Microwave Local Oscillator for a Cesium Frequency Standard Synthesized from a Cryogenic Sapphire Oscillator

Watabe, K.; Hartnett, John G.; Santarelli, Giorgio; Yanagimachi, Shinya; Ikegami, Takeshi; Ohshima, Shinichi

doi:10.1143/jjap.44.3283

Cited by 9 publications

(12 citation statements)

References 13 publications

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“…In NMIJ, the two liquid-helium-cooled CSOs were developed to be employed as local oscillators of the atomic fountains [30]- [33]. However, the helium gas has been very expensive recently due to a global supply shortage.…”

Section: Microwave Synthesismentioning

confidence: 99%

Preliminary Evaluation of the Cesium Fountain Primary Frequency Standard NMIJ-F2

Takamizawa

Yanagimachi

Tanabe

et al. 2015

IEEE Trans. Instrum. Meas.

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We describe the preliminary evaluation of the frequency corrections and their uncertainty in the cesium fountain primary frequency standard (PFS) NMIJ-F2 under development at National Metrology Institute of Japan (NMIJ). In NMIJ-F2, cold atoms generated from a vapor-loaded optical molasses in the (001) configuration are optically pumped to the Zeeman sublevels of m F = 0 to increase the number of atoms involved in the Ramsey interrogation. Moreover, a cryocooled sapphire oscillator with ultralow phase noise is employed as the local oscillator to avoid degradation of the frequency stability due to the Dick effect. As a result, we have obtained a very high fractional frequency stability of 9.7 × 10 −14 τ −1/2 . As for systematic frequency shifts, the fractional correction for the second-order Zeeman shift is experimentally estimated to be (−165.5 ± 0.5) × 10 −15 from the first-order Zeeman shift of atoms in m F = +1 launched to various heights. The fractional frequency correction for cold-atom collisions is estimated to be (+3.3 ± 0.4) × 10 −15 by extrapolating the frequency to zero density from the frequencies measured for various nonzero atom numbers. We will soon be able to make a comparison with other atomic fountain PFSs at the 1 × 10 −15 level.Index Terms-Atomic fountain clock, primary frequency standard (PFS), uncertainty evaluation.

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Section: Microwave Synthesismentioning

confidence: 99%

Preliminary Evaluation of the Cesium Fountain Primary Frequency Standard NMIJ-F2

Takamizawa

Yanagimachi

Tanabe

et al. 2015

IEEE Trans. Instrum. Meas.

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“…Since f c =1/T c ∼ 0.67 Hz, the contribution to the short-term frequency stability of the Cs fountain due to the phase noise at smaller offset frequency of the microwave frequency synthesizer is larger than that from larger offset frequency. The microwave frequency synthesizer based on an ultrastable laser [21][22][23][24]26 or a cryogenic sapphire oscillator (CSO) 25,[27][28][29][30][31] has superior phase noise and frequency stability properties. Thus, the Dick effect contribution can be considerably reduced and reach the quantum projection noise limit using the ultrastable and ultralow phase noise microwave frequency synthesizers from the schemes.…”

Section: Introductionmentioning

confidence: 99%

A low phase noise microwave frequency synthesizer based on parameters optimized NLTL for Cs fountain clock

