U.S. patent application number 17/167903 was filed with the patent office on 2021-12-23 for waveguide architectures 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 Momcilo Popovich, Jonathan David Waldern.
Application Number | 20210396998 17/167903 |
Document ID | / |
Family ID | 1000005813282 |
Filed Date | 2021-12-23 |
United States Patent
Application |
20210396998 |
Kind Code |
A1 |
Waldern; Jonathan David ; et
al. |
December 23, 2021 |
Waveguide Architectures and Related Methods of Manufacturing
Abstract
Systems and methods for generating head-up displays (HUDs) using
waveguides incorporating Bragg gratings in accordance with various
embodiments of the invention are provided. The term HUD is
typically utilized to describe a class of displays that
incorporates a transparent display that presents data without
requiring users to look away from their usual viewpoints. HUDs can
be incorporated in any of a variety of applications including (but
not limited to) vehicular and near-eye applications, such as
googles, eyewear, etc. HUDs that utilize planar waveguides that
incorporate Bragg gratings in accordance with various embodiments
of the invention can achieve significantly larger fields of view
and have lower volumetric requirements than HUDs implemented using
conventional optical components.
Inventors: |
Waldern; Jonathan David;
(Los Altos Hills, CA) ; Popovich; Milan Momcilo;
(Leicester, GB) ; Grant; Alastair John; (San Jose,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DigiLens Inc. |
Sunnyvale |
VA |
US |
|
|
Assignee: |
DigiLens Inc.
Sunnyvale
CA
|
Family ID: |
1000005813282 |
Appl. No.: |
17/167903 |
Filed: |
February 4, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16242979 |
Jan 8, 2019 |
10914950 |
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17167903 |
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62614947 |
Jan 8, 2018 |
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62614949 |
Jan 8, 2018 |
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62615000 |
Jan 8, 2018 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B60K 2370/334 20190501;
G02B 6/005 20130101; B60K 2370/70 20190501; G02B 6/0065 20130101;
G02B 27/0101 20130101; G02B 6/0026 20130101; G02B 27/0103 20130101;
G02B 2027/011 20130101; G02B 2027/0123 20130101; G02B 2027/0132
20130101; G02B 2027/0125 20130101; B60K 35/00 20130101; G02B
27/0179 20130101; B60K 2370/736 20190501; G02B 2027/0187
20130101 |
International
Class: |
G02B 27/01 20060101
G02B027/01; F21V 8/00 20060101 F21V008/00 |
Claims
1. A waveguide display comprising: an input image node providing
image modulated light in a first field of view (FOV) portion light
and a second FOV portion light; a waveguide supporting: an input
grating for coupling the first FOV portion light from the IIN into
a first set of total internal reflection (TIR) paths and coupling
the second FOV portion light from the IIN into a second set of TIR
paths; and an output grating multiplexing first and second gratings
for coupling the first FOV portion light in the first set of TIR
paths and the second FOV portion light in the second set of TIR
paths out of the waveguide into an exit pupil while providing a
beam expansion.
2. The waveguide display of claim 1, wherein the input image node
is coupled to the waveguide by an opto-mechanical interface that
allows the waveguide to be mechanically disconnected from the input
image node.
3. The waveguide display of claim 1, wherein the waveguide is
configured to direct light received from the input image node
towards a vehicular windshield.
4. The waveguide display of claim 3, wherein the waveguide is
configured to distort the light exiting the waveguide such that the
distorted light compensates for the curvature of the vehicular
windshield.
5. (canceled)
6. The waveguide display of claim 1, wherein the input grating and
the output grating are configured to be in inverse reciprocal
relationship for each FOV portion light.
7. The waveguide display of claim 1, wherein the input image node
comprises a transparent prism for coupling light into the
waveguide.
8. The waveguide display of claim 7, wherein the transparent prism
comprises a first surface for coupling light from the input image
node into the prism, a second surface for coupling light out of the
prism towards the waveguide, a third surface for providing an
internal reflection, and a fourth surface opposing the third
surface.
9. The waveguide display of claim 8, wherein the third surface is
configured to totally internally reflect the light, wherein the
third and fourth surfaces provide a window for viewing an external
scene.
10. The waveguide display of claim 1, further comprising a second
waveguide, wherein the two waveguides are configured to form a
binocular waveguide display.
11. The waveguide display of claim 1, wherein the input and output
gratings are formed of a mixture of monomer and liquid crystal.
12. The waveguide display of claim 1, wherein at least one of the
input grating or the output grating is formed as a surface relief
grating.
13. The waveguide display of claim 1, wherein at least one of the
input grating or the output grating is overlapped by a half wave
coating.
14. The waveguide display of claim 1, further comprising a quarter
wave coating applied to at least one of the input grating or the
output grating for compensating for polarization rotation within
the waveguide.
15. The waveguide display of claim 1, wherein the input grating and
the output grating are formed in a single layer.
16. The waveguide display of claim 1, further comprising a first
fold grating configured to direct the first FOV portion light into
the first set of TIR paths to the output grating and a second fold
grating configured to direct the second FOV portion light in the
second set of TIR paths to the output grating, wherein the first
fold grating and the second fold grating are each configured to
provide a pupil expansion orthogonal to the beam expansion provided
by the output grating.
17. The waveguide display of claim 16, wherein at least one of the
input grating, the first fold grating, the second fold grating, or
the output grating comprises a rolled K-vector grating.
18. The waveguide display of claim 1, wherein the input image node
comprises a light source.
19. The waveguide display of claim 18, wherein the input image node
further comprises a microdisplay panel.
20. The waveguide display of claim 1, further comprising an eye
tracker.
21. The waveguide display of claim 1, wherein the input grating
multiplexes a first grating for coupling the first FOV portion
light from the input image node into the first set of TIR paths and
a second grating for coupling the second FOV portion light from the
input image node into the second set of TIR paths.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The current application is a continuation of U.S. patent
application Ser. No. 16/242,979 entitled "Waveguide Architectures
and Related Methods of Manufacturing," filed Jan. 8, 2019, which
claims the benefit of and priority under 35 U.S.C. .sctn. 119(e) to
U.S. Provisional Patent Application No. 62/614,947 entitled
"Monocular Waveguide Displays," filed Jan. 8, 2018, U.S.
Provisional Patent Application No. 62/614,949 entitled, "Vehicular
Waveguide Displays," filed Jan. 8, 2018, and U.S. Provisional
Patent Application No. 62/615,000 entitled "Near-Eye Waveguide
Displays," filed Jan. 8, 2018, the disclosures which are
incorporated herein by reference in their entireties.
FIELD OF THE INVENTION
[0002] The present invention generally relates to apparatuses and
methods for displays and more specifically to apparatuses and
methods for waveguide displays.
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.
[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 heads-up displays ("HUDs") for
aviation and road transport, and sensors for biometric and laser
radar ("LIDAR") applications.
SUMMARY OF THE INVENTION
[0006] One embodiment includes a waveguide display including a
waveguide including a holographic polymer dispersed liquid crystal
mixture (HPDLC) layer sandwiched between first and second
transparent substrates, wherein the HPDLC layer includes an input
grating, a fold grating, and an output grating, and an input image
node optically coupled to the waveguide, wherein the input grating
is configured to receive light from the input image node and to
cause the light to travel within the waveguide via total internal
reflection to the fold grating, the fold grating is configured to
direct the light towards the output grating, and the output grating
is configured to cause the light to exit the waveguide.
[0007] In another embodiment, the input image node is coupled to
the waveguide by an opto-mechanical interface that allows the
waveguide to be mechanically disconnected from the input image
node.
[0008] In a further embodiment, the waveguide is configured to
direct light received from the input image node towards a vehicular
windshield.
[0009] In still another embodiment, the waveguide is configured to
distort the light exiting the waveguide such that the distorted
light compensates for the curvature of the vehicular
windshield.
[0010] In a still further embodiment, the input grating and the
output grating are configured to be reverse reciprocal of each
other.
[0011] In yet another embodiment, the input image node includes a
transparent prism for coupling light into the waveguide.
[0012] In a yet further embodiment, the transparent prism includes
a first surface for coupling light from the input image node into
the prism, a second surface for coupling light out of the prism
towards the waveguide, a third surface for providing an internal
reflection, and a fourth surface opposing the third surface.
[0013] In another additional embodiment, the third surface is
configured to totally internally reflect the light, wherein the
third and fourth surfaces provide a window for viewing an external
scene.
[0014] In a further additional embodiment, the waveguide display
further includes a second waveguide, wherein the two waveguides are
configured to form a binocular waveguide display.
[0015] In another embodiment again, at least one of the input
grating and the output grating is a multiplexed grating.
[0016] In a further embodiment again, the waveguide further
includes a second fold grating, wherein the multiplexed grating is
configured to direct a portion of incident light towards the first
fold grating and to direct another portion of incident light
towards the second fold grating.
[0017] In still yet another embodiment, the multiplexed gratings
provided by at least one of the input grating and the output
grating is configured to increase the field of view of the
waveguide display by providing a first waveguide path for light
forming a first portion of the field of view and a second waveguide
path for light forming a second portion of the field of view.
[0018] In a still yet further embodiment, the input and output
gratings each multiplex first and second gratings, wherein a second
fold grating is provided, wherein the first grating multiplexed
into the input grating, the fold grating and the first grating
multiplexed into the output grating together provide a first
waveguide path for in-coupling, beam expanding and extracting a
first field of view portion, wherein the second grating multiplexed
into the input grating, the second fold grating and the second
grating multiplexed into the output grating together provide a
second waveguide path for in-coupling, beam expanding, and
extracting a second field of view portion.
[0019] In still another additional embodiment, the waveguide
further includes a quarter wave coating for rotating polarization
of incoming light.
[0020] In a still further additional embodiment, the fold grating
is configured to provide pupil expansion in a first direction and
the output grating is configured to provide pupil expansion in a
second direction different than the first direction.
[0021] In still another embodiment again, at least one of the input
grating, fold grating, and output grating includes a rolled
K-vector grating.
[0022] In a still further embodiment again, the input image node
includes a light source.
[0023] In yet another additional embodiment, the input image node
further includes a microdisplay panel.
[0024] In a yet further additional embodiment, the waveguide
display further includes an eye tracker.
[0025] 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
[0026] The description and claims 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. It will apparent to those skilled in the art that the
present invention may be practiced with some or all of the present
invention as disclosed in the following description.
[0027] FIGS. 1A and 1B conceptually illustrate two volume Bragg
grating configurations in accordance with various embodiments of
the invention.
[0028] FIG. 2 conceptually illustrates a surface relief grating in
accordance with an embodiment of the invention.
[0029] FIGS. 3A and 3B conceptually illustrate HPDLC SBG devices
and the switching property of SBGs in accordance with various
embodiments of the invention.
[0030] FIGS. 4A-4D conceptually illustrate two-beam recording
processes in accordance with various embodiments of the
invention.
[0031] FIG. 5 conceptually illustrates a single-beam recording
process utilizing an amplitude grating in accordance with an
embodiment of the invention.
[0032] FIGS. 6A and 6B conceptually illustrate two implementations
of rolled K-vector gratings in accordance with various embodiments
of the invention.
[0033] FIG. 7 conceptually illustrates a multiplexed K-vector
grating in accordance with an embodiment of the invention.
[0034] FIG. 8 conceptually illustrates a waveguide utilizing
coupling gratings to diffract light into and out of the waveguide
in accordance with an embodiment of the invention.
[0035] FIGS. 9 and 10 conceptually illustrate waveguides utilizing
an output grating for exit pupil expansion in one dimension in
accordance with an embodiment of the invention.
[0036] FIG. 11 conceptually illustrates a waveguide system
utilizing two planar waveguides to provide exit pupil expansion in
two dimensions in accordance with an embodiment of the
invention.
[0037] FIG. 12 conceptually illustrates a waveguide utilizing a
three-grating structure to provide two dimensional exit pupil
expansion in accordance with an embodiment of the invention.
[0038] FIG. 13 conceptually illustrates a profile view of an RGB
stack of waveguides in accordance with an embodiment of the
invention.
[0039] FIG. 14 conceptually illustrates a dual axis expansion
waveguide display with two grating layers in accordance with an
embodiment of the invention.
[0040] FIG. 15 conceptually illustrates a plan view of a single
grating layer in accordance with an embodiment of the
invention.
[0041] FIG. 16 conceptually illustrates a plan view of a two
grating layer configuration in accordance with an embodiment of the
invention.
[0042] FIG. 17 conceptually illustrates a dual axis expansion
waveguide display in accordance with an embodiment of the
invention.
[0043] FIG. 18 conceptually illustrates an eye tracker display in
accordance with an embodiment of the invention.
[0044] FIG. 19 conceptually illustrates a dual expansion waveguide
display with a dynamic focusing element and an eye tracker in
accordance with an embodiment of the invention.
[0045] FIGS. 20A and 20B conceptually illustrate a waveguide
display coupled to an input image node by an opto-mechanical
interface in accordance with an embodiment of the invention.
[0046] FIGS. 21-24 conceptually illustrate various input image node
configurations in accordance with various embodiments of the
invention.
[0047] FIG. 25 conceptually illustrates a system diagram showing
components for waveguide displays in accordance with an embodiment
of the invention.
[0048] FIG. 26 is a conceptual illustration of a head-up display
within an automobile in accordance with an embodiment of the
invention.
[0049] FIGS. 27A and 27B conceptually illustrate the projection of
light into an eyebox.
[0050] FIG. 28 is a conceptual illustration of the field of view
and volumetric requirements of a HUD implemented in accordance with
an embodiment of the invention.
[0051] FIG. 29 is a conceptual illustration of a waveguide assembly
in accordance with an embodiment of an invention.
[0052] FIG. 30 is a conceptual illustration of a perspective view
of a waveguide assembly in accordance with an embodiment of the
invention.
