Patent ID: 7088413

Claim:
Bistable nematic liquid-crystal display device with a liquid-crystal optical mask, characterized in that it comprises: a) a nematic liquid-crystal material contained between two parallel substrates, which are provided with electrodes on their facing inner surfaces in order to allow an electric field to be applied to the said liquid crystal, at least the front substrate and the front electrode being optically transparent; b) alignment layers or treatments on the electrodes which orient the liquid crystal and produce an alternation of at least two distinct textures that are stable or metastable in the absence of a field, where one of the textures is either not twisted or twisted through a total angle of between −90° and +90° and the other texture has an additional twist through an angle of about 180°; c) the thickness d of the liquid-crystal layer covering the electrodes being chosen so that the product d.Δn is close either to λ/4 or λ/2, to within an integer multiple of the wavelength, or else is between these two values, λ 0 being the median wavelength of the useful spectral band of the display and Δn, the birefringence of the liquid crystal for this wavelength; d) means designed to apply, to the liquid crystal covering the electrodes, electrical signals which allow it to switch, by breaking the anchoring on at least one of the two substrates, between the said distinct textures and allow it to remain in one of them after the field has been removed; and e) means designed to promote the establishment of that one of the said textures giving the off state in the liquid crystal covering the inter-electrode spaces.