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Photonics Research

Measurement of atmospheric non-reciprocity effects for satellite-based two-way time-frequency transfer

Ting Zeng, Qi Shen, Yuan Wen Cao, Jian-Yu Guan, Meng-Zhe Lian, Jin-Jian Han, Lei Hou, Jian Lu, Xinxin Peng, Min Li, Wei-Yue Liu, Jincai Wu, Yong Wang, Juan Yin, Ji-Gang Ren, Haifeng Jiang, Qiang Zhang, Cheng-Zhi Peng, Jian-Wei Pan

Published Apr 2, 2024• 5 citations

Abstract

Future optical clock networks will require high-precision optical time-frequency transfer between satellites and ground stations. However, due to atmospheric turbulence, satellite motion and time delay between the satellite–ground transmission links will cause spatial and temporal variations, respectively, resulting in the breakdown of the time-of-flight reciprocity on which optical two-way time-frequency transfer is based. Here, we experimentally simulate the atmospheric effects by two-way spatio-temporally separated links between two stationary terminals located 113 km apart and measure the effects for optical two-way time-frequency transfer. Our experiment shows that the effect on the link instability is less than 2.3×10 −19 at 10,000 s. This indicates that when the link instability of satellite–ground optical time-frequency transfer is on the order of 10 −19 , it is not necessary to consider the atmospheric non-reciprocity effects.

DOI: 10.1364/prj.511141

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Abstract Timescale comparison between optical atomic clocks over ground-to-space and terrestrial free-space laser links will have enormous benefits for fundamental and applied sciences. However, atmospheric turbulence creates phase noise and beam wander that degrade the measurement precision. Here we report on phase-stabilized optical frequency transfer over a 265 m horizontal point-to-point free-space link between optical terminals with active tip-tilt mirrors to suppress beam wander, in a compact, human-portable set-up. A phase-stabilized 715 m underground optical fiber link between the two terminals is used to measure the performance of the free-space link. The active optical terminals enable continuous, cycle-slip free, coherent transmission over periods longer than an hour. In this work, we achieve residual instabilities of 2.7 × 10 −6 rad 2 Hz −1 at 1 Hz in phase, and 1.6 × 10 −19 at 40 s of integration in fractional frequency; this performance surpasses the best optical atomic clocks, ensuring clock-limited frequency comparison over turbulent free-space links.