U.S. patent application number 16/817524 was filed with the patent office on 2020-09-17 for holographic waveguide backlight and related methods of manufacturing.
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 Popovich, Jonathan David Waldern.
Application Number | 20200292745 16/817524 |
Document ID | / |
Family ID | 1000004722876 |
Filed Date | 2020-09-17 |
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United States Patent
Application |
20200292745 |
Kind Code |
A1 |
Waldern; Jonathan David ; et
al. |
September 17, 2020 |
Holographic Waveguide Backlight and Related Methods of
Manufacturing
Abstract
Systems and methods for holographic waveguide backlights in
accordance with various embodiments of the invention are
illustrated. One embodiment includes an optical illumination device
including at least one waveguide, a source of light optically
coupled to the at least one waveguide configured to emit light
having a first polarization state, a first plurality of grating
elements for diffracting the light having the first polarization
state out of the at least one waveguide into a first set of output
paths, a second plurality of grating elements for diffracting the
light having the first polarization state light out of the at least
one waveguide into a second set of output paths, and at least one
input coupler configured to couple at least a portion of the light
having the first polarization state towards the first and second
pluralities of grating elements.
Inventors: |
Waldern; Jonathan David;
(Los Altos Hills, CA) ; Popovich; Milan;
(Leicester, GB) ; Grant; Alastair John; (San Jose,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Digilens Inc. |
Sunnyvale |
CA |
US |
|
|
Assignee: |
DigiLens Inc.
Sunnyvale
CA
|
Family ID: |
1000004722876 |
Appl. No.: |
16/817524 |
Filed: |
March 12, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62817468 |
Mar 12, 2019 |
|
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|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 6/0056 20130101;
G02B 5/32 20130101; G02B 6/0035 20130101 |
International
Class: |
F21V 8/00 20060101
F21V008/00; G02B 5/32 20060101 G02B005/32 |
Claims
1. An optical illumination device comprising: a light guiding
structure with an upper surface for extracting illumination and a
lower surface; a light source optically coupled to said light
guiding structure and configured to provide polarized light, said
light undergoing total internal reflection within said light
guiding structure; and at least one plurality of grating elements
disposed in at least one grating layer for extracting light from
said light guiding structure.
2. The optical illumination device of claim 1, wherein said light
source is configured to emit at least first and second wavelength
collimated light color sequentially, wherein said at least one
plurality of grating elements comprises a first plurality of
grating elements for diffracting said first wavelength light out of
said light guiding structure into a first set of output paths, and
a second plurality grating elements for diffracting said second
wavelength light out of said light guiding structure into a second
set of output paths substantially overlapping said first set of
output paths.
3. The optical illumination device of claim 2, further comprising a
substrate having half-wave retarding regions interspersed with
clear regions overlaying said upper surface, wherein each said half
wave retarding region overlaps at least one grating element in each
of said first and second pluralities of grating elements; and
wherein each said clear region overlaps at least one grating
element in each of said first and second pluralities of grating
elements.
4. The optical illumination device of claim 2, further comprising a
quarter-wave retarding layer disposed, said quarter-wave retarding
layer having a first surface disposed in proximity to said lower
surface and a reflective surface.
5. The optical illumination device of claim 2, wherein said first
plurality of grating elements is disposed in a separate grating
layer to said second plurality of grating elements, wherein grating
elements for diffracting said first wavelength light overlap
grating elements for diffracting said second wavelength light.
6. The optical illumination device of claim 2, wherein grating
elements for diffracting first and second wavelength light are
disposed as uniformly interspersed first and second multiplicities
of grating elements in one layer.
7. The optical illumination device of claim 2, wherein grating
elements for diffracting first and second wavelength light are
disposed as uniformly interspersed first and second multiplicities
of grating elements in two layers, wherein grating element for
diffracting a first wavelength light overlap grating elements for
diffracting second wavelength light.
8. The optical illumination device of claim 2, wherein grating
elements for diffracting first wavelength light have a first
grating vector and grating elements for diffracting second
wavelength light have a second grating vector in an opposing
direction to said first grating vector.
9. The optical illumination device of claim 2, wherein grating
elements for diffracting first wavelength light and grating
elements for diffracting second wavelength light have grating
vectors aligned in substantially parallel directions.
10. The optical illumination device of claim 2, wherein grating
elements for diffracting first wavelength light and grating
elements for diffracting second wavelength light are off-Bragg with
respect to each other.
11. The optical illumination device of claim 2, wherein grating
elements for diffracting first wavelength light are disposed in a
first layer in which grating elements having a first grating vector
and grating elements having a second grating vector in an opposing
direction to said first grating vector are uniformly interspersed,
wherein grating elements for diffracting second wavelength light
are disposed in a second layer in which grating elements having a
first grating vector and grating elements having a second grating
vector in an opposing direction to said first grating vector are
interspersed.
12. The optical illumination device of claim 2, wherein said first
wavelength light has a first polarization and said second
wavelength light has a second polarization orthogonal to said first
polarization.
13. The optical illumination device of claim 2, wherein said first
wavelength light and said second wavelength light have the same
polarization.
14. The optical illumination device of claim 2, wherein grating
elements for diffracting first and second wavelength light are
disposed as first and second multiplicities of grating elements
multiplexed in a single layer, wherein grating elements for
diffracting said first wavelength are multiplexed with grating
elements for diffracting said second wavelength light.
15. The optical illumination device of claim 2, wherein grating
elements for diffracting first and second wavelength light are
disposed as first and second multiplicities of grating elements in
a stack of two contacting layers with grating elements for
diffracting said first wavelength light overlapping grating
elements for diffracting said second wavelength light.
16. The optical illumination device of claim 2, wherein grating
elements of said first plurality are switched into a diffracting
state when said light source emits said first wavelength light and
grating elements of said second plurality are switched into a
diffracting state when said light source emits said second
wavelength light.
17. The optical illumination device of claim 2, wherein said output
paths are angularly separated.
18. The optical illumination device of claim 2, wherein said output
paths are substantially normal to said upper surface.
19. The optical illumination device of claim 1, wherein said at
least one plurality of grating elements is disposed in at least one
grating layer, wherein said light guiding structure comprises at
least one waveguide, wherein each said waveguide supports at least
one of said grating layers.
20. The optical illumination device of claim 1, wherein said layer
is formed between transparent substrates with transparent
conductive coatings applied to each said substrate, at least one of
said coatings being patterned into independently addressable
elements overlapping said grating elements, wherein an electrical
control circuit operative to apply voltages across each said
grating elements is provided.
21. The optical illumination device of claim 1, wherein each said
grating element comprises at least one property selected from the
group consisting of: a planar Bragg surfaces, optical power,
optical retardation, diffusing properties, spatially varying
diffraction efficiency, diffraction efficiency proportional to a
voltage applied across said grating element, and phase retardation
proportional to a voltages applied across said grating element.
22. The optical illumination device of claim 1, wherein said at
least one plurality of grating elements comprises a two-dimensional
array.
23. The optical illumination device of claim 1, wherein said at
least one plurality of grating elements comprises a one-dimensional
array of elongate elements.
24. The optical illumination device of claim 1, wherein each said
grating element is recorded in a Holographic Polymer Dispersed
Liquid Crystal.
25. The optical illumination device of claim 1, wherein said light
is coupled into said light guide structure by a grating or a
prism.
26. The optical illumination device of claim 1, wherein said light
source is laser or LED.
27. The optical illumination device of claim 1, further comprising
at least one component selected from the group consisting of: a
beam deflector, a dichroic filter, a microlens array, beam shaper,
light integrator, and a polarization rotator.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The current application claims the benefit of and priority
under 35 U.S.C. .sctn. 119(e) to U.S. Provisional Patent
Application No. 62/817,468 entitled "Holographic Waveguide
Backlight," filed Mar. 12, 2019. The disclosure of U.S. Provisional
Patent Application No. 62/817,468 is hereby incorporated by
reference in its entirety for all purposes.
FIELD OF THE INVENTION
[0002] The present invention generally relates to waveguide devices
and, more specifically, to holographic waveguide backlights.
BACKGROUND
[0003] Waveguides can be referred to as structures with the
capability of confining and guiding waves (i.e., restricting the
spatial region in which waves can propagate). One subclass includes
optical waveguides, which are structures that can guide
electromagnetic waves, typically those in the visible spectrum.
Waveguide structures can be designed to control the propagation
path of waves using a number of different mechanisms. For example,
planar waveguides can be designed to utilize diffraction gratings
to diffract and couple incident light into the waveguide structure
such that the in-coupled light can proceed to travel within the
planar structure via total internal reflection (TIR).
[0004] Fabrication of waveguides can include the use of material
systems that allow for the recording of holographic optical
elements within the waveguides. One class of such material includes
polymer dispersed liquid crystal (PDLC) mixtures, which are
mixtures containing photopolymerizable monomers and liquid
crystals. A further subclass of such mixtures includes holographic
polymer dispersed liquid crystal (HPDLC) mixtures. Holographic
optical elements, such as volume phase gratings, can be recorded in
such a liquid mixture by illuminating the material with two
mutually coherent laser beams. During the recording process, the
monomers polymerize, and the mixture undergoes a
photopolymerization-induced phase separation, creating regions
densely populated by liquid crystal micro-droplets, interspersed
with regions of clear polymer. The alternating liquid crystal-rich
and liquid crystal-depleted regions form the fringe planes of the
grating. The resulting grating, which is commonly referred to as a
switchable Bragg grating (SBG), has all the properties normally
associated with volume or Bragg gratings but with much higher
refractive index modulation ranges combined with the ability to
electrically tune the grating over a continuous range of
diffraction efficiency (the proportion of incident light diffracted
into a desired direction). The latter can extend from
non-diffracting (cleared) to diffracting with close to 100%
efficiency.
