Highly efficient twisted nematic liquid crystal polarization gratings achieved by microrubbing

We demonstrate twisted nematic liquid crystal (LC) polarization gratings (TNPGs) with a high first-order diffraction efficiency (>90%) that have the twist angle as constant, whereas the azimuthal angle of the mid-plane liquid-crystal director varies linearly in space. The high diffraction-efficiency design scheme is derived by means of the Jones matrix method. The designed first-order diffraction efficiency theoretically reaches 100% for the thick LC layer in which the retardation equals (n+1/2)lambda (n is an integer and lambda is the wavelength). We also present a simple model for the grating period-and twist angle-dependent threshold voltage of the Freedericksz transition in TNPGs. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4737945]