Excelitas Technologies, a technology leader in delivering high-performance, market-driven photonic innovations to meet the illumination, optical, optronic, sensing, detection, and imaging needs of aerospace, defense, and industrial applications has introduced a new radiation-hardened space-qualified Rubidium Atomic Frequency Standard (RAFS).
The Excelitas Rubidium Atomic Frequency Standard (RAFS) is a high-performance and high-reliability Space-Qualified rubidium (Rb) clock developed for Global Navigational Satellite Systems. It is the highest-performance device of this type currently available, combining exceptional stability and low drift with negligible environmental sensitivity, while offering the low size, weight, and power advantages of a rubidium frequency standard. The design has been fully documented and qualified for all space requirements, including radiation. The RAFS offers exceptional performance as a precise time and frequency reference for demanding applications.
The RAFS employs classical rubidium gas cell atomic frequency standard principles. It utilizes a physics package with a discrete isotopic filter cell for the best stability. The relatively large, cool absorption cell and thin film spectral filter provide an exceptionally high signal-to-noise ratio and excellent short-term stability. Calorimetric Rb lamp process control and screening assures long life.
The "natural frequency" output of 13.4 MHz permits the use of low complexity, single-loop design for improved reliability. Operation at a low fixed magnetic bias field improves stability and reduces magnetic and radiation sensitivity. An integral baseplate temperature controller greatly reduces the overall temperature sensitivity by utilizing a thermal insulator that can be tailored to meet various panel operating temperatures.
While the RAFS may be operated in air, operating in a vacuum environment that eliminates barometric sensitivity, the extremely low temperature, magnetic, radiation, and voltage sensitivities mean that the unit has extremely low sensitivity to all environmental effects, providing a very low flicker floor. The low aging rate of less than 5x10-14/day is exceptionally smooth and modelable using either a log or diffusion fit to the data.
A crystal oscillator at a nominal 13.4 MHz produces the output signal via an output amplifier. This RF output path is hardened against transient radiation. The 13.4 MHz crystal oscillator also excites the Rb physics package via a phase modulator and frequency multiplier chain. This produces a discriminator signal that is processed by a servo amplifier to lock the crystal oscillator to the Rb atomic resonance. Temperature controllers, a lamp exciter, and a precision C-field source support the operation of the physics package, while a dc/dc converter and linear regulators provide power for the RAFS circuits. An integral controller stabilizes the RAFS baseplate temperature and several analog monitors are available to assess the operation of the unit.
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