1987-11-30
1990-01-16
Miller, Stanley D.
350351, 350347V, G02F 113
Patent
active
048939072
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to optical devices using liquid crystal material. Liquid crystal materials are liquids which exhibit the long range molecular order characteristic of crystals although they are in the liquid state. They display marked changes in their optical properties with changes of their temperature or in response to an applied electric field. These are three predominant meso-phases which may exist between the solid and isotropic liquid states and these are, in the order in which they generally occur with ascending temperature, the smectic, nematic and cholesteric phases. Not all liquid crystal materials exhibit all phases. In a common application of liquid crystal materials they are used to produce display devices for electronic calculators and portable computers. In addition, two-dimensional arrays of liquid crystal elements have been used to produce displays of images and also of television pictures.
With the advent of optical waveguides to convey information signals a need has arisen for optical devices which can be controlled electrically. To this end an attempt has been made to produce a light channel using liquid crystal material in the nematic phase. However, it was found that the channel imposed a loss of about 30 d8/cm on the light propagated through it which was considered to be unacceptable. It has also been noted that the propagation loss of light through an aligned smectic A liquid crystal material is much lower at about 2 d8/cm, but proposals have been made for display devices using such material in light scattering and transparent forms.
It is an object of the present invention to provide optical devices using liquid crystal material in the smectic phase.
According to one aspect of the present invention there is provided a liquid crystal device having smectic phase liquid crystal material in two transparent states of differing molecular orientation, thereby to present differing refractive indices to polarised light transmitted through the device.
According to a second aspect of the present invention there is provided an optical waveguide structure having a liquid crystal device with smectic phase liquid crystal material in two transparent state of differing molecular orientation, so that a part of the material in one state forms an optical waveguide for polarised light having a plane of polarisation related to the molecular orientation of the particular part and a part of the material in the other state abuts the part in the one state to form a boundary of the optical waveguide.
Optical waveguides may be connected to such a structure by being brought to the periphery of the cell containing the material and means, for example a laser, may be used to effect the change in state of the material along a line joining a point on the periphery of the cell where the guide selected as the input waveguide meets it to another point on the periphery of the cell where the waveguide selected as the output waveguide meets it. Alternatively, the waveguides joining the liquid crystal material may be used to link from and/or to waveguides embodied in the major walls of the cell and produced, for example, by ion exchange. The waveguides written into the liquid crystal material may be arranged as field couplers, ring resonators, or other waveguide circuit components.
According to a third aspect of the present invention there is provided an optical component including a liquid crystal device with smectic phase liquid crystal material in two transparent states of differing molecular orientations, the shapes of the parts in the two states being arranged to produce a required effect on polarised light transmitted through the device.
According to a fourth aspect of the present invention there is provided an adjustable optical component including a liquid crystal device with smectic phase liquid crystal material in two transparent states of differing effective refractive indices to polarised light, the boundary between the parts in the different states determining the effect of the component on polar
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British Telecommunications public limited company
Gross Anita Pellman
Miller Stanley D.
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