Wide angle imaging directional backlights

• US 10,175,418 B2
• Filed: 05/04/2017
• Issued: 01/08/2019
• Est. Priority Date: 05/18/2012
• Status: Active Grant

• Current Assignee: Reald Spark, LLC
• Original Assignee: Reald Spark, LLC
• Inventors: Robinson, Michael G., Woodgate, Graham J., Harrold, Jonathan, Schuck, Miller H.
• Primary Examiner(s): Ahn, Sejoon
• Application Number:
  US15/587,366
• Publication Number:
  US 20170235040A1
• Time in Patent Office: 614 Days
• 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 6/0043 provided on the surface 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 2354/00 Aspects of interface with display user
• CPC Class Codes: G09G 3/003 to produce spatial visual effects
• CPC Class Codes: G09G 3/342 using several illumination sources separately controlled corresponding to different display panel areas, e.g. along one dimension such as lines
• CPC Class Codes: G09G 5/14 Display of multiple viewports
• CPC Class Codes: H04N 13/312 the parallax barriers being placed behind the display panel, e.g. between backlight and spatial light modulator [SLM]
• 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 13/368 for two or more viewers
• CPC Class Codes: H04N 13/376 for tracking left-right translational head movements, i.e. lateral movements
• CPC Class Codes: H04N 2013/403 the images being monoscopic
• 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 and hence defines the relative positions of system elements and ray paths. The uncorrected system creates non-illuminated void portions when viewed off-axis preventing uniform wide angle 2D illumination modes. The system may be corrected to remove this non-uniformity at wide angles through the introduction of additional sources away from the system'"'"'s object plane, additional imaging surfaces, and/or by altering ray paths.

Claims

1. A directional backlight apparatus comprising:

a waveguide extending between an input end for receiving input light and a reflective end for reflecting the input light back through the waveguide;

an array of light sources disposed at different input positions in a lateral direction across the same input end of the waveguide, the waveguide having first and second, opposed guide surfaces extending between the input end and the reflective end for guiding light forwards and back along the waveguide, the waveguide being arranged to reflect input light from light sources at the different input positions across the input end after reflection from the reflective end into respective optical windows in output directions distributed in the lateral direction in dependence on the input positions; and

a control system arranged to selectively operate the light sources to direct light into selectable viewing windows at different locations and comprising at least one of the optical windows,

wherein the reflective end converges the reflected light such that reflected light from light sources that are offset from the optical axis of the waveguide fails to illuminate outer portions of the waveguide,

the waveguide further comprises sides, extending between the input end and the reflective end and between the guiding surfaces, that are planar surfaces arranged to reflect light from the light sources, and

the control system being arranged, on selective operation of a first light source to direct light into a first of the viewing windows, to simultaneously operate a second light source that directs light into the first of the viewing windows, wherein the light of the second light source is reflected by the reflective end and then by a side of the waveguide into the outer portion of the waveguide that fails to be illuminated by the first light source,

wherein the first guide surface is arranged to guide light by total internal reflection and the second guide surface comprises a plurality of light extraction features oriented to reflect light guided through the waveguide in directions allowing exit through the first guide surface as the output light,

wherein the light extraction features are facets of the second guide surface, and

wherein the second guide surface has a stepped shape comprising said facets and intermediate regions between the facets that are arranged to direct light through the waveguide without extracting the light.

2. A directional backlight apparatus according to claim 1, wherein the second light source is selected to direct light into the same viewing window as the first light source.

3. A directional backlight apparatus according to claim 1, wherein the sides of the waveguide are parallel.

4. A directional backlight apparatus according to claim 1, wherein the sides of the waveguide diverge from the input end to the reflective end.

5. A directional backlight apparatus according to claim 1, wherein the sides of the waveguide converge from the input end to the reflective end.

6. A directional backlight apparatus according to claim 1, wherein the sides of the waveguide are arranged to reflect light from the light sources by total internal reflection.

