Liquid crystal device

Abstract

A liquid crystal device comprises a cell ( ) formed by a layer ( ) of nematic or long pitch cholesteric liquid crystal material contained between two cell walls ( ). One wall ( ) carries a surface treatment giving a first azimuthal alignment direction with or without a surface pretilt to liquid crystal molecules. The other wall ( ) carries a surface treatment capable of separately providing both a preferred, substantially homeotropic alignment of the adjacent liquid crystal, and a defined azimuthal second alignment direction to the adjacent liquid crystal dependant upon liquid crystal molecular arrangement. The first and second alignment directions are approximately orthogonal. Polarisers ( ) may be arranged on either side of the cells walls with their polarization axes parallel or perpendicular to the two azimuthal directions. In addition one or more birefringent compensator layers ( ) are disposed on one side or on both sides of the cell ( ). The compensator layers ( ) may be formed of aligned polymer layers, or aligned liquid crystal material, either in a liquid form in a cell, or dispersed in a polymer sheet, or sheets of quartz or calcite slices. The device operates between two different voltage levels, one level (V ) providing a non twisted liquid crystal molecular arrangement, the other and higher voltage (V ) providing a twisted molecular arrangement.