Abstract: The use of a single circularly polarized light configuration to achieve a CPT state will generate a polarized dark state,resulting in a lower contrast of the CPT signal.Therefore,the frequency stability index of traditional CPT atomic clocks is not high.In order to improve the contrast of CPT signals and improve the performance of CPT atomic clocks,various schemes for eliminating polarized dark states have been proposed and studied.These schemes can be divided into parallel line polarized light configurations and phase delayed configurations based on the polarization state and generation method of the laser used σ⁺-σ^- Configuration,push-pull pump configuration,vertically polarized light configuration,polarization modulation configuration.Based on the principles and development level of these schemes,a comparative analysis of their advantages,disadvantages,and improvement plans can be conducted to explore new development directions for high-performance atomic clocks under different demand conditions.

Key words: Atomic clock, Coherent population trapping, Dark-state, Polarized light