Optical-to-microwave clock synchronization with few-femtosecond residual timing jitter for space ground segments

High-precision timing is vital in space communication for tasks like navigation, data transfer, and coordinating satellite constellations. Currently, ground segments rely on microwave clocks, but emerging optical clocks and links offer great improvements in resolution, precision, and stability for next generation systems. However, integrating optical clocks with conventional microwave sources presents a challenge. Our solution, an optical-to-microwave phase detector, addresses this by enabling synchronization with few-femtosecond residual jitter between an optical- and a microwave source. With a phase/timing resolution of 0.01 fs RMS and a noise-floor below 1 fs RMS, this detector becomes a key technology as optical clock adoption grows in ground segments.