U.S. patent application number 16/066292 was filed with the patent office on 2019-01-17 for privacy display and dual-mode privacy display system.
The applicant listed for this patent is LEIA INC.. Invention is credited to David A. Fattal.
Application Number | 20190018186 16/066292 |
Document ID | / |
Family ID | 59399104 |
Filed Date | 2019-01-17 |
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United States Patent
Application |
20190018186 |
Kind Code |
A1 |
Fattal; David A. |
January 17, 2019 |
PRIVACY DISPLAY AND DUAL-MODE PRIVACY DISPLAY SYSTEM
Abstract
A privacy display provides a private image exclusively visible
within a viewing cone of a viewbox. The privacy display includes a
light guide to guide light, a diffraction grating configured to
diffractively couple out a portion of the guided light as
diffractively coupled-out light and to direct the diffractively
coupled-out light into the viewbox, and a light valve array
configured to modulate the diffractively coupled-out light to
provide the private image. An extent of the viewbox is determined
by a collimation factor of the guided light. A dual-mode privacy
display system further includes a broad-angle backlight configured
to provide broad-angle light to separately provide a public image
visible both inside and outside the viewing cone. The private image
may be provided in a privacy mode and the public image may be
provided in a public mode of the dual-mode privacy display
system.
Inventors: |
Fattal; David A.; (Mountain
View, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LEIA INC. |
Menlo Park |
CA |
US |
|
|
Family ID: |
59399104 |
Appl. No.: |
16/066292 |
Filed: |
July 25, 2016 |
PCT Filed: |
July 25, 2016 |
PCT NO: |
PCT/US2016/043939 |
371 Date: |
June 26, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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PCT/US2016/040582 |
Jun 30, 2016 |
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16066292 |
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62289238 |
Jan 30, 2016 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02F 1/1336 20130101;
G02B 5/1842 20130101; G02F 2001/133626 20130101; G02B 6/0038
20130101; G02B 6/12 20130101; G02B 27/42 20130101; G02F 1/133602
20130101; G02B 6/0035 20130101 |
International
Class: |
G02B 6/12 20060101
G02B006/12; G02F 1/1335 20060101 G02F001/1335; G02B 5/18 20060101
G02B005/18; G02B 27/42 20060101 G02B027/42 |
Claims
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.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to and incorporates by
reference the entire contents of U.S. Provisional Patent
Application Ser. No. 62/289,238, filed Jan. 30, 2016, International
(PCT) Application No. PCT/US2016/40582, filed Jun. 30, 2016, and
International (PCT) Application No. PCT/US2016/40904, filed Jul. 2,
2016.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] N/A
BACKGROUND
[0003] Electronic displays are a nearly ubiquitous medium for
communicating information to users of a wide variety of devices and
products. Most commonly employed electronic displays include the
cathode ray tube (CRT), plasma display panels (PDP), liquid crystal
displays (LCD), electroluminescent displays (EL), organic light
emitting diode (OLED) and active matrix OLEDs (AMOLED) displays,
electrophoretic displays (EP) and various displays that employ
electromechanical or electrofluidic light modulation (e.g., digital
micromirror devices, electrowetting displays, etc.). Generally,
electronic displays may be categorized as either active displays
(i.e., displays that emit light) or passive displays (i.e.,
displays that modulate light provided by another source). Among the
most obvious examples of active displays are CRTs, PDPs and
OLEDs/AMOLEDs. Displays that are typically classified as passive
when considering emitted light are LCDs and EP displays. Passive
displays, while often exhibiting attractive performance
characteristics including, but not limited to, inherently low power
consumption, may find somewhat limited use in many practical
applications given the lack of an ability to emit light.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] Various features of examples and embodiments in accordance
with the principles described herein may be more readily understood
with reference to the following detailed description taken in
conjunction with the accompanying drawings, where like reference
numerals designate like structural elements, and in which:
[0005] FIG. 1A illustrates a side view of a privacy display in an
example, according to an embodiment consistent with the principles
described herein.
[0006] FIG. 1B illustrates a cross-sectional view of a portion of
the privacy display of FIG. 1A in an example, according to an
embodiment consistent with the principles described herein.
[0007] FIG. 1C illustrates a cross-sectional view of another
portion of the privacy display of FIG. 1A in an example, according
to an embodiment consistent with the principles described
herein.
[0008] FIG. 2A illustrates a perspective view of a privacy display
in an example, according to another embodiment consistent with the
principles described herein.
[0009] FIG. 2B illustrates a plan view of a portion of the privacy
display of FIG. 2A in an example, according to an embodiment
consistent with the principles described herein.
[0010] FIG. 3 illustrates a plot of diffractive feature spacing as
a function of distance in an example, according to an embodiment
consistent with the principles described herein.
[0011] FIG. 4A illustrates a cross sectional view of a portion of a
privacy display in an example, according to an embodiment
consistent with the principles described herein.
[0012] FIG. 4B illustrates a cross sectional view of a portion of a
privacy display in an example, according to another embodiment
consistent with the principles described herein.
[0013] FIG. 5A illustrates a cross sectional view of a portion of a
privacy display in an example, according to another embodiment
consistent with the principles described herein.
[0014] FIG. 5B illustrates a cross sectional view of a portion of a
privacy display in an example, according to another embodiment
consistent with the principles described herein.
[0015] FIG. 6A illustrates a side view of a privacy display having
a plurality of sub-gratings in an example, according to an
embodiment consistent with the principles described herein.
[0016] FIG. 6B illustrates plan view of a portion of a privacy
display having a plurality of sub-gratings in an example, according
to another embodiment consistent with the principles described
herein.
[0017] FIG. 6C illustrates a plan view of a portion of a privacy
display having a plurality of sub-gratings in an example, according
to another embodiment consistent with the principles described
herein.
[0018] FIG. 6D illustrates a plan view of a portion of a privacy
display having a plurality of sub-gratings in an example, according
to another embodiment consistent with the principles described
herein.
[0019] FIG. 7A illustrates a side view of a dual-mode privacy
display system in an example, according to an embodiment consistent
with the principles described herein.
[0020] FIG. 7B illustrates a side view of a dual-mode privacy
display system in another example, according to an embodiment
consistent with the principles described herein.
[0021] FIG. 8 illustrates a cross sectional view of a broad-angle
backlight in an example, according to an embodiment consistent with
the principles described herein.
[0022] FIG. 9 illustrates a flow chart of a method of privacy
display operation in an example, according to an embodiment
consistent with the principles described herein.
[0023] Certain examples and embodiments may have other features
that are one of in addition to and in lieu of the features
illustrated in the above-referenced figures. These and other
features are detailed below with reference to the above-referenced
figures.
DETAILED DESCRIPTION
[0024] Embodiments in accordance with the principles described
herein provide a privacy display with application to electronic
display systems. According to various embodiments, the privacy
display employs a diffraction grating configured to diffractively
couple light out of a light guide. Further, the diffraction grating
is configured to direct the diffractively coupled-out light within
a viewing cone and into a viewbox. According to various
embodiments, the privacy display may be used in an electronic
display system to provide privacy viewing (e.g., in a privacy
mode). In addition, a dual-mode privacy display system may provide
both of a public mode for general viewing and a privacy mode that
provides private viewing by a user, according to some
embodiments.
[0025] Herein, a `diffraction grating` is generally defined as a
plurality of features arranged to provide diffraction of light
incident on the diffraction grating. In some examples, the
plurality of features may be arranged in a periodic or
quasi-periodic manner. For example, the diffraction grating may
include a plurality of features (e.g., a plurality of grooves or
ridges in a material surface) arranged in a one-dimensional (1D)
array. In other examples, the diffraction grating may be a
two-dimensional (2D) array of features. The diffraction grating may
be a 2D array of bumps on or holes in a material surface, for
example.
[0026] As such, and by definition herein, the `diffraction grating`
is a structure that provides diffraction of light incident on the
diffraction grating. If the light is incident on the diffraction
grating from a light guide, the provided diffraction or diffractive
scattering may result in, and thus be referred to as, `diffractive
coupling` in that the diffraction grating may couple light out of
the light guide by or according to diffraction. The diffraction
grating also redirects or changes an angle of the light by
diffraction (i.e., at a diffractive angle). In particular, as a
result of diffraction, light leaving the diffraction grating by
diffractive coupling generally has a different propagation
direction than a propagation direction of the light incident on the
diffraction grating (i.e., incident light). The change in the
propagation direction of the light by diffraction is referred to as
`diffractive redirection` herein. Hence, the diffraction grating
may be understood to be a structure including diffractive features
that diffractively redirects light incident on the diffraction
grating and, if the light is incident from a light guide, the
diffraction grating may also diffractively couple out the light
from the light guide.
