ULISS-2G ultra stable cryocooled microwave sapphire oscillator: A mature and reproducible technology

The Cryogenic Sapphire Oscillator (CSO) bridges the gap between high spectral purity oscillators and Hydrogen masers, providing a relative frequency stability better than 3×10
⁻¹⁵
at short term and than 1×10
⁻¹⁴
for one day of integration. These exceptional performances are no longer re-served only for well-equipped metrology laboratories with liquid helium facilities. In 2010, we demonstrated for the first time the possibility to use a cryocooler while maintaining a state-of-the-art frequency stability. Today, our upgraded technology, i.e. ULISS-2G, is able to meet the most demanding current needs in frequency stability while offering autonomy and reliability compatible with field applications. In this paper we present the frequency performances of the different CSOs (currently 10 units) we built and validated, demonstrating the reproducibility of our CSO technology.