U.S. patent application number 17/478674 was filed with the patent office on 2022-05-05 for phase structure on surface-relief grating-based waveguide display.
The applicant listed for this patent is Facebook Technologies, LLC. Invention is credited to Ningfeng HUANG, Wai Sze Tiffany LAM, Hee Yoon LEE.
Application Number | 20220137410 17/478674 |
Document ID | / |
Family ID | |
Filed Date | 2022-05-05 |
United States Patent
Application |
20220137410 |
Kind Code |
A1 |
LAM; Wai Sze Tiffany ; et
al. |
May 5, 2022 |
PHASE STRUCTURE ON SURFACE-RELIEF GRATING-BASED WAVEGUIDE
DISPLAY
Abstract
A waveguide display includes a substrate transparent to visible
light, a first grating on the substrate and configured to couple
display light into or out of the substrate, and a phase structure
on the substrate and configured to change a polarization state of
the display light after or before the display light reaches the
first grating. The first grating is characterized by a
polarization-dependent diffraction efficiency. The first grating
includes, for example, a surface-relief grating or a volume Bragg
grating.
Inventors: |
LAM; Wai Sze Tiffany;
(Bothell, WA) ; LEE; Hee Yoon; (Kirkland, WA)
; HUANG; Ningfeng; (San Jose, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Facebook Technologies, LLC |
Menlo Park |
CA |
US |
|
|
Appl. No.: |
17/478674 |
Filed: |
September 17, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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63110241 |
Nov 5, 2020 |
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International
Class: |
G02B 27/01 20060101
G02B027/01; G02B 27/09 20060101 G02B027/09; G02B 27/00 20060101
G02B027/00; G02B 5/18 20060101 G02B005/18; G02B 6/34 20060101
G02B006/34 |
Claims
1. A waveguide display comprising: a substrate transparent to
visible light; a first surface-relief grating on the substrate and
configured to couple display light into or out of the substrate,
wherein the first surface-relief grating is characterized by a
polarization-dependent diffraction efficiency; and a phase
structure on the substrate and configured to change a polarization
state of the display light after or before the display light
reaches the first surface-relief grating.
2. The waveguide display of claim 1, wherein the phase structure
comprises a waveplate.
3. The waveguide display of claim 2, wherein the waveplate is
characterized by a waveplate thickness between zero and one
wavelength.
4. The waveguide display of claim 1, wherein the phase structure
comprises a layer of a birefringent material.
5. The waveguide display of claim 1, wherein the phase structure
comprises a subwavelength structure and an overcoat layer.
6. The waveguide display of claim 5, wherein the subwavelength
structure is etched in the substrate.
7. The waveguide display of claim 5, wherein the subwavelength
structure is etched in a material layer formed on the
substrate.
8. The waveguide display of claim 5, wherein a difference between a
refractive index of the substrate and an effective refractive index
of the phase structure including the subwavelength structure and
the overcoat layer is less than 0.35.
9. The waveguide display of claim 1, further comprising a second
surface-relief grating on the phase structure, wherein the phase
structure is between the substrate and the second surface-relief
grating.
10. The waveguide display of claim 9, wherein a waveplate thickness
of the phase structure is a quarter wavelength.
11. The waveguide display of claim 9, wherein the phase structure
is arranged such that an angle between a fast axis of the phase
structure and a grating vector of the first surface-relief grating
is 45.degree..
12. The waveguide display of claim 1, further comprising a second
surface-relief grating between the substrate and the phase
structure.
13. The waveguide display of claim 1, wherein: the first
surface-relief grating is on a first surface of the substrate and
is configured to couple the display light into the substrate; and
the phase structure is on a second surface of the substrate
opposing the first surface and is configured to change the
polarization state of the display light coupled into the
substrate.
14. The waveguide display of claim 1, wherein the phase structure
is in selected regions of the substrate.
15. The waveguide display of claim 1, wherein the phase structure
is characterized by a spatially varying phase retardation across
different regions of the phase structure.
16. The waveguide display of claim 1, wherein the phase structure
is configured to convert s-polarized light to p-polarized light,
convert p-polarized light to s-polarized light, convert linearly
polarized light to circularly polarized light, or convert
circularly polarized light to linearly polarized light.
17. A waveguide display comprising: a substrate transparent to
visible light; a first surface-relief grating on a first surface of
the substrate and configured to couple display light into the
substrate such that the display light propagates within the
substrate through total internal reflection, wherein the first
surface-relief grating is characterized by a polarization-dependent
diffraction efficiency; and a phase structure on a second surface
of the substrate opposing the first surface, the phase structure
configured to change a polarization state of the display light
coupled into the substrate.
18. The waveguide display of claim 17, wherein the phase structure
includes: a layer of a birefringent material; or a subwavelength
structure formed in an isotropic material or the birefringent
material.
19. The waveguide display of claim 17, wherein: the phase structure
includes a subwavelength structure and an overcoat layer; and a
difference between a refractive index of the substrate and an
effective refractive index of the phase structure including the
subwavelength structure and the overcoat layer is less than
0.35.
20. The waveguide display of claim 17, further comprising a second
surface-relief grating on the phase structure, wherein the phase
structure is between the substrate and the second surface-relief
grating or the second surface-relief grating is between the
substrate and the phase structure.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of and priority to U.S.
Provisional Application No. 63/110,241, filed Nov. 5, 2020,
entitled "Phase Structure on Waveguide Display," which is herein
incorporated by reference in its entirety for all purposes. The
following two U.S. patent applications (including this one) are
being filed concurrently, and the entire disclosure of the other
application is incorporated by reference into this application for
all purposes: [0002] U.S. patent application Ser. No. 17/______
(Attorney Docket No.: FACTP139AUS/P201132US01), filed Sep. 17,
2021, entitled "Phase Structure on Surface-Relief Grating-Based
Waveguide Display"; and [0003] U.S. patent application Ser. No.
17/______ (Attorney Docket No.: FACTP139BUS/P201132US02), filed
Sep. 17, 2021, entitled "Phase Structure on Volume Bragg
Grating-Based Waveguide Display."
BACKGROUND
[0004] An artificial reality system, such as a head-mounted display
(HMD) or heads-up display (HUD) system, generally includes a
near-eye display (e.g., in the form of a headset or a pair of
glasses) configured to present content to a user via an electronic
or optic display within, for example, about 10-20 mm in front of
the user's eyes. The near-eye display may display virtual objects
or combine images of real objects with virtual objects, as in
virtual reality (VR), augmented reality (AR), or mixed reality (MR)
applications. For example, in an AR system, a user may view both
images of virtual objects (e.g., computer-generated images (CGIs))
and the surrounding environment by, for example, seeing through
transparent display glasses or lenses (often referred to as optical
see-through).
[0005] One example of an optical see-through AR system may use a
waveguide-based optical display, where light of projected images
may be coupled into a waveguide (e.g., a transparent substrate),
propagate within the waveguide, and be coupled out of the waveguide
at different locations. In some implementations, the light of the
projected images may be coupled into or out of the waveguide using
diffractive optical elements, such as volume holographic gratings
and/or surface-relief gratings. Light from the surrounding
environment may pass through a see-through region of the waveguide
and reach the user's eyes as well.
SUMMARY
[0006] This disclosure relates generally to grating-based waveguide
displays for near-eye display. More specifically, disclosed herein
are techniques for improving the coupling efficiencies of
grating-based near-eye display systems. Various inventive
embodiments are described herein, including devices, systems,
methods, and the like.
[0007] According to some embodiments, a waveguide display may
include a substrate transparent to visible light, a first
surface-relief grating on the substrate and configured to couple
display light into or out of the substrate, and a phase structure
on the substrate and configured to change a polarization state of
the display light after or before the display light reaches the
first surface-relief grating. The first surface-relief grating is
characterized by a polarization-dependent diffraction
efficiency.
[0008] In some embodiments, the phase structure may include a
waveplate, where the waveplate may be characterized by a waveplate
thickness between zero and one wavelength. In some embodiments, the
phase structure may include a layer of a birefringent material, or
a subwavelength structure and an overcoat layer. The subwavelength
structure may be etched in the substrate or may be etched in a
material layer formed on the substrate. A difference between a
refractive index of the substrate and an effective refractive index
of the phase structure including the subwavelength structure and
the overcoat layer is less than about 0.35.
[0009] In some embodiments, the waveguide display may also include
a second surface-relief grating on the phase structure, where the
phase structure is between the substrate and the second
surface-relief grating. A waveplate thickness of the phase
structure may be a quarter wavelength. The phase structure may be
arranged such that an angle between a fast axis of the phase
structure and a grating vector of the first surface-relief grating
is 45.degree..
[0010] In some embodiments, the waveguide display may also include
a second surface-relief grating between the substrate and the phase
structure. In some embodiments, the first surface-relief grating
may be on a first surface of the substrate and may be configured to
couple the display light into the substrate, and the phase
structure may be on a second surface of the substrate opposing the
first surface and may be configured to change the polarization
state of the display light coupled into the substrate.
[0011] In some embodiments, the phase structure may be in selected
regions of the substrate. The phase structure may be characterized
by a spatially varying phase retardation across different regions
of the phase structure. The phase structure may be configured to
convert s-polarized light to p-polarized light, convert p-polarized
light to s-polarized light, convert linearly polarized light to
circularly polarized light, or convert circularly polarized light
to linearly polarized light.
[0012] According to some embodiments, a waveguide display may
include a substrate transparent to visible light, a first
surface-relief grating on a first surface of the substrate and
configured to couple display light into the substrate such that the
display light propagates within the substrate through total
internal reflection, where the first surface-relief grating is
characterized by a polarization-dependent diffraction efficiency.
The waveguide display may also include a phase structure on a
second surface of the substrate opposing the first surface, where
the phase structure may be configured to change a polarization
state of the display light coupled into the substrate.
[0013] In some embodiments, the phase structure may include a layer
of a birefringent material, or a subwavelength structure formed in
an isotropic material or the birefringent material. In some
embodiments, the phase structure may include a subwavelength
structure and an overcoat layer, and a difference between a
refractive index of the substrate and an effective refractive index
of the phase structure including the subwavelength structure and
the overcoat layer may be less than 0.35, such as less than about
0.2, less than about 0.1, or less than about 0.05. The waveguide
display may also include a second surface-relief grating on the
phase structure, where the phase structure may be between the
substrate and the second surface-relief grating or the second
surface-relief grating may be between the substrate and the phase
structure.
[0014] According to some embodiments, a waveguide display may
include a first substrate transparent to visible light, a second
substrate transparent to the visible light, a holographic material
layer between the first substrate and the second substrate and
including a volume Bragg grating characterized by a
polarization-dependent diffraction efficiency, and a phase
structure on the first substrate or the second substrate and
configured to change a polarization state of display light incident
on the phase structure after or before the display light is
diffracted by the volume Bragg grating.
[0015] In some embodiments of the waveguide display, the phase
structure may include a waveplate. The waveplate may be
characterized by a waveplate thickness between zero and one
wavelength. In some embodiments, the phase structure may include a
layer of a birefringent material, or a subwavelength structure and
an overcoat layer. The subwavelength structure may be etched in the
substrate or may be etched in a material layer formed on the
substrate. A difference between a refractive index of the substrate
and an effective refractive index of the phase structure including
the subwavelength structure and the overcoat layer may be less than
about 0.35.
[0016] In some embodiments, the phase structure may be in selected
regions of the first substrate or the second substrate. In some
embodiments, the phase structure may be characterized by a
spatially varying phase retardation across different regions of the
phase structure.
[0017] In some embodiments, the phase structure may be on the
second substrate, and the waveguide display may further include a
second phase structure on the first substrate. The phase structure
may be in a region of the waveguide display where the input grating
coupler is located. The phase structure may be in a region of the
waveguide display where the input grating coupler and the output
grating coupler are located. The input grating coupler may include
one or more volume Bragg gratings, and the output grating coupler
may include at least two volume Bragg gratings configured to expand
an eyebox of the waveguide display in two directions.
