Phase-Modulation-Based Stable Radio Frequency Transmission Via 125 Km Fiber Optic Link

This paper proposes a stable radio frequency (RF) transfer scheme based on phase modulation. The passive compensation method is used to compensate the phase variations. The use of only one mixer reduces the power consumption during the frequency mixing process. By utilizing a phase modulator, the issue of bias drifting, encountered in RF transmission systems with intensity modulation method, is eliminated. A single-mode fiber (SMF) serves as a dispersive medium for phase modulation-to-intensity modulation (PM-to-IM) conversion. Our passive compensation system with phase modulation has the characteristics of robustness and low insertion loss at the modulation module. The RF signal with frequency of 2.4 GHz is transferred via a 125 km fiber optic link. The measured standard Allan deviation (ADEV) of our transmission system is 3.66×10^{-13} at 1 s and 2.26×10^{-16} at 10000 s, which is better than that of the reference atomic clock. The proposed system will be useful for further applications such as in square kilometer arrays and remote clock comparison.