U.S. patent application number 16/705030 was filed with the patent office on 2020-07-16 for holographic waveguide display with light control layer.
This patent application is currently assigned to DigiLens Inc.. The applicant listed for this patent is DigiLens Inc.. Invention is credited to Alastair John Grant, Milan Momcilo Popovich, Jonathan David Waldern.
Application Number | 20200225471 16/705030 |
Document ID | / |
Family ID | 71517556 |
Filed Date | 2020-07-16 |
United States Patent
Application |
20200225471 |
Kind Code |
A1 |
Waldern; Jonathan David ; et
al. |
July 16, 2020 |
Holographic Waveguide Display with Light Control Layer
Abstract
Waveguides and waveguide displays having a layer for blocking
non-image light (i.e. haze) that could otherwise reduce contrast
and degrade color gamut and uniformity, while providing high
transmission to external light are provided. Many waveguides and
displays incorporate at least one light control layer applied to at
least one external surface of said waveguide and overlapping at
least a portion of said at least one grating, to divert or block
scattered light from said set of gratings that might otherwise
enter said eyebox.
Inventors: |
Waldern; Jonathan David;
(Los Altos Hills, CA) ; Grant; Alastair John; (San
Jose, CA) ; Popovich; Milan Momcilo; (Leicester,
GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DigiLens Inc. |
Sunnyvale |
CA |
US |
|
|
Assignee: |
DigiLens Inc.
Sunnyvale
CA
|
Family ID: |
71517556 |
Appl. No.: |
16/705030 |
Filed: |
December 5, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62792309 |
Jan 14, 2019 |
|
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|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 2027/0112 20130101;
G02B 27/0103 20130101; G02B 2027/0118 20130101; G02B 5/32
20130101 |
International
Class: |
G02B 27/01 20060101
G02B027/01; G02B 5/32 20060101 G02B005/32 |
Claims
1. A waveguide display comprising: a waveguide supporting at least
one grating; a source of data modulated light; a set of gratings
configured to: direct said data modulated light into a total
internal reflection path in said waveguide; and provide beam
expansion and extraction of data modulated light from said
waveguide into an eyebox; and at least one light control layer
applied to at least one external surface of said waveguide and
overlapping at least a portion of said at least one grating,
wherein said light control layer is operative to divert or block
scattered light from said set of gratings that might otherwise
enter said eyebox.
2. The apparatus of claim 1, wherein said set of gratings comprises
at least one fold grating and at least one output grating, said
fold grating directing said modulated light to said output grating
and providing a first beam expansion, said output grating directing
said modulated light out of said waveguide towards said eye box
with beam expansion orthogonal to said first beam expansion.
3. The apparatus of claim 1, wherein said set of gratings comprises
an input coupler comprising at least one of a prism or a
grating.
4. The apparatus of claim 1, wherein said light control layer has
at least one region having reflection characteristics dependent on
at least one property of light incident on said region selected
from the group of spectral bandwidth, incidence angle range, and
polarization state.
5. The apparatus of claim 4, wherein said light control layer
region overlaps a fold grating.
6. The apparatus of claim 4, said light control layer region
overlaps an output grating.
7. The apparatus of claim 4, wherein said light control layer has a
reflection characteristic that varies spatially across said at
least one region.
8. The apparatus of claim 1 wherein said at least one light control
layer comprises at least one layer comprising at least one selected
from the group of a narrow band interference filter, a dichroic
filter, a reflection hologram, a micro louvre film, a birefringent
film, a reflective polarizer, a polarization selective film, a film
containing microparticles, a transparent substrate and an air
space.
9. The apparatus of claim 1, wherein said data modulated light is
provided by one of a broadband light source, a laser emitter, a LED
emitter or a module comprising one or more selected from the group
of red, green and blue laser or LED emitters.