[0053] FIGS. 31A-31C conceptually illustrate a stack up including
input coupling gratings and waveguides within a waveguide assembly
in accordance with an embodiment of the invention.
[0054] FIG. 32 conceptually illustrates pairs of input coupling
gratings positioned adjacent to each of a Red, Green, and Blue
waveguide in a waveguide assembly in accordance with an embodiment
of the invention.
[0055] FIG. 33A conceptually illustrates use of a single coupling
grating to couple light into a waveguide in accordance with an
embodiment of the invention.
[0056] FIG. 33B conceptually illustrates use of waveguides
incorporating input, fold, and coupling gratings into a single
planar material to construct a waveguide assembly in accordance
with an embodiment of the invention.
[0057] FIGS. 34A and 34B are conceptual illustrations of coupling
of light reflected by a reflection surface from a projection system
into input gratings of a waveguide assembly in accordance with an
embodiment of the invention.
[0058] FIG. 35 is a schematic diagram of a waveguide in accordance
with an embodiment of the invention.
[0059] FIG. 36 conceptually illustrates K-vector prescriptions for
gratings in a waveguide implemented in accordance with an
embodiment of the invention.
[0060] FIGS. 37A and 37B conceptually illustrate the manner in
which modifying slant angle to increase diffraction efficiency can
compensate for decrease in coupling efficiency across an output
grating in accordance with an embodiment of the invention.
[0061] FIGS. 38A and 38B are conceptual illustrations of projection
of light by a waveguide in accordance with an embodiment of the
invention.
[0062] FIG. 39 is a conceptual illustration of reflection of light
projected by a waveguide assembly off a windshield in accordance
with an embodiment of the invention.
[0063] FIGS. 40A-40C conceptually illustrate corrections that can
be applied to a rolled K-vector prescription for an output grating
to correct for distortions introduced by a curved windshield in
accordance with an embodiment of the invention.
[0064] FIG. 41A-41E conceptually illustrates simulations showing
the impact of a fold grating of a waveguide upon vignetting in
accordance with an embodiment of the invention.
[0065] FIG. 42A-42E conceptually illustrates simulations showing
reduction of vignetting in accordance with an embodiment of the
invention.
[0066] FIG. 43 conceptually illustrates simulations showing
vignetting across an eyebox of a HUD that reflects light projected
from a waveguide assembly off a surface in accordance with an
embodiment of the invention.
[0067] FIG. 44 conceptually illustrates a waveguide that can be cut
with a tapered outline in accordance with an embodiment of the
invention.
[0068] FIG. 45 is a conceptual illustration of a HUD system in
accordance with an embodiment of the invention.
[0069] FIGS. 46A and 46B conceptually illustrate the positioning of
various components in a monocular display in accordance with an
embodiment of the invention.
[0070] FIG. 47 conceptually illustrates a monocular display with a
reverse reciprocal arrangement in accordance with an embodiment
with the invention.
[0071] FIG. 48 conceptually illustrates a profile view of an
exploded two-waveguide stack in accordance with an embodiment of
the invention.
[0072] FIG. 49 conceptually illustrates a monocular display
utilizing a prism and IIN module in accordance with an embodiment
of the invention.
[0073] FIG. 50 shows a 3D illustration of a near display having an
IIN and waveguide component in accordance with an embodiment of the
invention.
[0074] FIG. 51 conceptually illustrates the ray propagation path of
a monocular display in accordance with an embodiment of the
invention.
[0075] FIG. 52 conceptually illustrates a waveguide assembly
including three separate waveguides, an input, fold and output,
implemented in accordance with various embodiments of the
invention.
[0076] FIGS. 53A-53B conceptually illustrate embodiments of
bifurcated input gratings in accordance with various embodiments of
the invention.
[0077] FIG. 54 conceptually illustrates one or more of the
gratings, including the input grating, including a rolled K-vector
and/or a multiplexed K-vector in accordance with various
embodiments of the invention.
[0078] FIGS. 55A-55D conceptually illustrate gratings incorporating
specific K-vectors in accordance with various embodiments of the
invention.
[0079] FIGS. 56A and 56B conceptually illustrate diffraction within
a waveguide system in accordance with various embodiments of the
invention.
[0080] FIGS. 57A-57C conceptually illustrate projected light
reflected off a surface into an eyebox region in accordance with
various embodiments of the invention.
[0081] FIG. 58 conceptually illustrates rolled K-vector
prescriptions in accordance with various embodiments of the
invention.
[0082] FIGS. 59A-59E conceptually illustrate variation of the slant
angle of the fold grating in accordance with various embodiments of
the invention.
[0083] FIG. 60 conceptually illustrates improvements to the FOV and
reducing diffraction losses and vignetting in accordance with
various embodiments of the invention.
[0084] FIGS. 61A and 61B conceptually illustrate bifurcation of the
vertical and horizontal fields in accordance with various
embodiments of the invention.
[0085] FIG. 62 conceptually illustrates polarization of light in
accordance with various embodiments of the invention.
[0086] FIGS. 63A-63F conceptually illustrate the effect of
polarization on the efficiency of the gratings in accordance with
embodiments of the invention.
[0087] FIG. 64 conceptually illustrates an implementation of a HWP
film in accordance with embodiments of the invention.
[0088] FIGS. 65A-65N conceptually illustrate embodiments of various
waveguide architectures in accordance with embodiments of the
invention.
[0089] FIGS. 66A-66C conceptually illustrate an implementation of a
waveguide architecture in accordance with embodiments of the
invention.
[0090] FIGS. 67A-67D conceptually illustrate methods of
manufacturing multiplex (MUX) gratings in accordance with
embodiments of the invention.
DETAILED DESCRIPTION
[0091] 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.
[0092] Turning now to the drawings, systems and methods for
generating displays using waveguides incorporating Bragg gratings
in accordance with various embodiments of the invention are
illustrated. In many embodiments, the waveguide structures are
designed to be optical waveguides, which are structures that can
confine and guide electromagnetic waves in the visible spectrum, or
light. These optical waveguides can be implemented for use in a
number of different applications, such as but not limited to helmet
mounted displays, head mounted displays ("HMDs"), and HUDs. The
term HUD is typically utilized to describe a class of devices that
incorporates a transparent display that presents data without
requiring users to change their usual visual field. Optical
waveguides can integrate various optical functions into a desired
form factor depending on the given application.
[0093] Optical waveguides in accordance with various embodiments
can be designed to manipulate light waves in a controlled manner
using various methods and waveguide optics. For example, optical
waveguides can be implemented using materials with higher
refractive indices than the surrounding environment to restrict the
area in which light can propagate. Light coupled into optical
waveguides made of such materials at certain angles can be confined
within the waveguide via total internal reflection. In a planar
waveguide, the angles at which total internal reflection occurs can
be given by Snell's law, which can determine whether the light is
refracted or entirely reflected at the surface boundary.
[0094] In many embodiments, waveguides incorporating Bragg gratings
are implemented for HUD applications. HUDs can be incorporated in
any of a variety of applications including (but not limited to)
near-eye applications. HUDs that utilize planar waveguides
incorporating Bragg gratings in accordance with various embodiments
of the invention can achieve significantly larger fields of view
and have lower volumetric requirements than HUDs implemented using
conventional optical components. In some embodiments, the HUDs
include at least one waveguide incorporating a number of gratings.
In further embodiments, the waveguide incorporates at least three
Bragg gratings that can be implemented to provide various optical
functions, such as but not limited to dual-axis beam expansion. For
example, in a number of embodiments, the waveguide incorporates an
input grating, a fold grating, and an output grating. HUDs
utilizing waveguides can be implemented using varying numbers of
waveguide. In many embodiments, a HUD is implemented using a single
waveguide. In other embodiments, the HUD is implemented using a
stack of waveguides. Multiple waveguides can be stacked and
implemented to provide different optical functions, such as but not
limited to implementing color displays. In several embodiments, the
HUDs incorporate three separate waveguides, one waveguide for each
of a Red, Green, and Blue color channel.
[0095] Waveguides utilizing Bragg gratings in accordance with
various embodiments of the invention can be designed to have
different types of fringes. Use of multiple waveguides having the
same surface pitch sizes but different grating slanted angles can
increase the overall couple-in angular bandwidth of the waveguide.
In a number of embodiments, one or more of the gratings within the
waveguide incorporate a rolling K-vector and/or a slant angle that
varies across the grating to modify the diffraction efficiency of
the grating. The K-vector can be defined as a vector orthogonal to
the plane of the associated grating fringe, which can determine the
optical efficiency for a given range of input and diffracted
angles. By incorporating a grating with rolled K-vectors ("RKVs"),
the gratings can be designed to vary diffraction efficiency in a
manner that achieves desirable characteristics across the eyebox of
the HUD display. Configurations of grating fringes (such as RKVs)
and other aspects relating to the structures and implementations of
waveguides for use in HUDs are discussed below in further
detail.
Diffraction Gratings
[0096] Optical waveguides can incorporate different optical
elements to manipulate the propagation of light waves. As can
readily be appreciated, the type of grating selected can depend on
the specific requirements of a given application. Optical
structures recorded in waveguides can include many different types
of optical elements, such as but not limited to diffraction
gratings. In many embodiments, the grating implemented is a Bragg
grating (also referred to as a volume grating). 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 is can be used to make lossy
waveguide gratings for extracting light over a large pupil. By
strategically placing volume Bragg gratings within a waveguide, the
propagation of light within the waveguide can be affected in a
controlled manner to achieve various effects. The diffraction of
light incident on the grating can be determined by the
characteristic of the light and the grating. As can readily be
appreciated, volume Bragg gratings can be constructed to have
different characteristics depending on the specific requirements of
the given application. In a number of embodiments, the volume Bragg
grating is designed to be a transmission grating. In other
embodiments, the volume Bragg grating is designed to be a
reflection grating. In transmission gratings, incident light
meeting the Bragg condition is diffracted such that the diffracted
light exits the grating on the side which the incident light did
not enter. For reflection gratings, the diffracted light exits on
the same side of the grating as where the incident light
entered.
[0097] FIGS. 1A and 1B conceptually illustrate two volume Bragg
grating configurations in accordance with various embodiments of
the invention. Depending on the side out of which a light ray exits
after diffraction, the grating can be classified as either a
reflection grating 100 or a transmission grating 150. The
conditions for refraction/reflection, or Bragg condition, can
depend several factors, such as but not limited to the refractive
indices of the medium, the grating period, the wavelength of the
incident light, and the angle of incidence. FIG. 1A shows a
reflection grating 100 recorded in a transparent material. As
shown, light rays 101, 102 are of different wavelengths and are
incident at the same angle on the reflection grating 100, which has
fringes 103 that are parallel to the grating surface. Light ray 101
does not meet the Bragg condition and is transmitted through the
grating. On the other hand, light ray 102 does meet the Bragg
condition and is reflected back through the same surface on which
it entered. Another type of grating is a transmission grating,
which is conceptually illustrated in FIG. 1B. In the illustrative
embodiment, the transmission grating 150 has fringes 151 that are
perpendicular to the grating surface. As shown, light rays 152, 153
with different wavelengths are incident on the transmission grating
150 at the same angle. Light ray 152 meets the Bragg condition and
is refracted, exiting on the opposite side of the grating on which
the light ray 152 entered. Light ray 153 does not meet the Bragg
condition and is transmitted through with its original path of
propagation. Depending on the efficiency of the grating, light can
be partially reflected or refracted. Although FIGS. 1A and 1B
illustrate specific volume grating structures, any type of grating
structure can be recorded in a waveguide cell in accordance with
various embodiments of the invention. For example, volume gratings
can be implemented with fringes that are tilted and/slanted
relative to the grating surface, which can affect the angles of
diffraction/reflection. Although the discussions above denote the
grating structures as either transmission or reflection, both types
of gratings behave in the same manner according to the standard
grating equation.
[0098] Waveguide structures in accordance with various embodiments
of the invention can implement gratings in a number of different
ways. In addition to volume gratings, gratings can be implemented
as surface relief gratings. As the name suggests, surface relief
gratings can be implemented by physically forming grooves or
periodic patterns on the surface of the substrate. The periodicity
and angles formed by the grooves can determine the efficiency and
other characteristics of the grating. Any of a number of methods
can be used to form these grooves, such as but not limited to
etching and photolithography.
[0099] FIG. 2 conceptually illustrates a surface relief grating in
accordance with an embodiment of the invention. As shown, the
surface relief grating 200 contains periodic slanted grooves 201.
When light is incident on the grooves 201, diffraction can occur
under certain conditions. The slant and periodicity of the grooves
201 can be designed to achieve targeted diffraction behavior of
incident light.
[0100] Although FIGS. 1A-1B and 2 show specific grating structures,
it is readily appreciable that grating structures can be configured
in a number of different ways depending on the specific
requirements of a given application. Examples of such
configurations are discussed in the sections below in further
detail.
Switchable Bragg Gratings
[0101] One class of 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 glass plates or
substrates. In many cases, the glass plates are in a parallel
configuration. One or both glass plates 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.
[0102] 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.
[0103] Typically, the SBG elements are switched clear in 30 .mu.s
with a longer relaxation time to switch ON. Note that 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 glass plates 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.
[0104] FIGS. 3A and 3B conceptually illustrate HPDLC SBG devices
300, 350 and the switching property of SBGs in accordance with
various embodiments of the invention. In FIG. 3A, the SBG 300 is in
an OFF state. As shown, the LC molecules 301 are aligned
substantially normal to the fringe planes. As such, the SBG 300
exhibits high diffraction efficiency, and incident light can easily
be diffracted. FIG. 3B illustrates the SBG 350 in an ON position.
An applied voltage 351 can orient the optical axis of the LC
molecules 352 within the droplets 353 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.
