Research On Phase Processing Technology Of Passive Rubidium Atomic Clock

At present,all passive atomic clocks are frequency processing methods used,and their frequency stability changes as 1/?^1/2 over time.The active atomic clock adopts the phase processing method,and its frequency stability changes as 1/? with time.If we take the passive atomic clock as the research object and change its traditional frequency processing method to change the frequency processing to phase processing,then the frequency stability of the frequency source will be greatly improved,and even the long-term frequency stability index will be improved.Usually,people evaluate the quality of a frequency source with frequency stability and frequency accuracy.The steeper the frequency stability of the frequency stability curve,the better the frequency source.When an actual atomic frequency standard is used as a source,the output signal frequency may provide an accurate deviation in the case of low accuracy but high stability,but it cannot be a signal with poor frequency stability.Therefore,it is very valuable to improve the frequency stability of passive atomic clocks.In this paper,we focus on the passive cesium atomic frequency standard and explore the possible implementation of its phase processing.Observe that the passive cesium atomic clock will periodically jump to the point of maximum probability when the energy level jumps.Research and analysis show that this phenomenon is caused by the combined effect of the frequency difference signal and the low-frequency modulation signal contained in the excitation signal.The frequency-difference signal is actually transmitted from the crystal oscillator,and the specific output response is the irregularity of the optical detection signal waveform.Combining with the theory of virtual reconstruction,it is possible to recover the frequency difference at the maximum probability point of the transition of the atomic energy level from the light detection signal and the low-frequency modulation signal through continuous uninterval measurement.The specific method is to disconnect the frequency processing loop after the frequency of the passive chirped clock is stable,and continuously sample the optical detection signal and the modulation signal with no gaps.In each modulation cycle,the lowest point of the optical detection signal is found and corresponding to each other.Zero crossing of the modulated signal,recording the time difference between the two.Combined with the mathematical model of the physical part of the chime clock,the frequency difference corresponding to the time difference can be calculated.In combination with the relationship between the frequency-to-phase relationship and the coefficient between the phase difference of the control crystal oscillator and the phase difference of the excitation signal,the phase difference signal of the crystal oscillator can be obtained,and the voltage signal for controlling the crystal oscillator can be obtained to perform the crystal oscillator.Controls the completion of the phase processing of the passive chime clock.The entire process is digital,which greatly simplifies the processing of the analog line and improves the efficiency on the basis of improving the frequency stability.In this paper,the basic theories of frequency processing,phase processing,multi-period synchronization,and virtual reconstruction are briefly introduced.It is emphatically described how the required frequency difference can be found through the phenomenon of the maximum probability point of atomic energy level transition based on the theory of virtual reconstruction.The signal as well as the entire phase recovery process and the experimental verification of the theory.The experimental results show that the introduction of phase processing in the passive cesium atomic clock can improve its frequency stability.This treatment should also be introduced into other passive atomic clocks.