Study And Exploration On Physics Package Of Coherent Population Trapping Atomic Clock

Because of its small size and low power consumption, coherent population trapping (CPT) atomic clock has been applied in many fields, such as communication, time synchronization, navigation, and experimental research. At present, compact and chip-scale CPT atomic clock products have been applied to practical projects abroad, and some new schemes that can improve the quality of CPT resonance signal have been developed to further improve the frequency stability of CPT atomic clock. In order to develop CPT atomic clocks with independent intellectual property rights, we have carried out product transformation and new scheme exploration on compact CPT atomic clock. The main progress and research results of this paper are as follows:For CPT atomic clock engineering prototype, we designed and developed a physics package. The hidden trouble of frequency-hopping in former physics packages was erased in this physics package. The volume and power consumption of this physics package are respectively18.4mL and1.4W. The CPT atomic clocks that use these physics packages have been realized to small batch production, and the products can achieve a typical frequency stability better than4×10-11τ1/2for integration time1s≤τ≤100s, the overall performance of atomic clock reaches the international advanced level of like product.For the CPT atomic clock working under different temperature, we designed and developed a physics package with the volume of16mL and the power consumption of1.6W. The CPT atomic clock based on the physics package can work steadily in a large ambient temperature range, now it has been applied to an actual project.We have experimentally studied the scheme of realizing CPT resonance through the interaction between atoms and parallel linearly polarized bichromatic coherent light field (lin//lin CPT scheme). By eliminating the leaky-trap state due to optical pumping effect in conventional scheme which uses circularly polarized bichromatic coherent light field (στ-στ CPT scheme), more atoms will contribute to CPT resonance. We experimentally studied the two schemes, and better CPT resonance differential signal which used as frequency discriminating signal in atomic clock was obtained by lin//lin CPT scheme at lower temperature. Therefore, comparing to σ+-σ+CPT scheme, the lin//lin CPT scheme can be used to implement an atomic clock with comparable volume, lower power consumption and better frequency stability.We have experimentally studied the polarization-selectve CPT scheme of exciting CPT resonance with elliptical polarized bichromatic coherent light field. The elliptical polarized light can be seen as a linear superposition of σ+andσ-circularly polarized light with different amplitude. Due to the different light absorption intensity of atoms for σ+and σ-, it can suppress the background of CPT resonance signal, and the scheme provides a CPT resonance signal with greatly improved contrast (contrast is defined as the amplitude ratio of CPT signal to background). The experimental results show that the CPT signal contrast is about6times higher than that of conventional CPT atomic clock, so the frequency stability of atomic clock based on our studied scheme will be greatly improved.We have proposed and experimentally studied a frequency-switching Ramsey-CPT scheme (FS scheme). Driven by the periodically microwave modulated current, a vertical-cavity surface-emitting laser (VCSEL) emits continuous laser which switches between monochromatic and multichromatic laser, and Ramsey-CPT fringes has been studied with the frequency switching continuous laser. With elimination of the acousto-optic modulator (AOM) which is used to generate pulsed laser in conventional Ramsey-CPT atomic clock, the volume of physics package of the proposed scheme greatly decreases. By comparing Ramsey-CPT fringes obtained from the two Ramsey-CPT schemes, the frequency stability of the proposed scheme is expect to be46%better than that of the scheme with AOM. Additionally, comparing to conventional CPT atomic clock, the physics package of the proposed scheme is basically the same, while the resource budget of the electronics will be slightly increased as a microwave switch shall be added to it. Our experimental results suggest that it is feasible to implement a compact Ramsey-CPT atomic clock with the volume and power consumption of the conventional CPT atomic clock, and the frequency stability comparable to or even better than that of the conventional Ramsey-CPT atomic clock. We have proposed and experimentally studied a crossed-polarizers frequency-switching Ramsey-CPT scheme. It excites CPT resonance with lin//lin CPT configuration and implements Ramsey interference with FS scheme. A crossed-polarizers method is introduced in light signal detection, and it significantly reduces the background signal level due to the magneto-optical rotation effect. Typical Ramsey-CPT fringes with a linewidth of280Hz and a contrast of22%were observed. By comparing the detected signal with the Ramsey-CPT atomic clock realized only through the FS scheme, the contrast of the proposed scheme increased by8times. Because only the components setting of physics package need to be slightly adjusted, the volume will not increase, our proposed scheme could be implemented compact Ramsey-CPT atomic clock with higher performance.