ACTIVE RETARDATION FILMS BASED ON POLYMER STABILIZED CHOLESTERIC LIQUID CRYSTAL

摘要

This invention is related to electro-optical devices and active retardation films that can modulate one or more of the amplitude, phase or polarization of an electromagnetic wave. The active retardation film is based on a polymer-stabilized cholesteric liquid crystal (PS-CLC) in a cell with helix lying in the plane parallel to the substrates at zero voltage. An electro-optical cell to observe such electro-optical effect comprises of two substrates with transparent conductive electrodes coated inside the cell and the substrates are coated with alignment layers whereby the alignment layers are treated to provide uniform alignment of the cholesteric helix. Polymerizing a small amount of a reactive monomer in the cholesteric stabilize the ULH texture at zero voltage. The electro-optical effect is achieved by applying a bias field to induce an in-plane rotation of cholesteric helical initially parallel to one of a pair of polarizers crossed at 90 degrees. The retardation value of PS-CLC reaches maximum in response to a bias electric voltage when the rotation of the helix axis is at 45-degree tilt between the crossed polarizers. The active retardation films can be used as single or tandem films. These added features offer many new device applications including beam steering devices, spatial light modulators, displays and other devices.

主权项

1. A liquid crystal device comprising:
a first transparent substrate having an interior and exterior surface; a second transparent substrate having an interior and exterior surface, wherein the first and second substrates are separated by a predetermined distance; an electrically conductive layer located on the interior surface of each of the first and second substrates; at least one alignment layer formed on the interior surface of at least one of the substrates; a liquid crystal material comprising at least one nematic liquid crystal material having a small flexoelectric coefficient and a bimesogenic nematic liquid crystal dopant with a large flexoelectric coefficient; and a polymer matrix comprising at least one chiral material, at least one polymerizable monomer and a photo-initiator, wherein the liquid crystal material is contained within and between the electrically conductive layers of the first and second transparent substrates, and wherein the liquid crystal material forms a uniform lying helix (ULH) texture with no voltage applied and at room temperature, and is switchable by the application of an electric field.