Ultra-stable optical links for metrological applications

We have demonstrated the feasibility of a free-space ultra-stable optical link on a 3 meters test bench, operating at 100 MHz. With this type of link, it is possible to transfer a 100 MHz signal with a relative frequency stability of a few 10/sup -14/ at one second integration time, 10/sup -16/ at one day and a phase stability of a few picoseconds per day in presence of moderate mechanical vibrations and thermal fluctuations. The comparisons of modern clocks of distant (<100 km) time and frequency laboratories have a strong scientific interest. In this context we study a low noise frequency distribution via optical fibres. Some preliminary tests have been realized and the results are encouraging. We expect to transfer ultra stable oscillators with a relative frequency stability of a few 10/sup -14/ at one second integration time, 10/sup -16/ at one day.