10. The apparatus of claim 1, wherein said source of data modulated
light comprises: a microdisplay for displaying image pixels and
collimation optics and a lens for projecting the image displayed on
said microdisplay panel such that each image pixel on said
microdisplay is converted into a unique angular direction within
said waveguide.
11. The apparatus of claim 1, wherein said source of data modulated
light is a laser projector comprising a beam scanning mechanism and
a light modulator.
12. The apparatus of claim 1, wherein at least one of said set of
gratings is characterized by at least one of spatially varying
pitch, rolled k-vectors, multiplexed gratings, and dual interaction
gratings.
13. The apparatus of claim 1, wherein at least one of said set of
gratings is selected from the group of a switchable Bragg grating
recorded in a holographic photopolymer a HPDLC material or a
uniform modulation holographic liquid crystal polymer material and
a surface relief grating.
14. The apparatus of claim 1, wherein said set of gratings
comprises: an input coupler; an output coupler comprising
multiplexed first and second gratings; a first fold grating for
directing light in a first spectral band along a first path from
said input coupler to said output coupler and providing a first
beam expansion; and a second fold grating for directing light in a
second spectral band along a second path from said input coupler to
said output coupler and providing a first beam expansion, wherein:
said first multiplexed grating configured to direct said first
spectral band out of said waveguide in a first direction with beam
expansion orthogonal to said first beam expansion; said second
multiplexed grating configured to direct said second spectral band
out of said waveguide in said first direction with beam expansion
orthogonal to said first beam expansion; said at least one light
control layer comprises a first region having high reflectivity in
at least one portion of said first spectral band and overlapping
said first fold grating; and said at least one light control layer
further comprising a second region having high reflectivity in at
least one portion of said second spectral band and overlapping said
second fold grating.
15. The apparatus of claim 14, wherein said first spectral band
extends from blue to green and said first region has high
reflectivity for blue and green light with spectral bandwidths
substantially narrower than said first spectral band, wherein said
second spectral band extends from green to red and said second
region has high reflectivity for green and red light with spectral
bandwidths substantially narrower than said second spectral
band.
16. The apparatus of claim 14, wherein said input coupler comprises
at least one of a prism and a grating.
17. The apparatus of claim 14, wherein said first and second fold
grating and said multiplexed grating are formed in a single
layer.
18. The apparatus of claim 17, wherein said input coupler is a
grating formed in said single layer.
19. The apparatus of claim 14, wherein said at least one light
control layer is formed by a stack of layers each containing a
region providing reflection in spectral bandwidth substantially
narrower than said first spectral band or said second band.
20. The apparatus of claim 14, wherein said source of data
modulated light is a laser projector and said light is provided by
red, green, and blue laser emitters.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority to U.S. Provisional
Application No. 62/792,309, filed Jan. 14, 2019, the disclosure of
which is incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present disclosure generally relates to waveguide
devices and, more specifically, to a holographic waveguide display
using a light control layer to limit haze.
BACKGROUND OF THE INVENTION
[0003] Scatter from particulates suspended in holographic gratings,
and HPDLC gratings in particular, can result in haze, which reduces
image contrast, color fidelity, and brightness uniformity. The main
contributor to haze can stem from the fold grating where the large
number of beam grating interactions for beam folding and expansion
can lead to millions of scattering events. Much of this scatter can
find its way into the eye box of the display. In contrast, input
and output gratings typically have a very small number of beam
grating interactions.
[0004] The use of light control films in waveguides are described
in U.S. patent application Ser. No. 13/317,468 entitled
"Holographic Waveguide Display" which discloses "light control film
applied to either substrate to block stray light that would
otherwise reduce contrast and degrade color gamut" and U.S. patent
application Ser. No. 13/844,456 entitled "Transparent Waveguide
Display" which discloses the use of "holographic brightness
enhancing film, or other narrow band reflector" that is "affixed to
one side of the display, the purpose of which is to reflect the
display illumination wavelength light only. Both disclosures are
incorporated by reference herein in their entireties.
