Optical: systems and elements – Holographic system or element – Using a hologram as an optical element
Patent
1994-07-13
1995-10-17
Gross, Anita Pellman
Optical: systems and elements
Holographic system or element
Using a hologram as an optical element
359 80, 359100, G02F 11339
Patent
active
054595983
DESCRIPTION:
BRIEF SUMMARY
This invention relates to an optical modulation device including first and second optically transmissive parallel plates having a ferroelectric liquid crystal material sandwiched therebetween, a plurality of spacer members, each secured to a said plate, being located between said plates for maintaining spacing between said plates at a predetermined value, said spacer members defining substantially parallel liquid crystal material-containing channels extending parallel to the plates.
A device of the above general kind is known, for example, from GB-B-2157451. In such devices the facing surfaces of the two plates are normally provided with respective arrays of optically transmissive electrodes, for example, mutually orthogonal grids of electrodes, by means of which portions of the liquid crystal material can be selectively addressed. Such addressing enables optical properties of selected portions of the material to be changed. If the assembly of the two plates is positioned between crossed polarisers, the said addressing can result in modification of the optical transmissivity of selected areas of the resulting device, thereby enabling it to be used, for example, as a television display device.
In the device known from GB-B-2157451 the spacer members take the form of parallel solid walls all of which are secured to one plate and extend from one side of the plate to the other. According to the disclosure of GB-B-2157451 the walls of the device disclosed therein serve the additional purpose of improving monodomain formability in the liquid crystal material, and to this end they are oriented parallel with or perpendicular to a monaxial orientation treatment (conventionally a rubbing treatment) which has been applied to the face of at least one of the two plates contacting the liquid crystal material.
Devices of the general kind specified in the first paragraph can be subjected to substantial temperature variations. This can give rise to problems in some cases if spacer members of the kind disclosed in GB-B-2157451 are employed. In particular differences in the thermal expansion coefficients of the materials of the spacer members and the plate to which they are secured may give rise to disruption of the structural integrity of the device.
Devices of the general kind specified in the first paragraph can, moreover, be subjected to mechanical deformation forces which cause parts of the liquid crystal material to move relative to other parts thereof. If the spacing between the plates is small and the liquid crystal material has a high viscosity this can result in changes in physical properties of parts of the material which have a deleterious effect on operation of the device and which can only be reversed with difficulty.
It is an object of the present invention to enable one or both of the above problems to be mitigated.
The invention provides an optical modulation device including first and second optically transmissive parallel plates having a ferroelectric liquid crystal material sandwiched therebetween, a plurality of spacer members, each secured to a said plate, being located between said plates for maintaining spacing between said plates at a predetermined value, said spacer members defining substantially parallel liquid crystal material-containing channels extending parallel to the plates, which channels communicate along their lengths with cavities at least partly defined by the spacer members.
Sets of the spacer members may be each configured as successive spaced segments of a respective wall which runs between a said channel and an adjacent said channel, spaces between the segments constituting the said cavities. If this is the case segmented versions of the solid walls of GB-B-2157451 can in effect be obtained. It has been found that such segmented versions can have an adequate spacing and strengthening effect without causing the device to suffer unduly from the effects of temperature changes. Moreover, if the members of a first subset of a said set are secured to the first plate and the members of a se
REFERENCES:
patent: 4832460 (1989-05-01), Fujimura et al.
Gross Anita Pellman
Malinowski Walter J.
Thorn Emi plc
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