[0027] Further, by definition herein, the features of a diffraction
grating are referred to as `diffractive features` and may be one or
more of at, in and on a material surface (i.e., a boundary between
two materials). The surface may be a surface of a light guide, for
example. The diffractive features may include any of a variety of
structures that diffract light including, but not limited to, one
or more of grooves, ridges, holes and bumps at, in or on the
surface. For example, the diffraction grating may include a
plurality of substantially parallel grooves in the material
surface. In another example, the diffraction grating may include a
plurality of parallel ridges rising out of the material surface.
The diffractive features (e.g., grooves, ridges, holes, bumps,
etc.) may have any of a variety of cross sectional shapes or
profiles that provide diffraction including, but not limited to,
one or more of a sinusoidal profile, a rectangular profile (e.g., a
binary diffraction grating), a triangular profile and a saw tooth
profile (e.g., a blazed grating).
[0028] A `reflection mode` or `reflective` diffraction grating is
defined herein as a diffraction grating that both diffracts and
reflects incident light. Similarly, `reflection mode diffraction`
is defined as diffraction in a direction corresponding to a
light-incident side (e.g., of a reflection mode diffraction
grating). As such, light diffractively scattered by a reflection
mode diffraction grating generally exits or propagates away from a
side of the reflection mode diffraction grating that is the same as
the side that the light is incident on the reflection mode
diffraction grating (i.e., a `light-incident side`). By contrast, a
`transmission mode` or `transmissive` diffraction grating is
defined herein as a diffraction grating that diffracts light
passing through the diffraction grating such that diffracted light
generally exits from a side of a transmission mode diffraction
grating that is opposite to the light-incident side. In some
examples, a reflection mode diffraction grating may comprise a
reflective material or material layer (e.g., a reflective metal)
that reflects or at least partially reflects incident light. The
diffractive features of the reflection mode diffraction grating
(e.g., ridges or grooves) may be one or more of formed in a surface
of the reflective material and formed on or adjacent to the
reflective material surface, according to various embodiments.
[0029] Herein, `viewbox` is defined as a region or volume of space
in which an image formed by a display or other optical system
(e.g., lens system) is visible and thus may be viewed. In other
words, the viewbox defines a location or region in space within
which a user's eyes may be placed in order to view an image
produced by the display or display system. Moreover, the viewbox is
generally large enough to accommodate both of a user's eyes. In
some embodiments, the viewbox may represent a two dimensional
region of space (e.g., a region with length and width but without
substantial depth), while in other embodiments, the viewbox may
include a three-dimensional region of space (e.g., a region with
length, width and depth). Further, while referred to as a `box`,
the viewbox may not be restricted to a box that is polygonal or
rectangular in shape. For example, the viewbox may comprise a
cylindrical region of space, in some embodiments. In other
examples, the region of space may have various other shapes
including, but not limited to, an elliptical cylinder, a hyperbolic
cylinder and a general ellipsoid.
[0030] Herein, a `collimation factor,` denoted .sigma., is defined
as a degree to which light is collimated. In particular, a
collimation factor defines an angular spread of light rays within a
collimated beam of light, by definition herein. For example, a
collimation factor .sigma. may specify that a majority of light
rays in a beam of collimated light is within a particular angular
spread (e.g., +/-.sigma. degrees about a central or principal
angular direction of the collimated light beam). The light rays of
the collimated light beam may have a Gaussian distribution in terms
of angle and the angular spread may be an angle determined at
one-half of a peak intensity of the collimated light beam,
according to some examples.
[0031] As used herein, the article `a` is intended to have its
ordinary meaning in the patent arts, namely `one or more`. For
example, `a grating` means one or more gratings and as such, `the
grating` means `the grating(s)` herein. Also, any reference herein
to `top`, `bottom`, `upper`, `lower`, `up`, `down`, `front`, back',
`first`, `second`, `left` or `right` is not intended to be a
limitation herein. Herein, the term `about` when applied to a value
generally means within the tolerance range of the equipment used to
produce the value, or in some embodiments, may mean plus or minus
10%, or plus or minus 5%, or plus or minus 1%, unless otherwise
expressly specified. Further, the term `substantially` as used
herein means a majority, or almost all, or all, or an amount within
a range of about 51% to about 100%. Moreover, examples herein are
intended to be illustrative only and are presented for discussion
purposes and not by way of limitation.
[0032] In accordance with some embodiments of the principles
described herein, a privacy display is provided. FIG. 1A
illustrates a side view of a privacy display 100 in an example,
according to an embodiment consistent with the principles described
herein. FIG. 1B illustrates a cross-sectional view of a portion of
the privacy display 100 in FIG. 1A in an example, according to an
embodiment consistent with the principles described herein. FIG. 1C
illustrates a cross-sectional view of another portion of the
privacy display 100 in FIG. 1A in an example, according to an
embodiment consistent with the principles described herein. The
privacy display 100 is configured to provide or emit light,
referred to herein as `diffractively coupled-out` light 102, as
illustrated in FIGS. 1A and 1C. Further, the privacy display 100 is
configured to direct the diffractively coupled-out light 102 into a
predefined region of space adjacent to (e.g., above, as
illustrated) the privacy display 100. In particular, the
diffractively coupled-out light 102 may be directed by the privacy
display 100 into a viewbox 108 that is adjacent to the privacy
display 100, as is described in more detail below. In some
embodiments, primary rays of the diffractively coupled-out light
102 may be directed or `aimed` at a center or midpoint of the
viewbox 108. The privacy display 100 is also configured to modulate
the diffractively coupled-out light 102 to `form` or provide an
image. In some embodiments, the image is provided exclusively in or
only to the viewbox 108, i.e., as a `private image`. The private
image is configured to be preferentially or exclusively visible
within viewbox 108 as well as within a viewing cone 106 of the
viewbox 108 to provide viewing privacy, according to various
embodiments.
[0033] According to various embodiments, the privacy display 100
comprises a light guide 110. The light guide 110 may be a plate
light guide 110, in some embodiments (e.g., as illustrated herein).
The light guide 110 is configured to guide light as guided light
104. In particular, the guided light 104 may propagate in a
longitudinal direction (e.g., an x-direction, as illustrated) along
a length of the light guide 110. Further, the guided light 104 is
configured to propagate generally away from a light-entrance edge
112 of the light guide 110, e.g., as illustrated in FIGS. 1A and
1C. In FIG. 1A, bold arrows within the light guide 110 pointing
away from the light-entrance edge 112 illustrate the primary
propagation direction of the guided light 104 in the longitudinal
direction, for example, along the light guide length.
[0034] According to various embodiments, the light guide 110 is
configured to guide the guided light 104 using or according to
total internal reflection. In particular, the light guide 110 may
be an optical waveguide comprising an extended, substantially
planar sheet or slab of optically transparent, dielectric material.
As a plate optical waveguide, the light guide 110 may comprise any
one of a number of different optically transparent materials
including, but not limited to, various types of glass, such as
silica glass, alkali-aluminosilicate glass, borosilicate glass, as
well as substantially optically transparent plastics or polymers,
such as, but not limited to, poly(methyl methacrylate) or acrylic
glass, and polycarbonate. In some embodiments, the light guide 110
may include a cladding layer on at least a portion of a surface of
the light guide 110 (not illustrated) to further facilitate total
internal reflection.
[0035] In various embodiments, light may be coupled into the light
guide 110 along the light-entrance edge 112 thereof. In particular,
the light may be coupled into the light guide 110 at a
predetermined non-zero angle to propagate within the light guide
110 as the guided light 104 at a non-zero propagation angle.
Further, the light may be coupled into the light guide 110
according to a predetermined collimation factor .sigma.. That is,
the guided light 104 may be substantially collimated light and a
range of angles of or defined by the collimation factor .sigma. may
represent an angular distribution of light rays within the
coupled-in light that ultimately propagates within the light guide
110 as the guided light 104. According to various embodiments, the
diffractively coupled-out light 102 may include a range of angles
substantially similar to or at least determined by the collimation
factor .sigma., or the range of angles defined therein. For
example, dashed arrows adjacent to solid arrows representing the
diffractively coupled-out light 102 in FIG. 1A illustrate a range
of angles of various light beams or rays within the diffractively
coupled-out light 102.