[0105] In waveguide cell designs, in addition to the components
described above, adhesives and spacers can be disposed between the
substrates to affix the layers of the elements together and to
maintain the cell gap, or thickness dimension. In these devices,
spacers can take many forms, such as but not limited to materials,
sizes, and geometries. Materials can include, for example, plastics
(e.g., divinylbenzene), silica, and conductive spacers. They can
take any suitable geometry, such as but not limited to rods and
spheres. The spacers can take any suitable size. In many cases, the
sizes of the spacers range from 1 to 30 .mu.m. While the use of
these adhesive materials and spacers can be necessary in LC cells
using conventional materials and methods of manufacture, they can
contribute to the haziness of the cells degrading the optical
properties and performance of the waveguide and device.
HPDLC Material Systems
[0106] HPDLC mixtures in accordance with various embodiments of the
invention 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 comprising: 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.
[0107] 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: [0108] 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 comprises 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. [0109] 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. [0110] 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. [0111] 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. [0112] 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. [0113] G. S.
lannacchione 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.
[0114] 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 have also been used.
[0115] One of the known attributes of transmission SBGs is that the
LC molecules tend to align with an average direction normal to the
grating fringe planes (i.e., parallel to the grating or K-vector).
The effect of the LC molecule alignment is that transmission SBGs
efficiently diffract P polarized light (i.e., light with a
polarization vector in the plane of incidence), but have nearly
zero diffraction efficiency for S polarized light (i.e., light with
the polarization vector normal to the plane of incidence).
Recording Mechanisms for Volume Gratings
[0116] Volume gratings can be recorded in a waveguide cell using
many different methods in accordance with various embodiments of
the invention. The recording of optical elements in optical
recording materials can be achieved using any number and type of
electromagnetic radiation sources. Depending on the application,
the exposure source(s) and/or recording system can be configured to
record optical elements using varying levels of exposure power and
duration. As discussed above with regards to SBGs, techniques for
recording volume gratings can include the exposure of an optical
recording material using two mutually coherent laser beams, where
the superimposition of the two beams create a periodic intensity
distribution along the interference pattern. The optical recording
material can form grating structures exhibiting a refractive index
modulation pattern matching the periodic intensity distribution. In
HPDLC mixtures, the light intensity distribution results in
diffusion and polymerization of monomers into the high intensity
regions and simultaneous diffusion of liquid crystal into the dark
regions. This phase separation creates alternating liquid
crystal-rich and liquid crystal-depleted regions that form the
fringe planes of the grating. The grating structures can be formed
with slanted or non-slanted fringes depending on how the recording
beams are configured. FIG. 4A-4D conceptually illustrate two-beam
recording processes in accordance with various embodiments of the
invention. As shown, two methods can be used to create two
different types of Bragg gratings--i.e., a transmission grating 400
and a reflection grating 401. Depending on how the two recording
beams 402, 403 are positioned, the interference pattern 404 can
record either a transmission or a reflection grating in an optical
recording material 405. Differences between the two types of
gratings can be seen in the orientation of the fringes (i.e., the
fringes of a reflection volume grating are typically substantially
parallel to the surface of the substrate, and the fringes of a
transmission grating are typically substantially perpendicular to
the surface of the substrate). During playback, a beam 406 incident
on the transmission grating 400 can result in a diffracted beam 407
that is transmitted. On the other hand, a beam 408 that is incident
on the reflection grating 401 can result in a beam 409 that is
reflected.
[0117] Another method for recording volume gratings in an optical
recording material includes the use of a single beam to form an
interference pattern onto the optical recording material. This can
be achieved through the use of a master grating. In many
embodiments, the master grating is a volume grating. In some
embodiments, the master grating is an amplitude grating. Upon
interaction with the master grating, the single beam can diffract.
The first order diffraction and the zero order beam can overlap to
create an interference pattern, which can then expose the optical
recording material to form the desired volume grating. A
single-beam recording process utilizing an amplitude grating in
accordance with an embodiment of the invention is conceptually
illustrated in FIG. 5. As shown, a beam 500 from a single laser
source (not shown) is directed through an amplitude grating 501.
Upon interaction with the grating 501, the beam 500 can diffract
as, for example, in the case of the rays interacting with the black
shaded region of the amplitude grating, or the beam 500 can
propagated through the amplitude grating without substantial
deviation as a zero-order beam as, for example, in the case of the
rays interacting with the cross-hatched region of the amplitude
grating. The first order diffraction beams 502 and the zero order
beams 503 can overlap to create an interference pattern that
exposes the optical recording layer 504 of a waveguide cell. In the
illustrative embodiment, a spacer block 505 is positioned between
the grating 501 and the optical recording layer 504 in order to
alter the distance between the two components.
[0118] Although specific methods of recording volume gratings are
discussed and shown in FIGS. 4A-4D and 5, recording systems in
accordance with various embodiments of the invention can be
configured to implement any of a number of methods for recording
volume gratings.
Rolled K-Vector Gratings and Multiplexed K-Vector Gratings
[0119] In addressing the limited range of wavelengths and angles
over which diffraction occurs in volume Bragg gratings, several
methods can be utilized to increase the diffraction bandwidth of
the gratings. In many embodiments, gratings can employ fringes that
vary with respect to their K-vectors. In a number of embodiments,
the change across the rolled K-vectors is typically such that the
direction of the change in K-vectors is out of plane with the
waveguide or grating element. Varying fringes, or rolled K-vectors,
can be implemented in a number of different ways. In some
embodiments, fringes of gratings are designed to vary in a
progressive manner across the grating. In other embodiments,
different discrete sets of gratings with different fringes are
place serially. Gratings with rolled K-vectors can be designed and
configured in a variety of ways. In many embodiments, the rolled
K-vectors are designed such that the peak diffraction efficiency of
each grating segment is optimized for its corresponding output
angle at that position. In some embodiments, the peak diffraction
efficiency of each grating at different positions is at an offset
with its corresponding output angle at that position. It has been
shown that by introducing this offset, eyebox homogeneity can be
improved. In several embodiments, offsets can improve total image
brightness by a factor of two compared to just matching the peak
diffraction efficiencies at different positions.
[0120] Rolled K-vector gratings can be used to maximize the peak
diffraction efficiency of in-couple light in accordance with an
embodiment of the invention. The use of rolled k-vectors enables
high efficiency input coupling into a grating, and also allows the
beam spread angle to be optimized to minimize the thickness of the
waveguide; this may need balancing the waveguide thickness, the
angular bandwidth of the grating, and the spread of field angles at
any given point on the grating. The low angular response of
gratings as the K-vector is rolled (and surface pitch maintained)
can prevent output coupling, allowing the waveguide thickness to be
minimized. In a number of embodiments, the design aim is to ensure
maximum input coupling at a point and to minimize the angular
diversity such that the grating thickness can be minimized without
reciprocally out-coupling at different point.
[0121] FIGS. 6A and 6B conceptually illustrate two implementations
of rolled K-vector gratings in accordance with various embodiments
of the invention. Referring first to FIG. 6A, in some embodiments a
rolled K-vector grating can be implemented as a waveguide portion
containing discrete grating elements 600 having different
K-vectors. Referring next to FIG. 6B, in several embodiments a
rolled K-vector grating can be implemented as a waveguide portion
containing grating elements 601 within which the K-vectors
undergoes a smooth monotonic variation in direction. As
illustrated, the change in the direction of the K-vectors is out of
plane with the waveguide.
[0122] In many embodiments, different sets of discrete fringes are
superimposed into the same grating, creating a multiplexed grating
with essentially multiple gratings inside the same volume that work
independently and without interfering with each other. For example,
if two volume gratings are recorded in the same device for two
different Bragg wavelengths at the same incidence angle, the device
can diffract the two selected wavelengths into different output
directions with limited crosstalk. Multiplexing can be used to
produce improved angular profiles by combining two gratings of
similar prescription to extend the diffraction efficiency angular
bandwidth and give better luminance uniformity and color balance
across the exit pupil and field of view. Multiplexing can also be
used to encode two distinct diffraction prescriptions which can be
design to project light into distinct field of regions or diffract
light of two different wavelengths into a given field of view
region. Steps can be taken to ensure that there is no competition
between gratings during recording leading to unequal diffraction
efficiencies and crosstalk between gratings in playback.
Multiplexing can also offer the significant benefit of reducing the
number of layers in the waveguide structure. In some embodiments,
at least one of the input, fold, or output gratings can combine two
or more angular diffraction prescriptions to expand the angular
bandwidth. Similarly, in several embodiments, at least one of the
input, fold, or output gratings can combine two or more spectral
diffraction prescriptions to expand the spectral bandwidth. For
example, a color multiplexed grating may be used to diffract two or
more of the primary colors.
[0123] FIG. 7 conceptually illustrates a multiplexed K-vector
grating in accordance with an embodiment of the invention. As
illustrated, the multiplexed grating 700 contains two sets of
fringes 701, 702. The first set 701 is depicted by solid diagonal
lines and has K-vector K.sub.1 and period .LAMBDA..sub.1. The
second multiplexed grating 702 is illustrated by dot-dash lines and
has K-vector K.sub.2 and period .LAMBDA..sub.2. In the illustrated
embodiment, the two grating periods are the same, but the K-vectors
differ in direction. In operation, both of the multiplexed gratings
701, 702 are active and can provide broader incidence and
diffraction bandwidths. The angular bandwidth of incidence
.theta..sub.i for the multiplexed gratings covers the angular range
including the overlapping .theta..sub.i1 and .theta..sub.i2. The
angular bandwidth of diffraction .theta..sub.d for the multiplexed
gratings 701, 702 covers the angular range including the
overlapping .theta..sub.d1 and .theta..sub.d2. In some embodiments,
more than two gratings are multiplexed.
[0124] Although specific grating structures with varying fringes
are discussed above, any of a number of fringe configurations can
be utilized in accordance with specific requirements of a given
application. For example, any number of gratings can be multiplexed
as allowed by manufacturing constraints. Rolled K-vector gratings
can be designed to have K-vectors rolled in any discrete unit.
Waveguides Implementing Pupil Expansion
[0125] Gratings can be implemented in waveguides in a variety of
different ways. In some embodiments, the gratings reside on the
outer surface of the waveguide. In other embodiments, volume
gratings are implemented inside the waveguide. Gratings can also be
implemented to perform different optical functions, such as but not
limited to coupling light, directing light, and preventing the
transmission of light. FIG. 8 conceptually illustrates a waveguide
utilizing coupling gratings to diffract light into and out of the
waveguide in accordance with an embodiment of the invention. As
shown, the waveguide 800 includes a first surface 801, a second
surface 802, an input grating element 803, and an output grating
element 804. Collimated light 805 from a projection lens enters the
waveguide through the first surface 801 at an orthogonal angle. The
light travels through the waveguide 800 at its original angle and,
before reaching the second surface 802 at the other side of the
waveguide 800, interacts with an input grating element 803. The
input grating element 803 can be designed to diffract the light 805
at an oblique angle such that the refracted light 806 is incident
on the second surface 802 at an angle at which total internal
reflection can occur. As such, the light 805 is coupled into the
waveguide and is confined within the first and second surfaces 801,
802 of the waveguide 800. In the illustrative embodiment, the light
travels within the waveguide 800 until it interacts with an output
grating 804, which refracts and couples the light out of the
waveguide 800 and into a user's eye 807.
[0126] In many embodiments, diffraction gratings can be used to
preserve eye box 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 a user's
eyes. FIGS. 9 and 10 conceptually illustrate waveguides utilizing
an output grating for exit pupil expansion in one dimension in
accordance with an embodiment of the invention. The waveguide 900
in FIG. 9 includes a first surface 901, a second surface 902, an
input grating element 903, and an output grating element 904. As
shown, light 905 is coupled into the waveguide 900 by the input
grating 902 and can travel through the waveguide 900 via total
internal reflection. In the illustrative embodiment, the output
grating 904 is extended and designed to refract a portion of the
waveguided light. The light can be refracted such that the
refracted light 906 is incident on the second surface 902 at an
angle at which total internal reflection does not occur, allowing
the light 906 to couple out of the waveguide 900. This lossy
extraction permits exit pupil expansion as the remaining light can
continue to travel within the waveguide 900 and, once the light is
again incident on the output grating 904, the scenario described
above can occur again. Utilizing this technique, a continuous
expanded exit pupil can also be achieved with the correct design,
as shown in FIG. 10.
[0127] Expanding upon the ideas in FIGS. 9 and 10, an optical
waveguide can be designed to expand the exit pupil in two
dimensions. In many embodiments, two waveguides can be stacked
together to create a system where light coupled into the waveguide
stack can achieve exit pupil expansion in two dimensions. FIG. 11
conceptually illustrates a waveguide system utilizing two planar
waveguides to provide exit pupil expansion in two dimensions in
accordance with an embodiment of the invention. As shown, the
system 1100 includes a first waveguide 1101 and a second waveguide
1102. The first waveguide 1101 can include a first input coupling
grating 1103 and a first output coupling grating 1104, and the
second waveguide 1102 can include a second input coupling grating
1105 and a second output coupling grating 1106. The first input
coupling grating 1103 can be designed to couple collimated light
1107 from an image source 1108 into the first waveguide 1101.
Similar to the systems as described in FIGS. 9 and 10, the confined
light can travel through the first waveguide 1101 via total
internal reflection until the light reaches the first output
coupling grating 1104. In the illustrative embodiment, the first
output coupling grating 1104 is designed to provide lossy exit
pupil expansion in a first dimension and to couple the light out of
the first waveguide 1101. The second input coupling grating 1105
can be designed to receive light outputted from the first waveguide
1101, which is expanded in the first dimension, and refract the
received light such that the received light travels through the
second waveguide 1102 via total internal reflection. In many
embodiments, the first output coupling grating 1104 and the second
input coupling grating 1106 are extended in a similar manner. The
light traveling through the second waveguide 1102 can then interact
with the second output coupling grating 1106. In the illustrative
embodiment, the second output coupling grating 1106 is designed to
provide lossy exit pupil expansion in a second dimension that is
different from the first dimension and to couple the light out of
the second waveguide 1102. As a result, the exit pupil is expanded
in two dimensions, allowing for a smaller lens size with respect to
the eye box size 1109.