[0018] According to some embodiments, a waveguide display may
include a first substrate, a second substrate, an input grating
coupler between the first substrate and the second substrate and
configured to couple display light into the first substrate or the
second substrate, an output grating coupler between the first
substrate and the second substrate and configured to at least
partially couple the display light out of the waveguide display
towards an eyebox of the waveguide display, and a phase structure
on the first substrate or the second substrate and configured to
change a polarization state of the display light coupled into the
first substrate or the second substrate before the display light
coupled into the first substrate or the second substrate reaches
the output grating coupler or reaches the input grating coupler
again.
[0019] In some embodiments of the waveguide display, the phase
structure may include a layer of a birefringent material, or a
subwavelength structure formed in an isotropic material or the
birefringent material. The phase structure may include a
subwavelength structure and an overcoat layer, and a difference
between a refractive index of the first or second substrate and an
effective refractive index of the phase structure may be less than
about 0.35. The phase structure may include a subwavelength
structure etched in the first substrate, in the second substrate,
or in a material layer formed on the first substrate or the second
substrate. The phase structure may be on the second substrate, and
the waveguide display may further include a second phase structure
on the first substrate.
[0020] This summary is neither intended to identify key or
essential features of the claimed subject matter, nor is it
intended to be used in isolation to determine the scope of the
claimed subject matter. The subject matter should be understood by
reference to appropriate portions of the entire specification of
this disclosure, any or all drawings, and each claim. The
foregoing, together with other features and examples, will be
described in more detail below in the following specification,
claims, and accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The patent or application file contains at least one drawing
executed in color. Copies of this patent or patent application
publication with color drawing(s) will be provided by the Office
upon request and payment of the necessary fee.
[0022] Illustrative embodiments are described in detail below with
reference to the following figures.
[0023] FIG. 1 is a simplified block diagram of an example of an
artificial reality system environment including a near-eye display
system according to certain embodiments.
[0024] FIG. 2 is a perspective view of an example of a near-eye
display system in the form of a head-mounted display (HMD) device
for implementing some of the examples disclosed herein.
[0025] FIG. 3 is a perspective view of an example of a near-eye
display system in the form of a pair of glasses for implementing
some of the examples disclosed herein.
[0026] FIG. 4 is a simplified diagram illustrating an example of an
optical system in a near-eye display system.
[0027] FIG. 5 illustrates an example of an optical see-through
augmented reality system including a waveguide display for exit
pupil expansion according to certain embodiments.
[0028] FIG. 6 illustrates an example of an optical see-through
augmented reality system including a waveguide display for exit
pupil expansion according to certain embodiments.
[0029] FIG. 7A illustrates the spectral bandwidth of an example of
a reflective volume Bragg grating (VBG) and the spectral bandwidth
of an example of a transmissive surface-relief grating (SRG).
[0030] FIG. 7B illustrates the angular bandwidth of an example of a
reflective VBG and the angular bandwidth of an example of a
transmissive SRG.
[0031] FIG. 8A illustrates an example of an optical see-through
augmented reality system including a waveguide display and gratings
for exit pupil expansion according to certain embodiments.
[0032] FIG. 8B illustrates an example of an eyebox including
two-dimensional replicated exit pupils according to certain
embodiments.
[0033] FIG. 9 illustrates an example of a waveguide display with
grating couplers for exit pupil expansion according to certain
embodiments.
[0034] FIG. 10 illustrates another example of a VBG-based waveguide
display according to certain embodiments.
[0035] FIG. 11A illustrates an example of a grating coupler for
coupling display light into a waveguide display.
[0036] FIG. 11B illustrates examples of undesired light diffraction
by an example of a grating coupler in a waveguide display.
[0037] FIG. 12A illustrates the diffraction of s-polarized light by
an example of a grating coupler in a waveguide display.
[0038] FIG. 12B illustrates the diffraction of p-polarized light by
an example of a grating coupler in a waveguide display.
[0039] FIG. 13A illustrates an example of a waveguide display
including a grating coupler and a phase structure for changing the
polarization state of incident light according to certain
embodiments.
[0040] FIG. 13B illustrates an example of a waveguide display
including grating couplers and a phase structure for changing the
polarization state of incident light according to certain
embodiments.
[0041] FIG. 13C illustrates an example of a waveguide display
including grating couplers and a phase structure for changing the
polarization state of incident light according to certain
embodiments.
[0042] FIG. 14A illustrates the efficiencies of diffracting
s-polarized light by an example of a grating coupler in a waveguide
display.
[0043] FIG. 14B illustrates the efficiencies of diffracting
p-polarized light by an example of a grating coupler in a waveguide
display.
[0044] FIG. 14C illustrates the efficiencies of diffracting
s-polarized light by an example of a grating coupler and a phase
structure in a waveguide display according to certain
embodiments.
[0045] FIG. 14D illustrates the efficiencies of diffracting
p-polarized light by an example of a grating coupler and a phase
structure in a waveguide display according to certain
embodiments.
[0046] FIG. 15A illustrates simulated input coupling efficiencies
of examples of waveguide displays including a grating coupler and
various phase structures according to certain embodiments.
[0047] FIG. 15B illustrates simulated input coupling efficiencies
of an example of a waveguide display for light from different
regions in a field of view.
[0048] FIG. 15C illustrates simulated input coupling efficiencies
of an example of a waveguide display including a grating coupler
and a phase structure according to certain embodiments for light
from different regions in a field of view.
[0049] FIG. 15D illustrates the simulated input coupling efficiency
improvements by an example of a waveguide display including a
grating coupler and a phase structure according to certain
embodiments for light from different regions in a field of
view.
[0050] FIG. 16A illustrates simulated input coupling efficiencies
of examples of waveguide displays including a grating coupler and
various phase structures according to certain embodiments.
[0051] FIG. 16B illustrates simulated input coupling efficiencies
of an example of a waveguide display for light from different
regions in a field of view.
[0052] FIG. 16C illustrates simulated input coupling efficiencies
of an example of a waveguide display including a grating coupler
and a phase structure according to certain embodiments for light
from different regions in a field of view.
[0053] FIG. 16D illustrates simulated input coupling efficiency
improvements by an example of a waveguide display including a
grating coupler and a phase structure according to certain
embodiments for light from different regions in a field of
view.
[0054] FIG. 17A illustrates an example of a waveguide display
including a grating coupler and a phase structure between the
grating coupler and a substrate according to certain
embodiments.
[0055] FIG. 17B illustrates another example of a waveguide display
including a grating coupler and a phase structure between the
grating coupler and a substrate according to certain
embodiments.
[0056] FIG. 18A illustrates an example of a waveguide display
including VBG couplers according to certain embodiments.
[0057] FIG. 18B illustrates an example of an assembly of a
waveguide display.
[0058] FIG. 19A illustrates an example of a waveguide display
including volume Bragg grating couplers according to certain
embodiments.
[0059] FIG. 19B illustrates an example of an input coupler
including a volume Bragg grating in a substrate according to
certain embodiments.
[0060] FIG. 20A illustrates examples of reflection coefficients for
s-polarization and p-polarization light with different incident
angles at an interface between a low refractive index material and
a high refractive index material.
[0061] FIG. 20B illustrates examples of reflection coefficients for
s-polarization and p-polarization light with different incident
angles at an interface between a high refractive index material and
a low refractive index material.
[0062] FIG. 21A illustrates an example of an optical see-through
waveguide display including volume Bragg gratings for exit pupil
expansion.
[0063] FIG. 21B illustrates polarization states of light beams in
an example of a waveguide display.
[0064] FIG. 22A illustrates a cross-sectional view of an example of
a waveguide display including VBG couplers and a phase structure
according to certain embodiments.
[0065] FIG. 22B illustrates a top view of an example of a waveguide
display including VBG couplers and a phase structure according to
certain embodiments.
[0066] FIG. 23A illustrates a cross-sectional view of an example of
a waveguide display including VBGs and phase structures according
to certain embodiments.
[0067] FIG. 23B illustrates a top view of an example of an example
of a waveguide display including VBGs and at least one phase
structure according to certain embodiments.
[0068] FIG. 24A illustrates the simulation result of an example of
a waveguide display including VBGs.
[0069] FIG. 24B illustrates the simulation result of an example of
a waveguide display including VBGs and a phase structure according
to certain embodiments.
[0070] FIG. 25 illustrates simulated input coupling efficiencies of
examples of waveguide displays including various phase structures
according to certain embodiments.
[0071] FIGS. 26A-26C illustrate simulated input coupling
efficiencies of an example of a waveguide display for light from
different regions in a field of view and in different colors.
[0072] FIGS. 26D-26F illustrate simulated input coupling
efficiencies of an example of a waveguide display including a phase
structure according to certain embodiments for light from different
regions in a field of view and in different colors.
[0073] FIGS. 26G-26I illustrate simulated input coupling
efficiencies of an example of a waveguide display including a phase
structure according to certain embodiments for light from different
regions in a field of view and in different colors.
[0074] FIG. 27 is a simplified block diagram of an example of an
electronic system in an example of a near-eye display according to
certain embodiments.
[0075] The figures depict embodiments of the present disclosure for
purposes of illustration only. One skilled in the art will readily
recognize from the following description that alternative
embodiments of the structures and methods illustrated may be
employed without departing from the principles, or benefits touted,
of this disclosure.
[0076] In the appended figures, similar components and/or features
may have the same reference label. Further, various components of
the same type may be distinguished by following the reference label
by a dash and a second label that distinguishes among the similar
components. If only the first reference label is used in the
specification, the description is applicable to any one of the
similar components having the same first reference label
irrespective of the second reference label.
DETAILED DESCRIPTION
[0077] This disclosure relates generally to grating-based waveguide
displays for near-eye display. More specifically, disclosed herein
are techniques for improving the coupling efficiencies of
grating-based optical see-through near-eye display systems. Various
inventive embodiments are described herein, including devices,
systems, methods, and the like.
[0078] In a near-eye display system, it is generally desirable to
expand the eyebox, improve image quality (e.g., resolution and
contrast), reduce physical size, increase power efficiency, and
increase the field of view. In a waveguide-based near-eye display
system, light of projected images may be coupled into a waveguide
(e.g., a transparent substrate), propagate within the waveguide,
and be coupled out of the waveguide at different locations to
replicate exit pupils and expand the eyebox. Two or more gratings
may be used to expand the eyebox in two dimensions. In a
waveguide-based near-eye display system for augmented reality
applications, light from the surrounding environment may pass
through at least a see-through region of the waveguide display
(e.g., the transparent substrate) and reach the user's eyes. In
some implementations, the light of the projected images may be
coupled into or out of the waveguide using diffractive optical
elements, such as gratings, which may also allow light from the
surrounding environment to pass through.
[0079] Couplers implemented using diffractive optical elements may
have limited coupling efficiencies due to, for example, less than
100% diffraction efficiency to the desired diffraction order,
leakage, crosstalk, polarization dependence, angular dependence,
wavelength dependence, and the like. For example, in waveguide
displays using surface-relief grating (SRG) couplers or volume
Bragg grating (VBG) couplers, the display light coupled into the
waveguide by an input coupler may be reflected back to the input
coupler and may be diffracted again by the input coupler to
undesired directions. In addition, the diffraction efficiencies of
SRGs and VBGs may be polarization dependent. For example, the
diffraction efficiencies of reflective VBGs may be close to zero
for p-polarized light with incident angles near or at the
Brewster's angle. In another example, the diffraction efficiency of
an SRG for s-polarized light may be higher than the diffraction
efficiency of the SRG for p-polarized light, and thus there may be
higher leakage for s-polarized light due to the higher diffraction
efficiency of the SRG for s-polarized light.