[0036] In an example, the collimation factor .sigma. may represent
an angular spread equal to or less than about plus or minus forty
degrees (i.e., .sigma..ltoreq..+-.40.degree.). In other examples,
the collimation factor .sigma. may represent an angular spread
equal to or less than about thirty degrees (i.e.,
.sigma..ltoreq..+-.30.degree.), equal to or less than about twenty
degrees (i.e., .sigma..ltoreq..+-.20.degree.), or equal to or less
than about 10 degrees (i.e., .sigma..ltoreq..+-.10.degree.). In yet
other examples, the collimation factor .sigma. may represent an
angular spread that is less than about five degrees (i.e.,
.sigma..ltoreq..+-.5.degree.). As described below with respect to
equation (1), a size of the viewbox 108 may be a function of the
collimation factor .sigma.. Further, in addition to having the
predetermined collimation factor .sigma., the non-zero propagation
angle of the guided light 104 is generally less than a critical
angle of the light guide 110 with respect to total internal
reflection.
[0037] As illustrated, the privacy display 100 further comprises a
diffraction grating 120. In various embodiments, the diffraction
grating 120 is optically coupled to the light guide 110. For
example, the diffraction grating 120 may be located on, at or
adjacent to a surface of the light guide 110. The surface may be
one or both of a `top` surface (e.g., a light emitting surface) and
a `bottom` surface of the light guide 110 (e.g., opposite the light
emitting surface), for example. In FIGS. 1A-1C, the diffraction
grating 120 is illustrated at the top or light-emitting surface of
the light guide 110, by way of example and not limitation.
[0038] According to various embodiments, the diffraction grating
120 is configured to diffractively couple out a portion of the
guided light 104 from within the light guide 110. In particular,
the portion of guided light 104 may be diffractively coupled out as
the diffractively coupled-out light 102. Further, the diffraction
grating 120 is configured to direct the diffractively coupled-out
light 102 into the viewbox 108 located adjacent to and spaced apart
from the light guide surface (e.g., above the top surface, as
illustrated). For example, FIG. 1A illustrates the diffractively
coupled-out light 102 as arrows representing rays or beams of light
(e.g., `primary rays` or `principal light beams`) extending from
the light guide surface to the viewbox 108. Moreover, the
diffractively coupled-out light 102 may be substantially confined
to the viewing cone 106 (e.g., a generally conical or pyramidal
region or a `light-transmission` cone) in a region of space between
the light guide 110 and the viewbox 108 by the directing effects of
the diffraction grating 120. The solid arrows representing
principal light beams of the diffractively coupled-out light 102
are depicted as being directed or aimed at a center, midpoint or
middle of the viewbox 108 in FIG. 1A. In other embodiments (not
illustrated), the diffraction grating 120 may be configured to
direct the light beams of the diffractively coupled-out light to
other portions of the viewbox 108, e.g., the light beams or primary
rays may be distributed substantially throughout the viewbox
108.
[0039] A portion of the privacy display 100 illustrated in the
cross-sectional view of FIG. 1B depicts diffractive features of the
diffraction grating 120 as ridges 124 that protrude in a
z-direction from the light guide surface. Further, the ridges 124
are separated from one another by grooves 122, as illustrated. A
combination of a groove 122 and an adjacent ridge 124 represents a
`diffractive feature,` as illustrated in FIG. 1B. In other
instances, the ridges 124 and the grooves 122 individually may be
referred to as diffractive features.
[0040] As illustrated in FIG. 1B, a width of a groove 122 is
denoted by w.sub.g and a width of a ridge 124 is denoted by
w.sub.r. A sum of the groove width w.sub.g and the ridge width
w.sub.r is defined as a `feature spacing` herein and is denoted by
.LAMBDA. (i.e., .LAMBDA.=w.sub.g+w.sub.r). An alternate definition
of feature spacing (e.g., when the ridges 124 or the grooves 122
are individually referred to as the diffractive features) may be a
center-to-center distance between an adjacent pair of the ridges
124 (separated by a groove 122) or an adjacent pair of the grooves
122 (separated by a ridge 124), for example. According to some
embodiments (e.g., as illustrated in FIGS. 2A-2B, described below),
the widths of the grooves 122 and the ridges 124 may be
substantially constant along of a length of the diffractive
features (e.g., the length of the grooves 122 and the ridges 124).
Further, in some embodiments, the feature spacing .LAMBDA. along
the length of the diffractive features may be substantially
constant, e.g., also as illustrated in FIGS. 2A-2B. Moreover, the
feature spacing .LAMBDA. decreases from left to right in FIGS.
1B-1C, and in particular, the feature spacing .LAMBDA. decreases
from the light-entrance edge 112 of the light guide 110 to an end
of the light guide 110 that is opposite to an end at the
light-entrance edge 112, as illustrated in FIG. 1C.
[0041] FIG. 1C illustrates a cross-sectional view of a portion of
the privacy display 100, in particular, a portion of the light
guide 110 near the light-entrance edge 112. As illustrated therein,
light that is coupled into the light guide 110 along the
light-entrance edge 112 propagates within the light guide 110 as
the guided light 104 in the direction indicated by various extended
arrows. As illustrated, some of the guided light 104, 104a is
configured to remain within the light guide 110 due to total
internal reflection. Other portions of the guided light 104, 104b
is coupled-out by the diffraction grating 120 to become the
diffractively coupled-out light 102, as further illustrated FIG.
1C. Additionally, the guided light direction is in a general
direction of the decreasing feature spacing .LAMBDA. of the
diffraction grating 120, as further described below.
[0042] In particular, an extended arrow in FIG. 1C represents a
path of a ray of guided light 104a within the light guide 110 that
is guided by total internal reflection. For example, the ray may
`bounce` or alternate between top and bottom surfaces of the light
guide 110. That is, at various points along opposing top and bottom
surfaces of the light guide 110, the guided light 104a may strike
the opposing surfaces at angles less than a critical angle of the
light guide 110. As such, the guided light 104a is substantially
trapped by the total internal reflection within the light guide
110.
[0043] In FIG. 1C, another extended arrow represents a path of
another ray of guided light 104, 104b that is coupled-out of the
light guide 110 by the diffraction grating 120 as the diffractively
coupled-out light 102, e.g., as a ray of diffractively coupled-out
light 102. According to various embodiments, the guided light 104b
that interacts with the diffraction grating 120 is diffractively
coupled out of the light guide 110, e.g., as a first order
diffraction beam. As illustrated, the diffractively coupled-out
light 102 may represent first order, diffracted light that is
diffractively coupled out of the light guide 110 at a diffraction
angle .theta. with respect to a surface normal of the light guide
110. In various embodiments, a zero order diffraction beam of light
as well as higher order diffraction beams of light associated with
the diffraction grating 120 may be substantially suppressed.
[0044] In some embodiments, the diffraction grating 120 may
comprise diffractive features that are substantially straight
(e.g., straight along a length of the groove 122 or the ridge 124).
Substantially straight diffractive features (e.g., both straight
grooves 122 and ridges 124) may provide a viewbox 108 that is
substantially one-dimensional. That is, the viewbox 108 may have a
width (e.g., in the longitudinal direction of the light guide 110)
and may further have another dimension (e.g., a length) that is in
a direction that is orthogonal to the direction of the width. The
other dimension or length may be either substantially unconstrained
or constrained by a similar extent of the light guide 110, for
example. In other embodiments, the diffraction grating 120 may
comprise either curved diffractive features or diffractive features
arranged to approximate a curve along a length of the diffractive
feature. The curved diffractive features may provide a
two-dimensional viewbox 108.
[0045] FIG. 2A illustrates a perspective view of the privacy
display 100 in an example, according to an embodiment consistent
with the principles described herein. FIG. 2B illustrates a plan
view of a portion of the privacy display 100 of FIG. 2A in an
example, according to an embodiment consistent with the principles
described herein. In particular, as illustrated in FIGS. 2A-2B, the
diffraction grating 120 is located at the surface of the light
guide 110 of the privacy display 100 and comprises curved
diffractive features. As illustrated, a diffraction pattern of the
diffraction grating 120 is depicted as alternating black and white
bands representing the curved diffractive features of the
diffraction grating 120, e.g., one or both of grooves 122 and
ridges 124 in or at a surface of the light guide 110. Further, as
illustrated in FIG. 2B, concentric black and white curved lines
represent concentric curved diffractive features (e.g., both of
concentric curved ridges and concentric curved grooves) on the
light guide surface, by way of example and not limitation. The
concentric curved diffractive features have a center of curvature
C, which is located beyond an edge of the light guide 110. In some
embodiments, the curved diffractive features of the diffraction
grating 120 may be represented by semicircles (i.e., may be
semicircular curved diffractive features). In other embodiments, a
substantially non-circular curve may be employed to realize the
curved diffractive features. For example, the curved diffractive
features may have a hyperbolic-shaped curve. As such, the
concentric curved diffractive features may be concentric
hyperbolic-shaped curved diffractive features, in some embodiments.
