Sapphire Oscillators

Cryogenic sapphire oscillators provide the best short-term frequency stability available today from any technology, providing stability of 10^–14 to 10^–15 for measuring times from 1 to 1000 seconds or more. In combination with atomic frequency standards this stability can be extended to 10,000 to 100,000 seconds for the most demanding radio science applications. Sapphire oscillators are also needed to provide the "super L.O." local oscillator performance required by new generations of frequency standards. While conventional Quartz oscillators degrade the performance of new "laser-cooled" and "trapped ion" frequency standards, a sapphire L.O. allows their inherent stabilities to be achieved.

JPL has developed several generations of cryogenic sapphire oscillators, dubbed "77K CSO", "10K CSO" and the "40K CSO" still in development. All three of these oscillators have broken new ground with new capabilities. Previous sapphire oscillators had required cooling by liquid helium, with periodic refilling and with operating temperature requirements that varied from resonator to resonator, depending on the level of impurities in each resonator. The JPL "Compensated" sapphire oscillator approach allows the operating temperature to be adjusted as desired to match requirements of resonator performance and cryocooler capability.

• 77K CSO

  

  The 77K CSO provided the first example of an oscillator not cooled by liquid helium but which provided performance better than available quartz oscillators.







• 10K CSO

  

  The 10K CSO is the very first cryocooled frequency standard with ultra-high stability, providing ultra high stability of 2x10^–15 without the use of liquid helium, allowing a lifetime of 1-2 years between cryocooler maintenance. This compares to required monthly helium refills for helium-cooled units. Three units have been engineered for installation in the DSN in support of the CASSINI mission. One unit is presently installed at DSS-25 at the Goldstone site and a second unit is planned for DSS-14.




• 40K CSO

  

  The 40K CSO is designed to provide short term stability of 10¹⁴ or better while allowing the use of inexpensive single-stage cryocoolers. One unit is presently in development, and has demonstrated the viability of the technology with a preliminary stability of 2x10^–14.