[0080] Grating couplers may be optimized to maximize the power of
the display light in the desire path. For example, the grating
shape, the slant angle, the grating period, the duty cycle, the
grating height or depth, the refractive index, the refractive index
modulation, the overcoating material, and the spatial variations of
these grating parameters across the grating may be adjusted to
improve the efficiencies of directing display light to the desired
directions towards the eyebox. Varying these parameters may provide
some but limited improvements to the efficiencies of the waveguide
display due to the intrinsic characteristics of the SRGs and
VBGs.
[0081] According to certain embodiments, the efficiency of a
waveguide display may be improved by changing the polarization
state of the display light along its propagation path. For example,
a phase structure may be coupled to a surface of the waveguide and
used to change the polarization state of the light reflected at the
surface of the waveguide, such that the reflected light, when
reaching a grating coupler in its propagation path, may be more
preferentially diffracted or reflected to the desired directions to
improve the overall efficiency of the waveguide display. The phase
structure may include any birefringent materials (e.g.,
birefringent crystals, liquid crystals, or polymers) or structures
(e.g., gratings or other subwavelength structures) that can cause a
desired phase delay between two orthogonal linear polarization
components (e.g., s-polarized light and p-polarized light), such
that the incident light beam may be changed to an s-polarized,
p-polarized, circularly polarized, or elliptically polarized beam.
The phase structure may be placed at various locations in a
waveguide display, such as at the input coupler region, between the
input coupler and the output coupler, at the output coupler region,
or any combinations.
[0082] Adding phase structures to waveguide displays can add more
degrees of design freedom for optimizing the efficiencies of the
waveguide display. For example, the location, the phase delay, the
orientation, and other parameters of the phase structure may be
selected to change the polarization state of the display light such
that the display light may be more preferentially diffracted by the
polarization-dependent gratings to desired diffraction orders and
directions to reach user's eye eventually.
[0083] In the following description, various inventive embodiments
are described, including devices, systems, methods, and the like.
For the purposes of explanation, specific details are set forth in
order to provide a thorough understanding of examples of the
disclosure. However, it will be apparent that various examples may
be practiced without these specific details. For example, devices,
systems, structures, assemblies, methods, and other components may
be shown as components in block diagram form in order not to
obscure the examples in unnecessary detail. In other instances,
well-known devices, processes, systems, structures, and techniques
may be shown without necessary detail in order to avoid obscuring
the examples. The figures and description are not intended to be
restrictive. The terms and expressions that have been employed in
this disclosure are used as terms of description and not of
limitation, and there is no intention in the use of such terms and
expressions of excluding any equivalents of the features shown and
described or portions thereof. The word "example" is used herein to
mean "serving as an example, instance, or illustration." Any
embodiment or design described herein as "example" is not
necessarily to be construed as preferred or advantageous over other
embodiments or designs.
[0084] FIG. 1 is a simplified block diagram of an example of an
artificial reality system environment 100 including a near-eye
display 120 in accordance with certain embodiments. Artificial
reality system environment 100 shown in FIG. 1 may include near-eye
display 120, an optional external imaging device 150, and an
optional input/output interface 140, each of which may be coupled
to an optional console 110. While FIG. 1 shows an example of
artificial reality system environment 100 including one near-eye
display 120, one external imaging device 150, and one input/output
interface 140, any number of these components may be included in
artificial reality system environment 100, or any of the components
may be omitted. For example, there may be multiple near-eye
displays 120 monitored by one or more external imaging devices 150
in communication with console 110. In some configurations,
artificial reality system environment 100 may not include external
imaging device 150, optional input/output interface 140, and
optional console 110. In alternative configurations, different or
additional components may be included in artificial reality system
environment 100.
[0085] Near-eye display 120 may be a head-mounted display that
presents content to a user. Examples of content presented by
near-eye display 120 include one or more of images, videos, audio,
or any combination thereof. In some embodiments, audio may be
presented via an external device (e.g., speakers and/or headphones)
that receives audio information from near-eye display 120, console
110, or both, and presents audio data based on the audio
information. Near-eye display 120 may include one or more rigid
bodies, which may be rigidly or non-rigidly coupled to each other.
A rigid coupling between rigid bodies may cause the coupled rigid
bodies to act as a single rigid entity. A non-rigid coupling
between rigid bodies may allow the rigid bodies to move relative to
each other. In various embodiments, near-eye display 120 may be
implemented in any suitable form-factor, including a pair of
glasses. Some embodiments of near-eye display 120 are further
described below with respect to FIGS. 2 and 3. Additionally, in
various embodiments, the functionality described herein may be used
in a headset that combines images of an environment external to
near-eye display 120 and artificial reality content (e.g.,
computer-generated images). Therefore, near-eye display 120 may
augment images of a physical, real-world environment external to
near-eye display 120 with generated content (e.g., images, video,
sound, etc.) to present an augmented reality to a user.
[0086] In various embodiments, near-eye display 120 may include one
or more of display electronics 122, display optics 124, and an
eye-tracking unit 130. In some embodiments, near-eye display 120
may also include one or more locators 126, one or more position
sensors 128, and an inertial measurement unit (IMU) 132. Near-eye
display 120 may omit any of eye-tracking unit 130, locators 126,
position sensors 128, and IMU 132, or include additional elements
in various embodiments. Additionally, in some embodiments, near-eye
display 120 may include elements combining the function of various
elements described in conjunction with FIG. 1.
[0087] Display electronics 122 may display or facilitate the
display of images to the user according to data received from, for
example, console 110. In various embodiments, display electronics
122 may include one or more display panels, such as a liquid
crystal display (LCD), an organic light emitting diode (OLED)
display, an inorganic light emitting diode (ILED) display, a micro
light emitting diode (.mu.LED) display, an active-matrix OLED
display (AMOLED), a transparent OLED display (TOLED), or some other
display. For example, in one implementation of near-eye display
120, display electronics 122 may include a front TOLED panel, a
rear display panel, and an optical component (e.g., an attenuator,
polarizer, or diffractive or spectral film) between the front and
rear display panels. Display electronics 122 may include pixels to
emit light of a predominant color such as red, green, blue, white,
or yellow. In some implementations, display electronics 122 may
display a three-dimensional (3D) image through stereoscopic effects
produced by two-dimensional panels to create a subjective
perception of image depth. For example, display electronics 122 may
include a left display and a right display positioned in front of a
user's left eye and right eye, respectively. The left and right
displays may present copies of an image shifted horizontally
relative to each other to create a stereoscopic effect (e.g., a
perception of image depth by a user viewing the image).
[0088] In certain embodiments, display optics 124 may display image
content optically (e.g., using optical waveguides and couplers) or
magnify image light received from display electronics 122, correct
optical errors associated with the image light, and present the
corrected image light to a user of near-eye display 120. In various
embodiments, display optics 124 may include one or more optical
elements, such as, for example, a substrate, optical waveguides, an
aperture, a Fresnel lens, a convex lens, a concave lens, a filter,
input/output couplers, or any other suitable optical elements that
may affect image light emitted from display electronics 122.
Display optics 124 may include a combination of different optical
elements as well as mechanical couplings to maintain relative
spacing and orientation of the optical elements in the combination.
One or more optical elements in display optics 124 may have an
optical coating, such as an anti-reflective coating, a reflective
coating, a filtering coating, or a combination of different optical
coatings.
[0089] Magnification of the image light by display optics 124 may
allow display electronics 122 to be physically smaller, weigh less,
and consume less power than larger displays. Additionally,
magnification may increase a field of view of the displayed
content. The amount of magnification of image light by display
optics 124 may be changed by adjusting, adding, or removing optical
elements from display optics 124. In some embodiments, display
optics 124 may project displayed images to one or more image planes
that may be further away from the user's eyes than near-eye display
120.
[0090] Display optics 124 may also be designed to correct one or
more types of optical errors, such as two-dimensional optical
errors, three-dimensional optical errors, or any combination
thereof. Two-dimensional errors may include optical aberrations
that occur in two dimensions. Example types of two-dimensional
errors may include barrel distortion, pincushion distortion,
longitudinal chromatic aberration, and transverse chromatic
aberration. Three-dimensional errors may include optical errors
that occur in three dimensions. Example types of three-dimensional
errors may include spherical aberration, comatic aberration, field
curvature, and astigmatism.
[0091] Locators 126 may be objects located in specific positions on
near-eye display 120 relative to one another and relative to a
reference point on near-eye display 120. In some implementations,
console 110 may identify locators 126 in images captured by
external imaging device 150 to determine the artificial reality
headset's position, orientation, or both. A locator 126 may be an
LED, a corner cube reflector, a reflective marker, a type of light
source that contrasts with an environment in which near-eye display
120 operates, or any combination thereof. In embodiments where
locators 126 are active components (e.g., LEDs or other types of
light emitting devices), locators 126 may emit light in the visible
band (e.g., about 380 nm to 750 nm), in the infrared (IR) band
(e.g., about 750 nm to 1 mm), in the ultraviolet band (e.g., about
10 nm to about 380 nm), in another portion of the electromagnetic
spectrum, or in any combination of portions of the electromagnetic
spectrum.
[0092] External imaging device 150 may include one or more cameras,
one or more video cameras, any other device capable of capturing
images including one or more of locators 126, or any combination
thereof. Additionally, external imaging device 150 may include one
or more filters (e.g., to increase signal to noise ratio). External
imaging device 150 may be configured to detect light emitted or
reflected from locators 126 in a field of view of external imaging
device 150. In embodiments where locators 126 include passive
elements (e.g., retroreflectors), external imaging device 150 may
include a light source that illuminates some or all of locators
126, which may retro-reflect the light to the light source in
external imaging device 150. Slow calibration data may be
communicated from external imaging device 150 to console 110, and
external imaging device 150 may receive one or more calibration
parameters from console 110 to adjust one or more imaging
parameters (e.g., focal length, focus, frame rate, sensor
temperature, shutter speed, aperture, etc.).
[0093] Position sensors 128 may generate one or more measurement
signals in response to motion of near-eye display 120. Examples of
position sensors 128 may include accelerometers, gyroscopes,
magnetometers, other motion-detecting or error-correcting sensors,
or any combination thereof. For example, in some embodiments,
position sensors 128 may include multiple accelerometers to measure
translational motion (e.g., forward/back, up/down, or left/right)
and multiple gyroscopes to measure rotational motion (e.g., pitch,
yaw, or roll). In some embodiments, various position sensors may be
oriented orthogonally to each other.
[0094] IMU 132 may be an electronic device that generates fast
calibration data based on measurement signals received from one or
more of position sensors 128. Position sensors 128 may be located
external to IMU 132, internal to IMU 132, or any combination
thereof. Based on the one or more measurement signals from one or
more position sensors 128, IMU 132 may generate fast calibration
data indicating an estimated position of near-eye display 120
relative to an initial position of near-eye display 120. For
example, IMU 132 may integrate measurement signals received from
accelerometers over time to estimate a velocity vector and
integrate the velocity vector over time to determine an estimated
position of a reference point on near-eye display 120.
Alternatively, IMU 132 may provide the sampled measurement signals
to console 110, which may determine the fast calibration data.
While the reference point may generally be defined as a point in
space, in various embodiments, the reference point may also be
defined as a point within near-eye display 120 (e.g., a center of
IMU 132).
[0095] Eye-tracking unit 130 may include one or more eye-tracking
systems. Eye tracking may refer to determining an eye's position,
including orientation and location of the eye, relative to near-eye
display 120. An eye-tracking system may include an imaging system
to image one or more eyes and may optionally include a light
emitter, which may generate light that is directed to an eye such
that light reflected by the eye may be captured by the imaging
system. For example, eye-tracking unit 130 may include a
non-coherent or coherent light source (e.g., a laser diode)
emitting light in the visible spectrum or infrared spectrum, and a
camera capturing the light reflected by the user's eye. As another
example, eye-tracking unit 130 may capture reflected radio waves
emitted by a miniature radar unit. Eye-tracking unit 130 may use
low-power light emitters that emit light at frequencies and
intensities that would not injure the eye or cause physical
discomfort. Eye-tracking unit 130 may be arranged to increase
contrast in images of an eye captured by eye-tracking unit 130
while reducing the overall power consumed by eye-tracking unit 130
(e.g., reducing power consumed by a light emitter and an imaging
system included in eye-tracking unit 130). For example, in some
implementations, eye-tracking unit 130 may consume less than 100
milliwatts of power.
