Experimental Study On Performance Optimization For Chip-scale Atomic Clock

The passive coherent population trapping(CPT)atomic clock,with absence of microwave cavity,is an all-optical microwave atomic clock.Owing to the size of physics package is not limited by microwave cavity,the chip-scale physics package with a volume of 1 cm3 or less can be implemented through micro electro mechanical systems(MEMS)technique,and with the application of application specific integrated circuit(ASIC)technique,chip-scale atomic clock(CSAC)can be achieved.CSAC,with small size and low power consumption is a time and frequency device.CSAC will satisfy the high-performance applications where power consumption,volume and cost are confined,and it is with a decent prospect for application in the future.In this thesis,the works introduced are mainly on implementing CSAC,including the theoretical and experimental study of performance optimization and the technical researching to improve the quality of CPT signal for CSAC.The main content contains the followings:We experimentally measured and studied the performances of the previously developed 87Rb miniature vapor cells,and eventually obtained the high-performance cell.With the cell we have realized a CSAC tabletop experimental system,the achieved short term frequency stability of the tabletop CSAC is 3.60×10-10 ?-1/2.Generally,a CPT atomic clock can be conveniently optimized according to the CPT signal.However,with the limited resource of a CSAC,the quality of its CPT signal is pretty poor which makes it difficult to optimize a CSAC.According to that a CSAC can provide high quality differential CPT signal,we explored an approach of optimizing CSAC,which indirectly obtains the information of the CPT signal from the differential CPT signal and optimize the CSAC with the information.We experimentally verified the feasibility of the approach with a tabletop experimental system,the study result is helpful for practically optimize the CSAC.We theoretically studied the CPT spectral profile broadening mechanisms,experimentally studied main conditions which exerted an influence over the line-width and amplitude of CPT signal,and the way to optimize the parameters of CSAC was also explored.Through the computational analysis with two light-atom interaction models,we studied the influence of physical parameters on the quality of CPT signal and the mechanisms of physical parameters to light-atom interaction process.The study results recommend the working parameters to CSAC for its implement and optimization.The results of the two works have been applied to our realized CSAC,its power consumption is 210 mW,volume is 19 cm,and the frequency stability reaches 2×10-10 ?-1/2.Based on the AC Stark Effect of light-atom interaction,we analyzed the physical principle of frequency variation of CPT spectrum when frequency modulated laser field interacting with atoms,we also discussed the relationship between coefficient of the light shift and modulation index,and explored the technique of suppressing light shift effect on output frequency of CSAC through properly setting modulation index.In addition,we also studied the relational characteristics between the light shift and the power distribution on the frequency components of output multi-chromatic laser outputted by the vertical cavity surface emitting laser(VCSEL),the results revealed the power distribution has an influence on the light shift of CPT spectral line,and according to the power distribution to proper set operation point can reduce the light shift of CSAC's frequency output.We investigated the cause of formation of spin-polarized dark state produced when unidirectional circularly polarized light interacting with atoms to prepare CPT state by traditional scheme,and proposal an optical device,polarization orthogonalizer,for realizing ?+?+-?'-?-CPT scheme atomic clock.With the polarization orthogonaliizer,it is promising to realize ?+?+-?'-?-CPT atomic clock with similar volume and better performance when comparing with conventional CPT atomic clock.We set up experimental system and carried out comparison experiments,and the study results revealed that the ?+?+-?'-?-CPT atomic clock,with the polarization orthogonalizer,achieved frequency stability 2.5 times better than that of the traditional one.The results of the two works provide valuable knowledge for developing CSAC and small size CPT atomic clock.