Wide angle imaging directional backlights

• US 10,425,635 B2
• Filed: 05/18/2017
• Issued: 09/24/2019
• Est. Priority Date: 05/23/2016
• Status: Active Grant

• Current Assignee: Reald Spark, LLC
• Original Assignee: Reald Spark, LLC
• Inventors: Woodgate, Graham J., Robinson, Michael G.
• Primary Examiner(s): Tran, Trang U
• Application Number:
  US15/599,189
• Publication Number:
  US 20170339398A1
• Time in Patent Office: 859 Days
• Field of Search: 345207, 348 51, 362609
• CPC Class Codes: G02B 30/24 involving temporal multiplexing, e.g. using sequentially activated left and right shutters
• CPC Class Codes: G02B 6/0038 Linear indentations or grooves, e.g. arc-shaped grooves or meandering grooves, extending over the full length or width of the light guide
• CPC Class Codes: G02B 6/0048 with stepwise taper
• CPC Class Codes: G02B 6/0055 Reflecting element, sheet or layer
• CPC Class Codes: G02B 6/0068 Arrangements of plural sources, e.g. multi-colour light sources
• CPC Class Codes: G02B 6/0076 Stacked arrangements of multiple light guides of the same or different cross-sectional area
• CPC Class Codes: G09G 3/003 to produce spatial visual effects
• CPC Class Codes: H04N 13/32 using arrays of controllable light sources; using moving apertures or moving light sources
• CPC Class Codes: H04N 13/366 using viewer tracking
• CPC Class Codes: H04N 2013/405 the images being stereoscopic or three dimensional

Abstract

An imaging directional backlight apparatus including a waveguide, a light source array, for providing large area directed illumination from localized light sources. The waveguide may include a stepped structure, in which the steps may further include extraction features optically hidden to guided light, propagating in a first forward direction. Returning light propagating in a second backward direction may be refracted, diffracted, or reflected by the features to provide discrete illumination beams exiting from the top surface of the waveguide. Viewing windows are formed through imaging individual light sources by waveguide facets and rear reflector images in cooperation. Viewing windows may be provided at first and second different window planes to improve uniformity in a lateral direction. Further, stray light may be reduced by inner and outer portions of reflective facets with different inclinations for the rear reflector.

Claims

1. A directional backlight comprising:

a waveguide;

an array of light sources arranged to input light into the waveguide at different input positions laterally across the waveguide,

wherein the waveguide comprises first and second, opposed guide surfaces for guiding input light along the waveguide, the first guide surface being arranged to guide light by total internal reflection, and the second guide surface comprising;

(a) a plurality of extraction features that are (i) arranged to reflect some of the input light so as to output it from the waveguide through the first guide surface and (ii) laterally curved to have positive optical power laterally so that the input light reflected from the extraction features laterally forms real images of the light sources in front of the directional backlight in a first window plane that provide viewing windows, the extraction features also transmitting some of the input light; and

(b) intermediate regions between the extraction features that are arranged to guide light by total internal reflection; and

a rear reflector comprising a linear array of reflective facets that are (i) arranged to reflect at least some of the input light that is transmitted through the extraction features of the waveguide, so as to direct it back through the waveguide to exit through the first guide surface, and (ii) laterally curved to have optical power laterally so that the input light reflected from the reflective facets laterally forms images of the light sources in a second window plane that is separated from the first window plane.

2. A directional backlight according to claim 1, wherein the images formed from the input light reflected from the reflective facets are real images of the light sources in front of the directional backlight that provide further viewing windows.

3. A directional backlight according to claim 2, wherein the second window plane is closer to the directional backlight than the first window plane.

4. A directional backlight according to claim 2, wherein the second window plane is further from the directional backlight than the first window plane.

5. A directional backlight according to claim 1, wherein the images formed from the input light reflected from the reflective facets are virtual images of the light sources behind the directional backlight.

6. A directional backlight according to claim 1, wherein the waveguide further comprises a reflective end, the light sources being arranged to input light into the waveguide towards the reflective end, the reflective end being arranged to reflect the input light back along the waveguide, the extraction features being arranged to reflect some of the input light after reflection from the reflective end.