According to various embodiments, the curve of the diffractive
features may be configured to direct and, in some examples,
concentrate the diffractively coupled-out light 102 in two
orthogonal directions in a plane of the viewbox 108. As such, the
curved diffractive features may be configured to provide a
two-dimensional viewbox 108 having a predetermined length and a
predetermined width, for example. In various embodiments, the
two-dimensional viewbox 108 may be located in a plane parallel to
the light guide surface (e.g., see FIG. 2A).
[0046] According to various embodiments, a feature spacing of the
diffractive features in the diffraction grating 120 may vary as a
function of distance along the light guide length or in the
propagation direction of light within the light guide 110. For
example, as illustrated in the cross sectional view of FIG. 1C as
well as in the plan view of FIG. 2B, the feature spacing .LAMBDA.
of the diffraction grating 120 decreases with increasing distance
from light-entrance edge 112 (or equivalently from the center of
curvature C in FIG. 2B). The feature spacing .LAMBDA. is also
illustrated to be decreasing as a function of distance from the
light-entrance edge 112 of the light guide 110 in FIG. 2A. For
curved diffractive features, the distance from the center of
curvature or from the light-entrance edge 112 may be measured along
a radius R, for example. The feature spacing .LAMBDA. decrease as a
function of distance may be referred to as a `chirp` and the
diffraction grating 120 may be a referred to as a `chirped`
diffraction grating, for example. Moreover, the decrease in feature
spacing .LAMBDA. may represent a linear function of distance, in
some embodiments. In other embodiments, the feature spacing may
decrease according to another (i.e., non-linear) function of
distance including, but not limited to, an exponential function of
distance and a hyperbolic function of distance.
[0047] FIG. 3 illustrates a plot 200 of diffractive feature spacing
as a function of distance in an example, according to an embodiment
consistent with the principles described herein. As illustrated, a
horizontal axis represents distance (e.g., a distance from the
light-entrance edge 112 or a radial distance from the center of
curvature C along a radius R). For example, a point labeled `0` on
the horizontal axis may represent an intersection of the radius R
and the light-entrance edge 112 of the light guide 110 in FIG. 2B.
A vertical axis in the plot 200 represents the feature spacing
.LAMBDA. of the diffractive features of the diffraction grating
120. Curves 210, 220 and 230 represent examples of different ways
in which the feature spacing of the diffractive features may
decrease with or as a function of increasing distance. In
particular, the curve 210 represents an exponential decrease in
feature spacing with increasing distance, e.g., from the center of
curvature C. The curve 220 represents a linear decrease in feature
spacing as a function of increasing distance, e.g., a linear chirp
or linearly chirped diffraction grating. The curve 230 represents a
hyperbolic decrease in feature spacing with increasing
distance.
[0048] Referring again to FIG. 1A, as described above and as
illustrated, the feature spacing of the diffraction grating 120 is
configured to diffractively couple out and direct light into the
viewbox 108 located a distance f from the privacy display 100. For
example, the distance f may be measured from the top surface of the
light guide 110 and may represent an intended viewing distance, as
illustrated in FIG. 1A. According to various embodiments, an
approximate width w.sub.viewbox of the viewbox 108 may be given by
a product of the distance f and the collimation factor .sigma. of
the light propagating within the light guide 110 or, equivalently,
the collimation factor .sigma. at which light enters the light
guide 110 along the light-entrance edge 112. In particular, the
viewbox width w.sub.viewbox may be given by equation (1) as:
w.sub.viewbox=f.sigma. (1)
In some embodiments, the viewbox width w.sub.viewbox in the
longitudinal direction (e.g. light propagation direction) may be
greater than about seventy millimeters (70 mm). A viewbox width
w.sub.viewbox greater than about 70 mm may correspond to about an
average interpupillary distance between eyes of a user viewing the
privacy display 100, for example. In particular, the viewbox width
w.sub.viewbox may be large enough to accommodate both eyes of the
user to facilitate viewing of an image provided by the privacy
display 100. However, the viewbox width w.sub.viewbox may also be
small enough to substantially limit viewing by others outside of
the viewbox 108, and effectively, substantially limit viewing by
others located outside of the viewing cone 106, for example.
[0049] In particular, as is discussed above, the diffractively
coupled-out light 102 provided by the privacy display 100 may be
substantially directed into the viewbox 108 or equivalently
substantially confined within viewing cone 106 delineated by dashed
lines in FIG. 1A. As such, light from, as well as an image provided
by, the privacy display 100 may preferentially or exclusively enter
a user's eyes when the user's eyes are located within the viewbox
108. However, when another's eyes are located either outside the
viewbox 108 or outside the viewing cone 106 (e.g., in a region
106'), the light from, as well as the image provided by, the
privacy display 100 will substantially not enter the other's eyes
and thus be visible. As such, the privacy display 100 and in
particular the diffraction grating 120 may appear substantially
black (i.e., unlit) when viewed from outside the viewbox 108 or
from outside the viewing cone 106.
[0050] In some embodiments, a cone angle of the viewing cone 106
may be a negative cone angle. Herein a `negative cone angle` is
defined as a cone angle of emitted light that concentrates or
directs light toward either a point in space or a relatively
confined region of space. In other words, a negative cone angle
produces a viewing cone 106 that include converging light. As such,
the viewing cone 106 generally decreases in size as a function of
distance from the privacy display 100 with a negative cone angle,
at least until the point in space is reached at which the light is
directed. By way of example and not limitation, the viewing cones
106 in FIGS. 1A and 2A each have a negative cone angle, as
illustrated. By contrast, a positive cone angle generally results
in diverging emitted light, by definition herein.
[0051] In some embodiments, the privacy display 100 further
comprises a light valve array 130. As illustrated in FIGS. 1A and
2A, the light valve array 130 is located between the light guide
110 and the viewbox 108. The light valve array 130 is configured to
modulate the diffractively coupled-out light 102 to form or provide
an image at or in the viewbox 108. In particular, individual light
valves of the light valve array 130 may be independently configured
to provide pixels that together form the image at the viewbox 108.
According to various embodiments, the provided image is viewable by
a user within the viewbox 108 (and in some examples, within the
viewing cone 106). As such, the user may view the image when the
user's eyes are within the viewbox 108. According to various
embodiments, the formed image may not be viewable outside of the
viewbox 108 or viewing cone 106, e.g., in region 106'. In some
examples, `by not viewable` from the region 106' means that the
formed image may appear substantially black.
[0052] According to various embodiments, the light valve array 130
may comprise substantially any of a variety of light valves
including, but not limited to, liquid crystal light valves,
electrowetting light valves, electrophoretic light valves or a
combination of these. Further, as shown in FIGS. 1A and 2A, the
light valve array 130 may be oriented substantially parallel to the
light guide 110 to intersect the viewing cone 106 to which the
diffractively coupled-out light 102 is confined. For example, the
light valve array 130 may comprise an array of liquid crystal light
valves, each of which may be individually operated as a pixel by
modulating an amount of light passing through a light valve. In
some embodiments, the light valves may be colored light valves
(i.e., a light valve may include a color filter). For example, the
light valve array 130 may comprise a plurality of red light valves,
a plurality of green light valves, and a plurality of blue light
valves. Together the red, green and blue light valves of the light
valve array 130 may provide a red-green-blue (RGB) based `full
color` formed image by modulating the diffractively coupled-out
light 102, for example. In particular, the diffractively
coupled-out light 102 passing through individual ones of light
valves of the light valve array 130 may be selectively modulated to
create a full color image or a black and white image in the viewbox
108 and the viewing cone 106.
[0053] In some embodiments (e.g., as illustrated in FIG. 2A), the
privacy display 100 further comprises a light source 140. The light
source 140 is optically coupled to the light guide 110. For
example, the light source 140 may be optically coupled to the light
guide 110 along the light-entrance edge 112, as illustrated in FIG.
