Stable radio transfer via an optic cable with multiple fibers based on passive phase error correction

A novel passive phase error correction technique for stable radio transfer via an optic cable with three fibers is proposed. The single-tone radio (at f₀) to be transmitted is first frequency-divided by 2. The half-frequency signal is transmitted to the receiver through one fiber of the cable and then frequency-tripled. The obtained signal is mixed with another half-frequency signal that passes the optic cable three times through different fibers. The filtered frequency component at f₀ has the same phase with that of the original radio. Both the phase delay and its variation during fiber transmission are removed, which enables an endless phase error correction. The proposed technique can avoid the use of extra radio frequency sources and bidirectional transmission in the same fiber. An experiment is carried out for the delivery of a 6 GHz radio signal through a 1.5 km ribbon type fiber optic cable. The time delay variation of ~350 ps induced by the 6°C temperature change can be confined to ±1.3 ps using the proposed technique.