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 x 10(-14) at 1 s and similar to 8 x 10(-17) at 5 x 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.