Phase Processing And Locking Of The Passive Atomic Clock

The passive atomic clock is widely used in the field of national defense scientific research as frequency reference source which frequency stability curve is t^1/2due to its frequency-locking.But the active atomic clock because of its phase-locking,the frequency stability curve is1/t.It is meaningful for improving frequency stability of passive atomic clock if phase processing technique of active atomic clock could be applied in passive atomic clock.This paper studies the phase processing techniques and locking methods of the passive rubidium clock and the cesium fountain clock.It is proved that the frequency stability of controlled sources is influenced by the accuracy of phase synchronization by analyzing the laws of the changes of phase differences between signals and the way of signal control.In the case of low accuracy phase synchronization,the frequency stability of the frequency source is the effect of the frequency-locked control.As the phase synchronization accuracy increases,the result is between the effect of frequency-locked and phase-locked.The effect of phase-locked can be finally obtained when phase synchronization is very accurate.This paper,though exploring and analyzing the phase characteristics of the energy level transition phenomenon in rubidium atoms,constructs the mathematical model of phase difference recovery for the rubidium clock.Under the modulation of the periodic signal,the rubidium atom will jump at the center frequency.At this time,the photo detection output signal carries the error information.By capturing the photo detection signal,it compares with the zero time of the modulated signal to recover the excitation.The frequency difference information of the signal.Then,using the virtual reconstruction technology,combined with the phase difference law between complex signals,the phase difference of the atomic clock signals under different controlled sources is calculated.In the experiment,using different high-stability frequency sources to replace the locked source in the atomic clock,and comparing the frequency stability index calculated by the mathematical model with the actual index of the high-stability frequency source,the mathematical model was proved correct.On this basis,the rubidium phase-lock simulation experiment system was designed.The frequency stability of simulation output has been significantly improved compared to the original frequency-locking mode.Among them,the 8ms frequency stability of the simulated output signal is 6.652E-11,the 80 ms frequency stability is 8.847E-12,and the 800 ms frequency stability is 1.023E-12.The frequency stability curve is significantly better than t^1/2,slightly less than 1/ t.The feasibility of using phase lock for passive clocks is theoretically verified.The frequency offset values of the excitation signal of the cesium atomic fountain frequency standard is obtained on the experimental platform of the National Time Service Center.The frequency stability of the cesium atomic fountain frequency standard is improved by filtering the frequency modulation noise?FM noise?and processing algorithm optimization.The 400s-frequency stability is improved from 3.16E-14 to 4.64E-15,and the 4000s-frequency stability is increased from 9.85E-15 to 1.54E-15.