[0005] Waveguide optics, such as those described above, can be
considered for a range of display and sensor applications. In many
applications, waveguides containing one or more grating layers
encoding multiple optical functions can be realized using various
waveguide architectures and material systems, enabling new
innovations in near-eye displays for augmented reality (AR) and
virtual reality (VR), compact head-up displays (HUDs) and
helmet-mounted displays or head-mounted displays (HMDs) for road
transport, aviation, and military applications, and sensors for
biometric and laser radar (LIDAR) applications.
SUMMARY OF THE INVENTION
[0006] Systems and methods for holographic waveguide backlights in
accordance with various embodiments of the invention are
illustrated. One embodiment includes an optical illumination device
including a light guiding structure with an upper surface for
extracting illumination and a lower surface, a light source
optically coupled to the light guiding structure and configured to
provide polarized light, the light undergoing total internal
reflection within the light guiding structure, and at least one
plurality of grating elements disposed in at least one grating
layer for extracting light from the light guiding structure.
[0007] In another embodiment, the light source is configured to
emit at least first and second wavelength collimated light color
sequentially, wherein the at least one plurality of grating
elements includes a first plurality of grating elements for
diffracting the first wavelength light out of the light guiding
structure into a first set of output paths, and a second plurality
grating elements for diffracting the second wavelength light out of
the light guiding structure into a second set of output paths
substantially overlapping the first set of output paths.
[0008] In a further embodiment, the optical illumination device
further includes a substrate having half-wave retarding regions
interspersed with clear regions overlaying the upper surface,
wherein each the half wave retarding region overlaps at least one
grating element in each of the first and second pluralities of
grating elements, and each the clear region overlaps at least one
grating element in each of the first and second pluralities of
grating elements.
[0009] In still another embodiment, the optical illumination device
further includes a quarter-wave retarding layer disposed, the
quarter-wave retarding layer having a first surface disposed in
proximity to the lower surface and a reflective surface.
[0010] In a still further embodiment, the first plurality of
grating elements is disposed in a separate grating layer to the
second plurality of grating elements, wherein grating elements for
diffracting the first wavelength light overlap grating elements for
diffracting the second wavelength light.
[0011] In yet another embodiment, grating elements for diffracting
first and second wavelength light are disposed as uniformly
interspersed first and second multiplicities of grating elements in
one layer.
[0012] In a yet further embodiment, grating elements for
diffracting first and second wavelength light are disposed as
uniformly interspersed first and second multiplicities of grating
elements in two layers, wherein grating element for diffracting a
first wavelength light overlap grating elements for diffracting
second wavelength light.
[0013] In another additional embodiment, grating elements for
diffracting first wavelength light have a first grating vector and
grating elements for diffracting second wavelength light have a
second grating vector in an opposing direction to the first grating
vector.
[0014] In a further additional embodiment, grating elements for
diffracting first wavelength light and grating elements for
diffracting second wavelength light have grating vectors aligned in
substantially parallel directions.
[0015] In another embodiment again, grating elements for
diffracting first wavelength light and grating elements for
diffracting second wavelength light are off-Bragg with respect to
each other.
[0016] In a further embodiment again, grating elements for
diffracting first wavelength light are disposed in a first layer in
which grating elements having a first grating vector and grating
elements having a second grating vector in an opposing direction to
the first grating vector are uniformly interspersed, wherein
grating elements for diffracting second wavelength light are
disposed in a second layer in which grating elements having a first
grating vector and grating elements having a second grating vector
in an opposing direction to the first grating vector are
interspersed.
[0017] In still yet another embodiment, the first wavelength light
has a first polarization and the second wavelength light has a
second polarization orthogonal to the first polarization.
[0018] In a still yet further embodiment, the first wavelength
light and the second wavelength light have the same
polarization.
[0019] In still another additional embodiment, grating elements for
diffracting first and second wavelength light are disposed as first
and second multiplicities of grating elements multiplexed in a
single layer, wherein grating elements for diffracting the first
wavelength are multiplexed with grating elements for diffracting
the second wavelength light.
[0020] In a still further additional embodiment, grating elements
for diffracting first and second wavelength light are disposed as
first and second multiplicities of grating elements in a stack of
two contacting layers with grating elements for diffracting the
first wavelength light overlapping grating elements for diffracting
the second wavelength light.
[0021] In still another embodiment again, grating elements of the
first plurality are switched into a diffracting state when the
light source emits the first wavelength light and grating elements
of the second plurality are switched into a diffracting state when
the light source emits the second wavelength light.
[0022] In a still further embodiment again, the output paths are
angularly separated.
[0023] In yet another additional embodiment, the output paths are
substantially normal to the upper surface.
[0024] In a yet further additional embodiment, the at least one
plurality of grating elements is disposed in at least one grating
layer, wherein the light guiding structure includes at least one
waveguide, wherein each the waveguide supports at least one of the
grating layers.
[0025] In yet another embodiment again, the layer is formed between
transparent substrates with transparent conductive coatings applied
to each the substrate, at least one of the coatings being patterned
into independently addressable elements overlapping the grating
elements, wherein an electrical control circuit operative to apply
voltages across each the grating elements is provided.
[0026] In a yet further embodiment again, each the grating element
includes at least one property that is one of a planar Bragg
surfaces, optical power, optical retardation, diffusing properties,
spatially varying diffraction efficiency, diffraction efficiency
proportional to a voltage applied across the grating element, and
phase retardation proportional to a voltages applied across the
grating element.
[0027] In another additional embodiment again, the at least one
plurality of grating elements includes a two-dimensional array.
[0028] In a further additional embodiment again, the at least one
plurality of grating elements includes a one-dimensional array of
elongate elements.
[0029] In still yet another additional embodiment, each the grating
element is recorded in a Holographic Polymer Dispersed Liquid
Crystal.
[0030] In a still yet further additional embodiment, the light is
coupled into the light guide structure by a grating or a prism.
[0031] In yet another additional embodiment again, the light source
is laser or LED.
[0032] In a yet further additional embodiment again, the optical
illumination device further includes at least one component that is
one of a beam deflector, a dichroic filter, a microlens array, beam
shaper, light integrator, and a polarization rotator.
[0033] A still yet another embodiment again includes an optical
illumination device including at least one waveguide, a source of
light optically coupled to the at least one waveguide configured to
emit light having a first polarization state, a first plurality of
grating elements for diffracting the light having the first
polarization state out of the at least one waveguide into a first
set of output paths, a second plurality of grating elements for
diffracting the light having the first polarization state light out
of the at least one waveguide into a second set of output paths,
and at least one input coupler configured to couple at least a
portion of the light having the first polarization state towards
the first and second pluralities of grating elements.
[0034] In a still yet further embodiment again, the optical
illumination device further includes a quarter-wave plate having a
reflective surface, and a substrate including a plurality of
transparent regions and a plurality of regions supporting half-wave
plates, wherein at least one of the first plurality of grating
elements is configured to diffract a first portion of the light
having the first polarization state towards at least one of the
plurality of transparent regions, at least one of the second
plurality of grating elements is configured to diffract a second
portion of the light having the first polarization state towards
the quarter-wave plate, and the quarter-wave plate is configured to
reflect incident the light having the first polarization state
towards at least one of the plurality of regions supporting
half-wave plates, wherein the reflected incident light has its
polarization state changed to a second polarization state that is
orthogonal to the first polarization state, wherein the first and
second pluralities of grating elements are formed in at least one
grating layer disposed within the at least one waveguide.
[0035] In still yet another additional embodiment again, the
optical illumination device further includes third and fourth
pluralities of grating elements, wherein the light having a first
polarization state includes light of a first wavelength band and
light of a second wavelength band, the at least one input coupler
includes a first input coupler for coupling the light of the first
wavelength band towards the first and second pluralities of grating
elements, and a second input coupler for coupling the light of the
second wavelength band towards the third and fourth pluralities of
grating elements.
[0036] In a still yet further additional embodiment again, the at
least one waveguide includes first and second grating layers, the
first and second pluralities of grating elements are interspersed
within the first grating layer, the third and fourth pluralities of
grating elements are interspersed with the second grating layer,
the first and third pluralities of grating elements have grating
vectors in a first direction, and the second and fourth pluralities
of grating elements have grating vectors in an opposing direction
to the first direction.
[0037] In still another additional embodiment again, the emitted
light is collimated light, and source of light is configured to
emit the light of the first and second wavelength bands
sequentially.
[0038] In a still further additional embodiment again, the first
and second pluralities of grating elements are configured to switch
into a diffracting state when the source of light emits the light
of the first wavelength band is emitted, and the third and fourth
pluralities of grating elements are configured to switch into a
diffracting state when the source of light emits the light of the
second wavelength band.
[0039] In yet another additional embodiment again, the optical
illumination device further includes third and fourth pluralities
of grating elements, wherein the at least one waveguide includes
first and second grating layers, the first and third pluralities of
grating elements are interspersed within the first grating layer,
the second and fourth pluralities of grating elements are
interspersed within the second grating layer, the light having a
first polarization state includes light of a first wavelength band
and light of a second wavelength band, and the at least one input
coupler includes a first input coupler for coupling the light of
the first wavelength band towards the first and second pluralities
of grating elements, and a second input coupler for coupling the
light of the second wavelength band towards the third and fourth
pluralities of grating elements.
