Ganghua Mei

Characteristics of a novel kind of miniaturized cavity-cell assembly for rubidium frequency standards

A novel kind of cavity-cell assembly for rubidium frequency standards has been developed. The assembly utilizes a new magnetron-type microwave cavity. The cavity is of small size, easily manufactured with high machining precision, and the cavity frequency can be easily adjusted. Either the integrated filter technique (IFT) or the separated filter technique (SFT) can be used in this cavity-cell assembly. The assembly has a high signal-to-noise ratio. The frequency stabilities of rubidium atomic frequency standards with this assembly are 4times10 -12/tau1/2 for IFT and 2.7times10-12/tau1/2 for SFT, and its temperature coefficient and light shift are very low

A physics package for rubidium atomic frequency standard with a short-term stability of 2.4 × 10−13 τ−1/2

In this article, a new type of physics package with high signal to noise ratio for a rubidium atomic frequency standard is reported. To enhance the clock transition signal, a slotted tube microwave cavity with a field orientation factor of 0.93 and an absorption cell with the diameter of 30 mm were utilized in design of the cavity-cell assembly. Based on the spectral analysis of the three commonly used rubidium spectral lamps, the spectral lamp filled with Xe gas was chosen as the optical pumping source for its small line shape distortion. To suppress the shot noise of the signal, a band pass interference filter was used to filter out Xe spectral lines from the pumping light. A desk system of the rubidium frequency standard with the physics package was realized, and the short-term stability of the system was predicted and tested. The measured result is 2.4 × 10-13 τ-1/2 up to 100 s averaging time, in good agreement with the predicted one.

Investigation on physics package with slotted-tube microwave cavity for rubidium atomic frequency standard

In this paper, a unique physics package using slotted-tube cavity for rubidium atomic frequency standard has been described, including its structure, characteristics and performances. Due to the advantages of high cavity Q factor, large microwave filling factor, stable light intensity and so on, the physics package has obtained a high signal-to-noise ratio. The test results suggest that RAFS using this physics package has achieved an excellent short-term frequency stability of 1.2E-12 / τ½ (1s≤τ≤100s).

Influence of Lamp Spectral Profile on Short-Term Stability and Light Shift of a Rubidium Atomic Clock

Passive gas-cell rubidium atomic clock has been widely used in Global Navigation Satellite System (GNSS). Further improvement on the frequency stability of rubidium atomic clocks has extreme significance for promoting the positioning and timing precision of GNSS. Distortion of the lamp spectral profile, caused by self-absorption, is a common concern for the design of a rubidium clock. However, few literature has systematically investigated the impact of lamp spectral profile on a Rb clock. In this work, the influence of lamp spectral profile on both short-term frequency stability and light shift of a rubidium clock was studied theoretically and experimentally. The results showed that serious distortion of the lamp spectral profile could lead to one times deterioration to short-term frequency stability, and change the zero light shift point by a few degrees centigrade. Thus, we demonstrated that optimization of the lamp profile may be an effective way to improve the performance of a Rb clock, which should be paid more attention when designing a high performance spaceborne Rb clock.

A microwave cavity with low temperature coefficient for passive rubidium frequency standards

Cavity pulling effect has been fully considered in designing of various atomic frequency standards, but quite often it has been neglected for passive rubidium atomic frequency standards (RAFS). This situation may be acceptable for the commonly used RAFS but it is less so for high performance one. A new type of microwave cavity with low temperature coefficient (TC) was designed with coefficient of 28.2 kHz//spl deg/C, which is positive and nearly one order smaller than that of the traditional TE/sub 111/ cavity. Analyses show that the cavity pulling effect of the cavity can be neglected under reasonable temperature stabilization condition. The main cause of the small TC of the cavity was discussed, which is due to the compensation of the positive TC of the dielectric ring in the cavity to the negative TC of the metal part of the cavity.