[0128] In many embodiments, the optical waveguide utilizes a fold
grating, which can provide exit pupil expansion in one dimension
while directing the light within the waveguide. In further
embodiments, the fold grating directs the light towards an output
grating, which can provide exit pupil expansion in a second
dimension that is different from the first direction and also
couples the light out of the waveguide. By using the fold grating,
the waveguide display can require fewer layers than other systems
and methods of displaying information. In addition, by using fold
grating, light can travel by total internal refection within the
waveguide in a single rectangular prism defined by the waveguide
outer surfaces while achieving dual pupil expansion. As a result, a
two-dimension exit pupil expansion can be achieved using a single
waveguide. FIG. 12 conceptually illustrates a waveguide utilizing a
three-grating structure to provide two dimensional exit pupil
expansion in accordance with an embodiment of the invention. As
shown, the waveguide 1200 includes an input grating 1201, a fold
grating 1202, and an output grating 1203. Arrows 1204-1206 on the
gratings 1201-1203 show the k-vector associated with each grating.
In many embodiments, the fold grating 1202 can be designed to
provide exit pupil expansion in one dimension and to redirect the
direction of light propagating via total internal reflection from
the input grating 1201. In the illustrative embodiment, the fringes
of the fold gratings 1202 are at a 45 degree offset from either of
the other two gratings 1201, 1203. Light incident on the fold
grating is redirected 1207, 1208 to propagate towards the output
grating 1203, which provides exit pupil expansion in a second
dimension and couples the light out of the waveguide 1200.
[0129] Although the discussions above relating to FIGS. 8-12
describe specific waveguide structures, it is readily appreciated
that any number of waveguide structure configurations can be
utilized in accordance with specific requirements of a given
application. For example, gratings providing exit pupil expansion
can be designed with a gradient efficiency such that the portion of
light refracted changes depending on the area of incident.
Waveguide Layer Stacks
[0130] Waveguides in accordance with various embodiments of the
invention can be stacked together to implement certain optical
functions. For example, in many embodiments, the device can include
a stack of RGB diffracting layers, each layer comprising input and
output gratings. In each layer the SBGs are recorded to provide
peak diffraction efficiency vs. wavelength characteristics (along
the waveguide) shifted by small increments from the peak
wavelength. In some embodiments, RGB SBG layers are used and can be
switched sequentially and synchronously with RGB LEDs image
sources. FIG. 13 conceptually illustrates a profile view of an RGB
stack of waveguides 1300 in accordance with an embodiment of the
invention. In the illustrative embodiment, wavelength selective
absorptive layers 1301-1303 are used to selectively absorb unwanted
light in each waveguide layer 1304-1306. Dashed lines represent
weak coupling due to either off-polarization or off Bragg. The
stack of waveguides further includes various filters and waveplates
1307-1311. Polarization orientations are depicted with respect to
the input grating.
[0131] Although FIG. 13 illustrates a specific structure of a
waveguide stack, any of a number of stacking configuration can be
used in accordance with specific requirements of a given
application. For example, in many embodiments, only two layers, red
and blue/green, are used to implement an RGB stack. Such a system
can be achieved using several methods. In some embodiments,
multiplexed gratings containing different sets of gratings, each
correlating with an RGB color, are used to implement multiple color
waveguides in one waveguide layer.
Waveguide Displays
[0132] Waveguide displays in accordance with various embodiments of
the invention can be implemented and constricted in many different
ways. For example, waveguide displays can contain a varying number
of waveguide layers and different exit pupil expansion scheme. FIG.
14 conceptually illustrates a dual axis expansion waveguide display
with two grating layers in accordance with an embodiment of the
invention. As shown, the waveguide display 1400 includes a light
source 1401, a microdisplay panel 1402, and an input image node
("IIN") 1403 optically coupled to a waveguide 1404 having two
grating layers. In some embodiments, the waveguide is formed by
sandwiched the grating layers between glass or plastic substrates
to form a stack within which total internal reflection occurs at
the outer substrate and air interfaces. In several embodiments, the
stack can further comprise additional layers such as beam splitting
coatings and environmental protection layers. In the illustrative
embodiment, each grating layer contains an input grating
1405A,1405B, a fold grating exit pupil expander 1406A, 1406B, and
an output grating 1407A, 1407B where characters A and B refer to
the first and second waveguide layers. The input grating, fold
grating, and the output grating can be holographic gratings, such
as a switchable or non-switchable SBG. As used herein, the term
grating may encompass a grating can include a set of gratings, such
as multiplexed gratings or sets of discrete rolled K-vector
gratings. In the illustrative embodiment, the IIN 1403 integrates
the microdisplay panel 1402, the light source 1401, and optical
components needed to illuminate the display panel, separate the
reflected light, and collimate it into the required FOV. In the
embodiment of FIG. 14 and in the embodiments to be described below,
at least one of the input, fold, and output gratings can be
electrically switchable. In many embodiments, all three grating
types are passive (i.e., non-switching). In a number of
embodiments, the IIN can project the image displayed on the
microdisplay panel such that each display pixel is converted into a
unique angular direction within the substrate waveguide. The
collimation optics contained in the IIN can include lens and
mirrors. In further embodiments, the lens and mirrors are
diffractive lenses and mirrors.
[0133] In the illustrative embodiment, the light path from the
source to the waveguide via the IIN is indicated by rays 1408-1411.
The input grating 1405A, 1405B of each grating layer can couple a
portion of the light into a TIR path in the waveguide 1404, such
path being represented by the rays 1412, 1413. The output gratings
1407A, 1407B can diffract light out of the waveguide into angular
ranges of collimated light 1414, 1415 respectively for viewing by
the eye 1416. The angular ranges, which correspond to the field of
view of the display, can be defined by the IIN optics. In some
embodiments, the waveguide gratings can encode optical power for
adjusting the collimation of the output. In several embodiments,
the output image is at infinity. In other embodiments, the output
image may be formed at distances of several meters from the eye
box. Typically, the eye is positioned within the exit pupil or eye
box of the display.
[0134] Different IIN implementations and embodiments can be
utilized as discussed and taught in U.S. patent application Ser.
No. 13/869,866, entitled Holographic Wide Angle Display, and U.S.
patent application Ser. No. 13/844,456, entitled Transparent
Waveguide Display, the disclosures of which are hereby incorporated
by reference in their entireties. In some embodiments, the IIN
contains a beamsplitter for directing light onto a microdisplay and
transmitting the reflected light towards the waveguide. In many
embodiments, the beamsplitter is a grating recorded in HPDLC and
uses the intrinsic polarization selectivity of such gratings to
separate the light illuminating the display and the image modulated
light reflected off the display. In several embodiments, the beam
splitter is a polarizing beam splitter cube. In a number of
embodiments, the IIN incorporates a despeckler. Despecklers are
discussed in U.S. Pat. No. 8,565,560, entitled Laser Illumination
Device, the disclosure of which is hereby incorporated by reference
in its entirety.
[0135] The light source can be a laser or LED and can include one
or more lenses for modifying the illumination beam angular
characteristics. The image source can be a micro-display or laser
based display. LED can provide better uniformity than laser. If
laser illumination is used, there is a risk of illumination banding
occurring at the waveguide output. In many embodiments, laser
illumination banding in waveguides can be overcome using the
techniques and teachings disclosed in U.S. patent application Ser.
No. 15/512,500, entitled Method and Apparatus for Generating Input
Images for Holographic Waveguide Displays, the disclosure of which
is hereby incorporated by reference in its entirety. In some
embodiments, the light from the light source is polarized. In
several embodiments, the image source is a liquid crystal display
(LCD) micro display or liquid crystal on silicon (LCoS) micro
display.
[0136] In some embodiments, similar to the one shown in FIG. 14,
each grating layer addresses half the total field of view.
Typically, the fold gratings are clocked (i.e., tilted in the
waveguide plane) at 45 degrees to ensure adequate angular bandwidth
for the folded light. In other embodiments, other clock angles can
be used to satisfy spatial constraints on the positioning of the
gratings that can arise in the ergonomic design of the display. In
some embodiments, at least one of the input and output gratings
have rolled k-vectors. Rolling the K-vectors can allow the angular
bandwidth of the grating to be expanded without the need to
increase the waveguide thickness.
[0137] In many embodiments, the fold grating's angular bandwidth
can be enhanced by designing the grating prescription to provide
dual interaction of the guided light with the grating. Exemplary
embodiments of dual interaction fold gratings are disclosed in U.S.
patent application Ser. No. 14/620,969, entitled Waveguide Grating
Device, the disclosure of which is hereby incorporated in its
entirety.
[0138] FIG. 15 conceptually illustrates a plan view 1500 of a
single grating layer similar to the ones used in FIG. 14 in
accordance with an embodiment of the invention. The grating layer
1501, which is optically coupled to the IIN 1502, includes input
grating 1503, a first beamsplitter 1504, a fold grating 1505, a
second beamsplitter 1506, and an output grating 1507. The
beamsplitters can be partially transmitting coatings which
homogenize the waveguided light by providing multiple reflection
paths within the waveguide. Each beamsplitter can include more than
one coating layer with each coating layer being applied to a
transparent substrate. Typical beam paths from the IIN up to the
eye 1508 are indicated by the rays 1509-1513.
[0139] FIG. 16 conceptually illustrates a plan view 1600 of a two
grating layer configuration in accordance with an embodiment of the
invention. As shown, the grating layers 1601A, 1601B, which are
optically coupled to the IIN 1602, includes input gratings 1603A,
1603B, first beamsplitters 1604A, 1604B, fold gratings 1605A,
1605B, second beamsplitters 1606A, 1606B and output gratings 1607A,
1607B, where the characters A, B refer to the first and second
grating layers, respectively. In the illustrated embodiment, the
gratings and beams splitters of the two layers substantially
overlap.
[0140] In many embodiments, the grating layer can be broken up into
separate layers. For example, in some embodiments, a first layer
includes the fold grating while a second layer includes the output
grating. In further embodiments, a third layer can include the
input grating. In such embodiments, the number of layers can then
be laminated together into a single waveguide substrate. In several
embodiments, the grating layer includes a number of pieces,
including the input coupler, the fold grating, and the output
grating (or portions thereof) that are laminated together to form a
single substrate waveguide. The pieces can be separated by optical
glue or other transparent material of refractive index matching or
substantially similar that of the pieces.
[0141] In many embodiments, the grating layer can be formed via a
cell making process by creating cells of the desired grating
thickness and vacuum filling each cell with SBG material for each
of the input coupler, the fold grating, and the output grating. In
some embodiments, the cell can be formed by positioning multiple
plates of glass with gaps between the plates of glass that define
the desired grating thickness for the input coupler, the fold
grating, and the output grating. In several embodiments, one cell
can be made with multiple apertures such that the separate
apertures are filled with different pockets of SBG material. Any
intervening spaces can then be separated by a separating material
(e.g., glue, oil, etc.) to define separate areas. In a number of
embodiments, the SBG material can be spin-coated onto a substrate
and then covered by a second substrate after curing of the
material.
[0142] In many embodiments, the input coupler, the fold grating,
and the output grating can be created by interfering two waves of
light at an angle within the substrate to create a holographic wave
front, thereby creating light and dark fringes that are set in the
waveguide substrate at a desired angle. Additional, such optical
elements can also be fabricated using any of the various methods
described in the above sections.
[0143] In one embodiment, the input coupler, the fold grating, and
the output grating embodied as SBGs can be Bragg gratings recorded
in a holographic polymer dispersed liquid crystal (HPDLC) (e.g., a
matrix of liquid crystal droplets), although SBGs may also be
recorded in other materials. In one embodiment, SBGs are recorded
in a uniform modulation material, such as POLICRYPS or POLIPHEM
having a matrix of solid liquid crystals dispersed in a liquid
polymer. The SBGs can be switching or non-switching in nature. In
its non-switching form a SBG has the advantage over conventional
holographic photopolymer materials of being capable of providing
high refractive index modulation due to its liquid crystal
component. Exemplary uniform modulation liquid crystal-polymer
material systems are disclosed in United State Patent Application
Publication No.: US2007/0019152 by Caputo et al and PCT Application
No.: PCT/EP2005/006950 by Stumpe et al. both of which are
incorporated herein by reference in their entireties. Uniform
modulation gratings are characterized by high refractive index
modulation (and hence high diffraction efficiency) and low
scatter.
[0144] In many embodiments, the input coupler, the fold grating,
and the output grating is made of a reverse mode HPDLC material.
Reverse mode HPDLC differs from conventional HPDLC in that the
grating is passive when no electric field is applied and becomes
diffractive in the presence of an electric field. The reverse mode
HPDLC may be based on any of the recipes and processes disclosed in
PCT Application No. PCT/GB2012/000680, entitled Improvements to
Holographic Polymer Dispersed Liquid Crystal Materials and Devices,
the disclosure of which is hereby incorporated in its entirety. The
grating can be recorded in any of the above material systems but
used in a passive (non-switching) mode. The fabrication process is
identical to that used for switched but with the electrode coating
stage being omitted. LC polymer material systems are highly
desirable in view of their high index modulation. In some
embodiments, the gratings are recorded in HPDLC but are not
switched.
