Directional display and method of making a mask for a directional display

• US 20020126389A1
• Filed: 06/05/2001
• Published: 09/12/2002
• Est. Priority Date: 12/07/1996
• Status: Active Grant

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Moseley, Richard Robert, Woodgate, Graham John, Ezra, David
• Granted Patent: US 6,473,141 B2
• Time in Patent Office: Days
• US Class Current: 359/619
• CPC Class Codes: G02B 30/27 involving lenticular arrays
• CPC Class Codes: G02B 30/30 involving parallax barriers
• CPC Class Codes: G02B 5/32 Holograms used as optical elements
• CPC Class Codes: G02F 1/133512 Light shielding layers, e.g. black matrix G02F1/136209 takes precedence
• CPC Class Codes: G02F 1/133524 Light-guides, e.g. fibre-optic bundles, louvered or jalousie light-guides
• CPC Class Codes: G02F 1/133526 Lenses, e.g. microlenses or Fresnel lenses
• CPC Class Codes: G02F 1/1336 Illuminating devices
• CPC Class Codes: G02F 1/133606 including a specially adapted diffusing, scattering or light controlling members
• CPC Class Codes: G02F 1/133607 the light controlling member including light directing or refracting elements, e.g. prisms or lenses
• CPC Class Codes: G03H 2001/0439 for recording Holographic Optical Element [HOE] HOE per se G02B5/32
• CPC Class Codes: G03H 2210/22 2D SLM object wherein the object beam is formed of the light modulated by the SLM SLM per se G03H2001/0224
• CPC Class Codes: G03H 2270/54 Recording material filed in recessed substrate
• CPC Class Codes: H04N 13/305 using lenticular lenses, e.g. arrangements of cylindrical lenses
• CPC Class Codes: H04N 13/31 using parallax barriers
• 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 13/351 for displaying simultaneously
• CPC Class Codes: H04N 13/359 Switching between monoscopic and stereoscopic modes
• CPC Class Codes: H04N 13/376 for tracking left-right translational head movements, i.e. lateral movements

Abstract

A directional display comprises a display arrangement such as a spatial light modulator and a rear parallax barrier illuminated by a suitable backlight. The spatial light modulator and the parallax barrier cooperate to produce Fresnel diffraction which results in spatially non-uniform brightness across viewing windows of the display. Also, where the spatial light modulator has pixels of non-constant vertical aperture, further variations in the intensity profile at the windows occurs. In order to compensate for this, a mask is provided, for instance between the parallax barrier and the backlight. The mask cooperates with the parallax barrier to produce an intensity pattern having variations which are the inverse of the variations in intensity pattern produced by the parallax barrier and the spatial light modulator. The variations are superimposed and substantially cancel each other out so as to result in viewing windows which have substantially uniform light intensities.

Claims

1. A directional display comprising a display arrangement for producing a plurality of viewing zones, each of which has a non-uniform first angular intensity profile with a first angularly varying component,

the display further comprising a compensator for superimposing in the viewing zones a second angular intensity profile having a second angularly varying component which is substantially the inverse of the first angularly varying component.

2. A display as claimed in claim 1, wherein the display arrangement comprises a spatial light modulator having a plurality of the picture elements and array of discrete light sources.

3. A display as claimed in claim 2, wherein the picture elements are arranged as columns and the light sources comprise parallel evenly spaced line sources.

4. A display as claimed in claim 2, wherein the light sources comprise a diffuse backlight and a parallax barrier.

5. A display as claimed in claim 4, wherein the picture elements are of substantially constant vertical aperture, the spatial light modulator and the parallax barrier cooperate to produce Fresnel diffraction, and the compensator is arranged to compensate for the non-uniform first angular intensity profile caused by the Fresnel diffraction.

6. A display as claimed in claim 4, wherein the picture elements are of non-constant vertical aperture, the spatial light modulator and the parallax barrier cooperate to produce Fresnel diffraction, and the compensator is arranged to compensate for the non-uniform first angular intensity profile caused by the non-constant vertical aperture and the Fresnel diffraction.

7. A display as claimed in claim 3, wherein the light sources comprise a diffuse backlight and a parallax barrier, and

wherein the parallax barrier comprises a plurality of slits, each of which cooperates with a respective group of the picture element columns to form the viewing zones of a zeroth order lobe.

8. A display as claimed in claim 7, wherein the picture elements are of substantially constant vertical aperture, the spatial light modulator and the parallax barrier cooperate to produce Fresnel diffraction, and the compensator is arranged to compensate for the non-uniform first angular intensity profile caused by the Fresnel diffraction.

9. A display as claimed in claim 7, wherein the picture elements are of non-constant vertical aperture, the spatial light modulator and the parallax barrier cooperate to produce Fresnel diffraction, and the compensator is arranged to compensate for the non-uniform first angular intensity profile caused by the non-constant vertical aperture and the Fresnel diffraction.

