| The time and frequency standards are developing rapidly in the recent years.For example,the frequency precision of microwave atomic clocks has reached a level of 10-16,and the best accuracy performance of optical clocks has entered an order of 10-19.Therefore,optical clocks are also considered as a candidate to the redefinement of second.However,the traditional method via free-space telecommunication can no longer meet the requirements of time and frequency transmission.The optical fiber communication technology in development is almost immune from electromagnetic interference under the external environment during signal transmission.The communication fiber transmission attenuation is relative low(the loss is about 0.2 d B/km)and the infrasture is relatively simple,so the remote transmission of frequency signal based on optical fiber link has been widely concerned.This paper mainly aims to meet the requirements of the Precision Gravity Measurement Facility(PGMF)for the time and frequency transmission.High fidelity transmission of H-maser signal is realized based on the optical fiber link.In addition,in order to meet the demands of the optical atomic clock comparison in the future,ultra-narrow linewidth lasers are delievered over long distances.The main researches in the thesis include:Three optical fiber links are built and tested the loss to connect the PGMF building A and the old building of the center for gravity experiment(CGE),the PGMF building A and the cave laboratory,and the PGMF building A to the Institute of Precision Measurement Science and Technology Innovation and Chinese Academy of Sciences(formerly Wuhan Institute of Physics and Mathematics,WIPM).The frequency transmission is realized through the optical fiber link,including microwave signal and optical frequency signal transmission.The transmission of 10 MHz and 100 MHz microwave frequency signals from a H-maser is realized based on the optical fiber link from PGMF building A to other laboratories in the CGE.The additional noise of the optical fiber link leads to the 10MHz frequency instability of 2.0×10-14 at the integration time of 1 s.The frequency instability decreases with the longer integration time,and reaches 2.8×10-16 at the integration time of 10000 s.The frequency stability of the 100 MHz signal through the optical fiber link is 5.6×10-15 at the integration time of 1 s,and 2.7×10-17 at the integration time of 10000 s,which meets the requirements of PGMF.In order to transfer the Al+optical frequency standard signal by our team to the WIPM for long-term frequency comparison with the Ca+optical clock,the preliminary experiment is carried out by our group.The optical frequency signal generating by a narrow linewidth fiber laser is transmitted from the PGMF building A to other laboratories in the CGE.The system noise background was optimized to achieve better frequency transmission performance and passive temperature insulation was carried out.The phase noise of the fiber link is actively compensated by a phase-locked loop.The residual phase noise of fiber link leads to a frequency stability of 1.6×10-18 at an integration time of 1 s and 9.2×10-20 at an integration time of 1000 s for the system floor.Then the bare fiber loop was tested in the laboratory to transfer optical frequency,leading to an additional noise frequency stability of 9.0×10-18 at 1 s,and 2.0×10-19 at 1000 s for the out loop signal.In order to meet the requirements for optical frequency standards comparsion in the future,we distribute the optical frequency via optical fiber link from the PGMF building A to other labs in the CGE.The additional phase noise of fiber link leads to a frequency stability of 8.1×10-18 at the integration time of 1 s,and 1.8×10-19 at the integration time of 1000 s for the out loop information signal. |
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