2A. The light source 140 is configured to generate and inject light
142 into the light guide 110 as the guided light 104 having the
collimation factor .sigma., according to various embodiments. The
light source 140 includes an optical emitter such as, but not
limited to, a light emitting diode (LED), an organic LED (OLED), a
polymer LED, a plasma-based optical emitter, fluorescent lamp, an
incandescent lamp. According to various embodiments, light output
by the light source 140 may comprise monochromatic light or
polychromatic light. For example, the light may comprise a single
color of light (e.g., red light, green light, or blue light), a
plurality of colors of light, or light that is substantially white
light.
[0054] According to various embodiments, the diffraction grating
120 of the privacy display 100 may be provided according to any of
a variety different microfabrication or nanoscale fabrication
techniques including, but not limited to, wet etching, ion milling,
photolithography, imprint lithography, anisotropic etching, plasma
etching, or a combination thereof. For example, as shown in FIGS.
1A-1C, the diffraction grating 120 of the privacy display 100 may
be provided in a surface of a slab of optically transparent,
dielectric material of the light guide 110 using ion milling or
plasma etching. In another embodiment, the diffraction grating 120
of the privacy display 100 may be provided by depositing a layer of
dielectric material, a metal or another reflective material, or a
combination of both on a surface of the light guide 110. Depositing
the layer may be followed by etching the deposited layer to form
the diffraction grating 120, for example. In yet another example,
the diffraction grating 120 may be formed in a material layer that
is then subsequently affixed to a surface of the light guide
110.
[0055] In some embodiments, the diffraction grating 120 may
comprise a transmission mode diffraction grating. In other
embodiments, the diffraction grating 120 may comprise a reflection
mode diffraction grating. In yet other embodiments, the diffraction
grating 120 comprises both a transmission mode diffraction grating
and a reflection mode diffraction grating.
[0056] In particular, the diffraction grating 120 may comprise a
transmission mode diffraction grating at light emitting surface of
the light guide 110, e.g., as illustrated in FIG. 1A.
Alternatively, the diffraction grating 120 may comprise a
reflection mode diffraction grating at another surface of the light
guide 110 that is opposite to the light-emitting surface. According
to various examples, the diffractive grating 120 may include
grooves, ridges or similar diffractive features formed or otherwise
provided on or in the surface(s) of the light guide 110. For
example, grooves or ridges may be formed in or on the
light-emitting surface of the light guide 110 to serve as the
transmission mode diffraction grating (e.g., as illustrated in
FIGS. 1B-1C). Alternatively, grooves or ridges may be formed or
otherwise provided in or on the opposite surface to serve as the
reflection mode diffraction grating, for example.
[0057] According to some embodiments, the diffraction grating 120
may include a grating material (e.g., a layer of grating material)
on or in the respective light guide surface. As such, the grating
material may be substantially similar to a material of the light
guide 110. In other examples, the grating material may differ
(e.g., have a different refractive index) from the light guide
material. For example, the diffractive grating grooves in the light
guide surface may be filled with the grating material. In
particular, grooves of the diffraction grating 120 that is either
transmissive or reflective may be filled with a dielectric material
(i.e., the grating material) that differs from a material of the
light guide 110. The grating material of the diffraction grating
120 may include silicon nitride, for example, while the light guide
110 may be glass, according to some examples. Other grating
materials including, but not limited to, indium tin oxide (ITO) may
also be used.
[0058] In other embodiments, the diffraction grating 120, whether
transmissive or reflective, may include ridges, bumps, or similar
diffractive features that are deposited, formed or otherwise
provided on the respective surface of the light guide 110. The
ridges or similar diffractive features may be formed (e.g., by
etching, molding, etc.) in a dielectric material layer (i.e., the
grating material) that is deposited on the respective surface of
the light guide 110, for example. In some examples, the grating
material of the diffraction grating 120 may include a reflective
metal. For example, a reflection mode diffraction grating may
comprise a layer of reflective metal such as, but not limited to,
gold, silver, aluminum, copper or tin, to facilitate reflection in
addition to diffraction.
[0059] FIG. 4A illustrates a cross sectional view of a portion of a
privacy display 100 in an example, according to an embodiment
consistent with the principles described herein. FIG. 4B
illustrates a cross sectional view of a portion of a privacy
display 100 in an example, according to another embodiment
consistent with the principles described herein. In particular,
both FIGS. 4A and 4B may illustrate a privacy display 100 portion
that includes a portion of the light guide 110 and a portion of the
diffraction grating 120. Further, the diffraction grating 120
illustrated in FIGS. 4A-4B is a transmission mode diffraction
grating.
[0060] As illustrated in FIG. 4A, the diffraction grating 120
comprises grooves 122 (i.e., diffractive features) formed in the
light-emitting surface 114 of the light guide 110 to form the
transmission mode diffraction grating. FIG. 4B illustrates a
diffraction grating 120 comprising ridges 124 of a grating material
126 on the light-emitting surface 114 of the light guide 110 to
form a transmission mode diffraction grating. Etching or molding a
deposited layer of the grating material 126, for example, may
produce the ridges 124. In some embodiments, the grating material
126 that makes up the ridges 124 may include a material that is
substantially similar to a material of the light guide 110. In
other embodiments, the grating material 126 may differ from the
material of the light guide 110, e.g., as illustrated in FIG. 4B.
For example, the light guide 110 may include a glass or a
plastic/polymer sheet or slab and the grating material 126 may be a
different material such as, but not limited to, silicon nitride,
that is deposited on the light guide 110.
[0061] FIG. 5A illustrates a cross sectional view of a portion of a
privacy display 100 in an example, according to another embodiment
consistent with the principles described herein. FIG. 5B
illustrates a cross sectional view of a portion of a privacy
display 100 in an example, according to another embodiment
consistent with the principles described herein. In particular,
both FIGS. 5A and 5B illustrate portions of the light guide 110 and
of the diffraction grating 120. Further, the diffraction grating
120 illustrated in FIGS. 5A-5B is a reflection mode diffraction
grating. As illustrated, the diffraction grating 120 as a
reflection mode diffraction grating is at or on a surface 116 of
the light guide 110 opposite to the light-emitting surface 114.
[0062] In FIG. 5A, the diffraction grating 120, as a reflection
mode diffraction grating, comprises grooves 122 provided in the
surface 116 of the light guide 110 and a grating material 126' in
the grooves 122. In this example, the grooves 122 are filled with
and further backed by the grating material 126'. Further, the
grating material 126' illustrated in FIG. 5A may comprise a metal
or similar reflective material to provide additional reflection and
improve a diffractive efficiency of the diffraction grating 120. In
other examples (not illustrated), the grooves may be filled with a
grating material (e.g., silicon nitride) and then backed or
substantially covered by a metal layer, for example.
[0063] FIG. 5B illustrates a diffraction grating 120 as a
reflection mode diffraction grating including ridges 124 of the
grating material 126 on the surface 116 of the light guide 110. The
ridges 124 may be etched in a layer of the grating material 126
(e.g., silicon nitride) applied to the light guide 110, for
example. In some examples, a metal layer 128 is provided to
substantially cover the ridges 124 of the reflection mode
diffraction grating to provide increased reflection and improve the
diffractive efficiency, for example.
[0064] In some embodiments (e.g., as illustrated in FIGS. 1A and
2A-2B), the diffraction grating 120 of the privacy display 100 may
be a single diffraction grating configured to substantially cover a
light-emitting portion of the light guide 110. In other
embodiments, the diffraction grating 120 of the privacy display 100
may comprise a plurality of sub-gratings, wherein each diffractive
grating sub-grating of the plurality is located in a different
region of the light guide 110. In some embodiments, the diffractive
grating sub-gratings may be separated from one another (i.e., by
spaces or areas on the light guide 110 without diffractive
features). In various embodiments, the plurality of diffractive
grating sub-gratings is configured to cooperatively concentrate the
diffractively coupled-out light 102 into the viewbox 108.
