  There are conflicting statements in the literature about the gravitational
Faraday rotation of the plane of polarization of polarized electromagnetic
radiation travelling through a gravitational wave. This issue is reconsidered
using a simple formalism describing the rotation of the plane of polarization
in a gravitational field, in the geometric optics approximation. It is shown
that, to first order in the gravitational wave amplitude, the rotation angle is
a boundary effect which vanishes for localized (astrophysically generated)
gravitational waves and is non-zero, but nevertheless negligible, for
cosmological gravitational waves.
