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AssigneesDisplaytech, Inc., Hoechst Aktiengesellschaft
InventorsMichael D. Wand, Claus Escher, Mark A. Handschy, Rohini T. Vohra
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Fast response, high contrast Ferroelectric Liquid Crystal (FLC) electro-optic devices in which the FLC retains a helical director structure stable to unwinding are provided. In particular, high contrast distorted helix FLC electro-optic devices including half-wave plates in the visible wavelength region are provided. The FLC cells of this invention incorporate chiral FLCs which exhibit a ferroelectric phase and a chiral nematic phase at temperatures above the ferroelectric phase. The natural helix pitch of the FLC in the ferroelectric phase is sufficiently tighter than the thickness of the FLC layer such that it is not surface-stabilized. The chiral nematic phase has a natural helix pitch sufficiently greater than the cell thickness to facilitate alignment of the FLC in the device to achieve high contrast.
A high contrast electro-optic device having variable optical anisotropy comprising a ferroelectric liquid crystal layer of a predetermined thickness positioned between electrode plates at least one of which is transparent or semitransparent, a means for applying voltage to said electrodes across said ferroelectric liquid crystal layer such that the optical anisotropy of said device is thereby changed, means for optically distinguishing the variation in optical anisotropy of said device with applied voltage wherein the ferroelectric liquid crystal of said layer exhibits a ferroelectric phase and a chiral nematic phase at temperatures above said ferroelectric phase, in said ferroelectric phase, the natural helix pitch of the ferroelectric liquid crystal is sufficiently shorter than the thickness of the ferroelectric liquid crystal layer such that the ferroelectric liquid crystal has a helical director structure in the absence of an applied voltage and is not surface-stabilized and, in said chiral nematic phase, the natural helix pitch of the ferroelectric liquid crystal is sufficiently greater than the thickness of said ferroelectric liquid crystal layer to facilitate alignment of said ferroelectric liquid crystal layer in said device such that the contrast of said cell is at least about 40:1.
A high contrast electro-optic DHFLC device having variable optical anisotropy comprising a ferroelectric liquid crystal layer of a predetermined thickness positioned between electrode plates at least one of which is transparent or semitransparent, a means for applying voltage to said electrodes across said ferroelectric liquid crystal layer such that the optical anisotropy of said device is thereby changed, means for optically distinguishing the variation in optical anisotropy of said device with applied voltage wherein the ferroelectric liquid crystal of said layer exhibits a ferroelectric phase and a chiral nematic phase at temperatures above said ferroelectric phase, in said ferroelectric phase the natural helix pitch of the ferroelectric liquid crystal is sufficiently shorter than the thickness of the ferroelectric liquid crystal layer such that the ferroelectric liquid crystal has a helical director structure in the absence of an applied field and is not surface-stabilized and, in said chiral nematic phase the natural helix nematic of the ferroelectric liquid crystal is sufficiently greater than the thickness of said ferroelectric liquid crystal to facilitate alignment of said ferroelectric liquid crystal layer in said device such that the contrast of said cell is at least about 40:1.
Dependencies are inferred from the claim text.