Li,

Du,

et al. 2018

Preprint

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We report on the development and phase noise performance of a 9.1926 GHz microwave frequency synthesizer to be used as the local oscillator for a Cs fountain clock. It is based on frequency multiplication and synthesis from an ultralow phase noise 5 MHz Oven Controlled Crystal Oscillator (OCXO) and 100 MHz Voltage Controlled Crystal Oscillator (VCXO).The key component of the frequency multiplication is a non-linear transmission-line (NLTL) used as a frequency comb generator. The phase noise of the synthesizer is improved by carefully optimizing the input power, the input and output impedances of the NLTL. The absolute phase noises of the 9.1926 GHz output signal are measured to be −64 dBc/Hz, −83 dBc/Hz, −92 dBc/Hz, −117 dBc/Hz and −119 dBc/Hz at 1 Hz, 10Hz, 100Hz, 1 kHz and 10 kHz offset frequencies, respectively. The residual phase noise of the synthesizer is measured to be −82 dBc/Hz at 1 Hz offset frequency. The measurement result shows that the absolute phase noise at the frequency range of 1 -100 Hz is mainly limited by the phase noise of the OCXO. The contribution of the absolute phase noise to the fountain clock short-term frequency stability is calculated to be 7.0 × 10 −14 τ −1/2 . The residual frequency stability of the synthesizer is measured to be 1.5 × 10 −14 τ −1/2 , which is consistent with the calculated frequency stability due to the residual phase noise of the synthesizer. Meanwhile we designed and realized an interferometric microwave switch in the synthesizer to eliminate the frequency shifts induced by the microwave leakage. The extinction ratio of the switch is measured to be more than 50 dB. In the scheme, we use only commercially available components to build the microwave frequency synthesizer with excellent phase noise performance for high-performance Cs fountain clocks.

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“…(ii) The dominant effect of power variations is radiation pressure-induced permittivity change in the sapphire. 7) In a previous work, 8) we achieved a fractional frequency stability of 1 Â 10 À14 at an integration time of 320 s at 9.192 GHz synthesized from the CSO employing two servo systems; a Pound lock for frequency control of the loop oscillator and temperature stabilization at the turning point of the resonantor's frequency-temperature dependence. A power control servo 9) was not implemented.…”

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confidence: 96%

“…Details of the sapphire-loaded cavity (SLC) and oscillator configuration have been presented elsewhere. 8) The SLC was cooled in a cryostat with liquid helium. The sapphire crystal with a diameter of 50.0 mm and a height of 30.0 mm was manufactured from Crystal Systems ''HEMEX'' and supports a Whispering Gallery mode, WGH 15;0;0 at 10.812 GHz, which exhibits a loaded Q-factor of 5 Â 10 8 at 6 K. The sapphire resonator is mounted inside a silver-plated copper cavity, which is placed in a permanently evacuated vacuum cylinder.…”

mentioning

confidence: 99%

“…Figure 2 shows a schematic block diagram of the frequency synthesizer that produces the 100 MHz signal from the 10.812 GHz oscillation frequency of the CSO. A power splitter and a divide-by-2 were added to the previous frequency synthesizer 8) to obtain the output at 100 MHz. A 1 GHz voltage-controlled oscillator phase locked to the CSO was divided to 100 MHz using a divide-by-5 and a divideby-2.…”

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Reference Signal Synthesized from a Cryogenic Sapphire Oscillator Improved by Power Control Servo

Watabe

Hartnett

Locke

et al. 2006

jjap

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Improvements in the frequency stability of a reference signal synthesized from a cryogenic sapphire oscillator (CSO) have been realized. This has been achieved by a power control servo with active Pound frequency stabilization in the loop oscillator based on a high Q-factor cryogenic sapphire resonator with a loaded Q-factor of 5 ×108 at 10.812 GHz and operating at a temperature of 6 K. The reference signal of 100 MHz was synthesized from the 10.812 GHz oscillation frequency. When compared with a 100 MHz hydrogen maser signal, the 100 MHz reference exhibited a fractional frequency stability of 5.6 ×10-15 at an integration time of 510 s, which is approximately two times better than that without power servo control.

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Microwave Local Oscillator for a Cesium Frequency Standard Synthesized from a Cryogenic Sapphire Oscillator

Cited by 9 publications

References 13 publications

Preliminary Evaluation of the Cesium Fountain Primary Frequency Standard NMIJ-F2

Preliminary Evaluation of the Cesium Fountain Primary Frequency Standard NMIJ-F2

A low phase noise microwave frequency synthesizer based on parameters optimized NLTL for Cs fountain clock

Reference Signal Synthesized from a Cryogenic Sapphire Oscillator Improved by Power Control Servo

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