The accuracy of the time reference, provided through White Rabbit technology, is well-suited for most applications. However, for certain cutting-edge uses, even greater short- and long-term stability may be required.
Our goal is to implement, across the entire REFIMEVE network, a time transfer system capable of synchronisation with short-term precision on the order of a few femtoseconds and long-term stability better than 100 femtoseconds, while simultaneously delivering a radio frequency signal transfer with a long-term resolution of 10⁻¹⁷. The time uncertainty (with respect to UTC) could reach 100 ps, offering the possibility of synchronisation with any event on the planet provided that UTC generation is itself improved globally.
This level of extreme performance is essential for the most demanding users and is especially relevant for stringent tests of relativity, the development of reference systems, telemetry applications, and geodesic observations.
Our R&D efforts are focused on developing and characterising a phase modulation technique of the ultra-stable optical carrier, which must remain compatible with bidirectional optical transfer and data traffic. Implementation on existing REFIMEVE+ infrastructure will involve a high-performance time transfer module, including an electro-optic modulator, the key component for transferring a phase-modulated signal without degradation. This modulation (in the 40-100 MHz range) will be generated and directly connected to the LTE time reference, then applied to the electro-optic modulator to superimpose it onto the ultra-stable optical frequency.
We will also develop a module capable of repeating the high-performance time signal from one link to another, similar to what is already achieved for frequency signals using Laser Regeneration Stations.
Our objective is to demonstrate the feasibility of such a distribution on a national, and eventually European, scale, paving the way for future optical time scale comparisons and contributions to UTC.
