1400 km of optical fiber connect optical clocks in France and Germany

For years, researchers have been working on an optical fiber connection between the German and the French national metrology institutes, PTB and LNE-SYRTE. The 1400 km long link is now completed: it is based on standard telecom optical fibres and optical power losses of 200 dB (1020) are compensated by means of specially developed amplifiers. Furthermore, frequency fluctuations added during the propagation along the fibre are actively suppressed by up to 6 orders of magnitude. This allows the transmission of optical signals with very high stability.