VOLUME-STABILIZED ULH STRUCTURE FOR THE FLEXOELECTRO-OPTIC EFFECT ANDTHE PHASE-SHIFT EFFECT IN CHOLESTERICS

Flexoelectric coupling gives rise to a linear electro-optic response i n cholesterics (flexoelectro-optic effect) with a uniformly lying heli x (ULH) structure and this electro-optic effect is strongly reliant on the homogeneity and quality of the texture. The ULH structure, unfort unately, is complicated in itself and may be perturbed by factors such as dielectric coupling, surface/liquid crystal interactions and phase transitions, and often there is a tendency for relaxation into the Gr andjean texture (standing helix structure) with time. Hence, in order to exploit the flexoelectro-optic effect in cholesterics any instabili ty of the ULH structure must be ruled out. We have overcome these prob lems by incorporating a polymer network by means of photopolymerizatio n of a reactive monomer added to the cholesteric. The volume stabilize d ULH structure still exhibits the flexoelectro-optic effect, it is st able and it is also retained after heating to the isotropic phase and going back to the cholesteric phase. In addition to the flexoelectro-o ptic mode, the ULH structure is of interest in an electro-optic mode c haracterized by a pure phase-shift with no change in amplitude (transm ittance). This mode, which has obvious applications in spatial light m odulators, optical computing devices and electrically controlled kinof orms and phase holograms working without polarizers, is also briefly d iscussed.