BACKLIGHTING SYSTEM INCLUDING A SPECULAR PARTIAL REFLECTOR AND A CIRCULAR-MODE REFLECTIVE POLARIZER

• US 20110037922A1
• Filed: 12/22/2008
• Published: 02/17/2011
• Est. Priority Date: 12/28/2007
• Status: Active Grant

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Watson, Philip E., O'Neill, Mark B.
• Granted Patent: US 8,427,599 B2
• Time in Patent Office: Days
• US Class Current: 349/62
• CPC Class Codes: G02B 6/0055 Reflecting element, sheet or layer
• CPC Class Codes: G02B 6/0056 for producing polarisation effects, e.g. by a surface with polarizing properties or by an additional polarizing elements
• CPC Class Codes: G02F 1/133504 Diffusing, scattering, diffracting elements associated to illuminating devices G02F1/133606
• CPC Class Codes: G02F 1/133507 Films for enhancing the luminance
• CPC Class Codes: G02F 1/133536 Reflective polarizers G02F1/13362 takes precedence
• CPC Class Codes: G02F 1/133541 Circular polarisers
• CPC Class Codes: G02F 1/133603 with LEDs
• CPC Class Codes: G02F 1/13362 providing polarized light, e.g. by converting a polarisation component into another one
• CPC Class Codes: Y10T 29/49002 Electrical device making

Abstract

In a display backlight (120, 220, 420) a specular partial reflector (250, 450) is placed between a circular-mode reflective polarizer (242, 442) and an illumination device (230, 430). The specular partial reflector (450) recycles otherwise unused polarized light (468L) reflected from the circular-mode reflective polarizer (442) which results in an optimized backlight brightness. The main application of the backlight (120) is in liquid crystal displays (100)

Claims

1. A backlight, comprising:

an illumination device comprising at least one light source;

a circular-mode reflective polarizer; and

a specular partial reflector disposed between the illumination device and the circular-mode reflective polarizer;

wherein the specular partial reflector is in substantially direct polarization communication with the circular-mode reflective polarizer.

2. The backlight of claim 1, wherein the illumination device further comprises a lightguide, wherein the at least one light source is optically coupled to an edge of the lightguide.

3. The backlight of claim 1, wherein the circular-mode reflective polarizer comprises a cholesteric liquid crystal layer.

4. The backlight of claim 1, wherein the circular-mode reflective polarizer comprises:

a linear-mode reflective polarizer; and

a quarter-wave retarder disposed between the linear-mode reflective polarizer and the specular partial reflector.

5. The backlight of claim 1, wherein the specular partial reflector comprises a layer disposed on a substrate, the substrate having an optical function different from that of the specular partial reflector.

6. The backlight of claim 1, wherein the specular partial reflector comprises a coating disposed on the circular-mode reflective polarizer.

7. The backlight of claim 1, wherein the specular partial reflector comprises a metalized partial reflector.

8. The backlight of claim 1, wherein the specular partial reflector comprises a plurality of substantially specularly-reflecting major surfaces.

9. The backlight of claim 8, wherein the specular partial reflector comprises a multilayer optical film.

10. The backlight of claim 9, wherein the multilayer optical film comprises one or more polymeric layers.

11. The backlight of claim 1, wherein the specular partial reflector has an orthogonal reflection fraction value of at least 2%.

12. The backlight of claim 1, wherein the specular partial reflector has an orthogonal reflection fraction value of at least 4%.

13. The backlight of claim 1, wherein the specular partial reflector has an orthogonal reflection fraction value of at least 8%.

14. The backlight of claim 1, wherein the specular partial reflector has an orthogonal reflection fraction value selected to result in an optimized backlight brightness.

15. A display comprising a liquid crystal panel and a backlight that provides light to the liquid crystal panel, wherein the backlight comprises:

an illumination device comprising at least one light source;

a circular-mode reflective polarizer disposed between the liquid crystal panel and the illumination device; and

a specular partial reflector disposed between the illumination device and the circular-mode reflective polarizer;

wherein the specular partial reflector is in substantially direct polarization communication with the circular-mode reflective polarizer.

16. A backlight for providing polarized light, comprising:

an illumination device comprising at least one light source;

a circular-mode reflective polarizer configured to transmit a first portion of light having a first circular polarization and reflect a second portion of light having a second circular polarization orthogonal to the first circular polarization; and

a specular partial reflector disposed between the illumination device and the circular-mode reflective polarizer, the specular partial reflector suitable for receiving the second portion of light from the circular-mode reflective polarizer and returning a third portion of light to the circular-mode reflective polarizer, the third portion of light being a fraction of the second portion of light and having the first circular polarization that is transmittable by the circular-mode reflective polarizer.

17. A method of making a backlight, comprising:

providing an illumination device;

providing a circular-mode reflective polarizer;

selecting an orthogonal reflection fraction value for a specular partial reflector to result in an optimized backlight brightness; and

placing a specular partial reflector having the selected orthogonal reflection fraction value between the illumination device and the circular-mode reflective polarizer, wherein the specular partial reflector is in substantially direct polarization communication with the circular-mode reflective polarizer.