  The non-reciprocal and dynamic nature of polarization mode dispersion (PMD)
in optical fibers can be a problem for accurate time and frequency transfer.
Here a simple, passive solution is put forward that is based on transmitting
optical pulses with alternating orthogonal polarization. The fast and
deterministic polarization modulation means that the PMD noise is pushed far
away from the frequencies of interest and upon reflection from a Faraday mirror
at the receiver, the pulses have a well defined polarization when they return
to the transmitter, which facilitates stable optical phase detection and fibre
phase compensation. In an open-loop test setup that uses a mode-locked laser
and a simple pulse interleaver, the polarization mode dispersion is shown to be
reduced by more than two orders of magnitude