[0145] In many embodiments, the input grating can be replaced by
another type of input coupler, such as but not limited to a prism
and a reflective surface. In some embodiments, the input coupler
can be a holographic grating, such as an SBG grating or a passive
grating, which can be a passive SBG grating. The input coupler can
be configured to receive collimated light from a display source and
to cause the light to travel within the waveguide via total
internal reflection between the first surface and the second
surface to the fold grating. The input coupler can be orientated
directly towards or at an angle relative to the fold grating. For
example, in several embodiments, the input coupler can be set at a
slight incline in relation to the fold grating. In a number of
embodiments, the fold grating can be oriented in a diagonal
direction. The fold grating can be configured to provide pupil
expansion in a first direction and to direct the light to the
output grating via total internal reflection inside the
waveguide.
[0146] In many embodiments, a longitudinal edge of each fold
grating is oblique to the axis of alignment of the input coupler
such that each fold grating is set on a diagonal with respect to
the direction of propagation of the display light. The fold grating
can be angled such that light from the input coupler is redirected
to the output grating. In some embodiments, the fold grating is set
at a forty-five-degree angle relative to the direction that the
display image is released from the input coupler. This feature can
cause the display image propagating down the fold grating to be
turned into the output grating. For example, in several
embodiments, the fold grating can cause the image to be turned 90
degrees into the output grating. In this manner, a single waveguide
can provide dual axis pupil expansion in both the horizontal and
vertical directions. In a number of embodiments, each of the fold
grating can have a partially diffractive structure. In some
embodiments, each of the fold gratings can have a fully diffractive
structure.
[0147] The output grating can be configured to provide pupil
expansion in a second direction different than the first direction
and to cause the light to exit the waveguide from the first surface
or the second surface. The output grating can receive the display
image from the fold grating via total internal reflection and can
provide pupil expansion in a second direction. In many embodiments,
the output grating includes multiple layers of substrate, thereby
comprising multiple layers of output gratings. Accordingly, there
is no requirement for gratings to be in one plane within the
waveguide, and gratings may be stacked on top of each other (e.g.,
cells of gratings stacked on top of each other).
[0148] In many embodiments, a quarter wave plate on the substrate
waveguide rotates polarization of a light ray to maintain efficient
coupling with the SBGs. The quarter wave plate can be coupled to or
adhered to the surface of substrate waveguide. For example, in some
embodiments, the quarter wave plate is a coating that is applied to
substrate waveguide. The quarter wave plate can provide light wave
polarization management. Such polarization management can help
light rays retain alignment with the intended viewing axis by
compensating for skew waves in the waveguide. The quarter wave
plate is optional and can increase the efficiency of the optical
design in implementations. In several embodiments, the waveguide
does not include the quarter wave plate. The quarter wave plate may
be provided as multi-layer coating.
[0149] In many embodiments, the waveguide display can be operated
in monochrome. In some embodiments, the waveguide display can be
operated in color. Operating in color can be achieved using a stack
of monochrome waveguides of similar design to the one in FIG. 14.
The design can use red, green, and blue waveguide layers as shown
or, alternatively, red and blue/green layers. FIG. 17 conceptually
illustrates a dual axis expansion waveguide display 1700 that
includes a light source 1701, a microdisplay panel 1702, and an IIN
1703 optically coupled to red, green, and blue waveguides 1704R,
1704G, 1704B, with each waveguide including two grating layers in
accordance with an embodiment of the invention. In the illustrative
embodiment, the three waveguides are separated by air gaps. In some
embodiments, the waveguides are separated by a low index material
such as a nanoporous film. As shown, the red grating layer labelled
by R includes an input grating 1705R, 1706R, a fold grating exit
pupil expander 1707R, 1708R, and an output grating 1709R, 1710R.
The grating elements of the blue and green waveguides are labeled
using the same numerals with B, G designating blue and green. In
some embodiments, the input, fold, and output gratings are all
passive, that is non-switching. In several embodiments, at least
one of the gratings is switching. In a number of embodiments, the
input gratings in each layer are switchable to avoid color
crosstalk between the waveguide layers. In many embodiments, color
crosstalk can be avoided by disposing dichroic filters 1711, 1712
between the input grating regions of the red and blue and the blue
and green waveguides. In a variety of embodiments, a color
waveguide can be implemented using just one grating layer in each
monochromatic waveguide
[0150] FIG. 18 conceptually illustrates an eye tracker display in
accordance with an embodiment of the invention. Waveguide device
based eye trackers are discussed in PCT Application No.
PCT/GB2014/000197, entitled Holographic Waveguide Eye Tracker, PCT
Application No. PCT/GB2015/000274, entitled Holographic Waveguide
Optical Tracker, and PCT Application No. PCT/GB2013/000210,
entitled Apparatus for Eye Tracking, the disclosures of which are
hereby incorporated in their entireties. Turning again to FIG. 18,
the eye tracked display 1800 includes a dual axis expansion
waveguide display based on any of the embodiments described above.
The waveguide display can include a waveguide 1801 containing at
least one grating layer incorporating an input fold and output
grating, the IIN 1802, an eye tracker including waveguide 1803,
infrared detector 1804, and infrared source 1805. The eye tracker
and display waveguides can be separated by an air gap or by a low
refractive material. As explained in the above references, the eye
tracker can comprise separate illumination and detector waveguides.
In the illustrative embodiment, the optical path from the infrared
source to the eye is indicated by the rays 1806-1808, and the
backscattered signal from the eye is indicated by the rays 1809,
1810. The optical path from the input image node through the
display waveguide to the eye box is indicated by the rays
1811-1813.
[0151] In many embodiments, a dual expansion waveguide display can
further include a dynamic focusing element. FIG. 19 conceptually
illustrates a dual expansion waveguide display 1900 with a dynamic
focusing element 1901 disposed in proximity to a principal surface
of the waveguide display and an eye tracker in accordance with an
embodiment of the invention. In some embodiments, the dynamic
focusing element is an LC device. In several embodiments, the LC
device combines an LC layer and a diffractive optical element. In a
number of embodiments, the diffractive optical element is an
electrically controllable LC-based device. In various embodiments,
the dynamic focusing element is disposed between the waveguide
display and the eye tracker. In a variety of embodiments, the
dynamic focusing element can be disposed in proximity to the
surface of the display waveguide furthest from the eye.
[0152] The dynamic focus device can provide a multiplicity of image
surfaces 1902. In light field display applications, at least four
image surfaces can be used. The dynamic focusing element can be
based on dynamic focusing elements described in U.S. patent
application Ser. No. 15/553,120 entitled, Electrically Focus
Tunable Lens, the disclosure of which is hereby incorporated in its
entirety. In some embodiments, a dual expansion waveguide display
having a dynamic focusing element and an eye tracker can provide a
light field display, such as those based on the teachings disclosed
in U.S. patent application Ser. No. 15/543,013, entitled
Holographic Waveguide Light Field Displays, the disclosure of which
is hereby incorporated by reference in its entirety.
[0153] Although specific waveguide structures are discussed above,
any of a number of waveguide structures can be implemented
depending on the specific requirements of a given application. For
example, in many waveguide configurations, the input, fold, and
output gratings are formed in a single layer sandwiched by
transparent substrates. Such a configuration is shown in FIG. 14,
where two layers are stacked as such. In some embodiments, the
waveguide includes just one grating layer. In several embodiments,
switching transparent electrodes are applied to opposing surfaces
of the substrate layers sandwiching the switching grating. In a
number of embodiments, the cell substrates can be fabricated from
glass. One glass substrate that can be used is standard Corning
Willow glass substrate (index 1.51) which is available in
thicknesses down to 50 micrometers. In other embodiments, the cell
substrates can be optical plastics.
[0154] In many embodiments, the waveguide display is coupled to the
IIN by an opto-mechanical interface that allows the waveguide to be
easily retracted from the IIN assembly. The basic principle is
conceptually illustrated in FIG. 20A. FIG. 20A shows a dual axis
expansion waveguide display 2000 including a waveguide 2001
containing an input grating 2002, a fold grating 2003, an output
grating 2004, and an IIN 2005. The apparatus further includes an
optical link 2006 connected to the waveguide, a first optical
interface 2007 terminating the optical link, and a second optical
interface 2008 forming the exit optical port of the IIN. The first
and second optical interfaces can be decoupled as indicated by gap
2009 shown in FIG. 20B. In some embodiments, the optical link is a
waveguide. In several embodiments, the optical link is curved. In a
number of embodiments, the optical link is a GRIN image relay
device. In a variety of embodiments, the optical connection is
established using a mechanical mechanism. In some embodiments, the
optical connection is established using a magnetic mechanism. The
advantage of decoupling the waveguide from the IIN in helmet
mounted display applications is that the near eye portion of the
display can be removed when not in used. In some embodiments where
the waveguide includes passive gratings, the near eye optics can be
disposable.
[0155] FIG. 21 conceptually illustrates an IIN 2100 having a
microdisplay panel 2101, a spatially-varying NA component 2102, and
microdisplay optics 2103 in accordance with an embodiment of the
invention. As shown, the microdisplay optics 2103 accepts light
2104 from an illumination source (not illustrated) and deflects the
light onto the microdisplay in the direction indicated by ray 2105.
The light reflected from the microdisplay is indicated by the
divergent ray pairs 2106-2108 with numerical aperture ("NA") angles
varying along the X axis. In the illustrative embodiment, the
spatially-varying NA component is disposed between the microdisplay
optics and the microdisplay. In other embodiments, the
spatially-varying NA component is disposed adjacent the output
surface of the microdisplay optics. FIG. 22 conceptually
illustrates such an embodiment, shown by spatially-varying NA
component 2200.
[0156] In many embodiments, the microdisplay is a reflective
device. In some embodiments, the microdisplay is a transmission
device, typically a transmission LCoS device. FIG. 23 conceptually
illustrates an IIN 2300 including a backlight 2301, a microdisplay
2302, and a variable NA component 2303 in accordance with an
embodiment of the invention. Light from the backlight indicated by
the rays 2304-2306, which typically has a uniform NA across the
backlight, illuminates the back surface of the microdisplay and,
after propagation through the variable NA component, is converted
into output image modulated light indicated by the divergent ray
pairs 2307-2309 with NA angles varying along the X axis.
[0157] In many embodiments, the principles of the invention may be
applied to an emissive display. Examples of emissive displays for
use with the invention include ones based on LED arrays and light
emitting polymers arrays. FIG. 24 conceptually illustrates an IIN
2400 having an emissive microdisplay 2401 and a spatially-varying
NA component 2402 in accordance with an embodiment of the
invention. Light from the microdisplay indicated by rays 2403-2405,
which typically has a uniform NA across the emitting surface of the
display, illuminates the spatially-varying NA component and is
converted into output image modulated light indicated by divergent
ray pairs 2406-2408 with NA angles varying along the X axis.
[0158] In many embodiments, the microdisplay optics includes a
polarizing beam splitter cube. In some embodiments, the
microdisplay optics includes an inclined plate to which a beam
splitter coating has been applied. In a number of embodiments, the
microdisplay optics includes a waveguide device comprising a SBG,
which acts as a polarization selective beam splitter. Details
relating to such embodiments are discussed U.S. patent application
Ser. No. 13/869,866, entitled Holographic Wide Angle Display, and
U.S. patent application Ser. No. 13/844,456, entitled Transparent
Waveguide Display, the disclosures of which are hereby incorporated
in their entireties. In several embodiments, the microdisplay
optics contains at least one of a refractive component and curved
reflecting surfaces or a diffractive optical element for
controlling the numerical aperture of the illumination light. In
some embodiments, the microdisplay optics contains spectral filters
for controlling the wavelength characteristics of the illumination
light. In a number of embodiments, the microdisplay optics contains
apertures, masks, filter, and coatings for controlling stray light.
In many embodiments, the microdisplay optics incorporate birdbath
optics.
[0159] Although FIGS. 14-24 describe specific waveguide displays
and structures, any waveguide display system and configuration can
be used as appropriate to the specific requirements of a given
application. At its core, waveguides are simply used to manipulate
the direction of light. This property can be used generally in a
variety of different systems. An example of a general system that
can utilize waveguides is shown in FIG. 25. FIG. 25 conceptually
illustrates a system diagram showing components for waveguide
displays in accordance with various embodiments of the invention.
As shown, the system 2500 utilizes a light source 2501 that can
output light into a waveguide 2502. Light sources used can be a
variety of different systems. In some embodiments, the light source
2501 is from a projector. In many embodiments, the light source
2501 further includes a microdisplay panel and optical components
needed to illuminate the display panel. In further embodiments, the
light source 2501 includes collimators and other optical components
for manipulating the light into a desired form before entry into
the waveguide. In other embodiments, the light source 2501 is
natural light. Once the light source 2501 outputs light into the
waveguide 2502, the waveguide 2502 can then manipulate and redirect
light in a desired manner out and into a receiver 2503. Waveguides
can be any general waveguides known within the art and/or one of
the waveguides as described above. A receiver can be any of a
number of components capable of receiving light from the waveguide.
In many embodiments, the receiver 2503 is a user's eye(s). In some
embodiments, the receiver 2503 is another waveguide. In several
embodiments, the receiver 2503 is a display capable of displaying
the light from the waveguide 2502. In further embodiments, the
display is simply glass that can reflect the light onto another
receiver. The system 2500 can optionally include a switching device
2504 and electrical components for use in conjunction with SBGs. In
many embodiments, the switching device 2504 can optionally receive
data from the light source in order to introduce a voltage to turn
the SBGs in an ON position at the appropriate times.
Head-Up Displays
[0160] Waveguides incorporating Bragg gratings similar to those
described above can be utilized in a variety of applications
including (but not limited to) HUDs in vehicular applications such
as automotive and aerospace applications. In many embodiments, a
waveguide is utilized to direct light incident on the waveguide
from one or more projection sources toward a windshield, where the
light is reflected toward the operator of the vehicle. Windshields
are often curved. In several embodiments, the waveguides transmit
incident light to compensate for distortions introduced by the
curvature of a windshield (or other surface onto which light from
the waveguide is projected). As is discussed further below,
distortions introduced by curvature of a surface onto which light
is projected can be compensated for by selection of the K-vector
across the output grating of the waveguide and/or computationally
by modifying the manner in which an input image is projected into
the waveguide.
