  We report a method to determine propagation delays of optical 10 Gb/s data
traveling through a 75 km long amplified fiber link with an uncertainty of 4
ps. The one-way propagation delay is determined by two-way exchange and cross
correlation of short (< 1 ms) bursts of 10 Gb/s data, with a single-shot time
resolution better than 2.5 ps. We thus achieve a novel optical communications
link suited for both long-haul high-capacity data transfer and time transfer
with picosecond-range uncertainty. This opens up the perspective of
synchronized optical telecommunication networks allowing picosecond-range time
distribution and millimeter-range positioning.
