Towards accurate optical fibre time transfer in UTC

Accurate time transfers are now fully based on space techniques. The recently developed optical fibre technique is expected to be used in the UTC generation in the future. Some UTC labs operate optical fibre links using different approaches. In particular, the here called Two-Way Optical Fibre Time (and Frequency) Transfer (TWOFT/TWOTFT) is of special interest. The symmetry of the propagation conditions in both directions allows to substantially reducing the instability due to fluctuations of the propagation, and its capability of self-calibration. The first operational TWOTT between the UTC laboratories has been established in Poland between AOS and GUM since January 2012. The result has being submitted to the BIPM since March 2013. The BIPM started the monthly data processing and compares to the GNSS links. The TWOTT can reach an accuracy of hundred ps in a few minutes and therefore provide an effective new tool for the assessment of GNSS and TWSTT CP time link calibration and bring substantial improvement to the [UTC-UTC(k)]. However, time transfer by optical fibres today does not match the structure of the UTC time transfer network with a unique pivot. This requires the new network configuration, algorithm and will provoke fundamental changes in the UTC time link computation.