[0161] An HUD for vehicular applications in accordance with an
embodiment of the invention is conceptually illustrated in FIG. 26.
The HUD 2600 is located within the dashboard 2601 of a vehicle. A
projection system 2602 and a waveguide 2603 are contained within
the dashboard and light is projected from the waveguide through a
transparent aperture 2604 in the dashboard onto the windshield
2605. The light is reflected off the curved surface 2606 of the
windshield 2605 into a region that is commonly referred to as the
eyebox 2607 of the HUD. The term eyebox is generally utilized to
refer to a region in which the display is visible to the eye 2608
of a viewer. The display appears to the viewer as a virtual display
2609 on the opposite side of the windshield to the viewer. The
location of the display can be determined based upon projective
geometry 2610, 2611. Placement of the display within the field of
view of the vehicle enables the driver to view the road ahead and
projected information simultaneously.
[0162] Projection of light into an eyebox by reflection off a
curved windshield using a HUD system in accordance with an
embodiment of the invention is conceptually illustrated in FIGS.
27A and 27B.
[0163] Use of flat waveguides that incorporate Bragg gratings can
significantly reduce the volumetric requirements of a HUD compared
to conventional HUDs implemented using conventional refractive
and/or reflective optical components. Furthermore, the field of
view of a HUD that can be achieved using a waveguide can be
significantly greater despite the reduction in volumetric
requirements compared to a conventional HUD. A comparison of the
field of view and volumetric requirements of a HUD implemented
using a waveguide incorporating Bragg gratings and a conventional
HUD is shown in FIG. 28.
[0164] While various embodiments of HUDs incorporating waveguides
including Bragg gratings are described above with reference to
FIGS. 26-28, any of a variety of planar waveguides and/or HUD
system configurations can be utilized to implement a HUD for use in
a vehicle and/or any other display that projects on a planar and/or
curved surface as appropriate to the requirements of a given
application. Various waveguides that can be utilized in HUDs in
accordance with a number of embodiments of the invention are
discussed further below.
[0165] Waveguides incorporating Bragg gratings can provide
significant advantages when used in HUDs including (but not limited
to) wide field of view displays and reduced volumetric requirements
compared to HUDs implemented using conventional reflective and
refractive optical components. In many embodiments, vehicular HUDS
are implemented using one or more planar waveguides fabricated to
incorporate at least volumetric Bragg gratings that couple incident
light into the waveguide, fold the light within the waveguide and
direct light from the waveguide. As noted above, the gratings can
provide two dimensional exit pupil expansion.
[0166] A waveguide assembly including three separate waveguides for
each of a Red, Green, and Blue color channel implemented in
accordance with an embodiment of the invention is illustrated in
FIG. 29. The waveguide assembly includes a stack of three (3)
waveguides that receive light incident on the bottom surface of the
waveguide assembly. Each of a Red, Green, and Blue spectral band is
coupled into the Red, Green, and Blue waveguides respectively.
Input coupling can be achieved by a pair of input gratings that are
provided for each waveguide. The two input coupling gratings have
the same surface pitch sizes but different grating slanted angles,
which can increase the overall couple-in angular bandwidth of the
waveguide. Light coupled into a waveguide is diffracted within the
waveguide by a fold grating. In the illustrated embodiment, the
width of the fold gratings expand with increased distance from the
input grating. As is discussed further below, increasing the width
of the fold grating can address Vignetting. The fold grating also
includes a tapered diffraction efficiency (DE) profile to increase
uniformity of the display across the light box. As noted above, the
fold grating performs one dimensional pupil expansion. The
expansion of the second dimension of the pupil is achieved in the
output grating. In the illustrated embodiment, the output grating
also includes a rolled K-vector to taper the DE profile of the
grating. As is discussed further below, the K-vector across the
output grating can also correct for distortions introduced due to
the curvature of a surface (e.g. a windshield) onto which light is
projected by the waveguide. Each of the input, fold, and output
gratings are discussed in additional detail below.
Input Coupling Gratings for Vehicular Waveguide Displays
[0167] Input coupling gratings couple light from one or more
illumination sources into a waveguide. Referring again to FIG. 29,
each waveguide receives light from two input coupling gratings that
are separate from the planar material that incorporates the fold
and output gratings. The two input coupling gratings have the same
surface pitch sizes but different grating slanted angles, which can
increase the overall couple-in angular bandwidth of the waveguide.
Each of the input gratings that couple light into the waveguides
are plane gratings. In many embodiments, one or more of the input
gratings can include a rolled K-vector and/or a multiplexed
K-vector as appropriate to the requirements of a specific
application.
[0168] A perspective view of a waveguide assembly incorporating
separate input gratings for each waveguide is shown in FIG. 30. A
side view of a similar waveguide assembly is shown in FIGS. 31A-31C
showing the various layers utilized within the waveguide assembly
and their relative thicknesses. The gratings are formed in layers
of polymer using techniques similar to those described in U.S. PCT
Application Serial No. PCT/GB2012/000680, the relevant disclosure
from which is incorporated by reference herein in its entirety. In
many embodiments, the polymer layers that contain the waveguides
are separated by layers of glass or other appropriate optically
transparent material.
[0169] The input gratings for each of the waveguides can be
slightly offset within the waveguide assembly as can be appreciated
from the conceptual illustration of the placement of the input
gratings relative to the waveguides shown in FIG. 32. The inclusion
of the staggered offsets allows for better capture of the
transmitted light, which will be diffracted at different angles by
the gratings as a result of the different wavelengths of the light
being coupled into the waveguide.
[0170] While the waveguide assemblies illustrated above in FIGS.
29-32 include multiple input gratings per waveguide, waveguide
assemblies in accordance with several embodiments of the invention
utilize a single input coupling grating in a manner similar to the
configuration shown in FIG. 33A. In several embodiments, the
waveguide assembly does not include separate input gratings.
Instead, the waveguide can incorporate at least the input, fold,
and output gratings in a planar material in a manner similar to
that illustrated in FIG. 33B.
[0171] Coupling of light from a projection system into input
gratings of a waveguide assembly in accordance with an embodiment
of the invention is conceptually illustrated in FIGS. 34A and 34B.
The projector directs light toward a mirror that reflects the light
into the input gratings. In other embodiments, the projector can
directly project light into the input gratings, and/or a waveguide
can be utilized to direct light from the projection system into the
input gratings.
Fold and Output Gratings
[0172] Referring again to FIG. 29, each waveguide in the waveguide
assembly includes a fold grating designed for the specific
bandwidth of light coupled into the waveguide by the input coupling
gratings. The fold and output gratings together provide two
dimensional pupil expansion of the light coupled into the
waveguide.
[0173] The dimensions of the fold and output gratings of a
waveguide that can be utilized in a vehicular HUD in accordance
with an embodiment of the invention is illustrated in FIG. 35. In
the illustrated embodiment, the gratings support a 15.times.5
degree field of view using an output grating having an aperture
size of 380 mm.times.190 mm at a 1 meter relief from the eyebox
(reflected via a curved windshield). As is discussed further below
modification of the K-vector and/or slant angle across one or more
of the fold and/or output gratings can increase the homogeneity of
the display generated by the HUD within an eyebox region. Specific
K-vectors that can be utilized within a waveguide in accordance
with an embodiment of the invention are illustrated in FIG. 36. The
K-vector shown for the fold grating can be varied to modify
diffraction efficiency across the grating with the goal of
attaining homogeneity of the projected display across the light
box. The K-vector and/or the slant angle of the grating can be
similarly modified across the output grating to achieve desired
characteristics of the HUD system including (but not limited to)
increased homogeneity. Furthermore, the K-vector can be modified
using a correction function that accounts for distortion introduced
by reflection off a curved surface such as (but not limited to) a
windshield.
[0174] Impact of varying output grating slant angle in the manner
shown in FIG. 37A upon output power for different field angles can
be appreciated from FIG. 37B. FIG. 37B illustrates the extent to
which the energy coupled into the waveguide decreases across the
output grating. FIG. 37B also illustrates that modification of the
slant angle of the output grating can increase diffraction
efficiency across the waveguide to compensate for the decrease in
energy. As can readily be appreciated, the manner in which slant
angle can be modified across the output grating (and/or any other
gratings within a waveguide) can largely be determined based upon
the desired output characteristics of a given HUD system.
[0175] HUD systems in accordance with several embodiments of the
invention reflect light off a curved surface such as (but not
limited to a windshield). Projection of light by a waveguide
similar to the waveguide shown in FIG. 29 is conceptually
illustrated in FIGS. 38A and 38B. The manner in which projected
light can be reflected off a surface into an eyebox region in which
a viewer can see the display across a field of view is conceptually
illustrated in FIG. 39. The ability of the output grating to
diffract light across the grating into the eyebox increases the
field of view of the display. As noted above, the field of view of
the display can be increased by adding additional waveguides that
project light into eyebox region across a wider field of view. The
field of view into which light can be projected is typically
limited by the HUD form factor requirements of a given
application.
[0176] As noted above, the K-vectors and slant angles of the
fringes within an output Bragg grating can be chosen to correct for
curvature of the surface onto which the display is projected by the
output grating. A windshield correction function that is utilized
to modify the rolled K-vector prescription of an output grating in
accordance with an embodiment of the invention is illustrated in
FIGS. 40A-40C. The effect of the correction function is to cause
the output grating to modify the projected light so that light
reflected from the specific curved surface used to derive the
correction function will appear undistorted within the eyebox
region of the HUD system. As can readily be appreciated, the
specific manner in which the K-vector and/or slant angle of a
grating is modified across a waveguide to accommodate curvature of
a windshield and/or other surface upon which light is projected is
largely dependent upon the requirements of a given application.
[0177] Referring again to FIG. 29, the path length for light
projected into the eyebox from each of the three waveguides have
different path lengths and wavelengths. Accordingly, the gratings
in each of the waveguides in a waveguide assembly are separately
configured for each color channel. While specific waveguide
configurations incorporating specific grating implementations are
described above, any of a variety of Bragg grating combinations can
be utilized within waveguides including (but not limited to)
multiplexed K-vector gratings, gratings that include varying slant
angles and/or gratings that are electronically switchable as
appropriate to the requirements of a given application in
accordance with various embodiments of the invention.
Addressing Vignetting Through Fold Grating Design
[0178] Referring again to FIG. 35, the width of the fold grating
increases with distance from the input coupling grating. Increasing
the width of the fold grating can address vignetting. The term
vignetting is commonly used to refer to a reduction of an image's
brightness or saturation toward the periphery compared to the image
center. The roll that the fold grating can play with respect to the
unwanted introduction of vignetting within a display produced by a
HUD system can be readily appreciated with respect to the
simulations illustrated in FIG. 41A-41E. The region of the fold
grating closest to the input grating can introduce cropping and the
region of the fold grating furthest from the input grating can
introduce vignetting. The artifacts introduced by the fold grating
are significantly reduced in the simulation illustrated in FIG.
42A-42E. In the simulation illustrated in FIG. 46, the fold grating
is designed to increase in width with increased distance from the
input grating. The result is a significant reduction in vignetting.
The impact of utilizing a fold grating similar to the grating shown
in FIG. 42A-42E on vignetting across the eyebox of a HUD in
accordance with an embodiment of the invention can be appreciated
from the simulation shown in FIG. 43. In many embodiments, the
input grating is slightly offset from the center line of the fold
grating in a direction away from the output grating to further
improve the output performance of the HUD system.
[0179] In many embodiments, incorporation of a fold grating that
increases in width with distance from the input grating can enable
the construction of a variety of waveguide shapes. Many of the
waveguides illustrated above are largely rectangular. In many
embodiments, the form factor of the waveguide can be reduced. A
waveguide in which the output grating is contained within a region
that can be cut with a taper (indicated with dashed lines) in
accordance with an embodiment of the invention is illustrated in
FIG. 44. As can readily be appreciated, any of a variety of shapes
for waveguides can be utilized as appropriate to the requirements
of specific applications in accordance with various embodiments of
the invention.
HUD Projection Systems
[0180] A variety of illumination sources can be utilized to
implement HUDs in accordance with various embodiments of the
invention including (but not limited to) LED based and laser based
projection systems. A HUD projection system that couples Red,
Green, and Blue laser pulses into the respective Red, Green, and
Blue waveguides of a waveguide assembly in accordance with an
embodiment of the invention is conceptually illustrated in FIG.
45.
[0181] Although specific projection systems are described above
with reference to FIG. 45, any of a variety of projection systems
can be utilized to generate light that can be coupled into one or
more waveguides within a waveguide assembly of a HUD in accordance
with the requirements of specific applications in accordance with
various embodiments of the invention.
Monocular Displays
[0182] Waveguides incorporating Bragg gratings similar to those
described above can be utilized in a variety of applications, such
as but not limited to monocular displays. Monocular displays can be
implemented in a variety of different ways, including through the
use of methods, components, and structures as described above.
Additionally, it should be readily apparent that various aspects
can be modified as appropriate to the specific requirements of a
given application. For example, in many embodiments, it can be
desirable for the monocular display to have an optical element that
can facilitate the redirection of light from the light source onto
the waveguide. This can be due to the spatial and angle positioning
of the various components. In a number of embodiments, the
monocular display is designed to be compact, resulting in forced
positioning for the various components. An optical element used for
redirecting light in such embodiments can include, but are not
limited to, a prism. In several embodiments, a prism is used for
PGU coupling and TIR redirection. FIGS. 46A and 46B conceptually
illustrate the positioning of various components in a monocular
display in accordance with an embodiment of the invention. FIG. 46A
shows a side view of the monocular display along with the position
of a user's right eye, and FIG. 46B shows a top view of the same
system. As shown, the system includes a projector and a TIR prism
for manipulating the light before it enters the waveguide. FIGS.
