Privacy display apparatus
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. The directional backlight may be arranged to switch between at least a first wide angular luminance profile mode and a second narrow angular luminance profile mode. The directional backlight is arranged to illuminate an LCD with a bias electrode arranged to switch liquid crystal directors in black state pixels between a first wide angular contrast profile mode and a second narrow angular contrast profile mode. Performance of privacy operation for off-axis snoopers is enhanced in comparison to displays with only directional backlights or switchable contrast properties.
1. A privacy display device comprising:
a backlight arranged to output light; and
a transmissive spatial light modulator arranged to receive output light from the backlight and to modulate the output light from the backlight to provide an image that may be switched between at least two different angular contrast profiles, wherein the spatial light modulator comprises:
an input polariser;
an output polariser;
a pixelated liquid crystal display arranged between the input polariser and output polariser, the pixelated liquid crystal display comprising a liquid crystal pixel layer and pixel addressing electrodes arranged to provide in-plane electric fields to pixels of the pixelated liquid crystal display; and
at least one pixel layer bias electrode arranged to provide out-of-plane bias electric fields to the liquid crystal pixel layer; and
at least one additional polariser arranged on the input side of the input polariser between the input polariser and the backlight or on the output side of the output polariser; and
at least one retarder arranged between the at least one additional polariser and the input polariser in the case that the additional polariser is arranged on the input side of the input polariser or between the additional polariser and the output polariser in the case that the additional polariser is arranged on the output side of the input polariser, wherein the at least one retarder comprises a switchable liquid crystal retarder that is switchable by means of an applied voltage across the switchable liquid crystal retarder.
2. A privacy display device according to claim 1 , wherein the spatial light modulator further comprises a liquid crystal bias layer arranged between the input polariser and output polariser of the pixelated liquid crystal display; and bias layer electrodes arranged to provide out-of-plane bias electric fields to the liquid crystal bias layer.
3. A privacy display device according to claim 1 , wherein the bias electric fields are time varying.
4. A privacy display device according to claim 3 , wherein the at least one liquid crystal layer bias electrode is patterned to provide at least two pattern regions.
5. A privacy display device according to claim 4 , wherein at least one of the pattern regions is individually addressable.
6. A privacy display device according to claim 1 , wherein the additional polariser is arranged on the input side of the input polariser and said at least one retarder is arranged between the additional polariser and the input polariser, and the additional polariser is a reflective polariser.
7. A privacy display device according to claim 1 , wherein the additional polariser has an electric vector transmission direction that is parallel to the electric vector transmission of the input polariser in the case that the additional polariser is arranged on the input side of the input polariser or is parallel to the electric vector transmission of the output polariser in the case that the additional polariser is arranged on the output side of the input polariser.
8. A privacy display device according to claim 1 , wherein the at least one retarder further comprises a pair of retarders which have slow axes in the plane of the retarders that are crossed.
9. A privacy display device according to claim 8 , wherein the pair of retarders have slow axes that each extend at 45° with respect to an electric vector transmission direction that is parallel to the electric vector transmission of the input polariser in the case that the additional polariser is arranged on the input side of the input polariser or is parallel to the electric vector transmission of the output polariser in the case that the additional polariser is arranged on the output side of the input polariser.
10. A privacy display device according to claim 8 , wherein the pair of retarders each comprise a single A-plate.
11. A privacy display device according to claim 8 , wherein the pair of retarders each comprise plural A-plates having respective slow axes aligned at different angles from each other.
12. A privacy display device according to claim 8 , wherein the pair of retarders have slow axes that each extend at 0° and 90°, respectively, with respect to an electric vector transmission direction that is parallel to the electric vector transmission of the input polariser in the case that the additional polariser is arranged on the input side of the input polariser or is parallel to the electric vector transmission of the output polariser in the case that the additional polariser is arranged on the output side of the input polariser.
13. A privacy display device according to claim 1 , wherein the at least one retarder further comprises a retarder having a slow axis perpendicular to the plane of the retarder.
14. A privacy display device according to claim 1 , wherein the at least one retarder further comprises a retarder having a slow axis orientation with a component perpendicular to the plane of the retarder, and at least one component in the plane of the retarder.
15. A privacy display device according to claim 1 , wherein the switchable liquid crystal retarder comprises at least one homeotropic alignment layer.
16. A privacy display device according to claim 15 , wherein the at least one retarder further comprises at least one compensation retarder arranged between the at least one additional polariser and the input polariser in the case that the additional polariser is arranged on the input side of the input polariser or between the additional polariser and the output polariser in the case that the additional polariser is arranged on the output side of the input polariser.
17. A privacy display device according to claim 16 , wherein the compensation retarder comprises a negative C-plate or crossed positive A-plates.
18. A privacy display device according to claim 1 , wherein the switchable liquid crystal retarder comprises at least first and second regions that are independently addressable with first and second applied voltages.
19. A privacy display system according to claim 1 , wherein the switching between the at least first and second angular contrast profiles is provided by control of the bias electric field.
20. A privacy display system according to claim 1 , further comprising electrodes for applying a voltage across the switchable liquid crystal retarder for switching the switchable liquid crystal retarder.
21. A privacy display system according to claim 1 , wherein
in a first mode of operation, the image provided to a viewer at an angle of 45 degrees offset from the normal to the display is provided with a contrast ratio that is less than one tenth of the contrast ratio of the image provided to a viewer at an angle aligned to the normal of the display and the luminance provided to a viewer at an angle of 45 degrees offset from the normal to the display is provided with a luminance that is less than one tenth of the luminance of the image provided to a viewer at an angle aligned to the normal of the display; and
in a second mode of operation, the image provided to a viewer at an angle of 45 degrees offset from the normal to the display is provided with a contrast ratio that is greater than one tenth of the contrast ratio of the image provided to a viewer at an angle aligned to the normal of the display and the luminance provided to a viewer at an angle of 45 degrees offset from the normal to the display is provided with a luminance that is greater than one tenth of the luminance of the image provided to a viewer at an angle aligned to the normal of the display.