Optical element for lateral light spreading in back-lit displays and system using same

• US 20060290842A1
• Filed: 06/24/2005
• Published: 12/28/2006
• Est. Priority Date: 06/24/2005
• Status: Active Grant

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Hebrink, Timothy J., Weber, Michael F., Ouderkirk, Andrew J., Epstein, Kenneth A.
• Granted Patent: US 7,903,194 B2
• Time in Patent Office: Days
• US Class Current: 349/113
• CPC Class Codes: G02B 5/0247 by means of voids or pores
• CPC Class Codes: G02B 5/3008 comprising dielectric particles, e.g. birefringent crystals embedded in a matrix
• CPC Class Codes: G02F 1/1335 Structural association of cells with optical devices, e.g. polarisers or reflectors
• 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 1/133606 including a specially adapted diffusing, scattering or light controlling members
• CPC Class Codes: G02F 1/13362 providing polarized light, e.g. by converting a polarisation component into another one

Abstract

A display system has a controlled transmission mirror disposed between the light sources and the display panel. The controlled transmission mirror includes a light-diverting input coupling element facing the light sources, a light-diverting output coupling element facing the display panel and a multilayer reflector between the input and output coupling elements. The controlled transmission mirror laterally spreads the light, making the illumination of the panel more uniform. The controlled transmission mirror may include a transparent substrate between the input and output coupling elements for additional light spreading. The light sources may be positioned within the controlled transmission mirror, rather than behind it. The output coupling element can be insensitive to polarization, so the light passing out of the controlled transmission mirror is unpolarized, or the output coupling element can be polarization sensitive so that the output light is polarized.

Claims

1. An optical system, comprising:

an image-forming panel having an illumination side and a viewing side;

at least a first light source and a second light source disposed to the illumination side of the image-forming panel; and

a controlled transmission mirror between the image-forming panel and the light sources, the controlled transmission mirror comprising an input coupling element facing the first and second light sources and an output coupling element layer facing the image-forming panel, a first multilayer reflector disposed between the input and output coupling elements, the first multilayer reflector being reflective for normally incident light from the light sources, the input coupling element redirecting at least some of the light propagating from the light sources in a direction substantially perpendicular to the first multilayer reflector into a direction that is transmitted through the first multilayer reflector.

2. A system as recited in claim 1, wherein the image-forming panel is a liquid crystal display (LCD) panel, and further comprising a first polarizer disposed on the viewing side of the LCD panel and a second polarizer disposed on the illumination side of the LCD panel.

3. A system as recited in claim 1, further comprising a controller coupled to control an image displayed by the image-forming panel.

4. A system as recited in claim 1, wherein the light sources comprise fluorescent light sources.

5. A system as recited in claim 1, wherein the light sources comprise light emitting diodes.

6. A system as recited in claim 1, wherein the first light source emits light at a first wavelength and the second light source emits light at a second wavelength different from the first wavelength.

7. A system as recited in claim 1, further comprising a base reflector, the light sources being disposed between the base reflector and the controlled transmission mirror.

8. A system as recited in claim 1, wherein the first multilayer reflector comprises a polymeric multilayer film.

9. A system as recited in claim 1, wherein the input coupling element comprises at least one of a bulk diffuser, a surface diffuser, a structured surface and a totally internally reflecting input coupler.

10. A system as recited in claim 1, wherein the output coupling element comprises at least one of a bulk diffuser, a surface diffuser, a structured surface and a totally internally reflecting output coupler.

11. A system as recited in claim 1, further comprising a substrate disposed between the input coupling element and the output coupling element.

12. A system as recited in claim 11, wherein the substrate is disposed between the first multilayer reflector and the output coupling element.

13. A system as recited in claim 11, wherein the first multilayer reflector is disposed between the substrate and the output coupling element.

14. A system as recited in claim 11, further comprising a second multilayer reflector between the input and output coupling elements, the substrate being positioned between the first and second multilayer reflectors.

15. A system as recited in claim 11, further comprising a side reflector disposed at at least one edge of the substrate to reflect light that would escape from the substrate in the absence of the side reflector.

16. A system as recited in claim 1, wherein the output coupling element couples light out of the controlled transmission mirror in substantially only one polarization state.