46A and 46B also depict angle conventions with regards to elevation
and azimuth angles, shown by arrows calling out the angular
position of the waveguide with respect to a certain axis. Although
FIGS. 46A and 46B illustrates a specific monocular display system
with specific elevation and azimuth angles, it is readily apparent
that these angles can vary across various embodiments of the
invention and can depend on the specific requirements of a given
application.
[0183] In many embodiments, the monocular display includes a
waveguide implementing at least an input grating, a fold grating,
and an output grating. In some embodiments, the waveguide includes
reciprocal grating prescriptions designed for zero-dispersion.
Monocular displays can be designed to implement a variety of
different types of gratings, including those described in the
previous sections of this application. Positioning and orientation
of the gratings can depend on the specific requirements of a given
application. For example, in several embodiments, the gratings are
designed such that the monocular display can implement a reverse
reciprocal dual axis pupil expansion architecture where the
waveguide receives and outputs light from the same side. FIG. 47
conceptually illustrates a monocular display with a reverse
reciprocal arrangement in accordance with an embodiment with the
invention. As shown, the input and output of light occurs on the
same side of the waveguide. In some embodiments, the slant angles
of the input and output gratings are reversed in order to implement
reverse reciprocity. In further embodiments, the slant angles are
equivalent, but reversed. This reverse reciprocity property can be
implemented in both 1-axis and 2-axis expansion waveguides.
Although FIG. 47 illustrates a specific monocular display
implementation, reverse reciprocity can be implemented in a number
of different monocular displays. For example, monocular displays
with different azimuth rake angles can also implement reverse
reciprocity. As can readily be appreciated, the specific design of
a particular monocular display can depend on the specific
requirements of a given application.
[0184] Monocular displays can be implemented using waveguides with
properties described above, such as, and including, stacking
waveguide layers in order to implement RGB color. As such, in many
embodiments, the implemented waveguide can be made up of a stack of
waveguide layers. In further embodiments, the waveguide stack
includes two waveguide layers implementing a three-color system.
FIG. 48 conceptually illustrates such a stack. In other
embodiments, the waveguide stack includes three waveguide layers
implementing a three-color system. In several embodiments, the
waveguide includes dichroic filters for inter-waveguide color
management
[0185] In many embodiments, the monocular display includes a
compact PGU optical interface. In some embodiments, the monocular
display utilizes a projector as a PGU. In several embodiments, the
PGU can be an IIN module composed of several components. FIG. 49
conceptually illustrates a monocular display utilizing a prism and
IIN module in accordance with an embodiment of the invention. In
the illustrative embodiment, the monocular display 4900 includes an
IIN module 4901, a waveguide eyepiece 4902, and prismatic relay
optics 4903. In many embodiments, the IIN contains at least the
microdisplay panel 4901A illuminated by a light source, which is
not shown, and projection optics 4904, which typically includes
refractive optics. The IIN module can be coupled to the prismatic
relay optics by a mechanical assembly 4905 which provides
mechanical support and an optical port to admit light from the IIN
module into the prismatic relay optics.
[0186] The prismatic relay optics 4903 includes side walls 4903A,
4903B, an input surface 4903C and the output surface 4903D. The
reflective surface 4903A can be a TIR surface or can alternatively
support a reflection coating. The prismatic relay optics 4903 can
guide light from the IIN towards the waveguide eye piece along ray
paths that are refracted through the input surface (4903C),
reflected at the surface 4903A and refracted through the output
surface (4903D). Hence, the prismatic surface 4903A, 4903C, 4903D
serve to steer the input beam into the waveguide eyepiece along a
path that can be designed to be conformal with any display mounting
arrangement while delivering the beam at the correct angle for
diffraction at the input grating. When the surface 4903A is
configured as a TIR surface, the side walls provide a window for
viewing an external scene without obscuration.
[0187] Light from the prismatic relay optics can be coupled into
the waveguide via the optical interface layer 4906, which in some
embodiments provides polarization selectivity. In several
embodiments, the optical interface layer provides one of spectral
or angular selectivity. In a number of embodiments, the optical
interface layer 4906 is a diffractive optical element. In a variety
of embodiments, at least one of the transmitting or reflecting
surfaces of the prismatic relay optics has optical power. In some
embodiments, at least one of the transmitting or reflecting
surfaces of the prismatic relay optics supports at least one
coating for controlling at least one of polarization, reflection or
transmission as a function of wavelength or angle. The image light
from the IIN can be expanded in the prism to produce sufficient
beam width aperture to enable a high efficiency RKV input
aperture--thus preserving efficiency and brightness.
[0188] In some embodiments, the waveguide 4902 includes input, fold
and output gratings disposes in separate red, green and blue
diffracting layers or multiplexed into fewer layer as discussed
above or disclosed in the references. For simplicity, the gratings
in FIG. 49 are represented by the input grating 4902A, fold grating
4902B, and output grating 4902C. The light path from the projector
through the prismatic relay optics and the waveguide is represented
by the rays 4907-4909. The output image light viewed by the eye
4910 is represented by the rays 4911, 4912. The rays 4913, 4914
show the transparent of the waveguide to external light forward of
the eyepiece and the transparency of the prismatic relay optics to
external light in the periphery of the display wearer's field of
view. This enhance external field of view capability can be of
great importance in safety critical applications such as motorcycle
helmet HUDs.
[0189] Utilizing the techniques and methods as discussed above,
monocular displays can be implemented in a wide variety of
applications using various designs. FIG. 50 conceptually
illustrates one implementation of a monocular display. FIG. 50
shows a 3D illustration of a near display having an IIN and
waveguide component. The display 5000 includes an IIN 5001,
waveguide 5002 containing in a single layer an input grating 5003,
a fold grating 5004, and an output 5005. The waveguide path from
entrance pupil 5006 through the input grating, fold grating, and
output grating and up to the eye box 5007 is represented by the
rays 5008-5011. FIG. 51 conceptually illustrates the ray
propagation path of a monocular display in accordance with an
embodiment of the invention. In the illustrative embodiment, the
ray propagation path from the projector to the eyebox is shown.
Although specific monocular display designs are shown in FIGS. 50
and 51, any of a number of designs can be used as appropriate to
the specific requirements of a given application.
Near-Eye Head-Up Displays
[0190] Waveguides incorporating Bragg gratings similar to those
described above can be utilized in a variety of applications
including (but not limited to) HUDs in wearable near-eye display
applications such as eyeglasses, monocles, and visors. In many
embodiments, a waveguide is utilized to direct light incident on
the waveguide from one or more projection sources toward one or
more lenses, where the light is reflected toward the wearer of the
lens. In such embodiments, an important figure of merit is
out-couple efficiency of the light in the eyebox. In several
embodiments, the waveguides are configured to transmit incident
light to maximize out-coupling of light onto the lens and to
improve uniformity across the entire field of view (FOV) of the
wearable device (or other surface onto which light from the
waveguide is projected). As is discussed further below, out-couple
efficiency can be maximized by selection of the features of the
K-vectors across the output grating of the waveguide and/or
implementing polarization recycling. Similarly, the uniformity of
illumination across the FOV may be maximized by optimizing RKV
slant angle and modulation.
[0191] An HUD in accordance with various embodiments of the
invention can be implemented to be located within a near-eye
display device, such as glasses or monocle. A projection system and
a waveguide can be contained within the wearable device and light
can be projected from the waveguide onto the lens of the near-eye
display. The light can be reflected off the surface of the near-eye
display device into a region that is commonly referred to as the
eyebox of the HUD. The term eyebox is generally utilized to refer
to a region in which the display is visible to the eye of a viewer.
The display appears to the viewer as a virtual display on the
opposite side of the lens of the near-eye display device to the
viewer. The location of the display can be determined based upon
projective geometry. Placement of the display within the field of
view of the near-eye display device enables the wearer to view the
surrounding environment and projected information
simultaneously.
[0192] Use of flat waveguides that incorporate Bragg gratings can
significantly reduce the volumetric requirements of a HUD compared
to conventional HUDs implemented using conventional optical
components. Furthermore, the field of view of a HUD that can be
achieved using a waveguide can be significantly greater despite the
reduction in volumetric requirements compared to a conventional
HUD.
Near-Eye HUD Waveguides
[0193] Waveguides incorporating Bragg gratings can provide
significant advantages when used in HUDs including (but not limited
to) wide field of view displays and reduced volumetric requirements
compared to HUDs implemented using conventional reflective and
refractive optical components. In many embodiments, near-eye
wearable HUDS are implemented using one or more planar waveguides
fabricated to incorporate at least volume Bragg gratings that
couple incident light into the waveguide, fold the light within the
waveguide and direct light from the waveguide. As noted above, the
gratings can provide two dimensional exit pupil expansion.
[0194] A waveguide assembly including three types of gratings, an
input, fold and output, implemented in accordance with an
embodiment of the invention is illustrated in FIG. 52. The
waveguide assembly may be monochromatic, or may include a stack of
waveguides that receive light incident on the bottom surface of the
waveguide assembly such that each of a Red, Green, and Blue
spectral band is coupled into the Red, Green, and Blue waveguides
respectively, as shown schematically in FIG. 52. As shown in FIG.
52, input coupling is achieved by one or more input gratings. The
one or more input coupling gratings may be of a single or
multilayer design, and the multiple layers may be configured to
bifurcate the input illumination (this can be accomplished, for
example, by maintaining the surface pitch sizes but implementing
different grating slanted angles). Such input grating variation can
increase the overall couple-in angular bandwidth of the waveguide.
Light coupled into a waveguide is diffracted within the waveguide
by a fold grating. As noted above, the fold grating may be
configured to perform one dimensional pupil expansion. The
expansion of the second dimension of the pupil may be achieved in
the output grating. In the illustrated embodiments, the gratings
may also include a rolled K-vector (RKV) to taper the DE profile of
the grating. As is discussed further below, rolling and/or varying
the slant of the K-vector across the fold grating can also be
implemented improve diffraction efficiency and/or field-of-view
uniformity. Each of the input, fold, and output gratings are
discussed in additional detail below.
Input Coupling Gratings for Near-Eye Applications
[0195] Input coupling gratings couple light from one or more
illumination sources into a waveguide. Referring again to FIG. 52,
the input coupling gratings may be of a single or multilayer
design, as will be described in greater detail below. In some such
embodiments, the different layers of the input gratings may be
configured to bifurcate the light (either or both in a horizontal
or vertical plane) to allow for the coupling of different
polarizations of light, which can increase the overall couple-in
angular bandwidth and efficiency of the waveguide. Embodiments of
such bifurcated input gratings are shown in FIGS. 53A and 53B, and
are discussed in greater detail below. Each of the input gratings
that couple light into the waveguides are plane gratings. In many
embodiments, as shown in FIG. 54, one or more of the gratings,
including the input grating, can include a rolled K-vector and/or a
multiplexed K-vector as appropriate to the requirements of a
specific application.
[0196] Regardless of the specific input grating design the gratings
may be formed in layers of polymer using techniques similar to
those described in PCT Application Serial No. PCT/GB2012/000680,
the relevant disclosure from which is incorporated by reference
herein in its entirety. In many embodiments, the polymer layers
that contain the waveguides are separated by layers of glass.
[0197] Coupling of light from a projection system into input
gratings of a waveguide assembly can be implemented in many
different ways. The projector can direct light toward a mirror or
prism that reflects the light into the input gratings. In other
embodiments, the projector can directly project light into the
input gratings, and/or a waveguide can be utilized to direct light
from the projection system into the input gratings.
Fold and Output Gratings for Near-Eye Applications
[0198] Referring again to FIG. 52, each waveguide in the waveguide
assembly includes a fold grating designed for the specific
bandwidth of light coupled into the waveguide by the input coupling
gratings. The fold and output gratings together provide two
dimensional pupil expansion of the light coupled into the
waveguide.
[0199] Gratings and exemplary dimensions thereof, according to
embodiments capable of supporting 25 degree and 50 degree field of
view using an output grating having an aperture size of 25
mm.times.25 mm at a near-eye relief from the eyebox (reflected via
a transparent lens element) are shown in FIG. 55A. As is discussed
further below modification of the K-vector and/or slant angle
across one or more of the fold and/or output gratings can increase
the homogeneity of the display generated by the HUD within an
eyebox region. Specific K-vectors that can be utilized within a
waveguide in accordance with an embodiment of the invention are
illustrated in FIGS. 55B-55D. A conceptual drawing showing
effective (e.g., light with will hit the eyebox) and ineffective
(e.g., light which will be diffracted by the fold) diffraction
within a waveguide system is shown in FIGS. 56A and 56B. The
K-vector shown for the fold grating can be varied to modify
diffraction efficiency across the grating with the goal of
attaining homogeneity of the projected display across the light
box. The K-vector and/or the slant angle of the grating can be
similarly modified across the output grating to achieve desired
characteristics of the HUD system including (but not limited to)
increased homogeneity. Furthermore, the K-vector can be modified
using a correction function that accounts for distortion introduced
by reflection off a curved surface such as (but not limited to) a
windshield.
[0200] HUD systems in accordance with several embodiments of the
invention reflect light off a curved surface such as (but not
limited to a wearable lens). Projection of light by a waveguide is
conceptually illustrated in FIG. 52. The manner in which projected
light can be reflected off a surface into an eyebox region in which
a viewer can see the display across a field of view is conceptually
illustrated in FIGS. 57A-57C. The ability of the output grating to
diffract light across the grating into the eyebox increases the
field of view of the display. However, large fields of view pose
challenges to the formation of the exit pupil at the eyebox. As
shown in FIG. 57A, in the vertical field of view, the rays coming
from the top of the waveguide to the eyebox need to propagate
across the output grating resulting in losses. Similarly, as shown
in FIGS. 57B-57C in the horizontal field of view, the rays coming
from the right of the waveguide eyebox need to propagate across the
fold grating which also results in losses. As noted above, the
field of view of the display can be increased by adding additional
waveguides that project light into eyebox region across a wider
field of view. The field of view in to which light can be projected
is typically limited by the HUD form factor requirements of a given
application.
