  The interrogation of a sensor based on a highly birefringent film irradiated
by an incident beam whose polarization is oriented 45o with respect to the
normal film axes is shown to display exceptional features and resolve some
outstanding issues in interferometric sensing. The measured pattern as a
function of wavelength is complicated displaying a superposition of Fabri-Perot
and birefringence oscillations. By means of appropriate optical signal
processing based on Fourier analysis, three different periodicity patterns can
be elucidated when sensing a single event, improving the sensing process in
several ways: it allows sensing at several sensitivity scales, and it clears
out the problems of phase and direction ambiguities. A novel effect is observed
in which the phase displacement of different patterns move in opposite
directions as sensing takes place
