Ultra-Stable Wideband Signal Dissemination for Distributed Systems

We demonstrate an ultra-stable wideband signal dissemination scheme suitable for distributed systems. By inserting a 26 GHz probe signal whose round-trip delay variation is precisely measured with double optical mixing, the link length variation has been accurately detected. Assisted with a well-designed homodyne phase locked loop, the probe has time stability on the order of femtosecond for hours and fractional frequency stability of 8.3 x 10(-18) at 1000 s averaging time. Experimentally, a tunable single-frequency signal ranging from 8 GHz to 12 GHz is disseminated from a local end to 2 remote ends via 20 km fiber links. The root-mean-square delay jitters are between 10 to 20 femtoseconds within an hour, indicating exceptional stability. Additionally, an X-band 500 Mbps quadrature phase shift keying signal is also tested as a true wideband signal. The relative delay jitter is 1.88 picoseconds, which is close to the measurement noise floor. The proposed wideband signal dissemination scheme is highly desirable for distributed systems that require high stability and strict coherence.