Abstract: In order to meet the long-term frequency stability sharing requirement of 10 MHz hydrogen clock signal (HCS) between different buildings in the same scientific research park, a low-cost and highly integrated solution for optical-fiber-based 10 MHz HCS transferring setup is proposed. In the scheme, a 1 GHz radio-frequency signal (1GRFS) is used to modulate the laser intensity and optical fibers are used for signal transmission. In principle, the sum of the source 1GRFS and signal reflected from remote is frequency-divided firstly and then phase-compared with the HCS to be transferred. Then the error signal from the phase comparator is fed back to modulate the frequency of the 1 GHz oscillator to lock the phase between the remote 1GRFS and the HCS. Therefore, the remote 1GRFS has the same frequency stability as the HCS. Afterwards, a 10 MHz signal is generated at the remote site through a frequency divider as RF reference output. Furthermore, experiments are carried out to verify the precision of the system. It is shown that the additional frequency stability of the HCS transferring system is 2.4 ´ 10-13 at 1 s average time and 5.7 ´ 10-17 at 10000 s average time with a fiber link of 200 m, 4.8 ´ 10-13 at 1 s average time and 2.1 ´ 10-16 at 10000 s average time with a fiber link of 20 km. The verification results prove that the longterm stability of the transferring system is better than the frequency stability of the HCS, indicating that the system can be used for sharing HCS within kilometer range.

Key words: optical communication, hydrogen clock signal transferring, optical fiber, phase-locked loop; noise compensation