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.