  Similar to the light, gravitational waves traveling in multiple paths may
arrive at the same location if there is a gravitational lens on their way.
Apart from the magnification of the amplitudes and the time delay between the
gravitational wave rays, gravitational lensing also rotates their polarization
planes. This results in the changes in the antenna pattern function, which
describes the response of the detector to its relative orientation to the
gravitational wave. These effects are all reflected in the strain, the signal
registered by the interferometers. The gravitational wave rays in various
directions stimulate different strains. Their strains differ from each other
due to different magnification factors, the phases and the rotation of the
polarization plane. The phase difference mainly comes from the time delay.
Moreover, the rotation of the polarization plane seemingly introduces the
\textit{apparent} vector polarizations, when these strains are compared with
each other. Because of the smallness of the deflection angles, the effect of
the rotation is negligible.
