Research On The Critical Technology For Passive Coherent Population Trapping Atomic Clock

As the most precise time keeper, atomic clock was used for the definition of the time by the International System of Units since 1976. It employs the radiation corresponding to the transition between two hyperfine energy levels of the alkali metal atoms to count time. Because of its stable of time keeping, it has become the most basic component among communication, global positioning system, aeronautics and astronautics and network synchronization. However, due to the microwave resonant cavity, which needs to be used in the traditional atomic clock, was very large, it is very difficult to be miniaturized. Besides, there were more and more electronic to be miniaturized, the traditional atomic clock application was challenged. With the coherent population trapping (CPT) theory, the atomic clock could be made very small, even to be chip-scale. This dissertation focuses on the demand for the minaturization of the atomic clock. Taking realization of the CPT atomic clock system as our target, system modeling, physics system and circuit system design and the whole system assembly were studied in this dissertation.System modeling was based on the CPT theory and was studied on the device level. Through the CPT analysis, light resource, optical elements, alkali metal atomic cavity and signal detection were described mathematically. And based on the description the system model was constructed for CPT atomic clock specifically. At the same time, the CPT atomic clock system was divided into two parts, physics system and circuit system.With the requirements of the CPT theory, the physics system was studied. The physics system included the light source, optical elements, cavity with alkali metal atoms, heaters, light signal detection, inducing magnetic field and electromagnetic field shielding. All of them were designed respectively and the assembly of the physics system was given at the end of the chapter.Based on the designed physics system, the circuit system was studied. The circuit system was divided into four parts which were frequency modulated microwave signal synthesizing, light frequency stabilization, temperature controlling for light source and cavity and weak signal detection. Every part was designed and constructed specifically. Finally, the issues in the PCB (Printed Circuit Board) layout were discussed.Finally, with the designed physics system and circuit system, the realization of the CPT atomic clock system was studied. Every part of the CPT atomic clock system was realized and tested. Physics system test results showed that the light source which used VCSEL (Vertical Cavity Surface Emitting Laser) could emit the 795nm beam which was corresponding to the absorption wavelength of the 87Rb atoms; the optical elements could realize the polarization conversion; the PIN photodiode could be able to detect the error signal. Circuit system test results showed that the frequency modulated microwave signal synthesizing circuit could output 3.4 GHz frequency modulation (FM) signal; the light source frequency stabilization circuit could stabilize the wavelength of the VCSEL onto 795nm; the temperature controlling circuit could stabilize the VCSEL and the Rb cavity in the range of 0.02 degree C and 0.5 degree C respectively; the weak signal detection circuit could reveale the signal as lower as 1 microvoltgae with the large noise background. With these parts, the CPT atomic clock system was realized. Output frequency stability test veryfied the systematic model and all the design could give the important guidance to the chip-scale atomic clock design and fabrication.