[0040] In a yet further additional embodiment again, the optical
illumination device further includes a quarter-wave plate having a
reflective surface, third and fourth pluralities of grating
elements, wherein the source of light is further configured to emit
light having a second polarization state, the light having the
first polarization state is in a first wavelength band, and the
light having the second polarization state is in a second
wavelength band, the third and fourth pluralities of grating
elements are configured to diffract the light having the second
polarization state towards the quarter-wave plate, the at least one
waveguide includes first and second grating layers, the first and
third pluralities of grating elements are interspersed within the
first grating layer, and the second and fourth pluralities of
grating elements are interspersed within the second grating layer,
and the first plurality of grating elements spatially overlaps the
second plurality of grating elements.
[0041] In still yet another additional embodiment again, the first
plurality of grating elements has a grating vector in a first
direction, and the second plurality of grating elements has a
grating vector in an opposing direction to the first direction.
[0042] In a still yet further additional embodiment again, the
source of light is a laser source.
[0043] 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 invention. A further
understanding of the nature and advantages of the present invention
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
[0044] The description will be more fully understood with reference
to the following figures and data graphs, which are presented as
exemplary embodiments of the invention and should not be construed
as a complete recitation of the scope of the invention.
[0045] FIGS. 1A and 1B conceptually illustrate HPDLC SBG devices
and the switching property of SBGs in accordance with various
embodiments of the invention.
[0046] FIG. 2 conceptually illustrates a waveguide backlight in
accordance with an embodiment of the invention.
[0047] FIG. 3 conceptually illustrates a flow chart of a process
for providing a waveguide backlight in accordance with an
embodiment of the invention.
[0048] FIG. 4 conceptually illustrates a waveguide backlight with
two waveguide layers in accordance with an embodiment of the
invention.
[0049] FIG. 5 conceptually illustrates a waveguide backlight with a
single waveguide layer in accordance with an embodiment of the
invention.
[0050] FIG. 6 conceptually illustrates a waveguide backlight having
two waveguide layers with alternating wavelength-diffracting
grating elements in accordance with an embodiment of the
invention.
[0051] FIG. 7 conceptually illustrates a waveguide backlight having
a single waveguide layer with alternating wavelength-diffracting
grating elements in accordance with an embodiment of the
invention.
[0052] FIG. 8 conceptually illustrates a waveguide backlight having
two waveguide layers with alternating wavelength-diffracting
grating elements for input light having orthogonal polarizations in
accordance with an embodiment of the invention.
[0053] FIG. 9 conceptually illustrates a waveguide backlight having
a single waveguide layer with alternating wavelength-diffracting
grating elements for input light having orthogonal polarizations in
accordance with an embodiment of the invention.
DETAILED DESCRIPTION
[0054] 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 invention.
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 invention. 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.
[0055] An ideal backlight unit (BLU) should have a compact (i.e.,
thin) form factor and should deliver uniform luminance and color
with efficient coupling of light from the illumination source and
extraction from the BLU onto the display panel to be back-lit. In
mobile displays, the BLU thickness should be a few millimeters.
Television displays likewise require low thickness to image
diagonal ratios. Traditional edge-lit solutions have failed to meet
form factor and uniformity requirements. Waveguide or light
guiding, which carry the illumination light by total internal
reflection while extracting portions of such light from the
waveguide, can provide very thin form factors. However, waveguides
can suffer from spatial variations of luminance and color due to
the dispersive properties of gratings typically implemented in
waveguides. In some cases, dispersion can be greatly alleviated by
using laser sources.
[0056] Illumination nonuniformities can arise from
wavelength-dependent absorption within gratings; the small loss
incurred at each beam-grating interaction can be multiplied as the
beam propagates down the waveguide, leading to a progressive
dimming of light along the waveguide. Where laser sources are used,
which can make for a very compact light source-to-waveguide
coupling optics, the high coherence of the lasers can result in a
banding effect caused by gaps or overlaps due to imperfect
interlacing of the total internal reflection beams. Laser-lit BLUs
can also suffer from laser speckle. Another source of
nonuniformity, when birefringent materials are used to form
gratings, results from polarization rotations occurring at each
beam bounce. This polarization variation can manifest itself as
luminance nonuniformity. Color nonuniformity can also occur due to
wavelength dependence of birefringence. Finally, birefringent
gratings can result in spatially varying polarization at the output
of the BLU. This can result in luminance and color nonuniformity
when the display panel to be lit is a liquid crystal device.
[0057] Turning now to the drawings, holographic waveguide backlight
in accordance with various embodiments of the invention are
illustrated. In many embodiments, the waveguide backlight is
implemented as a compact, efficient, highly uniform, color
waveguide backlight that can be used in a range of display
applications, such as but not limited to LCD monitors, digital
holographic display, and mobile computing and telecommunications
devices. In many embodiments, the waveguide backlight includes a
waveguide and a source of light configured to provide input light.
The input light can be coupled into the waveguide in a total
internal reflection path using a variety of different methods. In
some embodiments, an input coupler, such as but not limited to a
grating or a prism, is utilized to couple light into the waveguide.
In several embodiments, the source of light is configured to
provide light of different wavelengths. In further embodiments, the
source of light is configured to emit at least first and second
wavelength collimated light color sequentially. The waveguide can
include at least two sets of grating elements disposed across at
least one grating layer. Each set of grating elements can be
configured to operate at a specific wavelength/angular band. In
many embodiments, each set of grating elements is configured to
diffract and extract either upward-going or downward-going light.
In several embodiments, each set of grating elements are configured
for a specific wavelength band. In further embodiments, each set of
grating elements include switchable Bragg gratings and is switched
into a diffracting state when the light source emits wavelength
light intended for that set. In some embodiments, waveplates and
retarders are implemented to control the polarization of light. As
can readily be appreciated, waveguide backlights in accordance with
various embodiments of the invention can be implemented in numerous
configurations, the specific of which can depend on the
application. Waveguide backlight configurations, optical waveguide
structures, materials, and manufacturing processes are discussed in
the sections below in further detail.
Optical Waveguide and Grating Structures
[0058] Optical structures recorded in waveguides can include many
different types of optical elements, such as but not limited to
diffraction gratings. Gratings can be implemented to perform
various optical functions, including but not limited to coupling
light, directing light, and preventing the transmission of light.
In many embodiments, the gratings are surface relief gratings that
reside on the outer surface of the waveguide. In other embodiments,
the grating implemented is a Bragg grating (also referred to as a
volume grating), which are structures having a periodic refractive
index modulation. Bragg gratings can be fabricated using a variety
of different methods. One process includes interferential exposure
of holographic photopolymer materials to form periodic structures.
Bragg gratings can have high efficiency with little light being
diffracted into higher orders. The relative amount of light in the
diffracted and zero order can be varied by controlling the
refractive index modulation of the grating, a property that can be
used to make lossy waveguide gratings for extracting light over a
large pupil.
[0059] One class of Bragg gratings used in holographic waveguide
devices is the Switchable Bragg Grating (SBG). SBGs can be
fabricated by first placing a thin film of a mixture of
photopolymerizable monomers and liquid crystal material between
substrates. The substrates can be made of various types of
materials, such glass and plastics. In many cases, the substrates
are in a parallel configuration. In other embodiments, the
substrates form a wedge shape. One or both substrates can support
electrodes, typically transparent tin oxide films, for applying an
electric field across the film. The grating structure in an SBG can
be recorded in the liquid material (often referred to as the syrup)
through photopolymerization-induced phase separation using
interferential exposure with a spatially periodic intensity
modulation. Factors such as but not limited to control of the
irradiation intensity, component volume fractions of the materials
in the mixture, and exposure temperature can determine the
resulting grating morphology and performance. As can readily be
appreciated, a wide variety of materials and mixtures can be used
depending on the specific requirements of a given application. In
many embodiments, HPDLC material is used. During the recording
process, the monomers polymerize, and the mixture undergoes a phase
separation. The LC molecules aggregate to form discrete or
coalesced droplets that are periodically distributed in polymer
networks on the scale of optical wavelengths. The alternating
liquid crystal-rich and liquid crystal-depleted regions form the
fringe planes of the grating, which can produce Bragg diffraction
with a strong optical polarization resulting from the orientation
ordering of the LC molecules in the droplets.
[0060] The resulting volume phase grating can exhibit very high
diffraction efficiency, which can be controlled by the magnitude of
the electric field applied across the film. When an electric field
is applied to the grating via transparent electrodes, the natural
orientation of the LC droplets can change, causing the refractive
index modulation of the fringes to lower and the hologram
diffraction efficiency to drop to very low levels. Typically, the
electrodes are configured such that the applied electric field will
be perpendicular to the substrates. In a number of embodiments, the
electrodes are fabricated from indium tin oxide (ITO). In the OFF
state with no electric field applied, the extraordinary axis of the
liquid crystals generally aligns normal to the fringes. The grating
thus exhibits high refractive index modulation and high diffraction
efficiency for P-polarized light. When an electric field is applied
to the HPDLC, the grating switches to the ON state wherein the
extraordinary axes of the liquid crystal molecules align parallel
to the applied field and hence perpendicular to the substrate. In
the ON state, the grating exhibits lower refractive index
modulation and lower diffraction efficiency for both S- and
P-polarized light. Thus, the grating region no longer diffracts
light. Each grating region can be divided into a multiplicity of
grating elements such as for example a pixel matrix according to
the function of the HPDLC device. Typically, the electrode on one
substrate surface is uniform and continuous, while electrodes on
the opposing substrate surface are patterned in accordance to the
multiplicity of selectively switchable grating elements.