17. A system as recited in claim 16, wherein the output coupling element comprises a disperse polymeric phase in a continuous polymeric matrix, at least one of the disperse polymeric phase and the continuous polymeric matrix comprising birefringent polymeric material.

18. A system as recited in claim 16, wherein the output coupling element comprises fibers disposed within a polymeric matrix, at least one of the fibers and the polymeric matrix comprising birefringent polymeric material.

19. A system as recited in claim 1, wherein light from the first light source does not reach the output coupling element at a substantially perpendicular position above the first light source, and light from the second light source is coupled out of the output coupling element at the substantially perpendicular position above the first light source.

20. A system as recited in claim 1, further comprising one or more light management films disposed between the controlled transmission mirror and the image-forming panel.

21. A system as recited in claim 20, wherein the light management films comprise at least one of a reflective polarizer and a brightness enhancing film.

22. An optical system, comprising:

an image-forming panel;

at least a first light source disposed behind the image-forming panel; and

in order from the first light source towards the image forming panel, a first diffuser, a first multilayer reflector and a second diffuser, at least some light from the first light source passing through the first diffuser, the first multilayer reflector and the second diffuser towards the image-forming panel, an intensity profile of light that has passed out of the second diffuser from the first light source having a minimum at a position along an axis from the first light source normal to a major surface of the first multilayer reflector.

23. A system as recited in claim 22, further comprising a substrate disposed between the first and second diffusers, the substrate being substantially transparent to the light from the first light source.

24. A system as recited in claim 22, further comprising a base reflector, the first light source being disposed between the base reflector and the first diffuser.

25. A system as recited in claim 22, wherein the first diffuser comprises at least one of a bulk diffuser and a surface diffuser.

26. A system as recited in claim 22, wherein the second diffuser comprises at least one of a bulk diffuser and a surface diffuser.

27. A system as recited in claim 22, further comprising at least one brightness enhancing layer disposed between the second diffuser and the image-forming panel.

28. A system as recited in claim 22, wherein the second diffuser preferentially diffuses light of substantially only one polarization state.

29. A system as recited in claim 28, wherein the second diffuser comprises a disperse polymeric phase in a continuous polymeric matrix, at least one of the disperse polymeric phase and the continuous polymeric matrix comprising birefringent polymeric material.

30. A system as recited in claim 28, wherein the output coupling element comprises fibers disposed within a polymeric matrix, at least one of the fibers and the polymeric matrix comprising birefringent polymeric material.

31. A system as recited in claim 22, wherein the at least a first light source comprises at least a first light source capable of emitting light at a first wavelength and at least a second light source capable of emitting light at a second wavelength different from the first wavelength.

32. A controlled transmission mirror, comprising:

an input coupling element;

an output coupling element;

a first multilayer reflector, reflective for normally incident light at a first wavelength; and

a substrate substantially transparent at the first wavelength, the substrate having an edge reflector disposed to reflect light propagating out of a peripheral edge of the substrate, the substrate and the first multilayer reflector both being disposed between the input coupling element and the output coupling element.

33. A mirror as recited in claim 32, wherein the first multilayer reflector comprises a polymeric multilayer film.

34. A mirror as recited in claim 32, wherein the input coupling element comprises at least one of a bulk diffuser, a surface diffuser and a replicated surface.

35. A mirror as recited in claim 32, wherein the output coupling element comprises at least one of a bulk diffuser, a surface diffuser and a replicated surface.

36. A mirror as recited in claim 32, wherein the substrate is disposed between the first multilayer reflector and the output coupling element.

37. A mirror as recited in claim 32, wherein the first multilayer reflector is disposed between the substrate and the output coupling element.

38. A mirror as recited in claim 32, further comprising a second multilayer reflector between the input and output coupling elements, the substrate being positioned between the first and second multilayer reflectors.

39. A mirror as recited in claim 32, wherein the output coupling element is polarization sensitive.

40. A mirror as recited in claim 39, wherein the output coupling element comprises a disperse polymeric phase in a continuous polymeric matrix, at least one of the disperse polymeric phase and the continuous polymeric matrix comprising birefringent polymeric material.

41. A mirror as recited in claim 39, wherein the output coupling element comprises fibers disposed within a polymeric matrix, at least one of the fibers and the polymeric matrix comprising birefringent polymeric material.

42. A mirror as recited in claim 32, wherein the reflector is provided at substantially the entire peripheral edge of the substrate.