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US 4,214,819 AGranted
Electro-optical modulator
AssigneeMerck Patent GmbH
InventorsLudwig Pohl, Rudolf Eidenschink, Joachim Krause, Georg Weber
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AssigneeMerck Patent GmbH
InventorsLudwig Pohl, Rudolf Eidenschink, Joachim Krause, Georg Weber
Estimating the term…
The optically active medium of an electro-optical cell sandwiched between a pair of crossed polarizers is a thin layer of liquid crystal with a positive dielectric anisotropy and a negative anisotropy of the diamagnetic susceptibility. The medium is positioned between two planar transparent electrodes across which a potential difference establishes, in the liquid crystal layer, an electric field perpendicular to the electrode layers. A magnet is provided for establishing in the medium a magnetic field that has a predetermined orientation relative to the electric field. When both fields are parallel, the threshold voltage of the cell is increased. The presence of such a magnetic field, when the electric field is switched off, reduces the turn-off time of the cell. When the fields are perpendicular to each other, the color of the display can be controlled in accordance with the magnitude of the magnetic field.
An electro-optical modulator comprising:
A method for reducing the turn-off time of a positive DKA liquid crystal cell in which a layer of liquid crystal material is sandwiched between transparent electrodes by which an electrical field can be established in the liquid crystal material to switch the cell to its display mode, which comprises employing a liquid crystal material having a negative DMA and establishing a magnetic field parallel to the electric field therein during at least a portion of the turn-off time.
A method for improving the contrast by reducing undesired "crosstalk" of a matrix-addressed liquid crystal display in which a layer of positive DKA liquid crystal material is sandwiched between transparent electrodes, consisting of a multiplicity of parallel horizontal conductor rows, and a multiplicity of parallel vertical conductor columns, respectively, by which the liquid crystal material at the crosspoint of any horizontal row with any vertical column can be separately triggered to its display mode, which comprises employing a liquid crystal material having negative DMA, and establishing at the adjacent untriggered crosspoints a magnetic field parallel to the electric field established at said triggered crosspoint.
Dependencies are inferred from the claim text.