LIQUID CRYSTAL DEVICES

摘要

A liquid crystal device comprises a layer of long pitch cholesteric liquid crystal material incorporating a pleochroic dye. The layer is contained between two cell walls surface treated to align liquid crystal molecules in a tilted homogeneous structure. The surface alignment and natural pitch of the cholesteric material are matched to provide a progressive molecular twist of between .pi. and 2.pi. , preferably about 3 .pi./2, with a uniform tilt direction. The ratio natural pitch P divided by thickness d of the liquid crystal layer is arranged to lie between 0.5 and 1.0 with a value of d less than 20.mu.m. Both low tilt and high tilt surface alignment may be used separately or in combination. Polarisers may be used to enhance contrast between ON and OFF states. The device has a sharp transmission/voltage characteristic which enables it to be used in large multiplex addressed matrix displays.