CESNET and GÉANT combining data and non-data services across single fibre optics

At SPIE West in January 2026, CESNET and GEANT presented the research results of their research into successfully combining data and non-data services across single fibre optics.

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At the event, Jan Radil talked about coexistence of different classes of optical signals transmitted simultaneously in one fibre. Optical networks are well known as the crucial backbone for all high-speed data transmissions, however, these are now being increasingly used for something which may be called non-data services. Metrology applications such as accurate (or precise) time and ultrastable frequency transfer are no longer exotic as used to be 15 years ago.

Given the geopolitical situation and the consequential national security challenges of the last few years, great interest has grown in using traditional optical data networks for fiber sensing based on technologies such as distributed fiber sensing (DAS) or state of polarization (SoP) and also for quantum technologies, including quantum key distribution (QKD). What is really critical is the reliability and stability of optical fibre links and not the huge amounts of data transmitted.

The concept sounds rather simple – just combining different optical signals in one fibre – but this is a rather challenging task for all Internet service providers (ISP), including both commercial operators and more academic operators, such as national research and educational networks (NREN). New non-data services do use slow ‘legacy’ signals, utilizing simple modulation schemes, which may interfere with high speed data signals, utilizing more advanced modulation schemes. Some engineering rules must be adhered to and elaborate considerations should be given to all technical aspects when combining all mentioned applications. It is rather surprising that after 15 years this situation has not been resolved, and it is the reason why CESNET and GÉANT have been working in this field for a number of years. Previously the work has been presented as posters in 2023, 2024, 2025 and finally in 2026 as oral presentation.

We have found that new generations of coherent systems are pretty resilient to slow data signals and new non-data services may be deployed together with standard data transmissions. We are convinced that the results are not just some academic exercises. While it is true that slow signals up to 10 Gb/s are becoming obsolete for data transmission, they are used by new applications like time transfer and distribution. Fiber sensing also do use slow amplitude modulated signals, and both applications (or services) are clearly very important for national security reasons, providing additional means for localization capabilities (e.g. sabotage vessels identification and determent) and adding profundity to GNSS based time services (which is also important for 5G, 6G and other mobile services).

You can find out more about the 2026 presentation here