Optimization of antiferroelectric liquid crystal devices at the degeneration point

Antiferroelectric liquid crystals (AFLCs) with 45° tilt angle have been shown recently [K. D’hav’e, Per Rudquist, S. T. Lagerwall, H. Pauwels, W. Drzewinski, and R. Dabrowski, Appl. Phys. Lett. 76, 3528 (2000)] to exhibit true dark state between crossed polarizers at normal incidence. We show that this situation is possible at any incidence or any tilt angle depending on the principal dielectric constants ${\epsilon }_{\text{1–3}}.$ In particular, when the deviation of ${\epsilon }_1$ from the average ${\mathrm{(\epsilon }}_2{\mathrm{+\epsilon }}_3\text{)/2}$ is small, the medium behaves nearly as isotropic medium. Hence using this class of AFLC materials it will be possible to build full color, high-resolution displays with large viewing angular range. The optimum viewing angular cone will be obtained when the degeneracy point corresponds to 45° incidence angle and tilt angle anywhere from 0 to 45° depending on the values of the principal dielectric constants and, in particular, on the biaxiality. For the uniaxial case this angle is practically 41°–42° without dependence on the optical anisotropy.