[0061] Typically, the SBG elements are switched clear in 30 .mu.s
with a longer relaxation time to switch ON. The diffraction
efficiency of the device can be adjusted, by means of the applied
voltage, over a continuous range. In many cases, the device
exhibits near 100% efficiency with no voltage applied and
essentially zero efficiency with a sufficiently high voltage
applied. In certain types of HPDLC devices, magnetic fields can be
used to control the LC orientation. In some HPDLC applications,
phase separation of the LC material from the polymer can be
accomplished to such a degree that no discernible droplet structure
results. An SBG can also be used as a passive grating. In this
mode, its chief benefit is a uniquely high refractive index
modulation. SBGs can be used to provide transmission or reflection
gratings for free space applications. SBGs can be implemented as
waveguide devices in which the HPDLC forms either the waveguide
core or an evanescently coupled layer in proximity to the
waveguide. The substrates used to form the HPDLC cell provide a
total internal reflection (TIR) light guiding structure. Light can
be coupled out of the SBG when the switchable grating diffracts the
light at an angle beyond the TIR condition. In a number of
embodiments, a reverse mode grating device can be
implemented--i.e., the grating is in its non-diffracting (cleared)
state when the applied voltage is zero and switches to its
diffracting stated when a voltage is applied across the
electrodes.
[0062] FIGS. 1A and 1B conceptually illustrate HPDLC SBG devices
100, 110 and the switching property of SBGs in accordance with
various embodiments of the invention. In FIG. 1A, the SBG 100 is in
an OFF state. As shown, the LC molecules 101 are aligned
substantially normal to the fringe planes. As such, the SBG 100
exhibits high diffraction efficiency, and incident light can easily
be diffracted. FIG. 1B illustrates the SBG 110 in an ON position.
An applied voltage 111 can orient the optical axis of the LC
molecules 112 within the droplets 113 to produce an effective
refractive index that matches the polymer's refractive index,
essentially creating a transparent cell where incident light is not
diffracted. In the illustrative embodiment, an AC voltage source is
shown. As can readily be appreciated, various voltage sources can
be utilized depending on the specific requirements of a given
application. Furthermore, different materials and device
configurations can also be implemented. In some embodiments, the
device implements different material systems and can operate in
reverse with respect to the applied voltage--i.e., the device
exhibits high diffraction efficiency in response to an applied
voltage.
[0063] In some embodiments, LC can be extracted or evacuated from
the SBG to provide a surface relief grating (SRG) that has
properties very similar to a Bragg grating due to the depth of the
SRG structure (which is much greater than that practically
achievable using surface etching and other conventional processes
commonly used to fabricate SRGs). The LC can be extracted using a
variety of different methods, including but not limited to flushing
with isopropyl alcohol and solvents. In many embodiments, one of
the transparent substrates of the SBG is removed, and the LC is
extracted. In further embodiments, the removed substrate is
replaced. The SRG can be at least partially backfilled with a
material of higher or lower refractive index. Such gratings offer
scope for tailoring the efficiency, angular/spectral response,
polarization, and other properties to suit various waveguide
applications.
[0064] Waveguides in accordance with various embodiments of the
invention can include various grating configurations designed for
specific purposes and functions. In many embodiments, the waveguide
is designed to implement a grating configuration capable of
preserving eyebox size while reducing lens size by effectively
expanding the exit pupil of a collimating optical system. The exit
pupil can be defined as a virtual aperture where only the light
rays which pass though this virtual aperture can enter the eyes of
a user. In some embodiments, the waveguide includes an input
grating optically coupled to a light source, a fold grating for
providing a first direction beam expansion, and an output grating
for providing beam expansion in a second direction, which is
typically orthogonal to the first direction, and beam extraction
towards the eyebox. As can readily be appreciated, the grating
configuration implemented waveguide architectures can depend on the
specific requirements of a given application. In some embodiments,
the grating configuration includes multiple fold gratings. In
several embodiments, the grating configuration includes an input
grating and a second grating for performing beam expansion and beam
extraction simultaneously. The second grating can include gratings
of different prescriptions, for propagating different portions of
the field-of-view, arranged in separate overlapping grating layers
or multiplexed in a single grating layer. Multiplexed gratings can
include the superimposition of at least two gratings having
different grating prescriptions within the same volume. Gratings
having different grating prescriptions can have different grating
vectors and/or grating slant with respect to the waveguide's
surface.
[0065] In several embodiments, the gratings within each layer are
designed to have different spectral and/or angular responses. For
example, in many embodiments, different gratings across different
grating layers are overlapped, or multiplexed, to provide an
increase in spectral bandwidth. In some embodiments, a full color
waveguide is implemented using three grating layers, each designed
to operate in a different spectral band (red, green, and blue). In
other embodiments, a full color waveguide is implemented using two
grating layers, a red-green grating layer and a green-blue grating
layer. As can readily be appreciated, such techniques can be
implemented similarly for increasing angular bandwidth operation of
the waveguide. In addition to the multiplexing of gratings across
different grating layers, multiple gratings can be multiplexed
within a single grating layer--i.e., multiple gratings can be
superimposed within the same volume. In several embodiments, the
waveguide includes at least one grating layer having two or more
grating prescriptions multiplexed in the same volume. In further
embodiments, the waveguide includes two grating layers, each layer
having two grating prescriptions multiplexed in the same volume.
Multiplexing two or more grating prescriptions within the same
volume can be achieved using various fabrication techniques. In a
number of embodiments, a multiplexed master grating is utilized
with an exposure configuration to form a multiplexed grating. In
many embodiments, a multiplexed grating is fabricated by
sequentially exposing an optical recording material layer with two
or more configurations of exposure light, where each configuration
is designed to form a grating prescription. In some embodiments, a
multiplexed grating is fabricated by exposing an optical recording
material layer by alternating between or among two or more
configurations of exposure light, where each configuration is
designed to form a grating prescription. As can readily be
appreciated, various techniques, including those well known in the
art, can be used as appropriate to fabricate multiplexed
gratings.
[0066] In many embodiments, the waveguide can incorporate at least
one of: angle multiplexed gratings, color multiplexed gratings,
fold gratings, dual interaction gratings, rolled K-vector gratings,
crossed fold gratings, tessellated gratings, chirped gratings,
gratings with spatially varying refractive index modulation,
gratings having spatially varying grating thickness, gratings
having spatially varying average refractive index, gratings with
spatially varying refractive index modulation tensors, and gratings
having spatially varying average refractive index tensors. In some
embodiments, the waveguide can incorporate at least one of: a half
wave plate, a quarter wave plate, an anti-reflection coating, a
beam splitting layer, an alignment layer, a photochromic back layer
for glare reduction, and louvre films for glare reduction. In
several embodiments, the waveguide can support gratings providing
separate optical paths for different polarizations. In various
embodiments, the waveguide can support gratings providing separate
optical paths for different spectral bandwidths. In a number of
embodiments, the gratings can be HPDLC gratings, switching gratings
recorded in HPDLC (such switchable Bragg Gratings), Bragg gratings
recorded in holographic photopolymer, or surface relief gratings.
In many embodiments, the waveguide operates in a monochrome band.
In some embodiments, the waveguide operates in the green band. In
several embodiments, waveguide layers operating in different
spectral bands such as red, green, and blue (RGB) can be stacked to
provide a three-layer waveguiding structure. In further
embodiments, the layers are stacked with air gaps between the
waveguide layers. In various embodiments, the waveguide layers
operate in broader bands such as blue-green and green-red to
provide two-waveguide layer solutions. In other embodiments, the
gratings are color multiplexed to reduce the number of grating
layers. Various types of gratings can be implemented. In some
embodiments, at least one grating in each layer is a switchable
grating.
[0067] Waveguides incorporating optical structures such as those
discussed above can be implemented in a variety of different
applications, including but not limited to waveguide displays. In
various embodiments, the waveguide display is implemented with an
eyebox of greater than 10 mm with an eye relief greater than 25 mm.
In some embodiments, the waveguide display includes a waveguide
with a thickness between 2.0-5.0 mm. In many embodiments, the
waveguide display can provide an image field-of-view of at least
50.degree. diagonal. In further embodiments, the waveguide display
can provide an image field-of-view of at least 70.degree. diagonal.
The waveguide display can employ many different types of picture
generation units (PGUs). In several embodiments, the PGU can be a
reflective or transmissive spatial light modulator such as a liquid
crystal on Silicon (LCoS) panel or a micro electromechanical system
(MEMS) panel. In a number of embodiments, the PGU can be an
emissive device such as an organic light emitting diode (OLED)
panel. In some embodiments, an OLED display can have a luminance
greater than 4000 nits and a resolution of 4 k.times.4 k pixels. In
several embodiments, the waveguide can have an optical efficiency
greater than 10% such that a greater than 400 nit image luminance
can be provided using an OLED display of luminance 4000 nits.
Waveguides implementing P-diffracting gratings (i.e., gratings with
high efficiency for P-polarized light) typically have a waveguide
efficiency of 5%-6.2%. Since P-diffracting or S-diffracting
gratings can waste half of the light from an unpolarized source
such as an OLED panel, many embodiments are directed towards
waveguides capable of providing both S-diffracting and
P-diffracting gratings to allow for an increase in the efficiency
of the waveguide by up to a factor of two. In some embodiments, the
S-diffracting and P-diffracting gratings are implemented in
separate overlapping grating layers. Alternatively, a single
grating can, under certain conditions, provide high efficiency for
both p-polarized and s-polarized light. In several embodiments, the
waveguide includes Bragg-like gratings produced by extracting LC
from HPDLC gratings, such as those described above, to enable high
S and P diffraction efficiency over certain wavelength and angle
ranges for suitably chosen values of grating thickness (typically,
in the range 2-5 .mu.m).