SUMMARY OF THE INVENTION
[0005] The present disclosure provides a waveguide with a layer for
blocking non-image light (i.e. haze) that could otherwise reduce
contrast and degrade color gamut and uniformity, while providing
high transmission to external light.
[0006] Many embodiments are directed to a waveguide display
including: [0007] a waveguide supporting at least one grating;
[0008] a source of data modulated light; [0009] a set of gratings
configured to: [0010] direct said data modulated light into a total
internal reflection path in said waveguide; and [0011] provide beam
expansion and extraction of data modulated light from said
waveguide into an eyebox; and [0012] at least one light control
layer applied to at least one external surface of said waveguide
and overlapping at least a portion of said at least one grating,
wherein said light control layer is operative to divert or block
scattered light from said set of gratings that might otherwise
enter said eyebox.
[0013] In many such embodiments, said set of gratings comprises at
least one fold grating and at least one output grating, said fold
grating directing said modulated light to said output grating and
providing a first beam expansion, said output grating directing
said modulated light out of said waveguide towards said eye box
with beam expansion orthogonal to said first beam expansion.
[0014] In still many such embodiments, said set of gratings
comprises an input coupler comprising at least one of a prism or a
grating.
[0015] In yet many such embodiments, said light control layer has
at least one region having reflection characteristics dependent on
at least one property of light incident on said region selected
from the group of spectral bandwidth, incidence angle range, and
polarization state.
[0016] In still yet many such embodiments, said light control layer
region overlaps a fold grating.
[0017] In still many such embodiments, said light control layer
region overlaps an output grating.
[0018] In still many such embodiments, said light control layer has
a reflection characteristic that varies spatially across said at
least one region.
[0019] In still many such embodiments, said at least one light
control layer comprises at least one layer comprising at least one
selected from the group of a narrow band interference filter, a
dichroic filter, a reflection hologram, a micro louvre film, a
birefringent film, a reflective polarizer, a polarization selective
film, a film containing microparticles, a transparent substrate and
an air space.
[0020] In still many such embodiments, said data modulated light is
provided by one of a broadband light source, a laser emitter, a LED
emitter or a module comprising one or more selected from the group
of red, green and blue laser or LED emitters.
[0021] In still many such embodiments, said source of data
modulated light comprises: a microdisplay for displaying image
pixels and collimation optics and a lens for projecting the image
displayed on said microdisplay panel such that each image pixel on
said microdisplay is converted into a unique angular direction
within said waveguide.
[0022] In still many such embodiments, said source of data
modulated light is a laser projector comprising a beam scanning
mechanism and a light modulator.
[0023] In still many such embodiments, at least one of said set of
gratings is characterized by at least one of spatially varying
pitch, rolled k-vectors, multiplexed gratings, and dual interaction
gratings.
[0024] In still many such embodiments, at least one of said set of
gratings is selected from the group of a switchable Bragg grating
recorded in a holographic photopolymer a HPDLC material or a
uniform modulation holographic liquid crystal polymer material and
a surface relief grating.
[0025] In still many such embodiments, said set of gratings
comprises: [0026] an input coupler; [0027] an output coupler
comprising multiplexed first and second gratings; [0028] a first
fold grating for directing light in a first spectral band along a
first path from said input coupler to said output coupler and
providing a first beam expansion; and [0029] a second fold grating
for directing light in a second spectral band along a second path
from said input coupler to said output coupler and providing a
first beam expansion, wherein: [0030] said first multiplexed
grating configured to direct said first spectral band out of said
waveguide in a first direction with beam expansion orthogonal to
said first beam expansion; [0031] said second multiplexed grating
configured to direct said second spectral band out of said
waveguide in said first direction with beam expansion orthogonal to
said first beam expansion; [0032] said at least one light control
layer comprises a first region having high reflectivity in at least
one portion of said first spectral band and overlapping said first
fold grating; and [0033] said at least one light control layer
further comprising a second region having high reflectivity in at
least one portion of said second spectral band and overlapping said
second fold grating.
