Passive-type Rubidium Atomic Frequency Standard Operating Parameters Optimization And New Technologies

It's of essential significance for an atomic frequency standard to work with properparameters. In the thesis, the author studied optimization of the working parameters ofthe passive rubidium frequency standard. Firstly, the history of the development of theatomic frequency standards is briefly reviewed. Secondly, the characteristics of thecontrol loop, the influence of the loop noise on the frequency stability and the parameteroptimization of the quantum package were studied theoretically and experimentally.Finally, some ideas about application of digital techniques to the rubidium frequencystandard was put forward and partly realized.The control loop and its noise were analyzed in both frequency and time domains.Result shows that loop time constant should be properly selected to get the best over-allphase noise performance for different quantum packages and voltage controlled crystaloscillators. The analysis also shows that the instabilities of the frequency, index and thephase shift of the modulation have strong effects on the stability and accuracy of theoutput frequency. Based on the analysis, a new digital method for modulation and phaseshifting was put forward and realized.By using the linear model of the loop and the noise theory, main factors that affect theshort-term stability were analyzed. It was shown that short-term stability highly dependson the frequency discrimination slope of the quantum package and the noise of the photodiode, the slope depends on the frequency modulation index, and there exist an optimummodulation index that corresponds the maximum of the slope.In order to minimize the frequency drift, some devices should be pre-aged. As anexample, the De-aging results of rubidium spectrum lamps were given and discussed. Amulti-channel data acquiring system was established to determine the relationshipbetween the frequency and the various parameters. With the help of the system, thetemperatures of the absorption cell and pumping lamp, the pumping light intensity,pumping lamp exciter current, C-field current, heater current, case temperature and theoutput frequency can be measured at the same time. The system has the advantages ofagility, flexibility, high accuracy, large data capacity, and the ability to record and treatdata in real-time.Some digital techniques and their applications to the rubidium atomic frequencystandard are analyzed. The techniques include the digital frequency modulation by DDS(Direct Digital Synthesizer), phase shift correction by software and low noiseself-correlation frequency multiplier. Based on the analysis, we gave the concept and atechnical scheme of smart atomic frequency standard based on the micro controller. If the-idea can be realized, much low environment sensitivity and frequency aging drift of thefrequency standard can be expected.