PRIVACY DISPLAY AND DUAL-MODE PRIVACY DISPLAY SYSTEM

1 . A privacy display comprising:

a light guide configured to guide light according to a 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 the diffractively coupled-out light into a viewbox; and

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

wherein an extent of the viewbox is determined by the collimation factor, the private image being configured to be exclusively visible within a viewing cone of the viewbox to provide viewing privacy.

2 . The privacy display of claim 1 , wherein principal light beams of the diffractively coupled-out light 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 the diffractively coupled-out light in two orthogonal directions into the parallel plane of the 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 3 , wherein the plurality of curved diffractive features has a hyperbolic-shaped curve.

6 . 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.

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

8 . 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 on the light guide surface and configured to cooperatively concentrate the diffractively coupled-out light into the viewbox.

9 . The privacy display of claim 1 , wherein the privacy display is optically transparent in a direction orthogonal to the light guide surface.

10 . 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, the light valve array being further configured to modulate the broad-angle light, wherein the dual-mode privacy display system has a privacy mode configured to provide the private image using the diffractively coupled-out light modulated by the light valve array, and further has a public mode configured to provide a public image using the broad-angle light modulated by the light valve array, the public image being configured to be visible both inside and outside of the viewing cone.

11 . 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; 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,

wherein the private image is configured to be exclusively visible within a viewing cone of the viewbox, the public image being configured to be visible both inside and outside the viewing cone.

12 . The dual-mode privacy display system of claim 11 , where the diffraction grating-based backlight comprises:

a light guide configured to guide light according to a 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 diffractively coupled-out light and to direct the diffractively coupled-out light as the directional emitted light into the viewbox, wherein an extent of the viewbox is determined by the collimation factor.

13 . The dual-mode privacy display system of claim 12 , 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.

14 . The dual-mode privacy display system of claim 12 , wherein the diffraction grating comprises a plurality of curved diffractive features configured to direct the diffractively coupled-out light as the directional emitted light in two orthogonal directions to provide the viewbox as a two-dimensional viewbox having a two-dimensional viewing cone.

15 . The dual-mode privacy display system of claim 12 , 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 with the collimation factor as the guided light.

16 . The dual-mode privacy display system of claim 12 , 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 the diffractively coupled-out light into the viewbox.

17 . The dual-mode privacy display system of claim 11 , wherein a cone angle of the viewing cone is a negative cone angle.

18 . A method of privacy display operation, the method comprising:

guiding light in a light guide as guided light according to a 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; and

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

wherein an extent of the viewbox is determined by the collimation factor, the private image being exclusively visible within a viewing cone of the viewbox to provide viewing privacy.

19 . The method of privacy display operation of claim 18 , 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.

20 . (canceled)

21 . The method of privacy display operation of claim 18 , further comprising providing broad-angle light using a broad-angle backlight and modulating the provided broad-angle light to form a public image, the public image being visible both inside and outside the viewing cone of the viewbox, wherein the public image is formed during a public mode and the private image is formed during a privacy mode.