Sub-picosecond active timing control over fiber optic cable

We have presented an all-optical active delay control system that was used to demonstrate sub-picosecond control of fiber delay over a 200 km link. Control hardware and algorithms were developed to demonstrate the ability to maintain the propagation delay of a fiber optic channel to less than 1 picosecond. The system was demonstrated using realworld fiber in Arizona. The results show that the performance limits encountered by the existing electrical control systems can be broken by implementing an all-optical approach. By pushing the performance envelope of time synchronization by more than an order of magnitude, this system enables coherent interferometer processing at RF frequencies up to 10 GHz. While this design enables control of fiber optic delay at the sub-picosecond level, it does not fully address the delivery of timing signals to the user at the sub-picosecond level. Further development work is required in the areas of absolute calibration of path symmetry, characterization of path delay changes in fiber optic equipment, and creation of sub-picosecond level signals or time tags for user equipment.