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.