[0034] In still many such embodiments, said first spectral band
extends from blue to green and said first region has high
reflectivity for blue and green light with spectral bandwidths
substantially narrower than said first spectral band, wherein said
second spectral band extends from green to red and said second
region has high reflectivity for green and red light with spectral
bandwidths substantially narrower than said second spectral
band.
[0035] In still many such embodiments, said input coupler comprises
at least one of a prism and a grating.
[0036] In still many such embodiments, said first and second fold
grating and said multiplexed grating are formed in a single
layer.
[0037] In still many such embodiments, said input coupler is a
grating formed in said single layer.
[0038] In still many such embodiments, said at least one light
control layer is formed by a stack of layers each containing a
region providing reflection in spectral bandwidth substantially
narrower than said first spectral band or said second band.
[0039] In still many such embodiments, said source of data
modulated light is a laser projector and said light is provided by
red, green, and blue laser emitters.
[0040] Additional embodiments and features are set forth in part in
the description that follows, and in part will become apparent to
those skilled in the art upon examination of the specification or
may be learned by the practice of the disclosed subject matter. A
further understanding of the nature and advantages of the present
disclosure may be realized by reference to the remaining portions
of the specification and the drawings, which forms a part of this
disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0041] These and other features and advantages of the present
apparatus and methods will be better understood by reference to the
following detailed description when considered in conjunction with
the accompanying data and figures, which are presented as exemplary
embodiments of the disclosure and should not be construed as a
complete recitation of the scope of the inventive method,
wherein:
[0042] FIG. 1 conceptually illustrates a schematic cross section
view of a waveguide display comprising a waveguide substrate, a
grating layer, and a light control layer disposed on the waveguide
surface facing the eye box in accordance with embodiments.
[0043] FIG. 2 conceptually illustrates a schematic cross section
view of a waveguide display comprising a waveguide substrate, a
grating layer, and a light control layer disposed on the outside
surface of the waveguide in accordance with embodiments.
[0044] FIG. 3 conceptually illustrates a schematic cross section
view of a waveguide display comprising a waveguide substrate, a
grating layer, and a light control layer disposed on the waveguide
surface facing the eye box and separated from the waveguide by an
air gap in accordance with embodiments.
[0045] FIG. 4 conceptually illustrates a schematic cross section
view of a waveguide display comprising a waveguide substrate, a
grating layer, and light control layers disposed on both outer
surfaces of the waveguide in accordance with embodiments.
[0046] FIG. 5 conceptually illustrates a schematic cross section
view of the waveguide display similar to the embodiment of FIG. 1
in which the light control layer contains a reflecting region
overlapping a fold grating in accordance with embodiments.
[0047] FIG. 6 conceptually illustrates a schematic cross section
view of the waveguide display similar to the embodiment of FIG. 1
in which the light control layer contains reflecting regions
overlapping a fold grating and an output grating in accordance with
embodiments.
[0048] FIG. 7 conceptually illustrates a schematic cross section
view of a waveguide display providing bifurcated waveguide paths
for two spectral bands using upper and lower fold gratings and a
multiplexed output grating and further comprising a light control
layer with reflecting regions overlapping the upper and lower fold
gratings in accordance with embodiments.
[0049] FIG. 8 conceptually illustrates a schematic cross section
view of a light control layer comprising two stacked narrow band
reflecting interference filters in accordance with embodiments.
[0050] FIG. 9 is a chart showing the spectral transmission
characteristics of a first light control layer region based on the
embodiment of FIG. 8 for use in the embodiment of FIG. 7 in
accordance with embodiments.
[0051] FIG. 10 is a chart showing the spectral transmission
characteristics of a second light control layer region based on the
embodiment of FIG. 8 configured for use in the embodiment of FIG. 7
in accordance with embodiments.
