Direct comparison of two Cryocooled Sapphire Oscillators presenting relative frequency instability at 10−15

In this paper we present the direct comparison of two microwave Cryocooled Sapphire Oscillators demonstrating a relative frequency stability better than 2×10^-15 at short term and of the order of 1×10^-14 over one day integration. We also report the frequency stability evaluation of a microwave signal generated from a planar waveguide external cavity laser (PW-ECL) referenced to a Fabry-Perot cavity through optical-to-microwave frequency division with a commercial Er:fiber optical frequency comb owned by the “laboratoire temps-fréquence” (LTF) of the university of Neuchâtel, Switzerland, and the phase noise measurement of the engineering model of the Pharao clock frequency synthesis owned by the “Centre National d´Etudes Spatiales” (CNES) at Toulouse, France. These lastest results were obtained by moving one of our Cryogenic Sapphire Oscillator (CSO) from the FEMTO-ST Institute to these two metrological sites.