architecture enabling cost-effective Terabit-scale capacity on the IP/MPLS layer.
Looking ahead
This field trial adds to a growing body of global demonstrations, including those recently performed in the global Research and Education Networking community by Internet2 and by AARNet, signalling mainstream adoption of Routed Optical Networking for expanded applications.
Following the trial’s success, GÉANT is confident that Cisco / Acacia technology is deployable on any of its terrestrial links, supporting a streamlined approach to capacity growth that is aligned with the evolving demands of Research and Education traffic and with modern technology lifecycles. As the technology evolves, coherent pluggable transceivers like the 400G ULH ones offer a strategic path toward more flexible, efficient, and scalable optical infrastructures.