[0065] FIG. 6A illustrates a side view of a privacy display 100
having a plurality of sub-gratings 120' in an example, according to
an embodiment consistent with the principles described herein. In
particular, FIG. 6A illustrates a privacy display 100 comprising
the light guide 110, the diffraction grating 120 and the light
valve array 130, as described above. Further, as illustrated, the
diffraction grating 120 comprises a plurality of sub-gratings 120'
(with individually labeled sub-gratings 120'a, 120'b, 120'c for
purposes of discussion below). The sub-gratings 120' are spaced
apart from one another at a surface of a light guide 110. In the
privacy display 100 of FIG. 6A, light may be coupled into the light
guide 110 along the light-entrance edge 112 with or having the
collimation factor .sigma.. The plurality of sub-gratings 120' of
the diffraction grating 120 is configured to diffractively couple
out a portion of the light guided in the light guide 110 as the
diffractively coupled-out light 102. Further, the sub-gratings 120'
of the plurality are configured to cooperatively direct the
diffractively coupled-out light 102 into the viewbox 108 at a
distance f from the light guide 110.
[0066] FIG. 6B illustrates a plan view of a portion of a privacy
display 100 having a plurality of sub-gratings 120' in an example,
according to another embodiment consistent with the principles
described herein. The privacy display 100 of FIG. 6B may be
substantially similar to the privacy display 100 illustrated in
FIG. 6A, for example. In particular, as illustrated in FIG. 6B, the
sub-gratings 120' of the diffraction grating 120, e.g., including
the individually labeled sub-gratings 120'a, 120'b, 120'c, form
strips across the light guide surface in a y-direction. The width
of the diffractive features and feature spacing (e.g., grooves or
ridges) within each sub-grating 120' decrease from left to right in
the x-direction (longitudinal direction of the light guide 110).
Further, as illustrated, spaces are provided between adjacent ones
of the strips that form the sub-gratings 120'. The spaces may
represent un-patterned or un-etched regions of the light guide
surface, for example. Together, the sub-gratings 120' of the
plurality may approximate a single or continuous diffraction
grating 120, e.g., representing a sub-grating embodiment of the
diffraction grating 120 illustrated in FIG. 2B.
[0067] FIG. 6C illustrates a plan view of a portion of a privacy
display 100 having a plurality of sub-gratings 120' in an example,
according to another embodiment consistent with the principles
described herein. In particular, as illustrated in FIG. 6C, the
sub-gratings 120' of the diffraction grating 120 comprise regions
(e.g., rectangular regions of one or both of curved grooves and
curved ridges) separated by spaces running in both an x-direction
and the y-direction. The width of the diffractive features and
feature spacing (e.g., grooves or ridges) within each sub-grating
120' decrease from left to right in the x-direction (longitudinal
direction of the light guide 110). The privacy display 100 of FIG.
6C may be substantially similar to the privacy display 100
illustrated in FIG. 6A, for example. As illustrated in FIG. 6C, the
sub-gratings 120' of the plurality, e.g., including the
individually labeled sub-gratings 120'a, 120'b, 120'c, form a
two-dimensional array across the light guide surface in both the
x-direction and the y-direction. Also as illustrated in FIG. 6B,
the sub-gratings 120' illustrated in FIG. 6C may approximate a
single diffraction grating 120, e.g., representing another
sub-grating embodiment of the diffraction grating 120 illustrated
in FIG. 2B.
[0068] In some embodiments, the sub-gratings 120' may comprise
substantially straight diffractive features arranged on the light
guide 110 to approximate curved diffractive features. FIG. 6D
illustrates a plan view of a portion of a privacy display 100
having a plurality of sub-gratings 120' in an example, according to
another embodiment consistent with the principles described herein.
As illustrated in FIG. 6D, different ones of the sub-gratings 120'
have different feature spacing and different diffraction grating
orientations that collectively approximate curved (albeit,
piece-wise curved) diffractive features of the diffraction grating
120. Moreover, the width of the diffractive features and feature
spacing (e.g., grooves or ridges) within each sub-grating 120'
decrease from left to right in the x-direction (longitudinal
direction of the light guide 110). For example, the approximated
curved diffractive features, in combination, may substantially
approximate the curved diffractive features of the diffraction
grating 120 illustrated in FIG. 2B. Moreover, the privacy display
100 of FIG. 6D may be substantially similar to the privacy display
100 illustrated in FIG. 6A, for example. In particular, as
illustrated in FIG. 6D, the sub-gratings 120', e.g., including the
individually labeled sub-gratings 120'a, 120'b, 120'c, form another
two-dimensional array across the light guide surface in both the
x-direction and they-direction, e.g., representing another
sub-grating embodiment of the diffraction grating 120.
[0069] Note that, in various illustrations herein, cross-sectional
views of the diffractive features are represented by
rectangular-shaped grooves and ridges for ease of illustration and
not by way of limitation. In particular, according to various
embodiments, the diffractive features of the diffraction grating
may have any of a variety of other cross-sectional shapes
including, but not limited to, a saw-tooth shape, a trapezoidal
shape, or a hemispherical shape. For example, diffractive features
of the diffraction grating may have ridges with a trapezoidal cross
section.
[0070] In accordance with other embodiments consistent with the
principles described herein, a dual-mode privacy display system is
provided. FIG. 7A illustrates a side view of a dual-mode privacy
display system 300 in an example, according to an embodiment
consistent with the principles described herein. FIG. 7B
illustrates a side view of a dual-mode privacy display system 300
in another example, according to an embodiment consistent with the
principles described herein. The dual-mode privacy display system
comprises a privacy operation mode and a public operation mode. In
particular, FIG. 7A illustrates the dual-mode privacy display
system 300 in or during a privacy mode of operation and FIG. 7B
illustrates the dual-mode privacy display system 300 in or during a
public mode of operation.
[0071] The dual-mode privacy display system 300 is configured to
provide an image formed by or using modulation of emitted light 302
in or during each of the private and public modes. In the private
mode, the dual-mode privacy display system 300 is configured to
provide a private image. According to various embodiments, the
private image may be configured to be exclusively visible within a
viewing cone 306 of a viewbox 308. Moreover, the private image is
substantially not visible in a region 306' outside of the viewing
cone 306. In some embodiments, the viewing cone 306 and the viewbox
308 may be substantially similar, respectively, to the viewing cone
106 and viewbox 108, described above with respect to the privacy
display 100. In the public mode, the dual-mode privacy display
system 300 is configured to provide a public image. The public
image is configured to be visible both inside and outside the
viewbox 308 and the viewing cone 306, according to various
embodiments. The dual-mode privacy display system 300 is configured
to be switchable between the privacy mode and the public mode. The
dual-mode privacy display system 300 may be switchable between the
privacy mode and the public mode to provide private images when a
user wants privacy and public images otherwise, for example.
[0072] As illustrated in FIGS. 7A and 7B, the dual-mode privacy
display system 300 comprises a broad-angle backlight 310. The
broad-angle backlight 310 is configured to provide broad-angle
emitted light 302, 302' in the public mode (of operation). By
definition, `broad-angle` emitted light 302' is defined as light
having a cone angle that is greater than a cone angle of the
viewing cone 306 of the viewbox 308. For example, if the viewing
cone 306 has a negative cone angle, the broad-angle light may have
a positive cone angle. In some examples, the broad-angle light may
have a cone angle that is greater than about ten degrees (e.g.,
>.+-.10.degree.). In other examples, the broad-angle light cone
angle may be greater than about twenty degrees (e.g.,
>.+-.20.degree.), or greater than about thirty degrees (e.g.,
>.+-.30.degree.), or greater than forty degrees (e.g.,
>.+-.40.degree.). For example, the cone angle of the broad-angle
light may be about sixty degrees (e.g., >.+-.60.degree.). In
some examples, the broad-angle light cone angle may be about the
same as a viewing angle of an LCD computer monitor, an LCD tablet,
an LCD television, or a similar digital display device meant for
broad-angle viewing (e.g., about .+-.40-65.degree.). Broad-angle
emitted light 302 provided by the broad-angle backlight 310 may
also be characterized as diffuse light, in some examples. The
broad-angle emitted light 302, 302' is illustrated in FIG. 7A as a
dashed arrows for ease of illustration. However, the dashed arrows
representing the broad-angle emitted light 302, 302' in FIG. 7A are
not meant to imply any particular directionality of the emitted
light 302, but instead merely represent the emission and
transmission of light, e.g., from the broad-angle backlight 310
through a diffraction grating-based backlight 320 and a light valve
array 330, described below.
[0073] According to some embodiments, the broad-angle backlight 310
has a light-emitting surface 310' configured to provide the
broad-angle emitted light 302, 302' (e.g., as illustrated in FIG.
7A). Moreover, the light-emitting surface 310' may be substantially
planar, in some embodiments. For example, the broad-angle backlight
310 may be a direct-emitting or directly illuminated planar
backlight having a planar light-emitting surface 310'.
