Latest improvements in the performances of a cryogenic sapphire oscillator

In this paper, we report the characterization results of our cryogenic sapphire oscillators. The oscillator incorporates a sapphire resonator cooled down at the liquid helium temperature in a cryocooled ultra-low vibration cryostat. The phase noise of a single CSO is -104dBc/Hz at 1 Hz offset of the 10 GHz carrier. The frequency fluctuations were measured with three frequency counters using different statistical algorithms. The best result at 1 s integration time is σy(1s) = 6.5 × 10-16. For the integration time above 10 s, the Allan deviation of a single CSOs computed from each data sets reaches a floor around 3.2 × 10-16 at 100 s integration time for a daily frequency stability of 3.5 × 10-15.