BIREFRINGENT STRUCTURED FILM FOR LED COLOR MIXING IN A BACKLIGHT

• US 20070297747A1
• Filed: 06/22/2006
• Published: 12/27/2007
• Est. Priority Date: 06/22/2006
• Status: Active Grant

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Biernath, Rolf W., Merrill, William W., Brott, Robert L., Kowitz, David A.
• Granted Patent: US 7,843,637 B2
• Time in Patent Office: Days
• US Class Current: 385/147
• CPC Class Codes: G02B 5/3083 Birefringent or phase retarding elements G02B5/3008, G02B5/3016 take precedence; systems for polarisation control G02B27/286; manufacturing phase modulating patterns by lithographic processes G03F7/001

Abstract

An article for use in light spreading includes a body having first and second surfaces, and first and second in-plane axes that are orthogonal with respect to each other and a third axis that is mutually orthogonal to the first and second in-plane axes in a thickness direction of the body. A portion of the first surface is a birefringent structured surface. The portion is structured such that, when the article receives a light signal within a particular range of wavelengths, the structured surface causes splitting the light signal into a plurality of divergent light signals. The article can be used for color mixing such as in a cavity providing a backlight for LCD devices or other display devices requiring a backlight.

Claims

1. An article for use in light spreading, comprising:

(a) a body having (i) first and second surfaces, and (ii) first and second in-plane axes that are orthogonal with respect to each other and a third axis that is mutually orthogonal to the first and second in-plane axes in a thickness direction of the body; and

(b) a portion of the first surface being a birefringent structured surface,

wherein the portion is structured such that, when the article receives light signals from a plurality of point light sources each emitting light within a particular range of wavelengths, the structured surface causes splitting of the light signals into a plurality of divergent light signals producing a substantially uniform color light signal.

2. The article of claim 1 wherein the structured surface causes a divergence of at least three degrees among the plurality of light signals.

3. The article of claim 1 wherein the structured surface causes a divergence of at least ten degrees among the plurality of light signals.

4. The article of claim 1 wherein the body is composed of a uniaxially oriented polymeric film having (i) a first index of refraction (n₁) along the first in-plane axis, (ii) a second index of refraction (n₂) along the second in-plane axis, and (iii) a third index of refraction (n₃) along the third axis, wherein n₁≠

n₂ and n₁≠

n₃, and n₂ and n₃ are substantially equal to one another relative to their differences with n₁.

5. The article of claim 1 wherein the first surface includes an index matching material on the structured surface causing the first surface to be substantially planar.

6. The article of claim 1 wherein the structured surface comprises a sawtooth pattern.

7. The article of claim 1 wherein the structured surface is formed from a diamond turning method.

8. The article of claim 1 wherein the body is composed of a polyester material.

9. The article of claim 1, further including a film placed proximate the body, wherein the film comprises at least one of the following:

a retarder, a wave plate, a multilayer optical film, an IR filter, a circular polarizer, or a partial mirror surface.

10. A method of making an article for use in light spreading, comprising the steps of:

(a) providing a body having (i) first and second surfaces, and (ii) first and second in-plane axes that are orthogonal with respect to each other and a third axis that is mutually orthogonal to the first and second in-plane axes in a thickness direction of the body; and

(b) forming a birefringent structured surface on a portion of the first surface,

wherein the portion is structured such that, when the article receives light signals from a plurality of point light sources each emitting light within a particular range of wavelengths, the structured surface causes splitting of the light signals into a plurality of divergent light signals producing a substantially uniform color light signal.

11. The method of claim 10, further including causing a divergence of at least three degrees among the plurality of light signals.

12. The method of claim 10, further including causing a divergence of at least ten degrees among the plurality of light signals.

13. The method claim 10, further comprising forming the body of a uniaxially oriented polymeric film having (i) a first index of refraction (n₁) along the first in-plane axis, (ii) a second index of refraction (n₂) along the second in-plane axis, and (iii) a third index of refraction (n₃) along the third axis, wherein n₁≠

n₂ and n₁≠

n₃, and n₂ and n₃ are substantially equal to one another relative to their differences with n₁.

14. The method of claim 10, further comprising including an index matching material on the structured surface causing the first surface to be substantially planar.

15. The method of claim 10, further comprising providing a sawtooth pattern on the structured surface.

16. The method of claim 10, further comprising forming the structured surface from a diamond turned method.

17. The method of claim 10, further comprising forming the body from a polyester material.

18. The method of claim 10, further comprising including a film placed proximate the body, wherein the film comprises at least one of the following:

a retarder, a wave plate, a multilayer optical film, an IR filter, or a circular polarizer.

19. An article for use in light spreading, comprising:

(a) a body having (i) first and second surfaces, and (ii) first and second in-plane axes that are orthogonal with respect to each other and a third axis that is mutually orthogonal to the first and second in-plane axes in a thickness direction of the body; and

(b) a portion of the first surface being a birefringent structured surface,

wherein the portion is structured such that, when the article receives a plurality of light signals each within a distinct range of wavelengths, the structured surface causes splitting the light signal into a plurality of divergent light signals among the wavelengths.

20. The article of claim 19, wherein the portion is structured such that, when the article receives a first light signal within a first range of wavelengths, a second light signal within a second range of wavelengths different from the first range, and a third light signal within a third range of wavelengths different from the first and second ranges, the structured surface causes splitting of the first, second, and third signals to produce a substantially uniform color light signal.

21. The article of claim 19, wherein the portion is structured such that, when the article receives red, green, and blue light signals, the structured surface causes splitting of the red, green, and blue light signals to produce a substantially white light signal.