Cascaded optical frequency transfer over 500-km fiber link using regenerative amplifier
Deng Xue1, 2, 3, Jiao Dong-Dong1, 2, 3, Liu Jie1, 3, Zang Qi1, 2, 3, Zhang Xiang1, 2, 3, Wang Dan1, 3, Gao Jing1, 2, 3, Dong Rui-Fang1, 2, 3, Liu Tao1, 3, †, Zhang Shou-Gang1, 2, 3
       

Allan deviation of single-span 500-km transfer (squares) and cascaded 500-km transfer (circles).