Director structures of cholesteric diffraction gratings

We study director structures of electrically-controlled cholesteric diffrac tion gratings (CDG's). The cholesteric liquid crystal (LC) is confined betw een two transparent non-patterned electrodes with either planar or homeotro pic anchoring. In cells with planar alignment, the applied electric field c auses reorientation of the initial (zero held) planar state and creates one -dimensionally modulated structures in the plane of the cell. The modulatio ns occur via two distinct scenarios: (I) nucleation and expansion of 'strip es' and (II) undulation of quasinematic layers in the plane normal to the c ell's plates. In the cells with homeotropic surface alignment, modulated st ructures exist without applied voltage. Magnetic field is used to provide u niform orientation of these structures. Confocal microscope studies and com puter simulations are carried out to reveal the fine structure of the CDG's .