[0096] Near-eye display 120 may use the orientation of the eye to,
e.g., determine an inter-pupillary distance (IPD) of the user,
determine gaze direction, introduce depth cues (e.g., blur image
outside of the user's main line of sight), collect heuristics on
the user interaction in the VR media (e.g., time spent on any
particular subject, object, or frame as a function of exposed
stimuli), some other functions that are based in part on the
orientation of at least one of the user's eyes, or any combination
thereof. Because the orientation may be determined for both eyes of
the user, eye-tracking unit 130 may be able to determine where the
user is looking. For example, determining a direction of a user's
gaze may include determining a point of convergence based on the
determined orientations of the user's left and right eyes. A point
of convergence may be the point where the two foveal axes of the
user's eyes intersect. The direction of the user's gaze may be the
direction of a line passing through the point of convergence and
the mid-point between the pupils of the user's eyes.
[0097] Input/output interface 140 may be a device that allows a
user to send action requests to console 110. An action request may
be a request to perform a particular action. For example, an action
request may be to start or to end an application or to perform a
particular action within the application. Input/output interface
140 may include one or more input devices. Example input devices
may include a keyboard, a mouse, a game controller, a glove, a
button, a touch screen, or any other suitable device for receiving
action requests and communicating the received action requests to
console 110. An action request received by the input/output
interface 140 may be communicated to console 110, which may perform
an action corresponding to the requested action. In some
embodiments, input/output interface 140 may provide haptic feedback
to the user in accordance with instructions received from console
110. For example, input/output interface 140 may provide haptic
feedback when an action request is received, or when console 110
has performed a requested action and communicates instructions to
input/output interface 140. In some embodiments, external imaging
device 150 may be used to track input/output interface 140, such as
tracking the location or position of a controller (which may
include, for example, an IR light source) or a hand of the user to
determine the motion of the user. In some embodiments, near-eye
display 120 may include one or more imaging devices to track
input/output interface 140, such as tracking the location or
position of a controller or a hand of the user to determine the
motion of the user.
[0098] Console 110 may provide content to near-eye display 120 for
presentation to the user in accordance with information received
from one or more of external imaging device 150, near-eye display
120, and input/output interface 140. In the example shown in FIG.
1, console 110 may include an application store 112, a headset
tracking module 114, an artificial reality engine 116, and an
eye-tracking module 118. Some embodiments of console 110 may
include different or additional modules than those described in
conjunction with FIG. 1. Functions further described below may be
distributed among components of console 110 in a different manner
than is described here.
[0099] In some embodiments, console 110 may include a processor and
a non-transitory computer-readable storage medium storing
instructions executable by the processor. The processor may include
multiple processing units executing instructions in parallel. The
non-transitory computer-readable storage medium may be any memory,
such as a hard disk drive, a removable memory, or a solid-state
drive (e.g., flash memory or dynamic random access memory (DRAM)).
In various embodiments, the modules of console 110 described in
conjunction with FIG. 1 may be encoded as instructions in the
non-transitory computer-readable storage medium that, when executed
by the processor, cause the processor to perform the functions
further described below.
[0100] Application store 112 may store one or more applications for
execution by console 110. An application may include a group of
instructions that, when executed by a processor, generates content
for presentation to the user. Content generated by an application
may be in response to inputs received from the user via movement of
the user's eyes or inputs received from the input/output interface
140. Examples of the applications may include gaming applications,
conferencing applications, video playback application, or other
suitable applications.
[0101] Headset tracking module 114 may track movements of near-eye
display 120 using slow calibration information from external
imaging device 150. For example, headset tracking module 114 may
determine positions of a reference point of near-eye display 120
using observed locators from the slow calibration information and a
model of near-eye display 120. Headset tracking module 114 may also
determine positions of a reference point of near-eye display 120
using position information from the fast calibration information.
Additionally, in some embodiments, headset tracking module 114 may
use portions of the fast calibration information, the slow
calibration information, or any combination thereof, to predict a
future location of near-eye display 120. Headset tracking module
114 may provide the estimated or predicted future position of
near-eye display 120 to artificial reality engine 116.
[0102] Artificial reality engine 116 may execute applications
within artificial reality system environment 100 and receive
position information of near-eye display 120, acceleration
information of near-eye display 120, velocity information of
near-eye display 120, predicted future positions of near-eye
display 120, or any combination thereof from headset tracking
module 114. Artificial reality engine 116 may also receive
estimated eye position and orientation information from
eye-tracking module 118. Based on the received information,
artificial reality engine 116 may determine content to provide to
near-eye display 120 for presentation to the user. For example, if
the received information indicates that the user has looked to the
left, artificial reality engine 116 may generate content for
near-eye display 120 that mirrors the user's eye movement in a
virtual environment. Additionally, artificial reality engine 116
may perform an action within an application executing on console
110 in response to an action request received from input/output
interface 140, and provide feedback to the user indicating that the
action has been performed. The feedback may be visual or audible
feedback via near-eye display 120 or haptic feedback via
input/output interface 140.
[0103] Eye-tracking module 118 may receive eye-tracking data from
eye-tracking unit 130 and determine the position of the user's eye
based on the eye tracking data. The position of the eye may include
an eye's orientation, location, or both relative to near-eye
display 120 or any element thereof. Because the eye's axes of
rotation change as a function of the eye's location in its socket,
determining the eye's location in its socket may allow eye-tracking
module 118 to more accurately determine the eye's orientation.
[0104] FIG. 2 is a perspective view of an example of a near-eye
display in the form of an HMD device 200 for implementing some of
the examples disclosed herein. HMD device 200 may be a part of,
e.g., a VR system, an AR system, an MR system, or any combination
thereof. HMD device 200 may include a body 220 and a head strap
230. FIG. 2 shows a bottom side 223, a front side 225, and a left
side 227 of body 220 in the perspective view. Head strap 230 may
have an adjustable or extendible length. There may be a sufficient
space between body 220 and head strap 230 of HMD device 200 for
allowing a user to mount HMD device 200 onto the user's head. In
various embodiments, HMD device 200 may include additional, fewer,
or different components. For example, in some embodiments, HMD
device 200 may include eyeglass temples and temple tips as shown
in, for example, FIG. 3 below, rather than head strap 230.
[0105] HMD device 200 may present to a user media including virtual
and/or augmented views of a physical, real-world environment with
computer-generated elements. Examples of the media presented by HMD
device 200 may include images (e.g., two-dimensional (2D) or
three-dimensional (3D) images), videos (e.g., 2D or 3D videos),
audio, or any combination thereof. The images and videos may be
presented to each eye of the user by one or more display assemblies
(not shown in FIG. 2) enclosed in body 220 of HMD device 200. In
various embodiments, the one or more display assemblies may include
a single electronic display panel or multiple electronic display
panels (e.g., one display panel for each eye of the user). Examples
of the electronic display panel(s) may include, for example, an
LCD, an OLED display, an ILED display, a pLED display, an AMOLED, a
TOLED, some other display, or any combination thereof. HMD device
200 may include two eyebox regions.
[0106] In some implementations, HMD device 200 may include various
sensors (not shown), such as depth sensors, motion sensors,
position sensors, and eye tracking sensors. Some of these sensors
may use a structured light pattern for sensing. In some
implementations, HMD device 200 may include an input/output
interface for communicating with a console. In some
implementations, HMD device 200 may include a virtual reality
engine (not shown) that can execute applications within HMD device
200 and receive depth information, position information,
acceleration information, velocity information, predicted future
positions, or any combination thereof of HMD device 200 from the
various sensors. In some implementations, the information received
by the virtual reality engine may be used for producing a signal
(e.g., display instructions) to the one or more display assemblies.
In some implementations, HMD device 200 may include locators (not
shown, such as locators 126) located in fixed positions on body 220
relative to one another and relative to a reference point. Each of
the locators may emit light that is detectable by an external
imaging device.
[0107] FIG. 3 is a perspective view of an example of a near-eye
display 300 in the form of a pair of glasses for implementing some
of the examples disclosed herein. Near-eye display 300 may be a
specific implementation of near-eye display 120 of FIG. 1, and may
be configured to operate as a virtual reality display, an augmented
reality display, and/or a mixed reality display. Near-eye display
300 may include a frame 305 and a display 310. Display 310 may be
configured to present content to a user. In some embodiments,
display 310 may include display electronics and/or display optics.
For example, as described above with respect to near-eye display
120 of FIG. 1, display 310 may include an LCD display panel, an LED
display panel, or an optical display panel (e.g., a waveguide
display assembly).
[0108] Near-eye display 300 may further include various sensors
350a, 350b, 350c, 350d, and 350e on or within frame 305. In some
embodiments, sensors 350a-350e may include one or more depth
sensors, motion sensors, position sensors, inertial sensors, or
ambient light sensors. In some embodiments, sensors 350a-350e may
include one or more image sensors configured to generate image data
representing different regions in a field of views in different
directions. In some embodiments, sensors 350a-350e may be used as
input devices to control or influence the displayed content of
near-eye display 300, and/or to provide an interactive VR/AR/MR
experience to a user of near-eye display 300. In some embodiments,
sensors 350a-350e may also be used for stereoscopic imaging.
[0109] In some embodiments, near-eye display 300 may further
include one or more illuminators 330 to project light into the
physical environment. The projected light may be associated with
different frequency bands (e.g., visible light, infra-red light,
ultra-violet light, etc.), and may serve various purposes. For
example, illuminator(s) 330 may project light in a dark environment
(or in an environment with low intensity of infra-red light,
ultra-violet light, etc.) to assist sensors 350a-350e in capturing
images of different objects within the dark environment. In some
embodiments, illuminator(s) 330 may be used to project certain
light pattern onto the objects within the environment. In some
embodiments, illuminator(s) 330 may be used as locators, such as
locators 126 described above with respect to FIG. 1.
[0110] In some embodiments, near-eye display 300 may also include a
high-resolution camera 340. Camera 340 may capture images of the
physical environment in the field of view. The captured images may
be processed, for example, by a virtual reality engine (e.g.,
artificial reality engine 116 of FIG. 1) to add virtual objects to
the captured images or modify physical objects in the captured
images, and the processed images may be displayed to the user by
display 310 for AR or MR applications.
[0111] FIG. 4 is a simplified diagram illustrating an example of an
optical system 400 in a near-eye display system. Optical system 400
may include an image source 410 and projector optics 420. In the
example shown in FIG. 4, image source 410 is in front of projector
optics 420. In various embodiments, image source 410 may be located
outside of the field of view of user's eye 490. For example, one or
more reflectors or directional couplers may be used to deflect
light from an image source that is outside of the field of view of
user's eye 490 to make the image source appear to be at the
location of image source 410 shown in FIG. 4. Light from an area
(e.g., a pixel or a light emitting device) on image source 410 may
be collimated and directed to an exit pupil 430 by projector optics
420. Thus, objects at different spatial locations on image source
410 may appear to be objects far away from user's eye 490 in
different viewing angles (FOVs). The collimated light from
different viewing angles may then be focused by the lens of user's
eye 490 onto different locations on retina 492 of user's eye 490.
For example, at least some portions of the light may be focused on
a fovea 494 on retina 492. Collimated light rays from an area on
image source 410 and incident on user's eye 490 from a same
direction may be focused onto a same location on retina 492. As
such, a single image of image source 410 may be formed on retina
492.
