Research On The Key Technology Of A Novel Rb Frequency Standard And Fiber-based Microwave Frequency Transfer

With the rapid development of the national economy and science and technology in the current information age,the high-precision time and frequency signal has been applied to a broader range.However,the high-performance atomic frequency standards,featured by large volume,heavy weight,considerable power consumption and high cost,has very limited scope of application.In order to meet more users' demand for high-precision time and frequency signal,on the one hand,the compact and high-performance atomic frequency standards are developed actively,aiming to meet the application demands such as industrial manufacture,digital communication,smart grid,military defense,and satellite navigation.On the other hand,high-precision time and frequency transfer is used based on the high-performance atomic frequency standards(such as Cs fountain clock and cold atomic light clock)to meet the demands for high-precision time and frequency signal and its compare and synchronization in such fields as time and frequency metrology,fundamental physics,radio astronomy,and deep space network.For the compact and high-performance atomic frequency standards,the research on novel atomic frequency standards are carried out actively,besides the mature products(traditional Rb clock and passive hydrogen maser).In particular,pulsed optically pumped(POP)Rb clock is a very typical one,which not only has the shared advantages of Rb clock,but is superior to the more cumbersome passive hydrogen maser in terms of performance and boasts a broad prospect.In terms of time and frequency transfer,the satellite link-based frequency transfer is insufficient to transmission the properties of cesium fountain clocks serving as primary frequency standards.By contrast,the optical fiber-based frequency transfer,featured by low loss,high reliability and easy noise compensation,has gradually become a new way of frequency transfer and the hotspot in the current researches.Therefore,this thesis focuses on the research of POP Rb clock and optical fiber-based microwave frequency transfer.In the research of POP Rb clock,some factors affecting the stability of the atomic clock are analyzed,and the C-field current source,the temperature control circuit of the physical system and the closed-loop servo circuit are designed.The contribution of the C-field current and the physical system temperature to the stability of the atomic clock is less than 1 × 10-16(?=10-104 s)and 1 × 10-15(?=10-104 s)respectively.The output resolution of the servo circuit is 1 ?V,and the contribution of its output voltage to the short-term stability of the atomic clock is about 5 × 10-14 in open loop.The research results show that all circuit designed could meet the demands of high-performance POP Rb clock.By analyzing the characteristic of Ramsey signal of POP Rb clock,it was found that the optimal Ramsey time TR of the system was about 3 ms.When TR=3 ms,the contrast of Ramsey signal is higher than 40%,which can reach the best level of similar atomic clock.It was concluded based on the characteristic of Ramsey signal that the population and coherence relaxation time of Rb vapor cell in the atomic clock is about 1.95 ms and 2.45 ms respectively.The research results provide an important basis for further improving the performance of the POP Rb clock.Finally,the limitation of the short-term stability by the phase noise of microwave frequency synthesis though the Dick effect in the POP Rb clock is analyzed.The result is less than 5 × 10-14?-1/2,which also can meet the performance demand of atomic clock.The theoretical and experimental researches are conducted for the fiber-based microwave frequency transfer.In the theoretical research,the noise generation mechanism and noise compensation principle of optical fiber transmission are analyzed,and the principle of fiber-based microwave frequency transfer based on optical path compensation and electrical phase compensation is analyzed and compared.The cause and advantage of electrical phase compensation chosen in this thesis are described.Various factors affecting the fiber-based microwave frequency transfer are analyzed,including fiber transmission delay,phase noise of transmission signal,parasitic reflections in optical fiber,fiber dispersion and polarization mode dispersion(PMD).In particular,fiber transmission delay limits the noise suppression bandwidth of feedback loop and is also one of the main factors limiting the transmission distance.In the experimental research,a fiber-based microwave frequency transfer scheme based on electrical phase compensation,which has a simple structure and facilitates cascading and networking application is designed after considering the actual application.We demonstrate the transmission of a microwave frequency signal at 10 GHz over a 56 km spooled fiber and a 112 km urban fiber link respectively.The frequency transfer instability of 56 km spooled fiber is 1.9 × 10-15@1 s and 4.9 × 10-18@104 s while that of 112 km urban fiber is 4.2 × 10-15@1s and 1.6 × 10-18@1d respectively,which is sufficient to transfer and compare modern cold atomic microwave clock.