Backlights having stacked waveguide and optical components with different coefficients of friction

Patent metadata

Field	Value
Publication number	US-10948648-B2
Application number	US-201816651277-A
Country	US
Kind code	B2
Filing date	Sep 28, 2018
Priority date	Sep 29, 2017
Publication date	Mar 16, 2021
Grant date	Mar 16, 2021

Abstract

A backlight includes a directional waveguide and a light source array, for providing large area directed illumination from localized light sources. Interfaces are provided between the directional waveguide and optical components adjacent the directional waveguide such that the coefficient of friction at the waveguide interfaces is greater than the coefficient of friction at least one outer interface on each side of the waveguide in the stack. Damage from compressive forces on the optical stack may be reduced, achieving improved optical performance and lifetime. Privacy display, low stray light display and autostereoscopic display may be provided with high uniformity, long lifetime and reduced cost mechanical components.

First claim

The invention claimed is:

1. A directional backlight comprising:
at least two light sources;
a directional waveguide including an input end extending in a lateral direction along a side of the directional waveguide, and opposed first and second guide surfaces extending across the directional waveguide from the input end, the light sources disposed along the input end to project light into the directional waveguide, the directional waveguide configured to deflect input light to exit through the first guide surface;
a plurality of optical components coupled to the directional waveguide to form a stack; and
a support component coupled to the stack,
wherein directional waveguide interfaces are defined between the directional waveguide and the optical components adjacent the directional waveguide, outer interfaces are defined between the optical components or between the optical components and the support component, and the coefficient of friction at the directional waveguide interfaces is greater than the coefficient of friction at an at least one outer interface on each side of the directional waveguide in the stack.

2. A directional backlight according to claim 1 , wherein at least one optical component adjacent the directional waveguide is transparent to at least one operating wavelength of the light sources.

3. A directional backlight according to claim 1 , wherein each optical component adjacent the directional waveguide has a surface at the directional waveguide interface on one side thereof that is shaped to prevent optical coupling between the directional waveguide and the optical component adjacent the directional waveguide in the absence of an external compressive force.

4. A directional backlight according to claim 1 , wherein each optical component adjacent the directional waveguide has a surface at the directional waveguide interface on one side thereof with an RMS roughness of at least 0.05 micrometres.

5. A directional backlight according to claim 1 , wherein the surface properties of at least one of the optical components at the directional waveguide interfaces are provided by the addition of asperity particles to the respective coating.

6. A directional backlight according to claim 1 , wherein the surface properties of at least one of the optical components at the directional waveguide interfaces are provided by the addition of asperity particles to the bulk of the substrate.

7. A directional backlight according to claim 1 , wherein the surface properties of, at least one of the optical components adjacent the directional waveguide, on one side are provided by the addition of asperity particles arranged in a surface coating layer of the optical components.

8. A directional backlight according to claim 1 , wherein said at least one of the optical components adjacent the directional waveguide comprises a surface formed by an embossing process.

9. A directional backlight according to claim 1 , wherein the outer layer of the optical component at the outer interface comprises a low friction additive or coating.

10. A directional backlight according to claim 1 , wherein the stack comprises optical components outside the second guide surface of the directional waveguide that include:
an optical component adjacent the directional waveguide;
a rear reflector outside said optical component adjacent the directional waveguide and comprising an array of reflective facets arranged to reflect light that is transmitted through the second guide surface back through the directional waveguide to exit through the first guide surface; and
a support component outside and adjacent the rear reflector, wherein both (i) the coefficient of friction at the directional waveguide interfaces and (ii) the coefficient of friction at the outer interface between the optical component adjacent the directional waveguide and the rear reflector are greater than the coefficient of friction at the outer interface between the rear reflector and the support component.

11. A directional backlight according to claim 1 , wherein each optical component adjacent the directional waveguide has a surface at the directional waveguide interface having a surface hardness of not more than two pencil hardness levels different from the pencil hardness of the directional waveguide surface, preferably not more than one pencil hardness level different from the pencil hardness of the directional waveguide surface and most preferably the same pencil hardness level as the pencil hardness of the directional waveguide surface.

12. A directional backlight according to claim 1 , wherein at least one of the optical components adjacent the directional waveguide has differing surface properties, which are provided with a coefficient of friction at the directional waveguide interface on one side thereof that is greater than the coefficient of friction at the outer interface on the other side thereof.

13. A directional backlight according to claim 12 , wherein said at least one of the optical components adjacent the directional waveguide has at least one surface that is treated or processed to provide said differing surface properties, and wherein said treatment is by chemical, plasma, flame or corona means.

14. A directional backlight according to claim 12 , wherein said at least one of the optical components adjacent the directional waveguide has a surface at the directional waveguide interface on one side thereof that is chemically treated to increase its roughness.

15. A directional backlight according to claim 12 , wherein the stack comprises optical components outside the first guide surface of the directional waveguide that include:
an optical component adjacent the directional waveguide having said differing surface properties.

16. A directional backlight according to claim 12 , wherein the stack comprises optical components outside the second guide surface of the directional waveguide that include:
an optical component adjacent the directional waveguide having said differing surface properties; and
a rear reflector comprising an array of reflective facets arranged to reflect light that is transmitted through the second guide surface back through the directional waveguide to exit through the first guide surface.

17. A directional backlight according to claim 12 , wherein the stack comprises components outside the second guide surface of the directional waveguide that include:
a rear reflector adjacent the directional waveguide and comprising an array of reflective facets arranged to reflect light that is transmitted through the second guide surface back through the directional waveguide to exit through the first guide surface, the rear reflector having said differing surface properties; and
a support component outside and adjacent the rear reflector, wherein the coefficient of friction at the directional waveguide interface between the directional waveguide and the rear reflector is greater than the coefficient of friction at the outer interface between the rear reflector and the support component.

18. A directional backlight according to claim 12 , wherein said at least one of the optical components adjacent the directional waveguide comprises plural layers, the outer layers of which provide said differing surface properties.

19. A directional backlight according to claim 18 , wherein one of said layers is a substrate and one or both of the outer layers is a coating applied to the substrate.

20. A directional backlight according to claim 18 , wherein said plural

Assignees

• Reald Spark Llc

Inventors

• Ihas Benjamin
• Ramsey Robert A
• Woodgate Graham J
• Harrold Jonathan

Classifications

• G02B6/0053

  Prismatic sheet or layer; Brightness enhancement element, sheet or layer · CPC title

• G02B6/0055

  Reflecting element, sheet or layer · CPC title

• G02B6/005

  provided by one optical element, or plurality thereof, placed on the light output side of the light guide · CPC title

• G02B6/0048

  with stepwise taper · CPC title

• G02B6/0088

  of the light guide or other optical sheets in the package · CPC title