[0052] FIG. 11 is a chart illustration the spatial variation of a
light control layer characteristic in accordance with
embodiments.
DETAILED DESCRIPTION OF THE INVENTION
[0053] For the purposes of describing embodiments, some well-known
features of optical technology known to those skilled in the art of
optical design and visual displays have been omitted or simplified
in order to not obscure the basic principles of the disclosure.
Unless otherwise stated the term "on-axis" in relation to a ray or
a beam direction refers to propagation parallel to an axis normal
to the surfaces of the optical components described in relation to
the embodiment. In the following description the terms light, ray,
beam, and direction may be used interchangeably and in association
with each other to indicate the direction of propagation of
electromagnetic radiation along rectilinear trajectories. The term
light and illumination may be used in relation to the visible and
infrared bands of the electromagnetic spectrum. Parts of the
following description will be presented using terminology commonly
employed by those skilled in the art of optical design. As used
herein, the term grating may encompass a grating comprised of a set
of gratings in some embodiments. For illustrative purposes, it is
to be understood that the drawings are not drawn to scale unless
stated otherwise.
[0054] FIG. 1 conceptually illustrates a schematic plan view of a
waveguide display in accordance with embodiments. In the
illustrative embodiment, the waveguide display 100 includes a
waveguide 101 supporting a grating layer containing an input
coupler grating 103, a fold grating 104, and an output grating 105.
The fold grating 104 can be configured to direct light to the
output grating 105 and to provide a first beam expansion. The
output grating 105 can be configured to direct light out of the
waveguide 101 towards an eye box 112 with beam expansion orthogonal
to the first beam expansion. Note that for simplicity the gratings
are shown as separated in the cross section whereas in a practical
display waveguide, at least two of the gratings could overlap in
any cross-sectional view. The apparatus further comprises a source
of data modulated light 106 and a light control layer 107 applied
to an external surface of the waveguide overlapping the grating
layer. For the purposes of explaining embodiments, the light
control layer will be considered to be a coating or film applied to
the outer surface of one or both of the waveguide substrates
sandwiching the grating layer. However, in many embodiments, the
light control layer may actually comprise more than one layer. The
beam paths from input to extraction from the waveguide are
illustrated by ray paths 108-111, which provide an image for
viewing from the eyebox 112. The light control layer 107 is
operative to divert or block scattered light from the grating that
might otherwise enter the eyebox. FIG. 1 also shows the cartesian
reference frame (113) of the waveguide.
[0055] Any of the gratings used in embodiments can be configured as
multiplexed gratings, rolled k-vector gratings, and/or dual
interaction gratings. In some embodiments, gratings with spatially
varying pitch can be used. The gratings can be implemented in
multiple layers or in a single layer. In many embodiments, the
gratings are Bragg gratings recorded in a holographic photopolymer,
in a HPDLC material, or in a uniform modulation holographic liquid
crystal polymer material. In some embodiments, one or more of the
gratings may be configured to be electrically switchable. In some
embodiments, surface relief gratings may be used.
[0056] Present embodiments may also use any of the embodiments
disclosed in U.S. application Ser. No. 16/242,979 entitled
"Waveguide Architectures and Related Methods of Manufacturing,"
disclosure of which is incorporated by reference herein in its
entirety.
[0057] Image data can be coupled into the waveguide by means of an
input coupler which can comprise at least one of a prism or a
grating, as shown in FIG. 1. In many embodiments, the source of
data modulated light comprises a microdisplay for displaying image
pixels and collimation optics and a lens for projecting the image
displayed on the microdisplay panel such that each image pixel on
the microdisplay is converted into a unique angular direction
within the waveguide. In many embodiments, the source of data
modulated light is a laser projector comprising a beam scanning
mechanism and a light modulator.