Optical Recording Material Systems
[0068] HPDLC mixtures generally include LC, monomers,
photoinitiator dyes, and coinitiators. The mixture (often referred
to as syrup) frequently also includes a surfactant. For the
purposes of describing the invention, a surfactant is defined as
any chemical agent that lowers the surface tension of the total
liquid mixture. The use of surfactants in PDLC mixtures is known
and dates back to the earliest investigations of PDLCs. For
example, a paper by R. L Sutherland et al., SPIE Vol. 2689,
158-169, 1996, the disclosure of which is incorporated herein by
reference, describes a PDLC mixture including a monomer,
photoinitiator, coinitiator, chain extender, and LCs to which a
surfactant can be added. Surfactants are also mentioned in a paper
by Natarajan et al, Journal of Nonlinear Optical Physics and
Materials, Vol. 5 No. I 89-98, 1996, the disclosure of which is
incorporated herein by reference. Furthermore, U.S. Pat. No.
7,018,563 by Sutherland; et al., discusses polymer-dispersed liquid
crystal material for forming a polymer-dispersed liquid crystal
optical element having: at least one acrylic acid monomer; at least
one type of liquid crystal material; a photoinitiator dye; a
coinitiator; and a surfactant. The disclosure of U.S. Pat. No.
7,018,563 is hereby incorporated by reference in its entirety.
[0069] The patent and scientific literature contains many examples
of material systems and processes that can be used to fabricate
SBGs, including investigations into formulating such material
systems for achieving high diffraction efficiency, fast response
time, low drive voltage, and so forth. U.S. Pat. No. 5,942,157 by
Sutherland, and U.S. Pat. No. 5,751,452 by Tanaka et al. both
describe monomer and liquid crystal material combinations suitable
for fabricating SBG devices. Examples of recipes can also be found
in papers dating back to the early 1990s. Many of these materials
use acrylate monomers, including: [0070] R. L. Sutherland et al.,
Chem. Mater. 5, 1533 (1993), the disclosure of which is
incorporated herein by reference, describes the use of acrylate
polymers and surfactants. Specifically, the recipe includes a
crosslinking multifunctional acrylate monomer; a chain extender
N-vinyl pyrrolidinone, LC E7, photoinitiator rose Bengal, and
coinitiator N-phenyl glycine. Surfactant octanoic acid was added in
certain variants. [0071] Fontecchio et al., SID 00 Digest 774-776,
2000, the disclosure of which is incorporated herein by reference,
describes a UV curable HPDLC for reflective display applications
including a multi-functional acrylate monomer, LC, a
photoinitiator, a coinitiators, and a chain terminator. [0072] Y.
H. Cho, et al., Polymer International, 48, 1085-1090, 1999, the
disclosure of which is incorporated herein by reference, discloses
HPDLC recipes including acrylates. [0073] Karasawa et al., Japanese
Journal of Applied Physics, Vol. 36, 6388-6392, 1997, the
disclosure of which is incorporated herein by reference, describes
acrylates of various functional orders. [0074] T. J. Bunning et
al., Polymer Science: Part B: Polymer Physics, Vol. 35, 2825-2833,
1997, the disclosure of which is incorporated herein by reference,
also describes multifunctional acrylate monomers. [0075] G. S.
Iannacchione et al., Europhysics Letters Vol. 36 (6). 425-430,
1996, the disclosure of which is incorporated herein by reference,
describes a PDLC mixture including a penta-acrylate monomer, LC,
chain extender, coinitiators, and photoinitiator. Acrylates offer
the benefits of fast kinetics, good mixing with other materials,
and compatibility with film forming processes. Since acrylates are
cross-linked, they tend to be mechanically robust and flexible. For
example, urethane acrylates of functionality 2 (di) and 3 (tri)
have been used extensively for HPDLC technology. Higher
functionality materials such as penta and hex functional stems can
also be used.
Modulation of Material Composition
[0076] High luminance and excellent color fidelity are important
factors in various waveguide applications. In each case, high
uniformity across the FOV can be desired. However, the fundamental
optics of waveguides can lead to non-uniformities due to gaps or
overlaps of beams bouncing down the waveguide. Further
non-uniformities may arise from imperfections in the gratings and
non-planarity of the waveguide substrates. In SBGs, there can exist
a further issue of polarization rotation by birefringent gratings.
In applicable cases, the biggest challenge is usually the fold
grating where there are millions of light paths resulting from
multiple intersections of the beam with the grating fringes.
Careful management of grating properties, particularly the
refractive index modulation, can be utilized to overcome
non-uniformity.
[0077] Out of the multitude of possible beam interactions
(diffraction or zero order transmission), only a subset contributes
to the signal presented at the eye box. By reverse tracing from the
eyebox, fold regions contributing to a given field point can be
pinpointed. The precise correction to the modulation that is needed
to send more into the dark regions of the output illumination can
then be calculated. Having brought the output illumination
uniformity for one color back on target, the procedure can be
repeated for other colors. Once the index modulation pattern has
been established, the design can be exported to the deposition
mechanism, with each target index modulation translating to a
unique deposition setting for each spatial resolution cell on the
substrate to be coated/deposited. The resolution of the deposition
mechanism can depend on the technical limitations of the system
utilized. In many embodiments, the spatial pattern can be
implemented to 30 micrometers resolution with full
repeatability.
[0078] Compared with waveguides utilizing surface relief gratings
(SRGs), SBG waveguides implementing manufacturing techniques in
accordance with various embodiments of the invention can allow for
the grating design parameters that impact efficiency and
uniformity, such as but not limited to refractive index modulation
and grating thickness, to be adjusted dynamically during the
deposition process without the need for a different master. With
SRGs where modulation is controlled by etch depth, such schemes
would not be practical as each variation of the grating would
entail repeating the complex and expensive tooling process.
Additionally, achieving the required etch depth precision and
resist imaging complexity can be very difficult.
[0079] Deposition processes in accordance with various embodiments
of the invention can provide for the adjustment of grating design
parameters by controlling the type of material that is to be
deposited. Various embodiments of the invention can be configured
to deposit different materials, or different material compositions,
in different areas on the substrate. For example, deposition
processes can be configured to deposit HPDLC material onto an area
of a substrate that is meant to be a grating region and to deposit
monomer onto an area of the substrate that is meant to be a
non-grating region. In several embodiments, the deposition process
is configured to deposit a layer of optical recording material that
varies spatially in component composition, allowing for the
modulation of various aspects of the deposited material. The
deposition of material with different compositions can be
implemented in several different ways. In many embodiments, more
than one deposition head can be utilized to deposit different
materials and mixtures. Each deposition head can be coupled to a
different material/mixture reservoir. Such implementations can be
used for a variety of applications. For example, different
materials can be deposited for grating and non-grating areas of a
waveguide cell. In some embodiments, HPDLC material is deposited
onto the grating regions while only monomer is deposited onto the
non-grating regions. In several embodiments, the deposition
mechanism can be configured to deposit mixtures with different
component compositions.
[0080] In some embodiments, spraying nozzles can be implemented to
deposit multiple types of materials onto a single substrate. In
waveguide applications, the spraying nozzles can be used to deposit
different materials for grating and non-grating areas of the
waveguide. In many embodiments, the spraying mechanism is
configured for printing gratings in which at least one the material
composition, birefringence, and/or thickness can be controlled
using a deposition apparatus having at least two selectable spray
heads. In some embodiments, the manufacturing system provides an
apparatus for depositing grating recording material optimized for
the control of laser banding. In several embodiments, the
manufacturing system provides an apparatus for depositing grating
recording material optimized for the control of polarization
non-uniformity. In several embodiments, the manufacturing system
provides an apparatus for depositing grating recording material
optimized for the control of polarization non-uniformity in
association with an alignment control layer. In a number of
embodiments, the deposition workcell can be configured for the
deposition of additional layers such as beam splitting coatings and
environmental protection layers. Inkjet print heads can also be
implemented to print different materials in different regions of
the substrate.
[0081] As discussed above, deposition processes can be configured
to deposit optical recording material that varies spatially in
component composition. Modulation of material composition can be
implemented in many different ways. In a number of embodiments, an
inkjet print head can be configured to modulate material
composition by utilizing the various inkjet nozzles within the
print head. By altering the composition on a "dot-by-dot" basis,
the layer of optical recording material can be deposited such that
it has a varying composition across the planar surface of the
layer. Such a system can be implemented using a variety of
apparatuses including but not limited to inkjet print heads.
Similar to how color systems use a palette of only a few colors to
produce a spectrum of millions of discrete color values, such as
the CMYK system in printers or the additive RGB system in display
applications, inkjet print heads in accordance with various
embodiments of the invention can be configured to print optical
recording materials with varying compositions using only a few
reservoirs of different materials. Different types of inkjet print
heads can have different precision levels and can print with
different resolutions. In many embodiments, a 300 DPI ("dots per
inch") inkjet print head is utilized. Depending on the precision
level, discretization of varying compositions of a given number of
materials can be determined across a given area. For example, given
two types of materials to be printed and an inkjet print head with
a precision level of 300 DPI, there are 90,001 possible discrete
values of composition ratios of the two types of materials across a
square inch for a given volume of printed material if each dot
location can contain either one of the two types of materials. In
some embodiments, each dot location can contain either one of the
two types of materials or both materials. In several embodiments,
more than one inkjet print head is configured to print a layer of
optical recording material with a spatially varying composition.
