Privacy display and dual-mode privacy display system

1. A privacy display comprising:

a light guide configured to guide light within the light guide as guided light having a predetermined collimation factor;

a diffraction grating at a surface of the light guide, the diffraction grating being configured to diffractively couple out a portion of the guided light from the light guide as diffractively coupled-out light and to direct and concentrate the diffractively coupled-out light into a viewbox, the diffractively coupled-out light including principal light beams emitting from respective locations over an extent of the diffraction grating, the principal light beams having propagation angles that vary over the extent of the diffraction grating; and

a light valve array configured to modulate the diffractively coupled-out light to provide a private image within the viewbox,

the predetermined collimation factor of the guided light within the light guide being selected to determine an extent of the viewbox,

the extent of the viewbox being less than an extent of the diffraction grating and an extent of the light valve array,

the private image being configured to be exclusively visible within the viewbox.

2. The privacy display of claim 1 , wherein the principal light beams are directed toward a middle of the viewbox.

3. The privacy display of claim 1 , wherein the viewbox is a two-dimensional viewbox located in a plane parallel to the light guide surface, and wherein the diffraction grating comprises a plurality of curved diffractive features configured to direct and concentrate the diffractively coupled-out light in two orthogonal directions into the two-dimensional viewbox.

4. The privacy display of claim 3 , wherein the plurality of curved diffractive features comprises one or both of concentric curved ridges and concentric curved grooves having a center of curvature.

5. The privacy display of claim 1 , wherein the diffraction grating comprises diffractive features having a feature spacing between adjacent diffractive features that decreases as a function of distance from a light-entrance edge of the light guide.

6. The privacy display of claim 1 , wherein a viewing cone of the viewbox has a negative cone angle.

7. The privacy display of claim 1 , wherein the diffraction grating comprises a plurality of sub-gratings, the sub-gratings of the plurality being spaced apart from one another on the light guide surface and configured to cooperatively direct and concentrate the diffractively coupled-out light into the viewbox.

8. A dual-mode privacy display system comprising the privacy display of claim 1 , the dual-mode privacy display system further comprising a broad-angle backlight configured to provide broad-angle light, the light guide being between the broad-angle backlight and the light valve array,

wherein the light guide is configured to pass the broad-angle light through the light guide from a bottom surface to a top surface and the light valve array is further configured to modulate the broad-angle light that passes through the light guide, the dual-mode privacy display system having a privacy mode configured to provide the private image using the diffractively coupled-out light modulated by the light valve array and a public mode configured to provide a public image using the broad-angle light modulated by the light valve array, the public image being visible both inside and outside the viewbox.

9. A dual-mode privacy display system comprising:

a broad-angle backlight configured to provide broad-angle emitted light in a public mode of the dual-mode privacy display system;

a diffraction grating-based backlight configured to provide diffractively coupled-out light as directional emitted light into a viewbox in a privacy mode of the dual-mode privacy display system, the diffractively coupled-out light including principal light beams emitting from respective locations over an extent of the diffraction grating-based backlight, the principal light beams having propagation angles that vary over the extent of the diffraction grating-based backlight; and

a light valve array configured to modulate the broad-angle emitted light to provide a public image in the public mode and to modulate the directional emitted light to provide a private image in the privacy mode, the private image being exclusively visible within the viewbox and the public image being visible both inside and outside the viewbox,

the diffraction grating-based backlight being separate from and located between the broad-angle backlight and the light valve array,

the viewbox having an extent that is less than an extent of the broad-angle backlight, the extent of the diffraction grating-based backlight, and an extent of the light valve array.

10. The dual-mode privacy display system of claim 9 , where the diffraction grating-based backlight comprises:

a light guide configured to guide light as guided light having a predetermined collimation factor; and

a diffraction grating at a surface of the light guide, the diffraction grating being configured to diffractively couple out a portion of the guided light from the light guide as the directional emitted light and to direct and concentrate the directional emitted light into the viewbox, wherein the predetermined collimation factor is selected to determine the extent of the viewbox at a viewing distance from the dual-mode privacy display system.

11. The dual-mode privacy display system of claim 10 , wherein the diffraction grating comprises diffractive features having a feature spacing between adjacent diffractive features that decreases with increasing distance from a light-entrance edge of the light guide.

12. The dual-mode privacy display system of claim 10 , wherein the diffraction grating comprises a plurality of curved diffractive features configured to direct and concentrate the directional emitted light in two orthogonal directions to provide the viewbox as a two-dimensional viewbox located in a plane parallel to a surface of the light guide.

13. The dual-mode privacy display system of claim 10 , further comprising a light source optically coupled to a light-entrance edge of the light guide, the light source being configured to inject light into the light guide to be guided within the light guide as the guided light having the predetermined collimation factor.

14. The dual-mode privacy display system of claim 10 , wherein the diffraction grating comprises a plurality of sub-gratings spaced apart from one another on the light guide surface, the plurality of sub-gratings being configured to cooperatively direct and concentrate the diffractively coupled-out light into the viewbox.

15. The dual-mode privacy display system of claim 9 , wherein a cone angle of a viewing cone is a negative cone angle.

16. A method of operation of a privacy display, the method further comprising:

guiding light in a light guide as guided light having a predetermined collimation factor;

diffractively coupling out a portion of the guided light as diffractively coupled-out light and directing the diffractively coupled-out light into a viewbox using a diffraction grating optically coupled to the light guide, the diffractively coupled-out light including principal light beams emitting from respective locations over an extent of the diffraction grating, the principal light beams having propagation angles that vary over the extent of the diffraction grating; and

modulating the diffractively coupled-out light using a light valve array to form a private image within the viewbox,

the predetermined collimation factor of the guided light being selected to determine an extent of the viewbox at a viewing distance from the privacy display,

the extent of the viewbox being less than the extent of the diffraction grating and an extent of the light valve array,

the private image being exclusively visible within the viewbox.

17. The method of operation of a privacy display of claim 16 , wherein the diffraction grating comprises a plurality of curved diffractive features having a feature spacing that decreases with increasing distance from a light-entrance edge of the light guide.

18. The method of operation of a privacy display of claim 16 , further comprising optically coupling light provided by a light source into the light guide at a light-entrance edge as the guided light, wherein optically coupling light provides collimated light having the predetermined collimation factor to be guided as the guided light.

19. The method of operation of a privacy display of claim 16 , further comprising:

providing broad-angle light using a broad-angle backlight that is separate and spaced apart from the light guide, the light guide being between the broad-angle backlight and the light valve array; and

modulating the provided broad-angle light to form a public image, the public image being visible both inside and outside the viewbox,

wherein the public image is formed during a public mode and the private image is formed during a privacy mode.

20. The method of operation of a privacy display of claim 16 , wherein the diffraction grating comprises a plurality of sub-gratings, the sub-gratings of the plurality being spaced apart on a guiding surface of the light guide and configured to cooperatively concentrate the diffractively coupled-out light into the viewbox.