7. A directional backlight according to claim 6, wherein the waveguide further comprises a rear end opposite to the reflective end, and side surfaces between the first and second guide surfaces.

8. A directional backlight according to claim 7, wherein the array of light sources are arranged along the rear end.

9. A directional backlight according to claim 7, wherein the light sources include light sources arranged along a said side surface, and

the reflective end comprises first and second facets alternating with each other laterally, the first facets being reflective and forming reflective facets of a Fresnel reflector having positive optical power laterally, the second facets forming draft facets of the Fresnel reflector, the Fresnel reflector having an optical axis that is inclined towards said side surface in a direction in which the Fresnel reflector deflects input light from the array of light sources into the waveguide.

10. A directional backlight according to claim 1, herein the reflective end has positive optical power laterally.

11. A directional backlight according to claim 10, wherein the reflective end is a Fresnel reflector.

12. A directional backlight according to claim 1, wherein the rear reflector further comprises intermediate facets extending between the reflective facets of the rear reflector and inclined in opposite senses from the reflective facets of the rear reflector so that pairs of a reflective facet and an intermediate facet together form corner facets arranged to reflect at least some of the input light that is incident thereon.

13. A directional display device comprising:

a directional backlight according to claim 1; and

a transmissive spatial light modulator arranged to receive the output light from the waveguide and to modulate it to display an image.

14. A directional display apparatus comprising:

a directional display device according to claim 13; and

a control system arranged to control the light sources.

15. A directional backlight comprising:

a waveguide;

an array of light sources arranged to input light into the waveguide at different input positions laterally across the waveguide,

wherein the waveguide comprises first and second, opposed guide surfaces for guiding input light along the waveguide, the first guide surface being arranged to guide light by total internal reflection, and the second guide surface comprising;

(a) a plurality of extraction features that are (i) arranged to reflect some of the input light so as to output it from the waveguide through the first guide surface, the extraction features also transmitting some of the input light; and

(b) intermediate regions between the extraction features that are arranged to guide light by total internal reflection; and

a rear reflector comprising a linear array of pairs of reflective corner facets that are arranged to reflect at least some of the input light that is transmitted through the extraction features of the waveguide, so as to direct it back through the waveguide to exit through the first guide surface, wherein each pair of reflective corner facets includes a first facet on which light transmitted through the extraction features of the waveguide is incident and second facet, each first facet comprising an outer portion and an inner portion with different inclinations.

16. A directional backlight according to claim 15, wherein the inner portion has a shallower inclination than the outer portion.

17. A directional backlight according to claim 15, wherein the inner portion of the first facet and the second facet have an internal angle in a range from 89.5 to 90.5 degrees.

18. A directional backlight according to claim 15, wherein the first facets are laterally curved to have optical power laterally so that the input light reflected from the reflective facets laterally forms images of the light sources in a second window plane that is separated from the first window plane.

19. A directional backlight according to claim 15, wherein the waveguide further comprises a reflective end, the light sources being arranged to input light into the waveguide towards the reflective end, the reflective end being arranged to reflect the input light back along the waveguide, the extraction features being arranged to reflect some of the input light after reflection from the reflective end.

20. A directional backlight according to claim 19, wherein the waveguide further comprises a rear end opposite to the reflective end, and side surfaces between the first and second guide surfaces.

21. A directional backlight according to claim 20, wherein the array of light sources are arranged along the rear end.

22. A directional backlight according to claim 20, wherein the light sources include light sources arranged along a said side surface, and

the reflective end comprises first and second facets alternating with each other laterally, the first facets being reflective and forming reflective facets of a Fresnel reflector having positive optical power laterally, the second facets forming draft facets of the Fresnel reflector, the Fresnel reflector having an optical axis that is inclined towards said side surface in a direction in which the Fresnel reflector deflects input light from the array of light sources into the waveguide.

23. A directional backlight according to claim 15, wherein the reflective end has positive optical power laterally.

24. A directional backlight according to claim 23, wherein the reflective end is a Fresnel reflector.

25. A directional display device comprising:

a directional backlight according to claim 15; and

a transmissive spatial light modulator arranged to receive the output light from the waveguide and to modulate it to display an image.

26. A directional display apparatus comprising:

a directional display device according to claim 25; and

a control system arranged to control the light sources.