Electrically tunable two-dimensional liquid crystals gratings induced by polarization holography

Two-dimensional (2D) gratings made up of an array ofdifferently twisted nematic structures are obtained by crossed assembling of1D polarization holograms recorded at the photoaligning substrates. Therotating linear polarization pattern, produced by the interference of twoopposite circularly polarized beams, is recorded on the azo-dye dopedpolyimide aligning layers. The 2D gratings diffract light in differentdirections with different polarization states, that can be optically controlled.Orthogonal circularly and linearly polarized diffraction orders aresimultaneously obtained irradiating the grating with a linearly polarizedbeam. An external ac voltage allows to completely control the diffractedenergy distribution.