[0112] The user experience of using an artificial reality system
may depend on several characteristics of the optical system,
including field of view (FOV), image quality (e.g., angular
resolution), size of the eyebox (to accommodate for eye and head
movements), and brightness of the light (or contrast) within the
eyebox. Field of view describes the angular range of the image as
seen by the user, usually measured in degrees as observed by one
eye (for a monocular HMD) or both eyes (for either biocular or
binocular HMDs). The human visual system may have a total binocular
FOV of about 200.degree. (horizontal) by 130.degree. (vertical). To
create a fully immersive visual environment, a large FOV is
desirable because a large FOV (e.g., greater than about 60.degree.)
may provide a sense of "being in" an image, rather than merely
viewing the image. Smaller fields of view may also preclude some
important visual information. For example, an HMD system with a
small FOV may use a gesture interface, but the users may not see
their hands in the small FOV to be sure that they are using the
correct motions. On the other hand, wider fields of view may
require larger displays or optical systems, which may influence the
size, weight, cost, and comfort of using the HMD.
[0113] Resolution may refer to the angular size of a displayed
pixel or image element appearing to a user, or the ability for the
user to view and correctly interpret an object as imaged by a pixel
and/or other pixels. The resolution of an HMD may be specified as
the number of pixels on the image source for a given FOV value,
from which an angular resolution may be determined by dividing the
FOV in one direction by the number of pixels in the same direction
on the image source. For example, for a horizontal FOV of
40.degree. and 1080 pixels in the horizontal direction on the image
source, the corresponding angular resolution may be about 2.2
arc-minutes, compared with the one-arc-minute resolution associated
with Snellen 20/20 human visual acuity.
[0114] In some cases, the eyebox may be a two-dimensional box in
front of the user's eye, from which the displayed image from the
image source may be viewed. If the pupil of the user moves outside
of the eyebox, the displayed image may not be seen by the user. For
example, in a non-pupil-forming configuration, there exists a
viewing eyebox within which there will be unvignetted viewing of
the HMD image source, and the displayed image may vignette or may
be clipped but may still be viewable when the pupil of user's eye
is outside of the viewing eyebox. In a pupil-forming configuration,
the image may not be viewable outside the exit pupil.
[0115] The fovea of a human eye, where the highest resolution may
be achieved on the retina, may correspond to an FOV of about
2.degree. to about 3.degree.. This may require that the eye rotates
in order to view off-axis objects with a highest resolution. The
rotation of the eye to view the off-axis objects may introduce a
translation of the pupil because the eye rotates around a point
that is about 10 mm behind the pupil. In addition, a user may not
always be able to accurately position the pupil (e.g., having a
radius of about 2.5 mm) of the user's eye at an ideal location in
the eyebox. Furthermore, the environment where the HMD is used may
require the eyebox to be larger to allow for movement of the user's
eye and/or head relative the HMD, for example, when the HMD is used
in a moving vehicle or designed to be used while the user is moving
on foot. The amount of movement in these situations may depend on
how well the HMD is coupled to the user's head.
[0116] Thus, the optical system of the HMD may need to provide a
sufficiently large exit pupil or viewing eyebox for viewing the
full FOV with full resolution, in order to accommodate the
movements of the user's pupil relative to the HMD. For example, in
a pupil-forming configuration, a minimum size of 12 mm to 15 mm may
be desired for the exit pupil. If the eyebox is too small, minor
misalignments between the eye and the HMD may result in at least
partial loss of the image, and the user experience may be
substantially impaired. In general, the lateral extent of the
eyebox is more critical than the vertical extent of the eyebox.
This may be in part due to the significant variances in eye
separation distance between users, and the fact that misalignments
to eyewear tend to more frequently occur in the lateral dimension
and users tend to more frequently adjust their gaze left and right,
and with greater amplitude, than adjusting the gaze up and down.
Thus, techniques that can increase the lateral dimension of the
eyebox may substantially improve a user's experience with an HMD.
On the other hand, the larger the eyebox, the larger the optics and
the heavier and bulkier the near-eye display device may be.
[0117] In order to view the displayed image against a bright
background, the image source of an AR HMD may need to be
sufficiently bright, and the optical system may need to be
efficient to provide a bright image to the user's eye such that the
displayed image may be visible in a background including strong
ambient light, such as sunlight. The optical system of an HMD may
be designed to concentrate light in the eyebox. When the eyebox is
large, an image source with high power may be used to provide a
bright image viewable within the large eyebox. Thus, there may be
trade-offs among the size of the eyebox, cost, brightness, optical
complexity, image quality, and size and weight of the optical
system.
[0118] FIG. 5 illustrates an example of an optical see-through
augmented reality system 500 including a waveguide display for exit
pupil expansion according to certain embodiments. Augmented reality
system 500 may include a projector 510 and a combiner 515.
Projector 510 may include a light source or image source 512 and
projector optics 514. In some embodiments, light source or image
source 512 may include one or more micro-LED devices. In some
embodiments, image source 512 may include a plurality of pixels
that displays virtual objects, such as an LCD display panel or an
LED display panel. In some embodiments, image source 512 may
include a light source that generates coherent or partially
coherent light. For example, image source 512 may include a laser
diode, a vertical cavity surface emitting laser, an LED, a
superluminescent LED (sLED), and/or a micro-LED described above. In
some embodiments, image source 512 may include a plurality of light
sources (e.g., an array of micro-LEDs described above) each
emitting a monochromatic image light corresponding to a primary
color (e.g., red, green, or blue). In some embodiments, image
source 512 may include three two-dimensional arrays of micro-LEDs,
where each two-dimensional array of micro-LEDs may include
micro-LEDs configured to emit light of a primary color (e.g., red,
green, or blue). In some embodiments, image source 512 may include
an optical pattern generator, such as a spatial light modulator.
Projector optics 514 may include one or more optical components
that can condition the light from image source 512, such as
expanding, collimating, scanning, or projecting light from image
source 512 to combiner 515. The one or more optical components may
include, for example, one or more lenses, liquid lenses, mirrors,
free-form optics, apertures, and/or gratings. For example, in some
embodiments, image source 512 may include one or more
one-dimensional arrays or elongated two-dimensional arrays of
micro-LEDs, and projector optics 514 may include one or more
one-dimensional scanners (e.g., micro-mirrors or prisms) configured
to scan the one-dimensional arrays or elongated two-dimensional
arrays of micro-LEDs to generate image frames. In some embodiments,
projector optics 514 may include a liquid lens (e.g., a liquid
crystal lens) with a plurality of electrodes that allows scanning
of the light from image source 512.
[0119] Combiner 515 may include an input coupler 530 for coupling
light from projector 510 into a substrate 520 of combiner 515.
Input coupler 530 may include a volume holographic grating or
another diffractive optical element (DOE) (e.g., a surface-relief
grating (SRG)), a slanted reflective surface of substrate 520, or a
refractive coupler (e.g., a wedge or a prism). For example, input
coupler 530 may include a reflective volume Bragg grating or a
transmission volume Bragg grating. Input coupler 530 may have a
coupling efficiency of greater than 30%, 50%, 75%, 90%, or higher
for visible light. Light coupled into substrate 520 may propagate
within substrate 520 through, for example, total internal
reflection (TIR). Substrate 520 may be in the form of a lens of a
pair of eyeglasses. Substrate 520 may have a flat or a curved
surface, and may include one or more types of dielectric materials,
such as glass, quartz, plastic, polymer, poly(methyl methacrylate)
(PMMA), crystal, ceramic, or the like. A thickness of the substrate
may range from, for example, less than about 1 mm to about 10 mm or
more. Substrate 520 may be transparent to visible light.
[0120] Substrate 520 may include or may be coupled to a plurality
of output couplers 540 each configured to extract at least a
portion of the light guided by and propagating within substrate 520
from substrate 520, and direct extracted light 560 to an eyebox 595
where an eye 590 of the user of augmented reality system 500 may be
located when augmented reality system 500 is in use. The plurality
of output couplers 540 may replicate the exit pupil to increase the
size of eyebox 595, such that the displayed image may be visible in
a larger area. As input coupler 530, output couplers 540 may
include grating couplers (e.g., volume holographic gratings or
surface-relief gratings), other diffraction optical elements
(DOEs), prisms, etc. For example, output couplers 540 may include
reflective volume Bragg gratings or transmission volume Bragg
gratings. Output couplers 540 may have different coupling (e.g.,
diffraction) efficiencies at different locations. Substrate 520 may
also allow light 550 from the environment in front of combiner 515
to pass through with little or no loss. Output couplers 540 may
also allow light 550 to pass through with little loss. For example,
in some implementations, output couplers 540 may have a very low
diffraction efficiency for light 550 such that light 550 may be
refracted or otherwise pass through output couplers 540 with little
loss, and thus may have a higher intensity than extracted light
560. In some implementations, output couplers 540 may have a high
diffraction efficiency for light 550 and may diffract light 550 in
certain desired directions (i.e., diffraction angles) with little
loss. As a result, the user may be able to view combined images of
the environment in front of combiner 515 and images of virtual
objects projected by projector 510. In some implementations, output
couplers 540 may have a high diffraction efficiency for light 550
and may diffract light 550 to certain desired directions (e.g.,
diffraction angles) with little loss.
[0121] In some embodiments, projector 510, input coupler 530, and
output coupler 540 may be on any side of substrate 520. Input
coupler 530 and output coupler 540 may be reflective gratings (also
referred to as reflective gratings) or transmissive gratings (also
referred to as transmission gratings) to couple display light into
or out of substrate 520.
[0122] FIG. 6 illustrates an example of an optical see-through
augmented reality system 600 including a waveguide display for exit
pupil expansion according to certain embodiments. Augmented reality
system 600 may be similar to augmented reality system 500, and may
include the waveguide display and a projector that may include a
light source or image source 612 and projector optics 614. The
waveguide display may include a substrate 630, an input coupler
640, and a plurality of output couplers 650 as described above with
respect to augmented reality system 500. While FIG. 5 only shows
the propagation of light from a single field of view, FIG. 6 shows
the propagation of light from multiple fields of view.
[0123] FIG. 6 shows that the exit pupil is replicated by output
couplers 650 to form an aggregated exit pupil or eyebox, where
different regions in a field of view (e.g., different pixels on
image source 612) may be associated with different respective
propagation directions towards the eyebox, and light from a same
field of view (e.g., a same pixel on image source 612) may have a
same propagation direction for the different individual exit
pupils. Thus, a single image of image source 612 may be formed by
the user's eye located anywhere in the eyebox, where light from
different individual exit pupils and propagating in the same
direction may be from a same pixel on image source 612 and may be
focused onto a same location on the retina of the user's eye. FIG.
6 shows that the image of the image source is visible by the user's
eye even if the user's eye moves to different locations in the
eyebox.
[0124] In many waveguide-based near-eye display systems, in order
to expand the eyebox of the waveguide-based near-eye display in two
dimensions, two or more output gratings may be used to expand the
display light in two dimensions or along two axes (which may be
referred to as dual-axis pupil expansion). The two gratings may
have different grating parameters, such that one grating may be
used to replicate the exit pupil in one direction and the other
grating may be used to replicate the exit pupil in another
direction.
[0125] As described above, the input and output grating couplers
described above can be volume holographic gratings or
surface-relief gratings, which may have very different Klein-Cook
parameter Q:
Q = 2 .times. .pi..lamda. .times. .times. d n .times. .LAMBDA. 2 ,
##EQU00001##
where d is the thickness of the grating, A is the wavelength of the
incident light in free space, A is the grating period, and n is the
refractive index of the recording medium. The Klein-Cook parameter
Q may divide light diffraction by gratings into three regimes. When
a grating is characterized by Q<<1, light diffraction by the
grating may be referred to as Raman-Nath diffraction, where
multiple diffraction orders may occur for normal and/or oblique
incident light. When a grating is characterized by Q>>1
(e.g., Q10), light diffraction by the grating may be referred to as
Bragg diffraction, where generally only the zeroth and the .+-.1
diffraction orders may occur for light incident on the grating at
an angle satisfying the Bragg condition. When a grating is
characterized by Q.apprxeq.1, the diffraction by the grating may be
between the Raman-Nath diffraction and the Bragg diffraction. To
meet Bragg conditions, the thickness d of the grating may be higher
than certain values to occupy a volume (rather than at a surface)
of a medium, and thus may be referred to as a volume Bragg grating.
