[1] KHALIGHI M A, UYSAL M. Survey on Free Space Optical Communi-cation: A Communication Theory Perspective[J]. IEEE Communications Surveys and Tutorials, 2014, 16(4): 2231-2258.
[3] RIEHLE F. Optical clock networks [J]. Nature Photonics, 2017(11): 25-31.
[4] GIORGETTA F R, SWANN W C, SINCLAIR L C, et al. Optical two-way time and frequency transfer over free space[J]. Nature Photonics, 2013, 7(6): 434-438.
[5] TAKENAKA H, TOYOSHIMA M, TAKAYAMA Y. Experimental verification of fiber-coupling efficiency for satellite-to-ground atmospheric laser downlinks[J]. Optics Express, 2012, 20(14): 15301-15308.
[6] DESCHENES J D, SINCLAIR L C, GIORGETTA F R, et al. Synchronization of Distant Optical Clocks at the Femtosecond Level [J]. Physics, 2015, 6(2): 519-530.
[9] ALLAN D W J P I. Statistics of Atomic Frequency Standards[J]. 1966, 54(2): 221-230.
