Abstract
We report the development, absolute phase noise, and residual phase noise characterization of a 9.192 GHz microwave frequency synthesis chain devoted to be used as a local oscillator in a high-performance cesium vapor cell atomic clock based on coherent population trapping (CPT). It is based on frequency multiplication of an ultra-low phase noise 100 MHz oven-controlled quartz crystal oscillator using a nonlinear transmission line-based chain. Absolute phase noise performances of the 9.192 GHz output signal are measured to be -42, -100, -117 dB rad(2)/Hz and -129 dB rad(2)/Hz at 1 Hz, 100 Hz, 1 kHz, and 10 kHz offset frequencies, respectively. Compared to current results obtained in a state-of-the-art CPT-based frequency standard developed at LNE-SYRTE, this represents an improvement of 8 dB and 10 dB at f = 166 Hz and f = 10 kHz, respectively. With such performances, the expected Dick effect contribution to the atomic clock short term frequency stability is reported at a level of 6.2 × 10(-14) at 1 s integration time, that is a factor 3 higher than the atomic clock shot noise limit. Main limitations are pointed out.
Highlights
Atomic frequency references provide the most stable signals over long integration times because their frequency is determined by an atomic transition
In the frame of the EURAMET MClocks project,18 this paper describes the development of a microwave 9.192 GHz frequency synthesis chain for a high-performance coherent population trapping (CPT) clock
We reported the development of a high-performance microwave frequency synthesis chain driven by an ultra-low phase noise 100 MHz OCXO
Summary
Atomic frequency references provide the most stable signals over long integration times because their frequency is determined by an atomic transition. Is the PSD of the microwave oscillator fractional frequency fluctuations at offset frequency f According to this relation, the development of a Cs atomic clock with a relative frequency stability of 10−13 at 1 s, operating at a LO modulation frequency fm = 83 Hz, requires a local oscillator with a phase noise at 2fm = 166 Hz lower than −99 dB rad2/Hz. In a pulsed clock, the effect of the LO frequency noise has been characterized by the sensitivity function g(t) which is the response of the atomic signal to a phase step of the interrogation oscillator at time t. The purest microwave signals are nowadays obtained through optical-microwave frequency division with optical frequency combs or the use of cryogenic sapphire oscillators and associated frequency synthesis.14 These systems remain voluminous, complex, and are not compatible with compactness requirements of vapor cell atomic clocks.
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