[0058] In many embodiments, the light control layer is disposed on
the lower face of the waveguide--i.e., between the waveguide and
the eye box as shown in FIG. 1. The advantage of this arrangement
is that scattered light reflected by the light control layer can be
extracted through the front surface of the waveguide and hence is
not visible from the eyebox. FIG. 2 shows an example of an
embodiment in which a light control layer (114) is disposed on the
outer face of the waveguide (114). In some embodiments, such as the
one shown in FIG. 3, a light control layer (115) can be disposed in
proximity to and air separated from an outer surface of the
waveguide. In such embodiments, the light control layer can
comprise a film applied to a thin substrate (not shown). In some
embodiments, upper and lower light control layers (116,117) are
disposed on the lower and upper faces of the waveguide (as shown in
FIG. 4).
[0059] In many embodiments, the light control layer has at least
one region having reflection characteristics dependent on at least
one property of the light incident on the region. In many
embodiments, the property can be selected from spectral bandwidth,
incidence angle range, and polarization state. In many embodiments,
the light control layer region overlaps a fold grating. For
example, FIG. 5 shows a light control layer 118 containing the
reflecting region 119 overlapping the fold grating 104. In some
embodiments, a light control layer region can overlap an output
grating. In some embodiments, the light control layer contains
regions overlapping more than one grating. For example, FIG. 6
shows a light control layer 120 containing a reflecting region 121
with a first reflecting characteristic overlapping the fold grating
104 and a reflecting region with a second reflecting characteristic
overlapping the output grating 105.
[0060] A light control layer according to the principles of
embodiments can be configured in many ways. In some embodiments,
the light control layer can comprise several layers combined in a
stack. In some embodiments, a light control layer can be configured
as a narrow band interference filter. In some embodiments, a light
control layer can be configured as a dichroic filter. In some
embodiments, a light control layer can be provided by a reflection
hologram. In some embodiments, a light control layer can be
provided by a micro louvre film, which controls reflections by
using a louvre structure to control the distribution of light
perpendicular to the film. An exemplary micro louvre film is the
3M.TM. Advanced Light Control Film (ALCF). In some embodiments, a
light control layer can be provided by a birefringent film, which
can be used to perform various polarization control functions such
as but not limited to retardation and/or polarization selection. In
some embodiments, a light control layer can be provided by a
reflective polarizer. In some embodiments, a light control layer
can be provided by a film containing microparticles. In many
embodiments, the light control layer can be formed using a coating
process such as for example a vacuum coating process in the case of
narrow band interference filter. In the case of a light control
layer based on a reflection hologram, conventional holographic
exposure processes may be used, which can include but are not
limited to processes based on ink jet printing disclosed In U.S.
patent application Ser. No. 16/203,071 entitled "Systems and
Methods for Manufacturing Waveguide Cells," the disclosure of which
is incorporated herein by reference in its entirety. In many
embodiments, the light control layer can be applied directly to an
outer surface of a waveguide substrate. In some embodiments, a
light control layer can be applied to a transparent substrate,
which is then mounted in proximity to a waveguide outer surface and
separated from the waveguide by a small air gap.
[0061] Embodiments may be applied using many types of light source.
In some embodiments, a broadband light source can be used. In many
embodiments, the light source can be a laser or LED emitters
configured for monochromatic illumination in a module comprising
emitters of more than one wavelength. In many embodiments, red,
green and blue emitters can be used to provide color displays.
Laser emitters can allow more precise control of light using narrow
band filters.
[0062] In some embodiments, a display waveguide with bifurcated
propagation paths for different spectral bands, for example
blue-green and green blue is provided. As shown in the schematic
plan view of FIG. 7, the display waveguide 130 comprises a
waveguide 131 supporting input grating 132 for coupling light from
a source of data modulated light (not shown) into a first
propagation path for a first spectral band and a second propagation
path for a second spectral band, upper and lower fold gratings
133,134, and an output coupler comprising multiplexed gratings
135,136. The first fold grating 133 can be configured to direct
light in a first spectral band .DELTA..DELTA..sub.1 along a first
path represented by rays 140-143 from the input coupler to the
output coupler grating 135 and to provide a first beam expansion.
