Hybrid Analog-Digital Fiber-Based Radio-Frequency Signal Distribution

We present a fiber-based radio-frequency signal distribution system. In our system, we use a hybrid technique, in which digital signal processing is combined with analog electronic architectures to effectively reduce the fiber-induced phase noises and ensure high-accuracy frequency distributions. The technique encompasses a digital signal processing module for active phase fluctuation analysis and a resistance-capacitance microwave phase shifter for the noise suppression. Our system achieves a fractional frequency transfer stability of $3\times 10^{-14}$ at 1 s and ${\sim}8\times 10^{-17}$ at $5\times 10^{4}$ s over a 22-km outdoor fiber link. The system is easily implemented and very scalable, while suppressing the fiber-induced phase noises by over two orders of magnitude in the long-term.