Liquid crystal shutter

• US 20040036821A1
• Filed: 03/21/2003
• Published: 02/26/2004
• Est. Priority Date: 08/22/2002
• Status: Abandoned Application

• Current Assignee: Nitto Denko Corporation
• Original Assignee: Optiva, Inc.
• Inventors: Paukshto, Michael V., Silverstein, Louis D.
• Application Number:
  US10/394,556
• Publication Number:
  US 20040036821A1
• Time in Patent Office: Days
• US Class Current: 349/74
• CPC Class Codes: G02F 1/13471 in which all the liquid crystal cells or layers remain transparent, e.g. FLC, ECB, DAP, HAN, TN, STN, SBE-LC cells G02F1/13475 takes precedence
• CPC Class Codes: G02F 1/1398 the twist being below 90°

Abstract

A liquid crystal shutter is provided comprising at least two liquid crystal cells and at least three polarizers. Each of the liquid crystal cells contains a plurality of layers between two substrates and is disposed between two adjacent polarizers. The adjacent two liquid crystal cells have substantially equal absolute values and opposite directions of twist angles. The liquid crystal shutter of the invention substantially increases the viewing angle and the contrast ratio at large viewing angles, provides a symmetrical dependence of the contrast ratio on the viewing angle, and decreases the switching time as well as the driving voltages. The shutter provides substantially improved angular characteristics, high contrast ratio, good transparency in the light state, and a fast switching time.

Claims

1. A liquid crystal shutter, comprising:

at least two liquid crystal cells; and

at least three polarizers,

wherein each of the liquid crystal cells contains a plurality of layers between two substrates and is disposed between two adjacent polarizers, and wherein adjacent two liquid crystal cells have substantially equal absolute values and opposite directions of twist angles.

2. The liquid crystal shutter of claim 1, wherein said two liquid crystal cells have substantially equal refractive indices of ordinary directions, substantially equal refractive indices of extraordinary directions, and substantially equal thickness of liquid crystals layers.

3. The liquid crystal shutter of claim 1, wherein the single polarizer is disposed between said two adjacent cells and operates as a rear polarizer of one cell and a front polarizer of another cell.

4. The liquid crystal shutter of claim 1, wherein at least one of said polarizers is internal.

5. The liquid crystal shutter of claim 1, wherein all of said polarizers are internal.

6. The liquid crystal shutter of claim 1 made of two identical liquid crystal cells distinguished only by a twist direction of LC molecules.

7. The liquid crystal shutter of claim 1 wherein said liquid crystal cells are combined without a gap between them by means of an optically transparent material whose refractive index equals a refractive index of transparent substrates.

8. The liquid crystal shutter of claim 1 wherein a front cell has a rear polarizer having a transmission axis, a rear cell has a front polarizer having a transmission axis, and the transmission axes constitute an angle in a range between 0°

and 90°

.

9. The liquid crystal shutter of claim 1 wherein each of said liquid crystal cells comprises a liquid crystal layer having an absolute twist angle substantially equal to 90°

.

10. The liquid crystal shutter of claim 1 wherein directors of liquid crystal molecules are twisted through an angle with absolute values from 20°

up to 85°

in each of the cells when passing through a liquid crystal layer.

11. The liquid crystal shutter of claim 1 further comprising functional layers of transparent electrodes, transparent protective insulating layers, and transparent aligning layers.

12. The liquid crystal shutter of claim 11, wherein the functional layers include electrodes, and an internal polarizer is disposed between a transparent substrate and an electrode in one of the cell panels.

13. The liquid crystal shutter of claim 1 wherein the substrates are made of glass or transparent plastic.

14. The liquid crystal shutter of claim 4, wherein at least one said internal polarizer is simultaneously a retarder or an aligning layer or a color-correcting light filter or ultraviolet filter or infrared filter or fulfills a function of at least two of said layers.

15. The liquid crystal shutter of claim 1 wherein said plurality layers comprises ultraviolet and/or infrared light filters.

16. The liquid crystal shutter of claim 15 wherein the ultraviolet and/or infrared light filters are disposed in a sequence of layers between an irradiation source and a polarizer, nearest to the latter, of the shutter.

17. The liquid crystal shutter of claim 15 wherein the ultraviolet and/or infrared light filters are disposed in a sequence of layers between an irradiation source and a liquid crystal, nearest to the latter, of the shutter.

18. The liquid crystal shutter of claim 1 further comprising retarders or color-correcting light filters or scattering layers or planarization layers.

19. The liquid crystal shutter of claim 1 wherein the shutter provides a time of switching from a dark state to a light state no greater than 0.02 second.

20. The liquid crystal shutter of claim 1 wherein in the absence of a voltage applied to each of the liquid crystal cells, the shutter is in a dark state and has a darkening degree of no less than 9 DIN units.

21. The liquid crystal shutter of claim 1 wherein the shutter provides a darkening degree no less than 10 DIN units in a dark state and no greater than 4 DIN units in a light state.

22. The liquid crystal shutter of claim 21, wherein the darkening degree in ultraviolet and infrared regions is no less than 10 DIN units in dark and light states.

23. The liquid crystal shutter of claim 1, further comprising a photosensitive element with an electrical circuit, which switches a shutter from a dark state to a light state by a signal from the photosensitive element.

24. The liquid crystal shutter of claim 1, further comprising a photosensitive element with an electrical circuit, which switches a shutter from a light state to a dark state by a signal from the photosensitive element.

25. The liquid crystal shutter of claim 1, wherein an azimuthal viewing angle, corresponding to a darkening degree of no less than 10, equals a value of no less than 60°

in any polar direction.

26. The liquid crystal shutter of claim 1 wherein at least one said polarizer is made of an optically anisotropic dichroic film crystal whose substance contains aromatic cycles and is characterized by an interplanar distance of 3.4±

0.3Å

in a direction of one of the optical axes.

27. The liquid crystal shutter of claim 26 wherein the layer of an optically anisotropic dichroic film crystal is treated with ions of bi- and/or trivalent metals.

28. The liquid crystal shutter of claim 26 wherein the molecules of at least one aromatic organic compound contain heterocycles.

29. The liquid crystal shutter of claim 26 wherein the layer of the optically anisotropic thin crystal film is formed from a lyotropic liquid crystal on the basis of at least one dichroic dye.