A femtosecond-precision, fiber-optic timing transfer system with long-term stable, polarization maintaining output

A fiber-based, all-optical system for femtosecond-precision, long-term, timing transfer and synchronization of microwave electronics and lasers at the kilometer scale is presented. This approach enables the implementation of femtosecond pulse, X-ray free-electron lasers, owing to the high-precision and robust operation. The system incorporates a fiber polarization controller for long-term synchronization of remote lasers, and operates with an optical timing detector based on balanced optical cross-correlation. We demonstrate continuous, unaided timing distribution over 168-hours with 5 fs rms precision. Also, the first demonstration of timing transfer from local to remote ultrafast, fiber laser with an all-optical, ultrafast technique is shown for over 5 hours with 4 fs rms transfer precision. This represents timing transfer over 340 m of fiber with an unprecedented fractional relative timing stability of 10^-19. A study of linear and non-linear effects impacting performance is presented, along with design guidelines, while it is shown that minimization of polarization mode dispersion and non-linearity are critical design considerations for optimal performance.