VBGs may generally have relatively small refractive index
modulations (e.g., .DELTA.n.ltoreq.0.05) and high spectral and
angular selectivity, while surface-relief gratings may generally
have large refractive index modulations (e.g., .DELTA.n.gtoreq.0.5)
and wide spectral and angular bandwidths.
[0126] FIG. 7A illustrates the spectral bandwidth of an example of
a volume Bragg grating (e.g., a reflective VBG) and the spectral
bandwidth of an example of a surface-relief grating (e.g., a
transmissive SRG). The horizontal axis represents the wavelength of
the incident visible light and the vertical axis corresponds to the
diffraction efficiency. As shown by a curve 710, the diffraction
efficiency of the reflective VBG is high in a narrow wavelength
range, such as green light. In contrast, the diffraction efficiency
of the transmissive SRG may be high in a very wide wavelength
range, such as from blue to red light, as shown by a curve 720.
[0127] FIG. 7B illustrates the angular bandwidth of an example of a
volume Bragg grating (e.g., a reflective VBG) and the angular
bandwidth of an example of a surface-relief grating (e.g., a
transmissive SRG). The horizontal axis represents the incident
angle of the visible light incident on the grating, and the
vertical axis corresponds to the diffraction efficiency. As shown
by a curve 715, the diffraction efficiency of the reflective VBG is
high for light incident on the grating from a narrow angular range,
such as about .+-.2.5.degree. from the perfect Bragg condition. In
contrast, the diffraction efficiency of the transmissive SRG is
high in a very wide angular range, such as greater than about
.+-.10.degree. or wider, as shown by a curve 725.
[0128] Due to the high spectral selectivity at the Bragg condition,
VBGs, such as reflective VBGs, may allow for single-waveguide
design without crosstalk between primary colors, and may exhibit
superior see-through quality. However, the spectral and angular
selectivity may lead to lower efficiency because only a portion of
the display light in the full FOV may be diffracted and reach
user's eyes.
[0129] FIG. 8A illustrates an example of an optical see-through
augmented reality system including a waveguide display 800 and
surface-relief gratings for exit pupil expansion according to
certain embodiments. Waveguide display 800 may include a substrate
810 (e.g., a waveguide), which may be similar to substrate 520.
Substrate 810 may be transparent to visible light and may include,
for example, a glass, quartz, plastic, polymer, PMMA, ceramic,
Si.sub.3N.sub.4, or crystal substrate. Substrate 810 may be a flat
substrate or a curved substrate. Substrate 810 may include a first
surface 812 and a second surface 814. Display light may be coupled
into substrate 810 by an input coupler 820, and may be reflected by
first surface 812 and second surface 814 through total internal
reflection, such that the display light may propagate within
substrate 810. Input coupler 820 may include a grating, a
refractive coupler (e.g., a wedge or a prism), or a reflective
coupler (e.g., a reflective surface having a slant angle with
respect to substrate 810). For example, in one embodiment, input
coupler 820 may include a prism that may couple display light of
different colors into substrate 810 at a same refraction angle. In
another example, input coupler 820 may include a grating coupler
that may diffract light of different colors into substrate 810 at
different directions. Input coupler 820 may have a coupling
efficiency of greater than 10%, 20%, 30%, 50%, 75%, 90%, or higher
for visible light.
[0130] Waveguide display 800 may also include a first output
grating 830 and a second output grating 840 positioned on one or
two surfaces (e.g., first surface 812 and second surface 814) of
substrate 810 for expanding incident display light beam in two
dimensions in order to fill an eyebox 850 with the display light.
First output grating 830 may be configured to expand at least a
portion of the display light beam along one direction, such as
approximately in the x direction. Display light coupled into
substrate 810 may propagate in a direction shown by a line 832.
While the display light propagates within substrate 810 along a
direction shown by line 832, a portion of the display light may be
diffracted by a region of first output grating 830 towards second
output grating 840 as shown by a line 834 each time the display
light propagating within substrate 810 reaches first output grating
830. Second output grating 840 may then expand the display light
from first output grating 830 in a different direction (e.g.,
approximately in the y direction) by diffracting a portion of the
display light to eyebox 850 each time the display light propagating
within substrate 810 reaches second output grating 840.
[0131] FIG. 8B illustrates an example of an eye box including
two-dimensional replicated exit pupils. FIG. 8B shows that a single
input pupil 805 may be replicated by first output grating 830 and
second output grating 840 to form an aggregated exit pupil 860 that
includes a two-dimensional array of individual exit pupils 862. For
example, the exit pupil may be replicated in approximately the x
direction by first output grating 830 and in approximately the y
direction by second output grating 840. As described above, output
light from individual exit pupils 862 and propagating in a same
direction may be focused onto a same location in the retina of the
user's eye. Thus, a single image may be formed by the user's eye
from the output light in the two-dimensional array of individual
exit pupils 862.
[0132] FIG. 9 is a perspective view of an example of a waveguide
display 900 with grating couplers for exit pupil expansion
according to certain embodiments. Waveguide display 900 may be an
example of waveguide display 800. Waveguide display 900 may include
a light source 910, which may include, for example, an array of red
micro-LEDs, an array of green micro-LEDs, and an array of blue
micro-LEDs. Each array of micro-LEDs may generate an image of a
corresponding color, and thus the three arrays of micro-LEDs may
generate a color image. Waveguide display 900 may include a
substrate 920 with grating couplers formed thereon or coupled
thereto. For example, waveguide display 900 may include three input
gratings 930, where each input grating 930 may be used to couple
display light of a monochromatic image generated by a corresponding
array of micro-LEDs into substrate 920. The display light coupled
into substrate 920 may propagate within substrate 920 through total
internal reflection at the surfaces of substrate 920, and may be
diffracted at multiple locations along a first direction by a first
output grating 940, which may replicate the input pupil along the
first direction. The display light diffracted at different
locations of first output grating 940 may reach a second output
grating 950, which may diffract the display light at different
locations along a second direction to replicate the input pupil
along the second direction as described above. The diffracted light
may then propagate towards an eyebox 960.
[0133] In waveguide display 900, input gratings 930, first output
grating 940, and second output grating 950 may include, for
example, SRG gratings formed at different locations on surfaces of
substrate 920, such as on two opposite broad surfaces of substrate
920. The grating vectors of an input grating 930, first output
grating 940, and second output grating 950 may form a closed
triangle.
[0134] FIG. 10 illustrates an example of a volume Bragg
grating-based waveguide display 1000 with exit pupil expansion,
dispersion reduction, and form-factor reduction according to
certain embodiments. Waveguide display 1000 may include a substrate
1010 that includes a first broad surface 1012 and a second broad
surface 1014. Display light from a light source (e.g., LEDs) may be
coupled into substrate 1010 by an input coupler 1020, and may be
reflected by first broad surface 1012 and second broad surface 1014
through total internal reflection, such that the display light may
propagate within substrate 1010. Input coupler 1020 may include a
diffractive coupler (e.g., a volume holographic grating) and may
couple display light of different colors into substrate 1010 at
different diffraction angles.
[0135] Waveguide display 1000 may also include a first output
grating 1030 and a second output grating 1040 formed on first broad
surface 1012 and/or second broad surface 1014. For example, first
output grating 1030 and second output grating 1040 may be formed on
a same broad surface or two different broad surfaces of substrate
1010. Second output grating 1040 may be formed in the see-through
region of the waveguide display and may overlap with an eyebox 1050
when viewed in the z direction (e.g., at a distance about 18 mm
from second output grating 1040 in +z or -z direction). First
output grating 1030 and second output grating 1040 may be
multiplexed VBG gratings that include many VBGs and may be used for
dual-axis pupil expansion to expand the incident display light beam
in two dimensions to fill eyebox 1050 with the display light. First
output grating 1030 may be a transmission grating or a reflective
grating. Second output grating 1040 may include a transmission
grating to at least partially overlap with first output grating
1030 and reduce the form factor of waveguide display 1000.
[0136] In addition, waveguide display 1000 may include a third
grating 1060 formed on first broad surface 1012 or second broad
surface 1014. In some embodiments, third grating 1060 and first
output grating 1030 may be on a same broad surface of substrate
1010. In some embodiments, third grating 1060 and first output
grating 1030 may be in different regions of a same grating or a
same grating material layer. In some embodiments, third grating
1060 may be spatially separate from first output grating 1030. In
some embodiments, third grating 1060 and first output grating 1030
may be recorded in a same number of exposures and under similar
recording conditions (but may be recorded for different exposure
durations to achieve different diffraction efficiencies), such that
each VBG in third grating 1060 may match a respective VBG in first
output grating 1030 (e.g., having the same grating vector in the
x-y plane and having the same and/or opposite grating vectors in
the z direction). For example, in some embodiments, a VBG in third
grating 1060 and a corresponding VBG in first output grating 1030
may have the same grating period and the same grating slant angle
(and thus the same grating vector), and the same thickness. In one
embodiment, third grating 1060 and first output grating 1030 may
have a thickness about 20 .mu.m and may each include about 40 or
more VBGs recorded through about 40 or more exposures. In some
embodiments, second output grating 1040 may have a thickness about
20 .mu.m or higher, and may include about 50 or more VBGs recorded
through about 50 or more exposures.
[0137] Input coupler 1020 may couple the display light from the
light source into substrate 1010. The display light may reach third
grating 1060 directly or may be reflected by first broad surface
1012 and/or second broad surface 1014 to third grating 1060, where
the size of the display light beam may be slightly larger than that
at input coupler 1020. Each VBG in third grating 1060 may diffract
a portion of the display light within a FOV range and a wavelength
range that approximately satisfies the Bragg condition of the VBG
to first output grating 1030. While the display light diffracted by
a VBG in third grating 1060 propagates within substrate 1010 (e.g.,
along a direction shown by a line 1032) through total internal
reflection, a portion of the display light may be diffracted by the
corresponding VBG in first output grating 1030 towards second
output grating 1040 each time the display light propagating within
substrate 1010 reaches first output grating 1030. Second output
grating 1040 may then expand the display light from first output
grating 1030 in a different direction by diffracting a portion of
the display light to eyebox 1050 each time the display light
propagating within substrate 1010 reaches second output grating
1040.
[0138] Because each VBG in third grating 1060 matches a respective
VBG in first output grating 1030 (e.g., having the same grating
vector in the x-y plane and having the same and/or opposite grating
vector in the z direction), and the two matching VBGs work under
opposite Bragg conditions (e.g., +1 order diffraction versus -1
order diffraction) due to the opposite propagation directions of
the display light at the two matching VBGs. For example, as shown
in FIG. 10, the VBG in third grating 1060 may change the
propagation direction of the display light from a downward
direction to a rightward direction, while the matching VBG in first
output grating 1030 may change the propagation direction of the
display light from a rightward direction to a downward direction.
Thus, the dispersion caused by first output grating 1030 may be
opposite to the dispersion caused by third grating 1060, thereby
reducing or minimizing the overall dispersion. In some embodiments,
the dispersion caused by input coupler 1020 may be opposite to the
dispersion caused by second output grating 1040, thereby reducing
or minimizing the overall dispersion.
[0139] Because first output grating 1030 and second output grating
1040 may have a small number (e.g., no greater than 50) of VBGs and
exposures, first output grating 1030 may also be placed in the
see-through region to overlap with second output grating 1040, thus
reducing the size of the waveguide display. The total number of
VBGs and exposures in a given see-through region may be less than,
for example, 100 or fewer (e.g., no more than about 40 in first
output grating 1030 and no more than 50 in second output grating
1040). Thus, the display haze may be low.
