Reflective liquid crystal display with improved contrast

• US 20030081154A1
• Filed: 11/01/2001
• Published: 05/01/2003
• Est. Priority Date: 11/01/2001
• Status: Active Grant

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Coleman, Zane Arthur, Valliath, George Thomas, Schindler, Jon Lindsay
• Granted Patent: US 6,636,285 B2
• Time in Patent Office: Days
• US Class Current: 349/106
• CPC Class Codes: G02B 5/0252 using holographic or diffractive means
• CPC Class Codes: G02F 1/133504 Diffusing, scattering, diffracting elements associated to illuminating devices G02F1/133606
• CPC Class Codes: G02F 1/133553 Reflecting elements associated to illuminating devices G02F1/133605
• CPC Class Codes: G02F 1/1362 Active matrix addressed cells G02F1/134336, G02F1/134363 take precedence
• CPC Class Codes: G02F 2203/02 reflective

Abstract

A display (200) includes a slanted fringe volume hologram (206) or other optical element that steers light that passes into and out of the display (200) so as to provide angular separation between unmodulated scattered light and modulated reflected light. As a result of the angular separation the effective contrast of the display (200) is improved. By placing the slanted fringe volume hologram (206) below a front polarizer of the display a further reduction in the amount of unmodulated scatter light is achieved. The slanted fringe volume hologram is preferably a hologram of a diffusive object (328), and consequently exhibits a degree of light diffusion that results in a viewing zone of an appreciable angular extent.

Claims

1. A display comprising:

a light modulating element;

a polarizer located on a first side of the light modulating element;

a reflective element located on a second side of the light modulating element; and

an optical element that is;

located between the light modulating element and the polarizer;

includes a first side facing the polarizer, and a second side facing the light modulating element; and

is adopted to;

receive a first pencil of light characterized by a first angle at the first side, and in response to receiving the first pencil of light, output a second pencil of light that is characterized by a second angle and includes a substantial portion of light from the first pencil of light at the second side;

receive a third pencil of light that is characterized by a third angle at the second side, and in response to receiving the third pencil of light output a fourth pencil of light that is characterized by a fourth angle and includes a substantial portion of light from the third pencil of light at the first side, wherein the first angle differs in magnitude from the fourth angle.

2. The display according to claim 1 wherein:

the reflective element is specular and is adapted to form the third pencil of light by reflecting the second pencil of light.

3. The display according to claim 1 wherein:

the optical element comprises a diffraction grating.

4. The display according to claim 1 wherein:

the optical element comprises a slanted fringe volume hologram that is characterized by a fringe slant angle.

5. The display according to claim 4 wherein the fringe slant angle is between about 6 and about 22 degrees from normal to the display.

6. The display according to claim 5 wherein the slanted fringe volume hologram is characterized by an average index of refraction of between about 1.4 and about 1.6.

7. The display according to claim 1 wherein the light modulating element comprises a light polarization modulating element.

8. The display according to claim 7 wherein the light polarization modulating element comprises a liquid crystal material.

9. A liquid crystal display comprising:

a layer of liquid crystal material;

a polarizer located on a first side of the layer of liquid crystal material; and

a slanted fringe volume hologram located between the layer of liquid crystal material and the polarizer.

10. The liquid crystal display according to claim 9 wherein the slanted fringe volume hologram is an off-axis hologram of a diffusive object.

11. The liquid crystal display according to claim 9 wherein:

the slanted fringe volume hologram is manufactured by making a hologram of a diffuser in a photosensitive material.

12. The liquid crystal display according to claim 11 wherein:

the slanted fringe volume hologram is manufactured by impinging a reference beam on the photosensitive material at an angle between about 19 and about 49 degrees; and

impinging an object beam on the photosensitive material at an angle between about zero and about 19 degrees.

13. The liquid crystal display according to claim 9 wherein:

the slanted fringe volume hologram is characterized by;

a average fringe slant angle of between about 6 and about 22 degrees; and

an average index of refraction of between about 1.4 and about 1.6.

14. The liquid crystal display according to claim 13 wherein:

the slanted fringe volume hologram is manufactured by creating a hologram of a diffuser in a photosensitive material.

15. The liquid crystal according to claim 14 wherein:

the slanted fringe volume hologram is less than about 30 microns thick.

16. The liquid crystal display according to claim 15 wherein:

the photosensitive material is a photopolymer.

17. The liquid crystal display according to claim 14 further comprising:

a first alignment layer characterized by a first alignment axis in contact with a first side of the layer of liquid crystal material layer;

a second alignment layer characterized by a second alignment axis that is different from the first alignment axis in contact with a second side of the layer of liquid crystal material layer; and

a plurality of reflective electrodes for applying electric fields to the layer of liquid crystal material in localized areas.

18. A handheld device comprising:

liquid crystal display including;

a layer of liquid crystal material;

a polarizer located on a first side of the layer of liquid crystal liquid crystal; and

a slanted fringe volume hologram located between the layer of liquid crystal material and the polarizer.

19. The handheld device according to claim 18 wherein:

the slanted fringe volume hologram is characterized by;

a average fringe slant angle of between about 6 and about 22 degrees; and

an average index of refraction of between about 1.4 and about 1.6.

20. The handheld device according to claim 19 wherein the slanted fringe volume hologram is an off-axis hologram of a diffusive object.