10. A display as claimed in claim 7, wherein the compensator comprises a mask disposed between the parallax barrier and the backlight, the mask comprising a plurality of strips of varying light transmissivity which cooperate with the slits of the parallax barrier to form the second angularly varying intensity profile.

11. A display as claimed in claim 10, wherein the strips are of substantially the same width as the picture element columns.

12. A display as claimed in claim 10, wherein the ratio of the lateral pitches of the strips and the slits is substantially equal to the ratio of the lateral pitches of the slits and the groups of the picture element columns.

13. A display as claimed in claim 10, wherein the parallax barrier and the mask are formed on opposite faces of a common transparent substrate.

14. A display as claimed in claim 10, wherein n₁t₁=n₂t₂, where n₁ is the effective refractive index between a picture element plane of the spatial light modulator and the parallax barrier, t₁ is the thickness between the picture element plane of the spatial light modulator and the parallax barrier, n₂ is the effective refractive index between the parallax barrier and the mask, and t₂ is the thickness between the parallax barrier and the mask.

15. A display as claimed in claim 10, wherein a lenticular screen is disposed between the mask and the parallax barrier.

16. A display as claimed in claim 15, wherein the lenticular screen comprises a plurality of lenticules, each of which is aligned with a respective strip of the mask.

17. A display as claimed in claim 2, wherein a switchable diffuser is disposed between the spatial light modulator and the array of light sources and is switchable between a diffusing mode and a substantially non-diffusing mode.

18. A display as claimed in claim 17, wherein the switchable diffuser comprises a polymer dispersed liquid crystal layer.

19. A display as claimed in claim 1, wherein the display arrangement comprises a diffuse backlight, parallax barrier and a spatial light modulator disposed between the backlight and parallax barrier.

20. A display as claimed in claim 19, wherein the spatial light modulator comprises a plurality of picture element columns and the parallax barrier comprises a plurality of parallel evenly spaced slits, each of which cooperates with a respective group of the picture element columns to form the viewing zones of a zeroth order lobe.

21. A display as claimed in claim 20, wherein the compensator comprises a mask comprising a plurality of strips of varying light transmissivity, the parallax barrier is disposed between the spatial light modulator and the mask, and each strip cooperates with a respective slit to form the second angularly varying intensity pattern.

22. A display as claimed in claim 2, wherein the compensator comprises means for defining aperture transmission properties of the picture elements.

23. A display as claimed in claim 22, wherein the defining means comprises a spatial light modulator black mask defining the shape of picture element apertures.

24. A display as claimed in claim 22, wherein the defining means spatially varies the transmissivity of picture element apertures.

25. A display as claimed in claim 4, wherein the parallax barrier comprises:

a first polariser;

a second polariser; and

a polarisation modifying layer disposed between the first and second polarisers and having slit regions and barrier regions for supplying light of orthogonal polarisations.

26. A display as claimed in claim 25, wherein the second polariser comprises part of the spatial light modulator.

27. A display as claimed in claim 25, wherein the first polariser is removable to provide a non-directional mode of operation.

28. A method of making a mask for a display as claimed in claim 10, the method comprising steps of:

disposing a photosensitive material in a plane substantially parallel to the spatial light modulator and intersected by the viewing zones;

operating the display with the picture elements being transmissive so as to expose the photosensitive material; and

reducing and repeating the image recorded by the photosensitive material.

29. A method as claimed in claim 28, wherein the parallax barrier is replaced with by a further parallax barrier of reduced slit width during exposure of the photosensitive material.

30. A method as claimed in claim 28, wherein the display is viewpoint corrected to form viewing windows in a preferred viewing plane and the photosensitive material is disposed at the viewing windows.

31. A method as claimed in claim 28, wherein the mask is formed on a transparent substrate of the parallax barrier.

32. A method of making a holographic mask for a display of the type claimed in claim 10 and of the viewpoint corrected type forming viewing windows in a preferred viewing plane, the method comprising steps of:

disposing a photosensitive material at a parallax barrier plane with respect to the spatial light modulator; and

exposing the photosensitive material by uniformly illuminating the viewing windows and supplying a front reference beam.

33. A method of making a holographic mask for a display of the type claimed in claim 10 and of the viewpoint corrected type forming viewing windows in a preferred viewing plane, the method comprising steps of:

disposing a photosensitive material in a parallax barrier position with respect to the viewing windows; and

exposing the photosensitive material by illuminating the viewing windows with a first intensity profile having a first spatially varying component which is substantially the inverse of a second spatially varying component of a second intensity profile produced by the display without the compensator and by supplying a front reference beam.