Superlens component for directional display
View Patent ↗Disclosed is an imaging directional backlight apparatus comprising a waveguide, a light source array, and a further optical element for providing large area directed illumination from localized light sources. The imaging directional backlight may comprise a stepped waveguide that 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. The further optical element may comprise a superlens comprising first and second aligned lens arrays that may be arranged to modify the output viewing windows to achieve enhanced window imaging from the directional backlight.
1. A display device, comprising:
a transmissive spatial light modulator comprising an array of pixels arranged to modulate light passing therethrough;
a waveguide having an input end, and first and second opposed guide surfaces for guiding light along the waveguide, the first and second opposed guide surfaces extending from the input end across the spatial light modulator, wherein the waveguide is arranged to output light through the first guide surface for supply through the spatial light modulator, the waveguide being arranged to direct input light from different input positions across the input end in output directions relative to the normal to the first guide surface that are dependent on said input position; and
an optical element disposed between the waveguide and the spatial light modulator, comprising first and second arrays of lenses, the lenses each having a positive optical power in respective first meridians and no optical power in respective second meridians perpendicular to the first meridians, the first and second arrays of lenses being arranged with respective focal planes that extend perpendicular to the normal to the spatial light modulator between the first and second arrays of lenses, the lenses of each array having parallel second meridians.
2. A display device according to claim 1 , wherein the first and second arrays of lenses are arranged with respective focal planes that are coincident.
3. A display device according to claim 1 , wherein the first and second arrays of lenses are arranged with respective focal planes that are offset.
4. A display device according to claim 1 , wherein the focal length of the lenses of the first array of lenses arranged to receive light from the waveguide is greater than the focal length of the lenses of the second array.
5. A display device according to claim 1 , wherein the first and second arrays of lenses have the same pitch.
6. A display device according to claim 5 , wherein the first and second arrays of lenses have optical axes that are aligned.
7. A display device according to claim 5 , wherein the first and second arrays of lenses have optical axes that are offset.
8. A display device according to claim 1 , wherein the first and second arrays of lenses have different pitches.
9. A display device according to claim 1 , further comprising a third array of lenses, the lenses each having a positive optical power in respective first meridians and no optical power in respective second meridians perpendicular to the first meridians, the third array of lenses having the same pitch as the first and second arrays of lenses and being disposed between the first and second arrays of lenses, and arranged to image the apertures of the first array of lenses onto the apertures of the second array of lenses.
10. A display device according to claim 1 , wherein the optical element is switchable between a first state in which the lenses of the first and second arrays have said positive optical power in said first meridians and a second state in which the lenses of the first and second arrays have no optical power in said first meridians.
11. A display device according to claim 10 , wherein the array of pixels are arranged in an aperture with a shape having two perpendicular axes of mirror symmetry, and the display device is arranged so that, in the first state of the optical element, the viewing windows are distributed across the one of said axes of mirror symmetry, and, in the second state of the optical element, the optical element is arranged to rotate the viewing windows around the normal to the spatial light modulator so that the viewing windows are distributed across the other one of said axes of mirror symmetry.
12. A display device according to claim 1 , wherein the lenses of each array have second meridians that extend parallel to the optical axis of the waveguide.
13. A display device according to claim 1 , wherein the lenses of each array having parallel second meridians that extend at a non-zero-acute angle to the optical axis of the waveguide.
14. A display device according to claim 13 , wherein the array of pixels are arranged in an aperture with a shape having two perpendicular axes of mirror symmetry, and the optical element is arranged to rotate the viewing windows around the normal to the spatial light modulator; and the output viewing, windows extend at an angle in a range from 65 to 115 degrees, 80 to 100 degrees or 90 degrees relative to one of said axes of the shape of the aperture.
15. A display device according to claim 1 , wherein the first and second arrays of lenses are formed by a common piece of material within which the respective focal planes are disposed.
16. A display device according to claim 1 , wherein the first guide surface is arranged to guide light by total internal reflection and the second guide surface has a plurality of light extraction features inclined to reflect light guided through the waveguide in directions allowing exit through the first guide surface of the output light.
17. A display device according to claim 16 , wherein the second guide surface has intermediate regions between the light extraction features that are arranged to direct light through the waveguide without extracting it.
18. A display device according to claim 17 , wherein the intermediate regions of the second guide surface extend parallel to the first guide surface.
19. A display device according to claim 17 , wherein the light extraction features are reflective facets extending laterally to the intermediate regions and the second guide surface has a stepped shape with reflective facets and the intermediate regions.
20. A display device according to claim 16 , wherein the extraction features of the waveguide are curved along the direction in which they are elongated.
21. A display device according to claim 1 , 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.
22. A display device according to claim 1 , wherein the waveguide has a reflective end facing the input end for reflecting light input through the input end back through the waveguide, the waveguide being arranged to output light through the first guide surface after reflection from the reflective end.
23. A display device according to claim 1 , further comprising:
an array of light sources at different input positions across the input end of the waveguide; and
a control system arranged to selectively operate the light sources to direct light into viewing windows corresponding to said output directions.
24. A display device according to claim 1 , wherein the first and second arrays of lenses are curved along the direction in which they are elongated.
25. A display apparatus, comprising:
a transmissive spatial light modulator comprising an array of pixels arranged to modulate light passing therethrough;
a waveguide having an input end, and first and second opposed guide surfaces for guiding, light along the waveguide, the first and second opposed guide surfaces extending from the input end across the spatial light modulator, wherein the waveguide is arranged to output light through the first guide surface for supply through the spatial light modulator, the waveguide being arranged to direct input light from different input positions across the input end in output directions relative to the normal to the first guide surface that are dependent on said input position;
an optical element disposed between the waveguide and the spatial light modulator, comprising, first and second arrays of lenses, the lenses each having a positive optical power in respective first meridians and no optical power in respective second meridians perpendicular to the first meridians, the first and second arrays of lenses being arranged with respective focal planes that extend perpendicular to the normal to the spatial light modulator between the first and second arrays of lenses, the lenses of each array having parallel second meridians;
an array of light sources at different input positions across the input end of the waveguide; and
a control system arranged to selectively operate the light sources to direct light into viewing windows corresponding to said output directions;
wherein the control system is arranged to control the light sources so that, when light is directed from a given light source into a given viewing window, in the event that the light from the given light source is directed into a viewing window other than the given viewing window by splitting through different lenses of the second array, a further, separated light source is operated to direct compensatory light into the given viewing window.
26. A display apparatus according to claim 25 , the display apparatus being an autostereoscopic display apparatus wherein the control system is further arranged to control the display apparatus to display temporally multiplexed left and right images and synchronously to direct the displayed images into viewing windows in positions corresponding to left and right eyes of an observer.
27. A display apparatus according to claim 26 , wherein the control system further comprises a sensor system arranged to detect the position of an observer across the display apparatus, and
the control system is arranged to direct the displayed images into viewing windows in positions corresponding to left and right eyes of an observer, in dependence on the detected position of the observer.
28. A display apparatus according to claim 25 , the display apparatus being, a dual view display apparatus, wherein the control system is arranged to direct the same displayed image into viewing windows in at least first and second viewing positions.