[0201] As noted above, the K-vectors and slant angles of the
fringes within an output Bragg grating can also be chosen to
correct for curvature of the surface onto which the display is
projected by the output grating. Rolled K-vector prescriptions for
all three gratings in accordance with an embodiment of the
invention is illustrated in FIG. 58. The effect of the correction
is to cause the input grating to modify the coupling of the light
to improve efficiency, to modify the fold RKV for horizontal pupil
formation, and to modify the output RKV for vertical pupil
formation. As can readily be appreciated, the specific manner in
which the K-vector and/or slant angle of a grating is modified
across a waveguide to improve diffraction efficiency is largely
dependent upon the requirements of a given application.
[0202] Referring again to FIG. 52, the path length for light
projected into the eyebox from each of the three waveguides have
different path lengths and wavelengths. Accordingly, the gratings
in each of the waveguides in a waveguide assembly are separately
configured for each color channel. While specific waveguide
configurations incorporating specific grating implementations are
described above, any of a variety of Bragg grating combinations can
be utilized within waveguides including (but not limited to)
multiplexed K-vector gratings, gratings that include varying slant
angles and/or gratings that are electronically switchable as
appropriate to the requirements of a given application in
accordance with various embodiments of the invention. Moreover,
although the figure shows a number of separate fold grating
locations, it will be understood that these could be of a
continuous nature.
[0203] Referring again to FIGS. 59A-59E, the slant angle of the
fold grating may be varied with distance from the input coupling
grating to address the vertical FOV. The roll that the fold grating
can play with respect to improving the FOV and reducing diffraction
losses and vignetting can be readily appreciated with respect to
the simulations illustrated in FIG. 60. The diffraction losses
introduced by the fold grating (as shown in FIGS. 57A-57C) are
significantly reduced in the simulation illustrated in FIG. 60. The
impact of utilizing a fold grating similar to the grating on
diffraction loss and uniformity of FOV across the eyebox of a HUD
in accordance with an embodiment of the invention can be
appreciated from the simulation shown in FIG. 60.
[0204] As shown in FIGS. 59A-59E the vertical and horizontal fields
of the fold grating can be bifurcated (as illustrated in FIGS. 61A
and 61B) such that the positive and negative fields of the coupled
light travel along different paths in the fold grating. Using such
a system, it is possible to narrow the fold grating such that the
overlap of incoming light can be reduced and efficiency increased.
Although specific bifurcation arrangements are shown, it should be
understood that any suitable arrangements for bifurcating and
narrowing the fold grating may be implemented in accordance with
embodiments.
Polarization Effects
[0205] Depending on nature of the grating, light may be p or s
polarized, and the nature of that polarization can have an effect
on the efficiency of overall coupling efficiency, and therefore
overall efficiency of the waveguide embodiments, as shown in FIG.
62. For example, due to the birefringent nature of the RMLM
materials used to form waveguides in accordance with embodiments,
interactions with the gratings will gradually rotate the
polarization of the light into a more circular state, however, each
interaction will have its p-component extracted.
[0206] Once again it is to be noted that the out-couple efficiency
of the light that finally hits the eyebox is the important metric
to determine efficiency of the waveguide system. This value can be
characterized by a percentage of coupled light. Turning to FIGS.
63A-63F, the effect of polarization on the efficiency of the
gratings is considered. In the idealized case (FIG. 63B) where the
polarization of light inside the waveguide is always in p-pol
direction according to the grating vector the overall efficiency is
determined by the diffraction efficiency of the grating (this can
be considered the upper limit). In the realistic case (FIG. 63C)
where there is random polarization of light within the waveguide,
the overall out-couple efficiency drops significantly due to the
disability of the grating to diffract s-pol light. Using a
birefringent material (FIG. 63D) (where the optical axis is
perpendicular to the fringes) the optical axis of the fold grating
layer may have a 60.degree. clocking angle compared to light in the
propagation direction hence it will act as a thin waveplate and
change the polarization of the transmitted light. As a result, some
of the s-pol light is rotated to a p-pol state and will get
diffracted out resulting in an efficiency enhancement. Note that
this effect will not occur in an O/P grating because the optical
axis is the same as the light propagation direction. To address
this deficiency in the O/P and optimize the gating a QWP film may
be applied (FIG. 63E) to recycle the s-pol light thus boosting
efficiency. Although specific birefringence values are shown with
relation to FIGS. 63A-63D, further optimization of the
birefringence (e.g. by biasing the preferred birefringent axis
towards the positive field angles), may allow one side of the field
of view to be traded off to balance the other.
[0207] In addition to these birefringence effects, coatings and
films may be implemented in embodiments of the invention to
increase the capture of light that might be rejected because of the
polarization selectivity of the waveguide. For example, in some
embodiments a QWP film may be implemented to suppress odd
interactions. In other embodiments, a HWP film may be implemented
to collect s-polarized light. Such implementations may be referred
to as polarization recycling. A conceptual illustration of an
implementation of such a coating is provided in FIG. 64.
Waveguide Architectures to Enhance Efficiency
[0208] Embodiments of near-eye waveguide devices may incorporate
one or more of the input, output and fold grating structures
discussed above. Embodiments may comprise any number of input and
output layers, these layers may be bifurcated, and these layers may
incorporate other optical features such as QWP or HWP films, MUX
gratings, and combinations thereof. Exemplary embodiments of
various combinations may be found in FIGS. 46A-46N. Although
specific architectures and combinations are shown, it will be
understood that other variations may be implemented in accordance
with the principals set forth herein.
[0209] FIG. 65A provides a conceptual illustration of a 1-axis
expansion waveguide architecture implementing a single layer input
and single layer output with QWP films disposed in association with
such input and output gratings to suppress odd interactions (input)
and allow s-polarization extraction (output).
[0210] FIG. 65B provides a conceptual illustration of a 1-axis
expansion waveguide architecture implementing a single layer input
and single layer output without the implementation of polarization
recycling films.
[0211] FIG. 65C provides a conceptual illustration of a 1-axis
expansion waveguide architecture implementing a dual layer input
and single layer output with an HWP film disposed in association
with the input grating to capture s-polarization in the second
grating layer, and QWP film in association with the output grating
to allow s-polarization extraction.
[0212] FIG. 65D provides a conceptual illustration of a 2-axis
expansion waveguide architecture implementing a dual layer input
and single layer output with an HWP film disposed in association
with the input grating to capture s-polarization in the second
grating layer, and QWP film in association with the output grating
to allow s-polarization extraction. This embodiment also implements
a fold grating to capture beams from the gratings and rotate the
input polarization to p-polarization for diffraction.
[0213] FIG. 65E provides a conceptual illustration of a 2-axis
expansion waveguide architecture implementing a single layer MUX
input and single layer MUX output at 60.degree. with QWP films
disposed in association with the input (to suppress odd
interactions) and output gratings (to rotate the polarization from
the fold). This embodiment also implements two fold gratings to
capture beams from the gratings and rotate the input polarization
to p-polarization for diffraction. In this embodiment loss occurs
from inefficient capture from the MUX input grating at
60.degree..
[0214] FIG. 65F provides a conceptual illustration of a 2-axis
expansion waveguide architecture implementing a single layer MUX
input and single layer MUX output both at 90.degree. with QWP films
disposed in association with the input (to suppress odd
interactions) and output gratings (to rotate the polarization from
the fold). This embodiment also implements two fold gratings to
capture beams from the gratings and rotate the input polarization
to p-polarization for diffraction.
[0215] FIG. 65G provides a conceptual illustration of a 2-axis
expansion waveguide architecture implementing a single layer MUX
input and dual layer MUX output both at 90.degree. with QWP films
disposed in association with the input (to suppress odd
interactions) and output gratings (to rotate the polarization from
the fold). This embodiment also implements two fold gratings to
capture beams from the gratings and rotate the input polarization
to p-polarization for diffraction. The dual layer output grating
doubles the number of interactions, improving polarization
efficiency.
[0216] FIG. 65H provides a conceptual illustration of a 2-axis
expansion waveguide architecture implementing a bifurcated dual
layer input where each layer is bifurcated to respond to half the
horizontal FOV, and a dual layer MUX output at 90.degree.. A HWP
film is associated with the input grating and is required to couple
the light of the same field angles to the same fold grating layers.
This embodiment also implements two fold gratings to capture beams
from the gratings and rotate the input polarization to
p-polarization for diffraction. A QWP film disposed in association
with one of the fold gratings to extract the light from both
polarizations. The dual layer output grating doubles the number of
interactions, improving polarization efficiency.
[0217] FIG. 65I provides a conceptual illustration of a 2-axis
expansion waveguide architecture implementing a dual layer input
(at 60.degree.) and output gratings. This embodiment also
implements two fold gratings to capture beams from the gratings and
rotate the input polarization to p-polarization for diffraction. A
QWP film is disposed in association with the output grating to
rotate the polarization of the fold.
[0218] FIG. 65J provides a conceptual illustration of a 2-axis
expansion waveguide architecture implementing a dual layer input
(at 90.degree.) and output gratings. This embodiment also
implements two fold gratings to capture beams from the gratings and
rotate the input polarization to p-polarization for diffraction. A
QWP film is disposed in association with the output grating to
rotate the polarization of the fold.
[0219] FIG. 65K provides a conceptual illustration of a 2-axis
expansion waveguide architecture implementing a bifurcated single
layer input (at 60.degree.) and an output MUX grating. This
embodiment also implements two fold gratings on a single layer to
capture half the FOV. QWP films are disposed in association with
the input and output gratings to suppress odd interactions and
rotate the polarization of the fold, respectively.
[0220] FIG. 65L provides a conceptual illustration of a 2-axis
expansion waveguide architecture implementing a single layer input
and output gratings. This embodiment also implements one fold
grating to capture beams from both gratings. A QWP film is disposed
in association with the output grating to rotate the polarization
of the fold.
[0221] FIG. 65M provides a conceptual illustration of a 2-axis
expansion waveguide architecture implementing a bifurcated single
layer input (at 90.degree.) and an output MUX grating. This
embodiment also implements two fold gratings on a single layer to
capture half the FOV. QWP films are disposed in association with
the input and output gratings to suppress odd interactions and
rotate the polarization of the fold, respectively.
[0222] FIG. 65N provides a conceptual illustration of a 2-axis
expansion waveguide architecture implementing a bifurcated dual
layer input at (90.degree.) where each layer is bifurcated to
respond to half the horizontal FOV, and a dual layer MUX output. A
HWP film is associated with the input grating and is required to
couple the light of the same field angles to the same fold grating
layers. This embodiment also implements two fold gratings in each
layer to capture beams from the gratings and rotate the input
polarization to p-polarization for diffraction. A QWP film disposed
in association with one of the fold gratings to extract the light
from both polarizations. A HWP is also disposed in association with
the input grating to couple light of the same field angles to the
same fold grating layers. The dual layer output grating doubles the
number of interactions, improving polarization efficiency.
[0223] One exemplary embodiment of an implementation of an
architecture according to the above is illustrated in FIGS.
66A-66C. As shown, in the embodiment the input grating (FIG. 66A)
consists of one RKV grating on each surface of the substrate. Each
grating is designed to capture the entire field of view (i.e., not
bifurcated). The fold grating (FIG. 66B) consists of a single RKV
grating where the RKV slant angle varies going from left to right
of grating and the RKV slant angle is constant going from top to
bottom of grating. Finally, the output grating (FIG. 66C) consists
of one plane grating on each surface of the substrate. Each grating
may be provided with a different prescription, and is designed to
respond to a certain range field angles.
Methods of Implementing Multiplex Gratings
[0224] Embodiments are also directed to methods of manufacturing
multiplex (MUX) gratings. In many embodiments a multiplex grating
comprises multiple prescriptions disposed in the same grating. As
shown in FIGS. 67A and 67B in one exemplary embodiment two master
plates (67A & 67B) are provided. As shown in FIG. 67C, the
mastering plate RMLCM material and waveguide substrate are disposed
in relation to each other and a rotatory aperture system (FIG. 67D)
is disposed between this mastering rig and the illumination source.
During operation (as shown in FIG. 67D) the chopper wheel allows
only on pair/set of beams to be incident at one instant in time.
This prevents simultaneous exposure of the mastering pairs, which
would cause unwanted diffraction grating vectors to be imprinted.
It will be understood that the specific mastering patterns and
chopper apertures shown are merely exemplary, any suitable
arrangement could be provided to allow for the fabrication of
desired MUX gratings.
Doctrine of Equivalents
[0225] Although specific systems and methods are discussed above,
many different embodiments can be implemented in accordance with
the invention. It is therefore to be understood that the present
invention can 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. Although specific embodiments have
been described in detail in this disclosure, many modifications are
possible (for example, variations in sizes, dimensions, structures,
shapes and proportions of the various elements, values of
parameters, mounting arrangements, use of materials, colors,
orientations, etc.). For example, the position of elements may be
reversed or otherwise varied and the nature or number of discrete
elements or positions may be altered or varied. Accordingly, all
such modifications are intended to be included within the scope of
the present disclosure. The order or sequence of any process or
method steps may be varied or re-sequenced according to alternative
embodiments. Other substitutions, modifications, changes, and
omissions may be made in the design, operating conditions and
arrangement of the exemplary embodiments without departing from the
scope of the present disclosure.
* * * * *