[0140] In the examples of waveguide displays described above,
couplers implemented using diffractive optical elements may have
limited coupling efficiencies due to, for example, less than 100%
diffraction efficiency to the desired diffraction order, leakage,
crosstalk, polarization dependence, angular dependence, wavelength
dependence, and the like. For example, in waveguide displays using
SRG couplers or VBG couplers, the display light coupled into the
waveguide by an input coupler may be reflected back to the input
coupler and may be at least partially diffracted by the input
coupler as leakage light to undesired directions. In addition, the
diffraction efficiencies of SRGs and VBGs may be polarization
dependent. For example, the diffraction efficiencies of VBGs may be
close to zero for p-polarized light with incident angles near or at
the Brewster's angle. In another example, the diffraction
efficiency of an SRG for a first linearly polarized light (e.g.,
s-polarized light) may be higher than the diffraction efficiency of
the SRG for a second linearly polarized light (e.g., p-polarized
light), and thus there may be higher leakage for the first linearly
polarized light (e.g., s-polarized light) due to the higher
diffraction efficiency of the SRG for the first linearly polarized
light.
[0141] FIG. 11A illustrates an example of a grating coupler 1120
for coupling display light into a waveguide 1110 of a waveguide
display 1100. Grating coupler 1120 may have a finite area to
receive an incident light beam 1105 having a finite beam width.
FIG. 11A shows the desired optical path of an incident light beam
1130. Grating coupler 1120 on a top surface 1112 of waveguide 1110
may diffract incident light beam 1130 into a first diffraction
order 1132 having a certain diffraction angle. First diffraction
order 1132 may propagate in waveguide 1110 and reach a bottom
surface 1114 of waveguide 1110. Bottom surface 1114 of waveguide
1110 may reflect all first diffraction order 1132 back towards
grating coupler 1120 as shown by a light beam 1134 due to total
internal reflection. It may be desirable that light beam 1134 is
fully reflected at top surface 1112 of waveguide 1110 as shown by a
light beam 1136, such that all first diffraction order 1132 coupled
into waveguide 1110 by grating coupler 1120 may propagate within
waveguide 1110 until it reaches an output coupler.
[0142] FIG. 11B illustrates examples of undesired light diffraction
by grating coupler 1120 that may reduce the efficiency of waveguide
display 1100. As illustrated, when incident light beam 1130 reaches
grating coupler 1120, it may be diffracted by grating coupler 1120
into multiple diffraction orders including first diffraction order
1132 and other diffraction orders 1140 (e.g., zeroth order,
-1.sup.st order, and higher orders). When the reflected light beam
1134 reaches top surface 1112 of waveguide 1110, it may be at least
partially diffracted by grating coupler 1120 into higher
diffraction orders (e.g., .+-.1, .+-.2, and the like) as shown by
light beams 1142 and 1144. Therefore, the power of the reflected
portion (shown by light beam 1136) may be much lower than the power
of incident light beam 1130 or first diffraction order 1132.
[0143] FIG. 12A illustrates the diffraction of s-polarized light by
an example of a grating coupler 1220 in a waveguide display 1200.
Grating coupler 1220 may have a higher diffraction efficiency for
s-polarized light than for p-polarized light. As described above,
when an s-polarized incident light beam 1230 reaches grating
coupler 1220 at a top surface 1212 of waveguide 1210, it may be
diffracted by grating coupler 1220 into multiple diffraction orders
including an s-polarized first diffraction order 1232 and other
diffraction orders, where the first order diffraction efficiency
for s-polarized incident light beam 1230 may be high. The
s-polarized first diffraction order 1232 may be reflected at a
bottom surface 1214 into s-polarized reflected light beam 1234.
When the s-polarized reflected light beam 1234 reaches top surface
1212 of waveguide 1210, a large portion of s-polarized reflected
light beam 1234 may be diffracted by grating coupler 1220 out of
waveguide 1210, and only a small portion of s-polarized reflected
light beam 1234 may not be diffracted and may be reflected at top
surface 1212. Therefore, the power of the reflected portion (shown
by light beam 1236) may be much lower than the power of s-polarized
first diffraction order 1232.
[0144] FIG. 12B illustrates the diffraction of p-polarized light by
grating coupler 1220 in waveguide display 1200. As described above,
grating coupler 1220 may have a higher diffraction efficiency for
s-polarized light than for p-polarized light. When a p-polarized
incident light beam 1240 reaches grating coupler 1220 at top
surface 1212 of waveguide 1210, it may be diffracted by grating
coupler 1220 into multiple diffraction orders including p-polarized
first diffraction order 1242 and other diffraction orders, where
the first order diffraction efficiency for p-polarized incident
light beam 1240 may be relatively low. The p-polarized first
diffraction order 1242 may be reflected at a bottom surface 1214
into p-polarized reflected light beam 1244. When the p-polarized
reflected light beam 1244 reaches top surface 1212 of waveguide
1210, a small portion of p-polarized reflected light beam 1244 may
be diffracted by grating coupler 1220 out of waveguide 1210, and a
large portion of p-polarized reflected light beam 1244 may not be
diffracted and may be reflected at top surface 1212. Therefore, the
power of the reflected portion (shown by light beam 1246) may be
lower than but close to the power of p-polarized first diffraction
order 1242.
[0145] Grating couplers, such as grating couplers 1120 and 1220,
may be optimized to maximize the power of the display light in the
desire path. For example, the grating shape, the slant angle, the
grating period, the duty cycle, the grating height or depth, the
refractive index, the refractive index modulation, the overcoating
material, and the spatial variations of these grating parameters
across the grating may be adjusted to improve the efficiencies of
directing display light to the desired directions. Varying these
parameters may provide some but limited improvements to the
efficiencies of the grating couplers due to the intrinsic
characteristics of SRGs and VBGs.
[0146] According to certain embodiments, the efficiency of a
waveguide display may be improved by changing the polarization
state of the display light beam along its propagation path. For
example, a phase structure may be coupled to the waveguide and used
to change the polarization state of the light reflected at the
surface of the waveguide, such that the reflected light, when
reaching a polarization-dependent grating coupler, may be
preferentially diffracted or reflected to the desired directions
towards the eyebox to improve the overall efficiency of the
waveguide display.
[0147] FIG. 13A illustrates an example of a waveguide display 1300
including a grating coupler 1320 and a phase structure 1322 for
changing the polarization state of incident light according to
certain embodiments. Grating coupler 1320 may have a higher
diffraction efficiency for s-polarized light than for p-polarized
light. When an s-polarized incident light beam 1330 reaches grating
coupler 1320 at a top surface 1312 of waveguide 1310, it may be
diffracted by grating coupler 1320 into multiple diffraction orders
including s-polarized first diffraction order 1332 and other
diffraction orders, where the first order diffraction efficiency
for s-polarized incident light beam 1330 may be high. The
s-polarized first diffraction order 1332 may reach a bottom surface
1314 of waveguide 1310, where phase structure 1322 may be attached.
Bottom surface 1314 and phase structure 1322 may reflect
s-polarized first diffraction order 1332 and convert s-polarized
first diffraction order 1332 into a p-polarized reflected light
beam 1334. When the p-polarized reflected light beam 1334 reaches
top surface 1312 of waveguide 1310, a small portion of p-polarized
reflected light beam 1338 may be diffracted by grating coupler 1320
out of waveguide 1310, and a large portion of p-polarized reflected
light beam 1334 may not be diffracted and may be reflected at top
surface 1312. Therefore, the power of the reflected portion (shown
by light beam 1336) may be lower than but close to the power of
s-polarized first diffraction order 1232.
[0148] Phase structure 1322 may include any birefringent materials
(e.g., birefringent crystals, liquid crystals, or polymers) or
structures (e.g., gratings, meta-gratings, micro-structures,
nano-structures, or other subwavelength structures) that can cause
a desired phase delay between two orthogonal linear polarization
components (e.g., s-polarized component and p-polarized component)
of a light beam, such that the incident light beam may be changed
to an s-polarized, p-polarized, circularly polarized, or
elliptically polarized beam. The phase structure may be placed at
various locations in a waveguide display, such as at the input
coupler region, between the input coupler and the output coupler,
at the output coupler region, or any combinations.
[0149] FIG. 13B illustrates an example of a waveguide display 1302
including grating couplers 1350 and 1370 and a phase structure 1360
for changing the polarization state of incident light according to
certain embodiments. In the example shown in FIG. 13B, waveguide
display 1302 includes a substrate 1340 that may function as the
waveguide. Grating coupler 1350 is on the top surface of substrate
1340. Phase structure 1360 is on the bottom surface of substrate
1340 and is between substrate 1340 and grating coupler 1370.
Grating couplers 1350 and 1370 may be used to diffract display
light of different colors and/or from different regions in a field
of view into substrate 1340 as guided wave.
[0150] Phase structure 1360 may include, for example, a
quarter-wave plate (QWP). The fast axis of the QWP may be at an
about 45.degree. angle with respect to the grating ridges or the
grating vector. Thus, as illustrated in FIG. 13B, s-polarized light
1380 that is diffracted by grating coupler 1350 may be converted to
left-handed circular polarization (LCP) light by the QWP as
s-polarized light 1380 passes through phase structure 1360 from
substrate 1340 to the interface between phase structure 1360 and
grating coupler 1370. The LCP light, when reflected at the
interface between phase structure 1360 and grating coupler 1370 or
the interface between grating coupler 1370 and air, may become
right-handed circular polarization (RCP) light because of the
change in the propagation direction. The reflected RCP light may
then be converted to p-polarized light by the QWP as the reflected
RCP light passes through phase structure 1360 back to substrate
1340. As such, the s-polarized light 1380 that is coupled into
substrate 1340 may become p-polarized when it reaches grating
coupler 1350, which may have a low diffraction efficiency for
p-polarized light and thus would have a lower loss for the light
coupled into substrate 1340.
[0151] FIG. 13C illustrates an example of a waveguide display 1304
including grating couplers 1352 and 1372 and a phase structure 362
changing the polarization state of incident light according to
certain embodiments. In the example shown in FIG. 13C, waveguide
display 1304 includes a substrate 1342 that may function as the
waveguide. Grating coupler 1352 is on the top surface of substrate
1342. Grating coupler 1372 is on the bottom surface of substrate
1342 and is between substrate 1342 and phase structure 1362.
Grating couplers 1352 and 1372 may be used to diffract display
light of different colors and/or from different regions in a field
of view into substrate 1342 as guided wave.
[0152] Phase structure 1362 may include, for example, a wave plate
or a birefringent subwavelength structure. As illustrated in FIG.
13C, s-polarized light 1382 that is diffracted by grating coupler
1352 may be converted to LCP light by grating coupler 1372 and
phase structure 1362 as s-polarized light 1382 passes through
grating coupler 1372 and phase structure 1362 from substrate 1342
to the bottom surface of phase structure 1362. The LCP light, when
reflected at the bottom surface of phase structure 1362, may become
RCP light because of the change in the propagation direction. The
RCP light may then be converted to p-polarized light by phase
structure 1362 and grating coupler 1372 as the RCP light passes
through phase structure 1362 and grating coupler 1372 back to
substrate 1342. As such, the s-polarized light 1382 that is coupled
into substrate 1342 may become p-polarized when it reaches grating
coupler 1352, which may have a low diffraction efficiency for
p-polarized light and thus would have a lower loss for the light
coupled into substrate 1342.
[0153] FIG. 14A illustrates the efficiencies of diffracting
s-polarized light by an example of a grating coupler 1420 in a
waveguide display 1400. FIG. 14A shows that grating coupler 1420 on
a waveguide 1410 diffracts an s-polarized incident light beam at an
about 66% diffraction efficiency into waveguide 1410. The
s-polarized light beam in waveguide 1410 may be totally reflected
at the bottom surface of waveguide 1410 and reach grating coupler
1420. About 20% of the reflected s-polarized light may be
diffracted out of waveguide 1410 by grating coupler 1420, only
about 1% of the reflected s-polarized light may be reflected at the
top surface of waveguide 1410, and other portions of the reflected
s-polarized light may be diffracted into other diffraction orders.