Although the printing of dots in a two-material application is
essentially a binary system, averaging the printed dots across an
area can allow for discretization of a sliding scale of ratios of
the two materials to be printed. For example, the amount of
discrete levels of possible concentrations/ratios across a unit
square is given by how many dot locations can be printed within the
unit square. As such, there can be a range of different
concentration combinations, ranging from 100% of the first material
to 100% of the second material. As can readily be appreciated, the
concepts are applicable to real units and can be determined by the
precision level of the inkjet print head. Although specific
examples of modulating the material composition of the printed
layer are discussed, the concept of modulating material composition
using inkjet print heads can be expanded to use more than two
different material reservoirs and can vary in precision levels,
which largely depends on the types of print heads used.
[0082] Varying the composition of the material printed can be
advantageous for several reasons. For example, in many embodiments,
varying the composition of the material during deposition can allow
for the formation of a waveguide with gratings that have spatially
varying diffraction efficiencies across different areas of the
gratings. In embodiments utilizing HPDLC mixtures, this can be
achieved by modulating the relative concentration of liquid
crystals in the HPDLC mixture during the printing process, which
creates compositions that can produce gratings with varying
diffraction efficiencies when the material is exposed. In several
embodiments, a first HPDLC mixture with a certain concentration of
liquid crystals and a second HPDLC mixture that is liquid
crystal-free are used as the printing palette in an inkjet print
head for modulating the diffraction efficiencies of gratings that
can be formed in the printed material. In such embodiments,
discretization can be determined based on the precision of the
inkjet print head. A discrete level can be given by the
concentration/ratio of the materials printed across a certain area.
In this example, the discrete levels range from no liquid crystal
to the maximum concentration of liquid crystals in the first PDLC
mixture.
[0083] The ability to vary the diffraction efficiency across a
waveguide can be used for various purposes. A waveguide is
typically designed to guide light internally by reflecting the
light many times between the two planar surfaces of the waveguide.
These multiple reflections can allow for the light path to interact
with a grating multiple times. In many embodiments, a layer of
material can be printed with varying composition of materials such
that the gratings formed have spatially varying diffraction
efficiencies to compensate for the loss of light during
interactions with the gratings to allow for a uniform output
intensity. For example, in some waveguide applications, an output
grating is configured to provide exit pupil expansion in one
direction while also coupling light out of the waveguide. The
output grating can be designed such that when light within the
waveguide interact with the grating, only a percentage of the light
is refracted out of the waveguide. The remaining portion continues
in the same light path, which remains within TIR and continues to
be reflected within the waveguide. Upon a second interaction with
the same output grating again, another portion of light is
refracted out of the waveguide. During each refraction, the amount
of light still traveling within the waveguide decreases by the
amount refracted out of the waveguide. As such, the portions
refracted at each interaction gradually decreases in terms of total
intensity. By varying the diffraction efficiency of the grating
such that it increases with propagation distance, the decrease in
output intensity along each interaction can be compensated,
allowing for a uniform output intensity.
[0084] Varying the diffraction efficiency can also be used to
compensate for other attenuation of light within a waveguide. All
objects have a degree of reflection and absorption. Light trapped
in TIR within a waveguide are continually reflected between the two
surfaces of the waveguide. Depending on the material that makes up
the surfaces, portions of light can be absorbed by the material
during each interaction. In many cases, this attenuation is small,
but can be substantial across a large area where many reflections
occur. In many embodiments, a waveguide cell can be printed with
varying compositions such that the gratings formed from the optical
recording material layer have varying diffraction efficiencies to
compensate for the absorption of light from the substrates.
Depending on the substrates, certain wavelengths can be more prone
to absorption by the substrates. In a multi-layered waveguide
design, each layer can be designed to couple in a certain range of
wavelengths of light. Accordingly, the light coupled by these
individual layers can be absorbed in different amounts by the
substrates of the layers. For example, in a number of embodiments,
the waveguide is made of a three-layered stack to implement a full
color display, where each layer is designed for one of red, green,
and blue. In such embodiments, gratings within each of the
waveguide layers can be formed to have varying diffraction
efficiencies to perform color balance optimization by compensating
for color imbalance due to loss of transmission of certain
wavelengths of light.
In addition to varying the liquid crystal concentration within the
material in order to vary the diffraction efficiency, another
technique includes varying the thickness of the waveguide cell.
This can be accomplished through the use of spacers. In many
embodiments, spacers are dispersed throughout the optical recording
material for structural support during the construction of the
waveguide cell. In some embodiments, different sizes of spacers are
dispersed throughout the optical recording material. The spacers
can be dispersed in ascending order of sizes across one direction
of the layer of optical recording material. When the waveguide cell
is constructed through lamination, the substrates sandwich the
optical recording material and, with structural support from the
varying sizes of spacers, create a wedge-shaped layer of optical
recording material. spacers of varying sizes can be dispersed
similar to the modulation process described above. Additionally,
modulating spacer sizes can be combined with modulation of material
compositions. In several embodiments, reservoirs of HPDLC materials
each suspended with spacers of different sizes are used to print a
layer of HPDLC material with spacers of varying sizes strategically
dispersed to form a wedge-shaped waveguide cell. In a number of
embodiments, spacer size modulation is combined with material
composition modulation by providing a number of reservoirs equal to
the product of the number of different sizes of spacers and the
number of different materials used. For example, in one embodiment,
the inkjet print head is configured to print varying concentrations
of liquid crystal with two different spacer sizes. In such an
embodiment, four reservoirs can be prepared: a liquid crystal-free
mixture suspension with spacers of a first size, a liquid
crystal-free mixture-suspension with spacers of a second size, a
liquid crystal-rich mixture-suspension with spacers of a first
size, and a liquid crystal-rich mixture-suspension with spacers of
a second size. Further discussion regarding material modulation can
be found in U.S. application Ser. No. 16/203,071 filed Nov. 18,
2018 entitled "Systems and Methods for Manufacturing Waveguide
Cells." The disclosure of U.S. application Ser. No. 16/203,491 is
hereby incorporated by reference in its entirety for all
purposes.
Waveguide Backlights
[0085] Waveguide backlights in accordance with various embodiments
of the invention can be implemented using a variety of different
configurations. As can readily be appreciated, the specific
configuration implemented can depend on various factors, including
but not limited to the intended application, cost constraints, form
factor constraints, etc. In many embodiments, the waveguide
backlight is implemented with at least one waveguide layer
containing at least one grating layer sandwiched by first and
second substrates. The substrates can include various transparent
materials, including but not limited to glass and plastics. The
grating layer(s) can include different sets of grating elements
configured for various purposes. In some embodiments, the grating
layer includes two different sets of grating elements, each set
configured and designed to have high diffraction efficiency for a
specific wavelength band and/or angular band. In a number of
embodiments, the grating layer includes two different sets of
grating elements, where each set contains grating elements having
the same K-vectors. In various embodiments, the two sets of grating
elements have opposing K-vectors. In several embodiments, the
grating layer includes two different sets of grating elements, each
set configured and designed to diffract and extract light from
different directions. For example, in a number of embodiments, the
grating layer includes a first set of grating elements configured
to diffract TIR light that is reflected off the first substrate and
to extract such light through the second substrate and a second set
of grating elements configured to diffract TIR light that is
reflected off the second substrate and to extract such light
through the first substrate.
[0086] The grating elements implemented in waveguide backlights can
be arranged in a number of different configurations. In many
embodiments, the waveguide backlight includes a grating layer
having first and second sets of grating elements that are
interspersed with one another. In some embodiments, the first and
second set of grating elements are disposed across two different
grating layers. The two different grating layers can be disposed
adjacent one another (i.e., the waveguide layer includes two
grating layers sandwiched between two substrates) or across two
different waveguide layers. As can readily be appreciated, such
grating architectures can be expanded to implement more than two
sets of grating elements. Furthermore, the waveguide layer(s) can
be configured to implement a variety of different grating
structures, including but not limited to HPDLC gratings, switching
gratings recorded in HPDLC (such switchable Bragg Gratings), Bragg
gratings recorded in holographic photopolymer, evacuated Bragg
gratings, backfilled evacuated Bragg gratings, and surface relief
gratings.
[0087] Depending on the type of gratings implemented, light
polarization responses can be a large factor in how and how well
the waveguide backlight operates. For example, in some embodiments,
the gratings are implemented using an HPDLC material that forms
gratings that are sensitive to P-polarized light. In such cases,
the waveguide backlight can be designed with the appropriate
considerations. The waveguide backlight can include various
waveplate and retarder configurations for manipulating the
polarization of light traveling throughout the waveguide backlight.
In some embodiments, the waveguide backlight includes a
quarter-wave plate (QWP). A QWP converts linearly polarized light
into circularly polarized light and vice versa. In further
embodiments, the QWP is implemented with a mirror, which can be
formed on an outer surface of the QWP. Such configurations can
allow for incident linearly polarized light to be reflected with
its polarization orthogonally changed. For example, an incident
P-polarized light ray can be converted into circularly polarized
light by the QWP, reflected by the mirror to give circularly
polarized light in an opposing direction, and finally converted
into linearly S-polarized light. In many embodiments, the waveguide
backlight includes a half-wave plate (HWP) for switching the
polarization of P-polarized light into S-polarized light and vice
versa. In a number of embodiments, the waveguide backlight includes
a substrate supporting half wave retarders. Various types of light
sources can be utilized to introduce light into the backlight. In a
number of embodiments, P- and/or S-polarized light is coupled into
the waveguide backlight. In several embodiments, unpolarized light
is coupled into the waveguide backlight. As can readily be
appreciated, the specific configuration of input light and grating
structures can depend on the specific requirements of a given
application.
[0088] Grating elements within a waveguide backlight can be
arranged and implemented in various configurations. In several
embodiments, all of the grating elements in a waveguide layer are
designed to operate at a common wavelength band. As described
above, the grating elements can have K-vectors configured to
diffract upward-going or downward-going rays in a waveguide layer.