Main features of space rubidium atomic frequency standard for BeiDou satellites

Wuhan Institute of Physics and Mathematics (WIPM) has been developing the space rubidium atomic frequency standard (RAFS) for BeiDou navigation satellite system since the late of 1990s. Design of the RAFS aims to realize high stability, small size, long lifetime, high reliability and space environmental adaptability. The physics package was designed in SFT scheme. A slotted tube cavity with small size and TE011 resonant mode was used to construct the cavity-cell assembly, and an argon lamp with long lifetime was used as the pumping source. The microwave chain includes a 10MHz VCXO, a 5.3125MHz synthesizer, a ×9 RF multiplier and a ×76 SRD multiplier. Electronic circuits were designed by using analog circuitry to minimize the risk of element failure in space. The day stability of the space RAFSs developed for BeiDou regional system distributes within 2~5×10-14. To meet the needs of BeiDou global system, design of the RAFS has been improved further. A slotted tube cavity with larger size and better resonant mode was used, the argon lamp was substituted with a filtered xenon lamp, and the phase noise of microwave chain was depressed further. A prototype of new generation space RAFS was built recently. Preliminary test showed that the day stability of the prototype has reached 3×10-15.

Demonstration of a Physics Package with High SNR for Rubidium Atomic Frequency Standards

The frequency stability of a rubidium atomic frequency standard (RAFS) depends mainly on the signal to noise ratio (SNR) of atomic discrimination signal provided by the physics package. In order to improve further the frequency stability of our RAFS, a new physics package with high SNR was designed recently. The physics package was designed based on an improved slotted tube cavity. Compared with our previous design, the new cavity has more uniform magnetic line distribution and larger size, so that a larger resonance cell can be used. In the design the separated filter technique (SFT) was used. A Helmholtz coil was substituted for a solenoid one to create a more uniform C field. At present a prototype of the physics package has been made. A preliminary test has been performed, and a short term frequency stability of 6 × 10−13/1 s was achieved. This result indicates that the SNR of the physics package could meet the requirement for building a RAFS with frequency stability better than 1 × 10−12/τ1/2.

Design of a Miniaturized High-Performance Rubidium Atomic Frequency Standard

A miniaturized high-performance rubidium atomic frequency standard (RAFS) is introduced in this paper. Physics package is composed of a newly developed slotted tube microwave cavity and a 87Rb spectral lamp with Xe as starter gas. Optical and hyperfine filter techniques are used in the design of the physics package. A PLL frequency multiplier is designed with a digital synthesizer chip with ultra-low-noise floor. The produced microwave interrogating signal is of low phase noise. To meet the needs of possible space applications, the RAFS has rigid mechanical structure and reliable thermal structure. The volume of the RAFS is 300 mL, and the short-term frequency stability is measured to be 1.5 × 10−12/√τ.

Study of the Physics Package for High Performance Rubidium Frequency Standards

Frequency stability of an atomic frequency standard depends mainly on the Signal to Noise Ratio (SNR) of atomic discrimination signal. For a Rubidium Atomic Frequency Standard (RAFS), the SNR is closely related to the characteristics of the cavity-cell assembly in physics package. The RAFS in our laboratory is designed based on the slotted tube cavity, and a typical stability of 1.5 × 10−12 τ−1/2 (1–1000 s) has been achieved. The current cavity used in our design is of a disadvantage of field inhomogeneity. To improve further the stability of the RAFS, a modification of the cavity has been carried out. With this modification, the field homogeneity has been greatly improved, and the cavity size was increased also, enabling to hold a larger absorption cell. According to a theoretical evaluation, the SNR of physics package was enhanced by nearly two times, meeting the need to design a RAFS with a stability better than 1.0 × 10−12 τ−1/2.

A Subminiature Microwave Cavity for Rubidium Atomic Frequency Standards

A subminiature microwave cavity for rubidium atomic frequency standards has been developed. The cavity has volume of 8.1 cm3, and is of strong resonant signal with high Q factor. Based on the cavity a small size cavity-cell assembly with volume of 9.5 cm3 for rubidium frequency standards has been developed. A preliminary test showed that the cavity-cell assembly is of ability to achieve a short-term frequency stability of 3times10-11/radictau.