Liquid crystal cells – elements and systems – Liquid crystal optical element – Liquid crystal diffraction element
Patent
1996-10-25
2000-01-11
Sikes, William L.
Liquid crystal cells, elements and systems
Liquid crystal optical element
Liquid crystal diffraction element
349123, 349124, 349202, G02F 113, G02F 11337
Patent
active
060141972
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a device for controlling a beam of electro-magnetic radiation comprising two composed elements and an electro-optic medium between these elements, each of the elements successively comprising a substrate layer, an electrode layer and an orientation layer, each of the orientation layers facing the electro-optic medium and the electro-optic medium being switchable between at least two states. The invention also relates to an image display panel. Such panel may be used in a direct view display apparatus or in an image projection apparatus, for example for video applications, or as a monitor. The device of the invention may also be used in a wavelength selector or in a beam direction controller.
A device as mentioned in the opening paragraph is described in U.S. Pat. No. 5,262,882. In this patent, a liquid crystal cell is shown with orientation layers of an oriented polymer comprising liquid crystal material. Due to the strong interaction between the orientation layer and the switchable liquid crystalline material, the latter is oriented in the direction of orientation of the oriented polymer.
If such a cell is used in a display or shutter application, it is usually placed between two mutually crossed polarizers. The first polarizer transmits one of the polarization components of the incident visible radiation and absorbs the other polarization component. Dependent on the voltage across the cell the polarization direction of the transmitted component is more or less rotated and partly or entirely transmitted by the second polarizer. The radiation which is not transmitted by the second polarizer is absorbed by this polarizer. Moreover, radiation losses due to reflections at the polarizers surfaces may occur so that considerably more than 50% of the radiation incident on the first polarizer is lost.
OBJECTS AND SUMMARY OF THE INVENTION
It is, inter alia, an object of the present invention to provide a device of the type described above for use in an image display apparatus such that the said drawbacks are entirely or partly obviated. To this end the device according to the invention is characterized in that at least one of the orientation layers has a linear periodic surface profile of alternating higher and lower strip-shaped surface portions and comprises a birefringent material having refractive indices which are substantially equal to those of the electro-optic medium in one of the states.
In the latter state, at the interface of the orientation layer and the electro-optic medium, for example a liquid crystalline medium, no change in refractive indices occur, so that an incident visible radiation beam does not "see" the surface profile and is not influenced thereby. If, the electro-optic medium is in one of the other states the surface profile of an orientation layer influences the extraordinary beam component, i.e. the component having the direction of polarization parallel to the length direction of the strip-shaped surface portions, whereas the ordinary beam component, i.e. the component having the direction of polarization transverse to said length direction is passed unhindered. In this way one of the polarization components of a beam incident on the device can be controlled.
A preferred embodiment of the device which enables the two polarization components to be controlled is characterized in that the second orientation layer has a linear periodic surface profile of alternating higher and lower strip-shaped surface portions and comprises a birefringent material having refractive indices which are substantially equal to those of the electro-optic medium in said one of the states, and in that the length direction of the surface portions of the second orientation layer is substantially different from said length direction of the first orientation layer.
The extraordinary beam component is substantially entirely transmitted due to the second surface profile at the other side of the electro-optic medium, and also dependent on the mutual angle between
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Chowdhury Tarifur R.
Fox John C.
Sikes William L.
U.S. Philips Corporation
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