In many embodiments, the first spectral band corresponds to
blue-green and the second spectral band corresponds to green-red.
The second fold grating 134 can be configured to direct light in a
second spectral band .DELTA..lamda..sub.2 along a second path
represented by the rays 144-147 from the input coupler to the
output coupler grating 136 and to provide a first beam expansion.
The first and second multiplexed gratings can be configured to
direct the first and second spectral bands out of the waveguide
with beam expansion orthogonal to the first beam expansion. In the
illustrative embodiment, the waveguide 130 includes a light control
layer 137 having a first region 138 with high reflectivity in at
least one portion of the first spectral band and overlapping the
first fold grating 133. The light control layer further includes a
second region 139 having high reflectivity in at least one portion
of the second spectral band and overlapping the second fold grating
134. In some embodiments, the first spectral band extends from blue
to green and the first region has high reflectivity for blue and
green light with spectral bandwidths substantially narrower than
the first spectral band. In some embodiments, the second spectral
band extends from green to red and the second region has high
reflectivity for green and red light with spectral bandwidths
substantially narrower than the second spectral band. The input
coupler can include a prism or a grating. In some embodiments, the
first and second fold gratings and the multiplexed grating are
formed in a single layer. In some embodiments, the input coupler is
a grating formed in the same layer as the fold and output gratings.
In some embodiments, the light control layer is formed by a stack
of layers each containing a region providing reflection in spectral
bandwidth substantially narrower than the first spectral band or
the second band. In some embodiments, the source of data modulated
light is a laser projector and the light is provided by red, green
and blue laser emitters.
[0063] FIG. 8 is a schematic cross section view showing a light
control layer configured from two stacked layers 150,151 each
supporting narrow band interference filter regions 152,153. In some
embodiments, a light control layer in which the regions 152,153
provide narrow band reflectivity in blue and green respectively can
be overlaid over the first fold grating 133. Similarly, a light
control layer in which the regions 152,153 providing narrow band
reflectivity in green and red respectively can be overlaid over the
second fold grating 134. FIG. 9 shows the light transmission (T)
versus wavelength characteristics 160 resulting from the green
(161) and red (162) narrow band filter spectral regions 161. FIG.
10 shows the light transmission (T) versus wavelength
characteristics 170 resulting from the blue (163) and green (161)
narrow band filter spectral regions 161.
[0064] In many embodiments, it can be advantageous to vary the
reflection characteristic of a light control layer spatially. FIG.
11 shows a chart 180 illustrating the variation of a reflection
characteristic as a function of a spatial coordinate (x). The
characteristic F may depend on wavelength band, polarization state,
angle of incidence, and other parameters.
DOCTRINE OF EQUIVALENTS
[0065] Although specific fabrication processes are discussed above,
many different processes can be implemented in accordance with many
different embodiments. It is therefore to be understood that
embodiments can be practiced in ways other than specifically
described, without departing from the scope and spirit of the
present disclosure. Thus, embodiments presented should be
considered in all respects as illustrative and not restrictive.
Accordingly, the scope of the disclosure should be determined not
by the embodiments illustrated, but by the appended claims and
their equivalents. Although specific embodiments have been
described in detail in this disclosure, many modifications are
possible (for example, variations in sizes, dimensions, structures,
shapes and proportions of the various elements, values of
parameters, mounting arrangements, use of materials, colors,
orientations, etc.). For example, the position of elements may be
reversed or otherwise varied and the nature or number of discrete
elements or positions may be altered or varied. Accordingly, all
such modifications are intended to be included within the scope of
the present disclosure. The order or sequence of any process or
method steps may be varied or re-sequenced according to alternative
embodiments. Other substitutions, modifications, changes, and
omissions may be made in the design, operating conditions and
arrangement of the exemplary embodiments without departing from the
scope of the present disclosure.
* * * * *