7. A directional backlight apparatus according to claim 1, wherein the sides of the waveguide have a reflective coating.

8. A display apparatus comprising:

a directional backlight apparatus comprising;

a waveguide extending between an input end for receiving input light and a reflective end for reflecting the input light back through the waveguide;

an array of light sources disposed at different input positions in a lateral direction across the same input end of the waveguide, the waveguide having first and second, opposed guide surfaces extending between the input end and the reflective end for guiding light forwards and back along the waveguide, the waveguide being arranged to reflect input light from light sources at the different input positions across the input end after reflection from the reflective end into respective optical windows in output directions distributed in the lateral direction in dependence on the input positions; and

a control system arranged to selectively operate the light sources to direct light into selectable viewing windows at different locations and comprising at least one of the optical windows,

wherein the reflective end converges the reflected light such that reflected light from light sources that are offset from the optical axis of the waveguide fails to illuminate outer portions of the waveguide,

the waveguide further comprises sides, extending between the input end and the reflective end and between the guiding surfaces, that are planar surfaces arranged to reflect light from the light sources, and

the control system being arranged, on selective operation of a first light source to direct light into a first of the viewing windows, to simultaneously operate a second light source that directs light into the first of the viewing windows, wherein the light of the second light source is reflected by the reflective end and then by a side of the waveguide into the outer portion of the waveguide that fails to be illuminated by the first light source; and

a transmissive spatial light modulator extending across the directional backlight apparatus for modulating the light output therefrom,

wherein the first guide surface is arranged to guide light by total internal reflection and the second guide surface comprises a plurality of light extraction features oriented to reflect light guided through the waveguide in directions allowing exit through the first guide surface as the output light,

wherein the light extraction features are facets of the second guide surface, and

wherein the second guide surface has a stepped shape comprising said facets and intermediate regions between the facets that are arranged to direct light through the waveguide without extracting the light.

9. A display apparatus according to claim 8, wherein the transmissive spatial light modulator is disposed across the first guide surface of the waveguide.

10. A display apparatus according to claim 8, being an autostereoscopic display apparatus, wherein the control system is arranged to control the spatial light modulator to display temporally multiplexed left and right eye images and synchronously to operate the light sources to direct light into viewing windows in positions corresponding to the left and right eyes of an observer.

11. A display apparatus according to claim 10, further comprising a sensor system arranged to detect the position of an observer relative to the display device, the control system to direct the displayed images into viewing windows in positions corresponding to the left and right eyes of the observer, in dependence on the detected position of the observer.

12. A display apparatus according to claim 8, wherein the first guide surface is arranged to guide light by total internal reflection and the second guide surface is substantially planar and inclined at an angle to reflect light in directions that break the total internal reflection for outputting light through the first guide surface,

the display device further comprising a deflection element extending across the first guide surface of the waveguide for deflecting light towards the normal to the spatial light modulator.

13. A display apparatus comprising:

a display device including;

a waveguide extending between an input end for receiving input light and a reflective end for reflecting the input light back through the waveguide;

an array of light sources disposed at different input positions in a lateral direction across the same input end of the waveguide, the waveguide having first and second, opposed guide surfaces extending between the input end and the reflective end for guiding light forwards and back along the waveguide, the waveguide being arranged to reflect input light from light sources at the different input positions across the input end after reflection from the reflective end into respective optical windows in output directions distributed in the lateral direction in dependence on the input positions; and

a transmissive spatial light modulator extending across the waveguide for modulating the light output therefrom, wherein the spatial light modulator extends across only part of the area of the waveguide; and

a control system arranged to selectively operate the light sources to direct light into selectable viewing windows at different locations and comprising at least one of the optical windows,

wherein the first guide surface is arranged to guide light by total internal reflection and the second guide surface comprises a plurality of light extraction features oriented to reflect light guided through the waveguide in directions allowing exit through the first guide surface as the output light, wherein the light extraction features are facets of the second guide surface, and wherein the second guide surface has a stepped shape comprising said facets and intermediate regions between the facets that are arranged to direct light through the waveguide without extracting the light.

14. A display apparatus according to claim 13, being an autostereoscopic display apparatus, wherein the control system is arranged to control the spatial light modulator to display temporally multiplexed left and right eye images and synchronously to operate the light sources to direct light into viewing windows in positions corresponding to the left and right eyes of an observer.

15. A display apparatus according to claim 14, further comprising a sensor system arranged to detect the position of an observer relative to the display device, the control system to direct the displayed images into viewing windows in positions corresponding to the left and right eyes of the observer, in dependence on the detected position of the observer.