In several embodiments, both types of gratings are provided in a
waveguide layer. In further embodiments, both types of gratings are
provided in a single grating layer. In some embodiments, the
grating elements can have K-vectors in differing directions but
operating at a common wavelength band. It should be appreciated
from the discussions that any number of separate wavelength bands
can be provided. FIG. 2 conceptually illustrates a waveguide
backlight having two sets of interspersed grating elements in
accordance with an embodiment of the invention. As shown, the
waveguide backlight 200 includes: a waveguide 201 formed by
substrates 202,203 sandwiching a grating layer 204. In many
embodiments, a source of light (which is not illustrated) can be
optically coupled to the waveguide structure 201 and can be
configured to emit collimated light. The substrates 202,203 can
provide a TIR structure for the input light. The grating layer 204
can include a plurality of grating elements for diffracting light
out of the waveguide and, ultimately, towards an external
illumination surface. In the illustrative embodiment, the grating
layer 204 includes two sets of plane gratings having two grating
configurations (e.g., grating elements 205,206) with opposing
K-vectors for diffracting TIR light coming from different
directions. For example, grating element 205 is configured to
diffract light reflected from the outer surface of substrate 202
while grating element 206 is configured to diffract light reflected
from the outer surface of substrate 203. For ease of clarity, the
two different directions of light can also be referred to as
upward- and downward-going TIR light, respectively, with the
orientation of the waveguide in the figure as a frame of reference.
The pair of grating configurations are repeated along the grating
layer 204 in the embodiment of FIG. 2 to form two sets of
interspersed grating elements.
[0089] The waveguide backlight 200 of FIG. 2 further includes a
quarter wave plate 207 and a transparent layer 208 divided into
clear regions 209 and regions supporting half wave retarders 210.
In the illustrative embodiment, the QWP 207 is implemented along
with a mirror to provide reflection of incident light while
changing its polarization orthogonally. The QWP 207 and the
transparent layer 208 can be separated from the waveguide 201 by
air gaps or layers of low refractive index material, including but
not limited to a nanoporous material. Methods of such
implementations are discussed in the sections above. Referring back
to FIG. 2, the illustrative embodiment shows operation of the
waveguide backlight 200 where input P-polarized light 211 (which is
the preferred light polarization state for diffraction by SBGs)
undergoes TIR within the waveguide 201. A portion of this light
(upward-going TIR light) can be diffracted (212) by grating element
205 and directed towards a clear region 209 of the transparent
layer 208 to provide P-polarized output light 213. Downward-going
TIR light incident on the grating element 206 can be diffracted
(214) downwards and reflected (215) by the QWP 207 with its
polarization rotated from P to S. The S-polarized light can travel
through the grating layer 204 and proceed out of the waveguide 201
towards a half wave retarder region 210 of the transparent layer
208. After transmission through a half wave retarder region 210,
the light has its polarization rotated from S to P (216). By
repeating the above ray-grating interactions across the waveguide,
extraction of the incident light towards a similar direction can be
accomplished to a high degree. As can readily be appreciated, such
configurations can include various modifications, which can depend
on the specific requirements of a given application. For example,
in several embodiments, the diffraction efficiencies of the grating
elements can be varied along the waveguide path to control
uniformity. In many embodiments, the grating elements can be
electrically switchable. In some embodiments, a grating layer can
be formed between transparent substrates with transparent
conductive coatings applied to each substrate. At least one of the
coatings can be patterned into independently addressable elements
overlapping the grating elements. An electrical control circuit
operative to apply voltages across each of the grating elements can
be provided.
[0090] FIG. 3 conceptually illustrates a flow chart of a process
for providing a waveguide backlight in accordance with an
embodiment of the invention. As shown, the process 300 includes
providing (301) a waveguide having a first set of grating elements
for diffracting downward-going rays and a second set of grating
elements diffracting upward-going rays, wherein the grating
elements are disposed between first and second transparent
substrates. Input light can be coupled (302) into a total internal
reflection path within the waveguide. Various types of input light
can be utilized. In many embodiments, narrow band laser
illumination is utilized. In some embodiments, the input light is
P-polarized light. A portion of the input light can be extracted
(303) through an outer surface of the first transparent substrate
using the first set of grating elements, and a portion of the input
light can be extracted (304) through an outer surface of the second
transparent substrate using the second set of grating elements. In
many embodiments, the first set of grating elements is configured
to extract light reflected from the outer surface of the second
substrate, and the second set of grating elements is configured to
extract light reflected from the outer surface of the first
substrate. Various types of gratings can be implemented. In several
embodiments, P-polarization sensitive gratings are utilized. In a
number of embodiments, S-polarization sensitive gratings are
utilized. In some embodiments, both types of gratings are
implemented. As can readily be appreciated, the types of gratings
utilized can depend on the type of input light. The light extracted
from the second transparent surface can have its polarization
rotated (305) and can be reflected towards the waveguide,
propagating through to the outer surface of the first transparent
surface. In many embodiments, a QWP is utilized to rotate the
polarization of the light and to reflect it towards the waveguide.
The light with its polarization rotated can optionally have its
polarization rotated (306) again after its propagation through the
outer surface of the first transparent substrate. In some
embodiments, a substrate containing HWP regions can be implemented
to rotate the polarization of the light after its propagation
through the first transparent substrate. Although FIG. 3
illustrates a specific method of providing a waveguide backlight,
various other processes can be implemented as appropriate depending
on the specific requirements of a given application. For example,
in some embodiments, the input light contains only P-polarized
light. In other embodiments, the input light contains both S- and
P-polarized light.
[0091] Waveguide backlights in accordance with various embodiments
of the invention can be configured for many different applications.
In many embodiments, the waveguide backlight is configured for
narrow band illumination applications--i.e., the wavelength band
can have a narrow bandwidth as is typically provided by a laser. In
some embodiments, the wavelength band can have a broader bandwidth
such as can be provided by an LED. As can readily be appreciated,
the backlight can also be used to provide non-visible radiation
such as infrared and ultraviolet. In some embodiments, the
waveguide backlight is configured as a color waveguide backlight.
Such backlights can be implemented based on principles similar to
those shown in FIG. 2. In some embodiments, the backlight provides
light from red, green, and blue (RGB) sources. In such embodiments,
the backlight can include RGB grating elements interspersed within
a single layer or disposed in some way over two or more layers. In
some embodiments, separate RGB layers can be used. In several
embodiments, the waveguide backlight operates using first and
second wavelength input light that covers a large portion of the
visible band. For example, in various embodiments, the first
wavelength light covers the blue to green band, and the second
wavelength light can cover the green to red band. In several
embodiments, a color waveguide backlight can be implemented
utilizing separate grating layers for each color component to be
emitted from the backlight. In some embodiments, the waveguide
backlight incorporates SBGs. In such cases, the waveguide backlight
can include a first set of grating elements configured to switch
into a diffracting state when the light source emits light of a
first wavelength band and a second set of grating elements
configured to switch into a diffracting state when the source emits
light of a second wavelength band.
[0092] FIG. 4 conceptually illustrates a waveguide backlight with
two waveguide layers in accordance with an embodiment of the
invention. In the following paragraphs, to simplify the description
of the invention, the discussions will include waveguides for
emitting light in two different wavelength bands (first and second
wavelength light) using first and second sets of grating elements
formed in two waveguide layers, each waveguide layer containing a
single grating layer. However, any number of waveguides layers and
grating layers can be utilized as appropriated depending on the
specific requirements of a given application. Referring back to
FIG. 2A, the waveguide backlight 400 shown includes first and
second waveguides 401,402. The backlight 400 further includes a
quarter wave plate (QWP) 403 and a transparent substrate 404
divided into clear regions 405 and regions supporting half wave
retarders 406. Each waveguide can be configured to operate
according to principles similar to those shown in FIG. 2. For
example, the first waveguide 401 can be configured to receive
p-polarized light of a first wavelength band, and the second
waveguide 402 can be configured to receive p-polarized light of a
second wavelength band. In the illustrative embodiment, each of the
first and second waveguides 401,402 includes a grating layer
407,408. The second waveguide 402 can include a similar
configuration of grating elements to that of the first waveguide
401 but operating in a different wavelength band. For example, in
the illustrative embodiment, the first waveguide 401 can include
grating elements configured to operate in the red-green wavelength
band while the second waveguide 402 can include grating elements
configured to operate in the green-blue wavelength band, allowing
for the implementation of a full color waveguide backlight. In
other embodiments, a full color waveguide backlight can be
implemented with three waveguide layers, each configured to operate
in one of red, green, and blue wavelength band. As indicated by the
two sets of rays (dashed and solid, representing rays of different
wavelength light), it is shown that the ray and grating
interactions of the second waveguide 402 are similar to those of
the first waveguide 401. The first and second wavelength light
extracted from the two waveguides can be combined to provide
uniform illumination. In many embodiments, the first and second
wavelength light can be introduced to the waveguides
sequentially.
[0093] The waveguide structure of FIG. 4 can be equivalently
implemented using a variety of different grating configurations. In
some embodiments, the backlight can be implemented as a single
waveguide layer containing pluralities of grating elements
configured for operation at different wavelength bands. FIG. 5
conceptually illustrates a waveguide backlight with a single
waveguide layer in accordance with an embodiment of the invention.
