  The polarization exchange effect in a twisted-nematic Fabry-P\'erot resonator
is experimentally confirmed in the regimes of both uniform and
electric-field-deformed twisted structures. The polarization of output light in
the transmission peaks is shown to be linear rather than elliptical. The
polarization deflection from the nematic director grows from $0^\circ$ to
$90^\circ$ angle and exchanges the longitudinal and transverse directions.
Untwisting of a nematic by a voltage leads to the rotation of the polarization
plane of light passing through the resonator. The polarization exchange effect
allows using the investigated resonator as a spectral-selective linear
polarizer with the voltage-controlled rotation of the polarization plane.
