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A structure for an electro-optically controlled liquid crystal diffraction grating is proposed, which can dramatically simplify the fabrication process of liquid crystal optical gratings. The structure consists of two alternating stripes. Each stripe is a hybrid liquid crystal cell with adjacent stripes oriented perpendicularly. This kind of electro-optically controlled diffraction grating in principle gives 100% diffraction efficiency and no polarization direction dependence. The detailed fabrication process is presented.

To estimate numerically multidimensional director configurations in a liquid crystal cell, it is important to use the Q tensor representation of the strain free energy because it solves the problem of the difference between the directors, n and -n, in the Frank-Oseen free energy representation. In this paper, we discuss the numerical methods for calculating the multidimensional director configurations, using Berreman's Q tensor representation. Numerical issues discussed include the relaxation method for the director calculation, the liquid crystal (LC)/glass interface problem, the boundary conditions for the electric potential, and the possible ways to obtain faster convergence. We compare the calculated results obtained from the Frank-Oseen and Q tensor representations. By considering a π cell with patterned electrodes, we show the consistency of the model used with experimental observations. The calculated data explain well the position shift of the defects that appear in the test π cell.

Electrically switchable diffractive gratings based on cholesteric liquid crystals are suggested. An electric field switches the cholesteric cell between three states: two with a uniform in-plane director and one with a periodic in-plane director modulation. The modulated state produces a Raman–Nath diffractive effect. Characteristic time of switching is of the order of 10 ms. Diffractive properties depend on the polarization of the incident beam and the direction of surface orientation.