Direct-emitting or directly illuminated planar backlights include,
but are not limited to, a backlight panel employing a planar array
of cold-cathode fluorescent lamps (CCFLs), neon lamps or light
emitting diodes (LEDs), that are configured to directly illuminate
the planar light-emitting surface 310' and provide the broad-angle
emitted light 302, 302'. An electroluminescent panel (ELP) is
another non-limiting example of a direct-emitting planar
backlight.
[0074] In other examples, the broad-angle backlight 310 may
comprise a backlight that employs an indirect light source. Such
indirectly illuminated backlights may include, but are not limited
to, any one or more of various forms of edge-coupled or so-called
edge-lit' backlights. An edge-lit backlight typically includes a
light source (not illustrated in FIGS. 7A-7B) coupled to an edge or
side of a light guide or similar guiding structure (e.g., a hollow
guiding cavity). The edge-coupled light source is configured to
illuminate the guiding structure to provide light within the
edge-lit backlight. The edge-coupled light source may include, but
is not limited to, a CCFL or an LED, for example. The guiding
structure may be configured to guide light from the edge-coupled
light source using total internal reflection (TIR), a mirrored
surface (e.g., a mirrored back surface), or a combination thereof,
according to various examples. Further, in some examples, the
guiding structure of the edge-lit backlight employed in the
broad-angle backlight 310 may have a substantially rectangular
cross section with parallel opposing surfaces (e.g., top and bottom
surfaces). In other examples, the guiding structure may have a
tapered or wedge-shaped cross section (i.e., the guiding structure
may be `wedge-shaped`) with a first surface that is substantially
non-parallel to a second, opposing surface.
[0075] The edge-lit backlight employed as the broad-angle backlight
310 may further include an extraction feature (not illustrated in
FIGS. 7A-7B). The extraction feature is configured to extract light
from the guiding structure and redirect the extracted light in a
direction away from the guiding structure. For example, the
extraction feature may extract light and direct the extracted light
as the broad-angle emitted light 302, 302' away from the planar
light-emitting surface 310' of the edge-lit backlight. Extraction
features may include, but are not limited to, various
micro-prismatic films or layers adjacent to a surface (e.g., a top
surface) of the guiding structure, or various scatters or
reflectors located either within the guiding structure itself or
adjacent to one or both of a pair of opposing surfaces thereof.
[0076] FIG. 8 illustrates a cross sectional view of a broad-angle
backlight 310 in an example, according to an embodiment consistent
with the principles described herein. In particular, the
broad-angle backlight 310 illustrated in FIG. 8 represents an
example of an indirect or edge-lit backlight. As illustrated in
FIG. 8, the broad-angle backlight 310 comprises a light source 312
coupled to an edge of the broad-angle backlight 310. The
edge-coupled light source 312 is configured to produce light within
the broad-angle backlight 310. Further, as illustrated by way of
example and not limitation, the broad-angle backlight 310
illustrated in FIG. 8 comprises a wedge-shaped guiding structure
314 having extraction features 316. The illustrated extraction
features 316 include a micro-prism layer 316' adjacent to the
planar light-emitting surface 310' (i.e., top surface) and a
reflective layer 316'' on a surface (i.e., a back surface) of the
guiding structure 314 opposite to the planar light-emitting surface
310'. The light from the edge-coupled light source 312 guided
within the guiding structure 314 is redirected, scattered out of or
otherwise extracted from the guiding structure 314 by the
extraction features 316 to provide the broad-angle emitted light
302, 302', according to various embodiments.
[0077] In some embodiments, the broad-angle backlight 310, whether
direct-emitting or edge-lit (e.g., as illustrated in FIG. 8), may
further have one or more additional layers or films including, but
not limited to, a brightness enhancement film (BEF), a diffuser or
diffusion layer, and a turning film or layer. For example, a
diffuser may be configured to provide the broad-angle emitted light
302, 302' as substantially diffuse light. FIG. 8 illustrates the
broad-angle backlight 310 further comprising a diffuser 318
adjacent to the planar light-emitting surface 310' and configured
to provide diffuse broad-angle emitted light 302, 302'. According
to various embodiments (not illustrated in FIG. 8), other layers or
films of the broad-angle backlight 310 (e.g., BEF, turning layer,
etc.) may also be adjacent to the planar light-emitting surface
310'.
[0078] Referring again to FIGS. 7A-7B, the dual-mode privacy
display system 300 further comprises a diffraction grating-based
backlight 320. The diffraction grating-based backlight 320 is
configured to provide and to direct into the viewbox 308
diffractively coupled-out light in or during the privacy mode of
operation of the dual-mode privacy display system 300. In
particular, the diffraction grating-based backlight 320 is
configured to provide the diffractively coupled-out light as
directional emitted light 302, 302'' during the privacy mode (e.g.,
for use in providing the private image). Moreover, when provided in
the privacy mode, the directional emitted light 302, 302'' is
directed toward the viewbox 308 that is spaced from the dual-mode
privacy display system 300. Moreover, the directional emitted light
302, 302'' is substantially confined to the viewing cone 306
between the dual-mode privacy display system 300 and the viewbox
308, e.g., as illustrated in FIG. 7B.
[0079] According to various embodiments, the diffraction
grating-based backlight 320 is substantially transparent to the
broad-angle emitted light 302, 302'. In particular, the broad-angle
emitted light 302, 302' may readily pass through the diffraction
grating-based backlight 320 in or during the public mode of
operation of the dual-mode privacy display system 300, according to
various embodiments, e.g., as illustrated in FIG. 7A.
[0080] In some embodiments, the diffraction grating-based backlight
320 may be substantially similar to a combination of the light
guide and the diffraction grating of the privacy display 100,
described above. In particular, as illustrated in FIGS. 7A-7B, the
diffraction grating-based backlight 320 may comprise a light guide
322 configured to guide light. The light guide 322 may be
substantially similar to the light guide 110 of the privacy display
100. For example, the light guide 322 may comprise a slab of
optically transparent material configured to guide light by total
internal reflection. Further, the light may be introduced into and
guided within the light guide 322 at a non-zero propagation angle
and according to a collimation factor .sigma.. In various
embodiments, the light guided within the light guide 322 may be
provide by a light source (not illustrated) and introduced or
coupled into the light guide 322 at a light-entrance edge of the
light guide 322.
[0081] As illustrated in FIGS. 7A-7B, the diffraction grating-based
backlight 320 may further comprise a diffraction grating 324. The
diffraction grating 324 may be located at a surface of the light
guide 322, as illustrated in FIG. 7A-7B. The diffraction grating
324 is configured to diffractively couple out a portion of the
guided light from the light guide 322 as the diffractively
coupled-out light. Further, the diffraction grating 324 is
configured to direct the diffractively coupled-out light into the
viewbox 308, i.e., the directed, diffractively coupled-out light is
the directional emitted light 302, 302'' of the diffraction
grating-based backlight 320. In some embodiments, the diffraction
grating 324 may be substantially similar to the diffraction grating
120, described above with respect to the privacy display 100.
[0082] For example, the diffraction grating 324 may comprise
diffractive features having a feature spacing between adjacent
diffractive features that decreases with increasing distance from
the light-entrance edge, according to some embodiments. In
addition, an extent of the viewbox 308 may be determined by the
collimation factor .sigma. of the guided light within the light
guide 322, for example. Moreover, the viewbox extent may be
selectable or adjustable by selecting or adjusting the collimation
factor .sigma., according to some embodiments. In some embodiments,
the diffraction grating 324 may comprise a plurality of curved
diffractive features (e.g., hyperbolic or semicircular curved
diffractive features) configured to direct the diffractively
coupled-out light in two orthogonal directions to provide the
viewbox 308 as a two-dimensional viewbox 308 having a
two-dimensional viewing cone 306. In some embodiments, the
diffraction grating 324 may comprise a plurality of sub-gratings
(not illustrated) separated from one another by spaces. The
plurality of sub-gratings may be configured to cooperatively direct
the diffractively coupled-out light into the viewbox 308, for
example. In some embodiments, the viewbox cone angle may be a
negative cone angle.
