NIST researchers are developing a new optical time-frequency transfer technique called OTWTFT to synchronize distant optical clocks with femtosecond precision over free-space links. The project involves two optical clocks located in a rooftop lab on the NIST campus, connected via a folded free-space link with a retroreflector on a flying quadcopter.
The key technical achievement is maintaining femtosecond-level synchronization despite turbulence and rapid motion (25 m/s) of the retroreflector. This technique could enable optical clock networks for fundamental physics tests, improved coherent sensing, and enhanced precision timing and navigation.
The researchers have successfully demonstrated femtosecond-level OTWTFT over 12 km in Boulder, even with strong turbulence. They are now exploring the technique’s performance in the presence of motion, which can cause breakdowns in reciprocity.
Source: https://www.nist.gov/programs-projects/optical-two-way-time-frequency-transfer
Keywords: clocks, synchronization, reciprocity, time-frequency, metrology
