article ｜China Science Daily reporter Ni Sijie
On October 5, Nature magazine published online Professor of the University of Science and Technology of China Academician Pan Jianwei and his colleagues Zhang Qiang, Jiang Haifeng, Peng Chengzhi and others cooperated with Shanghai Institute of Technology and Technology , Xinjiang Observatory , National Time Center of the Chinese Academy of Sciences, Jinan Quantum Technology Research Institute and Ningbo University and other units. This achievement has realized high-precision time frequency transmission of free space at a level of 100 kilometers internationally through the development of high-power, low-noise optical combs, high sensitivity, high-precision linear sampling, and high-stability and high-efficiency optical transmission for the first time, effectively verifying the feasibility of high-precision optical frequency standard comparison of satellite-ground links, and taking an important step towards establishing a wide-area optical frequency standard network.
reviewer commented: "This work is a major breakthrough in the field of long-distance optical time frequency transmission in free space of satellites and ground, and will have an important impact on basic physics research such as dark matter detection, basic constant test of physics, and relativity test."
In recent years, the stability of the optical band atomic clock ( light clock ) based on ultra-cold atomic light lattice has entered the order of E-19, and a new generation of time frequency standards (optical frequency standards) will be formed. Combined with wide-area and high-precision time frequency transmission, wide-area time frequency network can be built, which will play an important role in the fields of precision navigation and positioning, global timing, wide-area quantum communication , and basic principles inspection of physics. For example, when the stability of time-frequency transmission on the global scale reaches the order of E-18, a new generation of "seconds" definition can be formed. will discuss this redefinition of "seconds". Furthermore, high-orbit space has a lower gravitational field noise environment, and the stability of optical frequency scale and time frequency transmission can theoretically enter the E-21 order, which is expected to have major applications in the research of basic physics issues such as gravitational wave detection and dark matter search.
However, the traditional microwave-based satellite time frequency transmission stability is only on the order of E-16 and cannot meet the needs of high-precision time frequency networks. The free space time-frequency transmission technology based on optical frequency comb and coherent detection can reach the E-19 order, which is the development trend of high-precision time-frequency transmission. However, the previous international related work has low signal-to-noise ratio and close transmission distance, making it difficult to meet the needs of high-precision time-frequency transmission of satellite-ground links.
In the results published this time, the research team developed the fully polarized fiber femtosecond laser technology, realizing a high-stable optical frequency comb with watt-level power output; based on low-noise balance detection and integrated interference fiber optical path module, combined with high-precision phase extraction post-processing algorithm, high-sensitivity linear optical sampling detection of the order of nanowatts, with a single-time measurement accuracy of better than 100 femtoseconds; further improving the stability and reception efficiency of the optical transmission telescope.
Based on the above technological breakthroughs, the research team successfully achieved time-frequency transmission in 113 kilometers of free space in Urumqi, Xinjiang. The stability of time-transmission 10,000 seconds reaches the order of femtosecond , and the stability of frequency-transmission 10,000 seconds is better than 4E-19. The system can tolerate the maximum link loss of up to 89dB, which is far higher than the typical expected value of medium and high-orbit satellite-ground link loss (about 78dB), fully verifying the feasibility of high-precision optical frequency standard comparison of satellite-ground links.
Associate researcher Shen Qi, Guan Jianyu, and researcher Ren Jigang are co-first authors of this paper. This work has been funded and supported by HTM3, the Ministry of Science and Technology, the Foundation of China, Anhui Province, Shanghai City and Shandong Province.
0km high-precision time-frequency transmission experiment diagram provided by the University of Science and Technology of China
related paper information:
https://doi.org/10.1038/s41586-022-05228-5
