Method and apparatus for reducing optical cross talk in a liquid crystal optical switch
First Claim
1. In an optical display system comprising a liquid crystal switching device which includes a liquid crystal material captured between a pair of spaced-apart and generally parallel transparent substrates, one substrate comprising first and second electrode structures and the other substrate comprising a common electrode structure, the first and common electrode structures defining a first cell segment and the second and common electrode structures defining a second cell segment, a method for sequentially electrically driving the first and second cell segments to reduce optical cross talk between the segments during operation of the display system, comprising the steps of:
- applying an excitation potential difference between the first and common electrode structures of the first cell segment during a first time interval to bias the first cell segment to its "ON" state;
applying an excitation potential difference between the second and common electrode structures of the second cell segment during a second time interval to bias the second cell segment to its "ON" state; and
introducing between the first and common electrode structures of the first cell segment during the second time interval a high impedance condition for at least part of the time while the second cell segment is biased in its "ON" state, thereby to optically isolate the first and second cell segments.
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Abstract
A field sequential color display system (10) employs a liquid crystal device operating as a variable optical retarder (12) which is positioned in front of the screen (40) of a raster scanned cathode ray tube (38) to develop a high quality multicolored image. The liquid crystal device is divided into upper and lower cell segments (34 and 36) to decrease the time between successive color fields. Each cell segment has a separate electrode structure (30 and 32) and a common electrode structure (22) and is separately commanded by a switching circuit (46) to a predetermined optical retardation state when the electron beam scans the portion of the screen covered by the cell segment. The switching circuit provides signals in a predetermined time sequence to the cell segments to minimize the optical cross talk between them and thereby minimize the spurious transmission of colored light from the display system.
54 Citations
22 Claims
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1. In an optical display system comprising a liquid crystal switching device which includes a liquid crystal material captured between a pair of spaced-apart and generally parallel transparent substrates, one substrate comprising first and second electrode structures and the other substrate comprising a common electrode structure, the first and common electrode structures defining a first cell segment and the second and common electrode structures defining a second cell segment, a method for sequentially electrically driving the first and second cell segments to reduce optical cross talk between the segments during operation of the display system, comprising the steps of:
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applying an excitation potential difference between the first and common electrode structures of the first cell segment during a first time interval to bias the first cell segment to its "ON" state; applying an excitation potential difference between the second and common electrode structures of the second cell segment during a second time interval to bias the second cell segment to its "ON" state; and introducing between the first and common electrode structures of the first cell segment during the second time interval a high impedance condition for at least part of the time while the second cell segment is biased in its "ON" state, thereby to optically isolate the first and second cell segments. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. An optical switching system including a liquid crystal device that receives from a light source light rays in a defined polarization state, wherein the device comprises:
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first and second contiguous cell segments, the first cell segment including a first separate electrode structure and a common electrode structure having a liquid crystal material captured therebetween and the second cell segment including a second separate electrode structure and the common electrode structure having a liquid crystal material captured therebetween; and
wherein the switching system comprises;switching means in communication with the first separate electrode structure for applying a first signal to the first cell segment to change the character of the polarization state of the light rays passing therethrough and with the second separate electrode structure for applying a second signal to the second cell segment to change the character of the polarization state of light rays passing therethrough, the switching means being operable to apply the first and second voltage signals in a manner to separately change the character of the polarization state of the light rays passing through each one of the cell segments and being operable to induce on the separate electrode structure of one of the cell segments a signal of the character of a noise voltage signal induced on the common electrode structure by the signal applied to the separate electrode structure of the other cell segment, thereby to optically isolate the cell segments by minimizing any change in character of the polarization state of the light rays passing through the one cell segment resulting from a change in the character of the polarization state of the light rays passing through the other cell segment. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16, 17, 18)
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19. A high-speed color switch which receives light of a plurality of wavelengths emitted from a light source, comprising:
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first and second light polarizing means in optical communication with the light source, the first light polarizing means including a color selective polarizing filter; variable optical retarding means disposed between the first and second light polarizing means, the variable optical retarding means including a liquid crystal cell comprising first and second contiguous cell segments, the first cell segment including a first electrode structure and a common electrode structure having a liquid crystal material captured therebetween and the second cell segment including a second electrode structure and the common electrode structure having a liquid crystal material captured therebetween; and switching means in communication with the first and second electrode structures for applying a separate potential difference to each cell segment, thereby to selectably transmit a light output of one of two colors through the first cell segment during a first time interval and a light output of one of two colors through the second cell segment during a second time interval. - View Dependent Claims (20, 21, 22)
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Specification