SMECTIC LIQUID CRYSTAL DEVICES

A liquid crystal display is arranged to provide very low minimum light trmission in one of its two switchable states. This makes it useful for a shutter (FIG. 1) and for high contrast digital displays (FIG. 2). A layer of a chiral smectic liquid crystal material is contained between two cell walls carrying electrode structures. The liquid crystal material has the following phases with temperature: isotropic.revreaction.cholesteric.revreaction.chiral smectic.revreaction.solid. The cholesteric pitch is large. The cell walls are surface treated to provide a parallel alignment of liquid crystal molecules. Crossed polarizers are arranged either side of the cell walls, one aligned with its optical axis parallel to the surface alignment of the adjacent cell wall. The device is switched by means of .+-.-d.c. voltage pulses and utilizes the ferro electric effect.