Simultaneous time and frequency transfer over 100 km optical fiber based on sub-carrier modulation

In this paper a novel scheme is proposed to realize the simultaneous transfer of precise time and frequency signals. By performing sub-carrier modulation to the time signal, the time and frequency signals can be directly transferred in the same optical channel without causing mutual interference. The remote user does not need a slave oscillator to clear up the frequency signal and therefore can maintain a simple structure. We test the scheme in the proof-of-concept experiment, in which the 50 MHz modulated time signal and 400 MHz frequency signal are transferred together over 100 km optical fiber link. Good signal compatibility and system performance is observed in the experimental results.