[0083] According to various embodiments (e.g., as illustrated in
FIGS. 7A-7B), the dual-mode privacy display system 300 further
comprises a light valve array 330. The light valve array 330 is
configured to modulate the broad-angle emitted light 302, 302' to
provide the public image in the public mode. Further, the light
valve array 330 is configured to modulate the diffractively
coupled-out light (i.e., the directional emitted light 302, 302'')
to provide the private image in the privacy mode. As noted above,
the provided private image is configured to be exclusively visible
within the viewing cone 306 of the viewbox 308. Also, as noted
above, the public image is configured to be visible both inside and
outside the viewing cone 306 of the viewbox 308. According to some
embodiments, the light valve array 330 may be substantially similar
to the light valve array 130, described above with respect to
privacy display 100. For example, the dual-mode privacy display
system 300 may represent or be substantially similar to a
combination of the privacy display 100 and the broad-angle
backlight 310, in some embodiments.
[0084] According to some embodiments, the dual-mode privacy display
system 300 may further comprise a light-blocking layer 340 between
the broad-angle backlight 310 and the diffraction grating-based
backlight 320. The light-blocking layer 340 is configured to
selectively block light emitted from the diffraction grating-based
backlight 320 from entering the broad-angle backlight 310,
according to some embodiments. In particular, the light-blocking
layer 340 is configured to block light emitted from the diffraction
grating-based backlight 320 generally toward the broad-angle
backlight 310. On the other hand, the light-blocking layer 340 is
configured to transmit light emitted from the broad-angle backlight
310 generally toward the diffraction grating-based backlight 320.
As such, the light-blocking layer 340 may represent a
unidirectional light-blocking layer 340, according to some
embodiments. In other embodiments, the light-blocking layer 340 may
be configured to selectively block light from passing through the
light-blocking layer 340 and reaching the diffraction grating-based
backlight 320, e.g., from the broad-angle backlight 310. In these
embodiments, the light-blocking layer 340 may block the light only
during specific modes of the dual-mode privacy display system 300.
The light-blocking layer 340 configured to block light is
illustrated using cross-hatching in FIG. 7B, while absence of the
cross-hatching in FIG. 7A illustrates the light-blocking layer 340
being configured to transmit light (e.g., broad-angle emitted light
302, 302' from the broad-angle backlight 310).
[0085] According to some embodiments, the light-blocking layer 340
may be configured to provide either passive light blocking or
active (e.g., switched) light blocking. For example, the
light-blocking layer 340 may be a substantially passive layer that
provides direction-selective light blocking. Examples of a passive
layer that may be employed as the light-blocking layer 340 include,
but are not limited to, a so-called unidirectional perfect
absorber, a polarizer or polarization layer, or an angular filter.
Other examples of a passive layer may include a multi-band filter
(e.g., multi-band color filter) configured to selectively block
(e.g., reflect, absorb, etc.) particular wavelengths of light
produced by the diffraction grating-based backlight 320 while
allowing different wavelengths of light produced by the broad-angle
backlight 310 to pass, for example.
[0086] In another example, the light-blocking layer 340 may be an
active layer configured to block light transmission in a
light-blocking mode or condition and to transmit light in a
light-transmitting mode or condition. The active light-blocking
layer 340 may be selectively switched into the light-blocking
condition to prevent light from being transmitted toward and into
the broad-angle backlight 310 when the diffraction grating-based
backlight 320 is active. The diffraction grating-based backlight
320 is active in the privacy mode of the dual-mode privacy display
system 300 to provide the directional emitted light 302, 302'', as
illustrated in FIG. 7B for example. Moreover, the active
light-blocking layer 340 may be selectively switched into the
light-transmitting condition, when the broad-angle backlight 310 is
active, to allow light to propagate out of the activated
broad-angle backlight 310 and through the diffraction grating-based
backlight 320 as the broad-angle emitted light 302, 302', e.g., as
illustrated in FIG. 7A. The broad-angle backlight 310 is active
when the dual-mode privacy display system 300 is in the public
mode, for example. Examples of active light-blocking layers 340
include, but are not limited to, a light valve (e.g., liquid
crystal light valve) or a similar switchable absorption layer.
Other examples include various other so-called `active` shutter
configurations based on electromechanical structures (e.g.,
microelectromechanical or MEMS mirrors, etc.), electroabsorption
(e.g., semiconductor-based), or various non-linear crystals or
organic polymers.
[0087] In accordance with other embodiments of the principles
described herein, a method of privacy display operation is
provided. FIG. 9 illustrates a flow chart of a method 400 of
privacy display operation in an example, according to an embodiment
consistent with the principles described herein. As illustrated in
FIG. 9, the method 400 of privacy display operation comprises
guiding 410 light in a light guide as guided light. In some
embodiments, the guided light may be guided 410 along a length of
the light guide. For example, the light may be guided in a
longitudinal direction. Further, the light is guided 410 according
to a collimation factor. According to some embodiments, the light
guide may be substantially similar to the light guide 110 described
above with respect to the privacy display 100. For example, the
light guide may be a plate light guide comprising a slab of
optically transparent material that is configured to guide 410
light using total internal reflection. Further, the guided light
may have a predetermined collimation factor that is substantially
similar to the collimation factor .sigma., described above with
respect to the light guide 110. Also, the guided light may be
guided at a non-zero propagation angle.
[0088] As illustrated in FIG. 9, the method 400 of privacy display
operation further comprises diffractively coupling out 420 a
portion of the guided light and directing the diffractively
coupled-out light into a viewbox. According to various embodiments,
diffractively coupling out 420 the guided light portion uses a
diffraction grating optically coupled to the light guide. The
diffraction grating used in diffractively coupling out 420 the
guided light portion may be located at a surface of the light
guide, in some embodiments. Further, the viewbox into which the
light is directed by diffractively coupling out 420 may be located
spaced from and adjacent to the light guide surface. The
diffraction grating used in diffractively coupling out 420 the
guided light portion may be substantially similar to the
diffraction grating 120 of the privacy display 100, described
above. In particular, the diffraction grating may be a chirped
diffraction grating comprising diffractive features having a
feature spacing that decreases with increasing distance from a
light-entrance edge of the light guide. Further, the diffraction
grating may comprise curved diffractive features. The curved
diffractive features may be configured to direct the diffractively
coupled-out light in two orthogonal directions to provide a
two-dimensional (2D) viewbox, for example, which has an extent
determined by the collimation factor of the guided light. Further,
in some embodiments, the viewbox may be substantially similar to
the viewbox 108 having a viewing cone 106, described above.
[0089] The method 400 of privacy display operation illustrated in
FIG. 9 further comprises modulating 430 the diffractively
coupled-out light to form a private image within the viewbox. In
addition, the private image may be exclusively visible within a
viewing cone of the viewbox to provide viewing privacy, according
to various embodiments. According to various embodiments,
modulating 430 the diffractively coupled-out light uses a light
valve array located between the light guide and the viewbox.
According to some embodiments, the light valve array may be
substantially similar to the light valve array 130 described above
with respect to the privacy display 100. For example, the light
valve array may comprise a plurality of liquid crystal light
valves.
[0090] In some embodiments (not illustrated in FIG. 9), the method
of privacy display operation may further comprise optically
coupling light into the light guide at the light-entrance edge as
the guided light, for example, using a light source. In some
embodiment, the light source may be substantially similar to the
light source 140 of the privacy display 100, described above. In
particular, according to some embodiments, optically coupling light
into the light guide may comprise providing the guided light with a
predetermined collimation factor, as described above.
[0091] In some embodiments (not illustrated), the method of privacy
display operation may further comprise providing broad-angle light
using a broad-angle backlight and modulating the provided
broad-angle light to form a pubic image. The public image may be
visible both inside and outside the viewing cone of the viewbox,
according to various embodiments. Further, the public image may be
formed during a pubic mode and the private image may be formed
during a privacy mode. As such, the method of privacy display
operation that includes forming both the public image and the
private image may be a method of dual-mode privacy display system
operation, in some embodiments. In particular, the broad-angle
backlight used to provide broad-angle light may be substantially
similar to the broad-angle backlight 310 described above with
respect to the dual-mode privacy display system 300, in some
embodiments, and may further include a light-blocking layer that is
substantially similar to the light-blocking layer 340 between the
broad-angle backlight 310 and the diffraction grating-based
backlight 320, also described above.
[0092] Thus, there have been described examples and embodiments of
a privacy display, a dual-mode privacy display system and a method
of privacy display operation that provide a private image in an
viewbox and within a viewing cone. It should be understood that the
above-described examples are merely illustrative of some of the
many specific examples that represent the principles described
herein. Clearly, those skilled in the art can readily devise
numerous other arrangements without departing from the scope as
defined by the following claims.
* * * * *