As shown, the waveguide backlight 500 includes a grating
configuration 501 formed of two adjacent grating layers 502,503
sandwiched by two substrates 504,505. The waveguide backlight 500
further includes a QWP 506 and a transparent substrate 507 divided
into clear regions 508 and regions supporting half wave retarders
509. In the illustrative embodiment, the grating configuration 501
includes two grating layers 508,509 capable of operating in a
different wavelength band. In many embodiments, the operating
wavelength band of the two grating layers covers a large portion of
the visible band. Each grating layer further includes two
interspersed sets of grating elements 510,511 and 512,513 for
diffracting upward- (510,512) and downward-going (511,513) TIR
light. As can readily be appreciated, the backlight shown in FIG. 5
can operate in accordance with principles similar to those shown in
FIG. 4. In FIG. 5, the two grating layers are shown in separate
adjacent layers, the combination of which provides the grating
configuration. In other embodiments, the grating elements across
the two grating layers are multiplexed and superimposed into a
single layer. For example, grating elements 510 can be multiplexed
with grating elements 512, and grating elements A 311 can be
multiplexed with grating elements 513.
[0094] Although FIGS. 4 and 5 illustrate specific polychromatic
waveguide backlight implementations, various configurations can be
implemented as appropriate depending on the specific requirements
of a given application. For example, in several embodiments, the
waveguide backlight includes two waveguide layers, each containing
interspersed grating elements configured to operate in two
wavelength bands. FIG. 6 conceptually illustrates a waveguide
backlight 600 having two waveguide layers 601,602 each containing a
grating layer 603,604 with alternating first wavelength-diffracting
605 and second wavelength-diffracting 606 grating elements in
accordance with an embodiment of the invention. The grating
elements 605,606 can all have K-vectors configured to diffract one
of upward-going or downward-going TIR light through an outer
surface (e.g., upward-going in the illustrative embodiment of FIG.
6) of the waveguide. In the illustrative embodiment, the first
wavelength-diffracting and second wavelength-diffracting grating
elements 605,606 are spatially overlapped. During operation, first
wavelength P-polarized light 607 and second wavelength P-polarized
light 608 can be coupled into the waveguides and undergo
diffraction and extraction as indicated by rays 609,610
corresponding to first wavelength light and rays 611,612
corresponding to second wavelength light. The waveguide structure
of FIG. 6 can be equivalently implemented using a variety of
different grating configurations. Similar to the embodiment shown
in FIG. 5, the backlight shown in FIG. 6 can be implemented with a
single waveguide layer. FIG. 7 conceptually illustrates a waveguide
backlight having a single waveguide layer with alternating
wavelength-diffracting grating elements in accordance with an
embodiment of the invention. As shown, the waveguide backlight 700
includes a single grating configuration 701 sandwiched by two
substrates 702,703. The grating configuration 701 includes two
grating layers 704,705. In the illustrative embodiment, two sets of
grating elements 706,707 are interspersed within and across both
grating layers 704,705. Grating elements from the first set 706
spatially overlap grating elements from the second set 707. The
grating elements can be configured in a variety of different ways.
In some embodiments, each set of grating elements are configured to
diffract a specific wavelength band. In many embodiments, all of
the grating vectors are configured to have similar K-vectors. In
the embodiment of FIG. 7, all of the grating elements are
configured with diffract and direct light towards the same
direction. As can readily be appreciated, the waveguide backlight
shown in FIG. 7 can operate in accordance with principles similar
to those shown in FIG. 6. In FIG. 7, the two grating layers 704,705
are shown in separate adjacent layers, the combination of which
provides the single grating configuration 701. In other
embodiments, the grating elements within the two grating layers
704,705 are multiplexed and superimposed in the same layer--i.e.,
each multiplexed region contains grating element 706 and grating
element 707.
[0095] Although FIGS. 2-7 illustrate specific waveguide backlights
receiving P-polarized input light, waveguide backlights in
accordance with various embodiments of the invention can be
configured for operation with various light sources. FIG. 8
conceptually illustrates a waveguide backlight 800 having two
waveguide layers 801,802 with alternating wavelength-diffracting
grating elements for input light having orthogonal polarizations in
accordance with an embodiment of the invention. As shown, the first
waveguide layer 801 includes a first grating layer 803 with a first
set of alternating first wavelength-diffracting 804 and second
wavelength-diffracting 805 grating elements. Similarly, the second
waveguide layer 802 includes a second grating layer 806 with a
second set of alternating first wavelength-diffracting 804 and
second wavelength-diffracting 805 grating elements. The waveguide
backlight 800 further includes a QWP 807. Various light sources can
be implemented as appropriate with such configurations. In the
illustrative embodiment, the input light includes first and second
wavelength light 808,809 having orthogonal polarizations. For
example, the input first wavelength light 808 can be P-polarized
and the input second wavelength light 809 can be S-polarized. In
the illustrative embodiment, the first wavelength-diffracting
grating elements 804 have K-vectors configured to diffract
upward-going TIR light through the upper waveguide surface 810 of
the first waveguide layer 801, and the second
wavelength-diffracting grating elements 805 have K-vectors
configured to diffract downward-going TIR light through the lower
waveguide surface 811 of the second waveguide layer 802. As shown,
the first wavelength-diffracting and second wavelength-diffracting
grating elements 804,805 are spatially overlapped. The light
(second wavelength light) extracted from the lower waveguide
surface 813 has its polarization rotated from S to P by the QWP 807
before being retransmitted through the two waveguide layers 801,802
and out of the upper surface 810. Hence, the output light from the
waveguide backlight 800 is all P-polarized. Similar to the
embodiments shown in FIGS. 5 and 7, the configuration shown in FIG.
8 can be implemented within a single waveguide layer. FIG. 9
conceptually illustrates a waveguide backlight implementation 900
of the embodiment of FIG. 8 using a single waveguide layer 901 with
adjacent grating layers 902,903. As can readily be appreciated,
such a waveguide backlight can operate according to principles
similar to those shown in FIG. 8. Furthermore, such grating layers
can also be implemented as a single layer containing multiplexed
gratings.
[0096] An important principle underlying the embodiments discussed
above is that Bragg gratings diffract with high efficiency when
light satisfies the Bragg equation to within angular and wavelength
tolerances set by the angular and spectral bandwidths of the
grating. The spectral and angular bandwidths can be computed using
theory of volume holographic gratings. Waveguided rays falling
within the above bandwidth limits are referred to as being on-Bragg
while rays falling outside the bandwidth are referred to as
off-Bragg.
[0097] Another factor to be addressed in displays and illumination
devices, particularly those using lasers, results from beam edge
mismatching as a beam undergoes TIR. For a waveguide of thickness
D, distance between successive beam-surface interactions W, and a
TIR angle U, the condition for seamless matching of upward and
downward going TIR beams is given by the equation 2D tan(U)=W. When
this condition is not met, gaps or overlaps between adjacent beam
portions can occur, which result in a non-uniformity in the output
illumination called banding. Banding can be alleviated to some
extent by using broadband sources such as LEDs. However, the effect
can be much more difficult to overcome with lasers. In many
embodiments, the waveguide backlight can be configured to operate
entirely in collimated space. In other words, the input light and
the output beams replicated at each beam grating interaction are
all collimated. In some embodiments, the input beam is scanned in
at least one angular direction. In several embodiments, the cross
section of the input beam can be varied with incidence angle to
match a debanding condition according to the embodiments or
teaching disclosed in PCT/US2018/015553 "WAVEGUIDE DEVICE WITH
UNIFORM OUTPUT ILLUMINATION", the disclosure of which is
incorporated herein by reference in its entirety. In a number of
embodiments, the input beam cross section can be adjusted by means
of edges formed on a surface or layer supported by the waveguide as
discussed in the above references.
[0098] In many embodiments, light is coupled into the waveguide
using a grating or a prism. In many embodiments, the optics for
coupling light into the waveguides may further include, beam
splitters, filters, dichroic filters, polarization components,
light integrators, condenser lenses, micro lenses, beam shaping
elements and other components commonly used in display illumination
systems.
[0099] In many embodiments, the light source is a laser scanned in
at least one angular direction using an electromechanical beam
deflector. In some embodiments, the laser scanner may be an electro
optical device.
[0100] In many embodiments, light can be extracted from the
waveguide into output paths that are angularly separated. In many
embodiments that output paths can be substantially normal to a
total internal reflection surface of the waveguide. In many
embodiments, the light extracted from the waveguide is
collimated.
[0101] In many embodiments, a grating element includes at least one
selected from the group of a planar grating, a grating with optical
power, a grating providing optical retardation, and a grating with
diffusing properties. In many embodiments, the grating elements can
have spatially varying diffraction efficiencies to enable
extraction of light along the waveguide. In many embodiments, the
grating elements have diffraction efficiencies proportional to
voltages applied across the electrodes. In some embodiments, the
grating elements can have phase retardations proportional to
voltages applied across said electrodes. In many embodiments, the
grating elements can be configured as a one-dimensional array of
elongate elements. In many embodiments, the gratings can be
configured as two-dimensional arrays. In many embodiments, the
gratings elements are recorded in a Holographic Polymer Dispersed
Liquid Crystal. In many embodiments the spatio-temporal addressing
of grating elements by an electrical control circuit addresses can
be characterized by a cyclic process. In many embodiments, the
spatio-temporal addressing of grating elements by an electrical
control circuit can be characterized by a random process.
DOCTRINE OF EQUIVALENTS
[0102] While the above description contains many specific
embodiments of the invention, these should not be construed as
limitations on the scope of the invention, but rather as an example
of one embodiment thereof. It is therefore to be understood that
the present invention may be practiced in ways other than
specifically described, without departing from the scope and spirit
of the present invention. Thus, embodiments of the present
invention should be considered in all respects as illustrative and
not restrictive. Accordingly, the scope of the invention should be
determined not by the embodiments illustrated, but by the appended
claims and their equivalents.
* * * * *