Temperature-Independent Achromatic Liquid-Crystal Grating with Spatially Distributed Twisted-Nematic Orientation

We propose an electrically tunable liquid crystal (LC) grating unit consisting of a conventional homogeneous LC cell and an LC grating with spatially varied twisted-nematic (TN) orientation domains (-pi to pi). The former cell controls the Stokes parameter S-3 and the latter functions as a TN-LC grating that is highly sensitive to S-3. We demonstrate the unique characteristics of the proposed TN-LC grating: it is highly efficient, is almost achromatic, and has minimal temperature-dependent diffraction properties. These properties are a result of the retardation- and wavelength-insensitive polarization rotation nature of general TN-LC cells under Mauguin's condition. (C) 2012 The Japan Society of Applied Physics