Thus, only about 66%.times.1%=0.66% of the incident s-polarized
beam may become guided light within waveguide 1410.
[0154] FIG. 14B illustrates the efficiencies of diffracting
p-polarized light by grating coupler 1420 in waveguide display
1400. FIG. 14B shows that grating coupler 1420 on waveguide 1410
diffracts a p-polarized incident light beam at an about 40%
diffraction efficiency into waveguide 1410. The p-polarized light
beam in waveguide 1410 may be totally reflected at the bottom
surface of waveguide 1410 and reach grating coupler 1420. About 5%
of the reflected p-polarized light may be diffracted out of
waveguide 1410 by grating coupler 1420, about 15% of the reflected
p-polarized light may be reflected at the top surface of waveguide
1410, and other portions of the reflected p-polarized light may be
diffracted into other diffraction orders. Thus, about
40%.times.15%=6% of the incident p-polarized beam may become guided
light within waveguide 1410. As a result, on average, about 3.33%
of the incident light may become guided light within waveguide 1410
to reach an output coupler.
[0155] FIG. 14C illustrates the efficiencies of diffracting
s-polarized light by an example of a grating coupler 1422 and a
phase structure 1430 in a waveguide display 1402 according to
certain embodiments. FIG. 14C shows that grating coupler 1422 on a
waveguide 1412 diffracts an s-polarized incident light beam at an
about 66% diffraction efficiency into waveguide 1412. The
s-polarized light beam in waveguide 1412 may be converted to
p-polarized light by phase structure 1430 and totally reflected at
the bottom of waveguide 1412 and reach grating coupler 1422. About
15% of the reflected p-polarized light may be reflected at the top
surface of waveguide 1412. Thus, about 66%.times.15%=9.9% of the
incident s-polarized beam may become p-polarized guided light
within waveguide 1412.
[0156] FIG. 14D illustrates the efficiencies of diffracting
p-polarized light by grating coupler 1422 and phase structure 1430
in waveguide display 1402 according to certain embodiments. FIG.
14D shows that grating coupler 1422 on waveguide 1412 diffracts a
p-polarized incident light beam at an about 40% diffraction
efficiency into waveguide 1412. The p-polarized light beam in
waveguide 1412 may be converted to s-polarized light by phase
structure 1430 and totally reflected at the bottom of waveguide
1412 and reach grating coupler 1422. About 1% of the reflected
s-polarized light may be reflected at the top surface of waveguide
1412. Thus, about 40%.times.1%=0.4% of the incident p-polarized
beam may become s-polarized guided light within waveguide 1412. As
a result, on average, about 5.15% of the incident light may become
guided light within waveguide 1412 to reach an output coupler.
[0157] FIG. 15A includes a diagram 1500 illustrating simulated
input coupling efficiencies of examples of waveguide displays
including a grating coupler and various phase structures according
to certain embodiments. In the simulations, phase structures (e.g.,
waveplates) with different thicknesses and orientations with
respect to the input grating coupler are placed between a waveguide
and a bottom grating coupler (e.g., grating coupler 1370) as shown
in FIG. 13B. For each phase structure configuration (e.g., a unique
combination of thickness and orientation of the waveplate), the
average input coupling efficiency for light from different regions
in a field of view is measured at a location in the optical path
that is after the input grating coupler (e.g., input coupler 820,
input grating 930, third grating 1060, grating coupler 1320, or
grating coupler 1422) and before the first output grating coupler
(e.g., first output grating 830, first output grating 940, or first
output grating 1030).
[0158] In FIG. 15A, the horizontal axis corresponds to the
thickness of the waveplate (in .mu.m for physical thickness and
wavelengths for waveplate thickness), where the waveplate has a
birefringence characterized by a .DELTA.n about 0.601. The
waveplate thickness of the waveplate may be determined based on the
physical thickness (t) of the waveplate, the birefringence
(.DELTA.n), and the wavelength (.lamda.) according to
t.times..DELTA.n/.lamda.. In the simulations, the waveplate
thickness may vary between 0 and about one wavelength. The vertical
axis corresponds to the average input coupling efficiency for each
phase structure configuration and the corresponding change of the
average input coupling efficiency with respect to a baseline
efficiency measured without using a phase structure. Each curve in
FIG. 15A corresponds to a certain orientation of the fast axis of
the waveplate with respect to the grating ridges, where the angle
between the fast axis of the waveplate and the grating ridges may
vary from about 0.degree. to about 165.degree..
[0159] FIG. 15A shows that the maximum input coupling efficiency
may be achieved when the phase structure is a QWP (e.g., with a
physical thickness about 0.5 .mu.m) and is oriented such that the
fast axis of the QWP is at about 45.degree. with respect to the
grating ridges. The maximum input coupling efficiency may be about
11.5% higher than the baseline efficiency.
[0160] FIG. 15B illustrates simulated input coupling efficiencies
of an example of a waveguide display for light from different
regions in a field of view. The waveguide display may not include a
phases structure described above. FIG. 15B shows that the input
coupling efficiency may vary for different regions in the field of
view. The average input coupling efficiency for the field of view
is about 26.5%.
[0161] FIG. 15C illustrates simulated input coupling efficiencies
of an example of a waveguide display including a grating coupler
and a phase structure for light from different regions in a field
of view according to certain embodiments. The phase structure may
be between a substrate and a grating coupler as shown in FIG. 13B.
The phase structure may have an waveplate thickness about 0.484
wavelengths or a physical thickness about 0.4993 .mu.m. FIG. 15C
shows that the input coupling efficiency may vary for different
regions in the field of view. The average input coupling efficiency
for the field of view is about 29.5%.
[0162] FIG. 15D illustrates simulated input coupling efficiency
improvements by the example of waveguide display of FIG. 15C (e.g.,
waveguide display 1302) for light from different regions in the
field of view according to certain embodiments. FIG. 15D may be
generated by comparing the input coupling efficiency for each
region in the field of view shown in FIG. 15C with the input
coupling efficiency for the corresponding region shown in FIG. 15B.
FIG. 15D shows that, with the phase structure (e.g., a QWP oriented
at about 45.degree. with respect to the grating ridges), the input
coupling efficiency may be improved for almost every region in the
field of view. The maximum improvement is about 25.7%, and the
average improvement for the full field of view is about 11.1%.
[0163] FIG. 16A includes a diagram 1600 illustrating simulated
input coupling efficiencies of examples of waveguide displays
including a grating coupler and various phase structures according
to certain embodiments. In the simulations, phase structures (e.g.,
waveplates) with different thicknesses and orientations with
respect to the grating ridges (or grating vector) of the input
grating coupler are coupled to a bottom grating coupler (e.g.,
grating coupler 1372) on the bottom surface of a waveguide as shown
in FIG. 13C. For each phase structure configuration (e.g., a unique
combination of the thickness and orientation of the waveplate), the
average input coupling efficiency for light from different regions
in a field of view is measured at a location on the optical path
that is after the input grating coupler (e.g., input coupler 820,
input grating 930, third grating 1060, grating coupler 1320, or
grating coupler 1422) and before the first output grating coupler
(e.g., first output grating 830, first output grating 940, or first
output grating 1030).
[0164] In FIG. 16A, the horizontal axis corresponds to the
thickness of the waveplate (in .mu.m for physical thickness and
wavelengths for waveplate thickness), where the waveplate has a
birefringence characterized by a .DELTA.n about 0.952. The
waveplate thickness of the waveplate may vary between 0 and about
one wavelength. The vertical axis corresponds to the average input
coupling efficiency for each phase structure configuration and the
corresponding change of the average input coupling efficiency with
respect to a baseline efficiency measured without using a phase
structure. Each curve in FIG. 16A corresponds to a certain
orientation of the fast axis of the waveplate with respect to the
grating ridges, where the angle between the fast axis of the
waveplate and the grating ridges may vary from about 0.degree. to
about 165.degree..
[0165] FIG. 16A shows that the maximum input coupling efficiency
may be achieved when the waveplate thickness of the phase structure
is about 0.1 wavelength (e.g., with a physical thickness about 0.06
.mu.m) and is oriented such that the fast axis of the phase
structure is at about 165.degree. with respect to the grating
ridges. The maximum input coupling efficiency may be about 11.8%
higher than the baseline efficiency. The waveplate thickness of the
phase structure for the maximum input coupling efficiency may be
less than about a quarter wavelength, which may be caused by the
polarization-dependent characteristics of the bottom grating
coupler (e.g., grating coupler 1372).
[0166] FIG. 16B illustrates simulated input coupling efficiencies
of an example of a waveguide display for light from different
regions in a field of view. The waveguide display may not include a
phases structure described above. FIG. 16B shows that the input
coupling efficiency may vary for different regions in the field of
view. The average input coupling efficiency for the field of view
is about 26.5%.
[0167] FIG. 16C illustrates simulated input coupling efficiencies
of an example of a waveguide display including a grating coupler
and a phase structure for light from different regions in a field
of view according to certain embodiments. The phase structure may
be coupled to a grating coupler on a substrate as shown in FIG.
13C. The phase structure may have an waveplate thickness about 0.1
wavelengths or a physical thickness about 0.06 nm. FIG. 16C shows
that the input coupling efficiency may vary for different regions
in the field of view. The average input coupling efficiency for the
field of view is about 29.6%.
[0168] FIG. 16D illustrates simulated input coupling efficiency
improvements of the example of waveguide display of FIG. 16C for
light from different regions in the field of view according to
certain embodiments. FIG. 16D may be generated by comparing the
input coupling efficiency for each region shown in FIG. 16C with
the input coupling efficiency for the corresponding region shown in
FIG. 16B. FIG. 16D shows that, with the phase structure (e.g., a
0.1-wavelength waveplate oriented at about 165.degree. with respect
to the grating ridges), the input coupling efficiency may be
improved for almost every region in the field of view. The maximum
improvement is about 30.5%, and the average improvement for the
full field of view is about 11.6%.
[0169] The phase structures described above (e.g., phase structure
1322, 1360, 1362, or 1430) may include any birefringent materials
(e.g., birefringent crystals, liquid crystals, or polymers) or
structures (e.g., gratings, meta-gratings, nano-structures, or
other subwavelength structures) that can cause a desired phase
delay between two orthogonal linear polarization components (e.g.,
s-polarized light and p-polarized light), such that an incident
light beam may be changed to an s-polarized, p-polarized,
circularly polarized, or elliptically polarized beam.
[0170] In some embodiments, in order to reduce the loss (e.g., due
to undesired Fresnel reflection) at the interfaces between the
phase structures and the adjacent components of the waveguide
display, such as the substrate and/or the grating coupler, it may
be desirable to use a phase structure that has an effective
refractive index close to the refractive index of the adjacent
component. In some embodiments where the substrate has a high
refractive index (e.g., >2.0, such as 2.5), it may be difficult
to find a birefringent material that has a matching refractive
index. In such cases, gratings or other subwavelength structures
may be used to achieve the phase retardation and refractive index
matching.
[0171] FIG. 17A illustrates an example of a waveguide display 1700
including a grating coupler 1730 and a phase structure 1720 between
grating coupler 1730 and a substrate 1710 according to certain
embodiments. Phase structure 1720 may include a grating 1722 (or a
micro- or nano-structure) etched in substrate 1710 and an overcoat
layer 1724 on grating 1722. Grating 1722 may include subwavelength
features, and may change the polarization state of incident light
in a certain wavelength range and incident angle range. Overcoat
layer 1724 may have a refractive index different from the
refractive index of substrate 1710 to form the grating with a
certain refractive index modulation.
[0172] FIG. 17B illustrates another example of a waveguide display
1705 including a grating coupler 1745 and a phase structure 1740
between grating coupler 1745 and a substrate 1715 according to
certain embodiments. In the illustrated example, phase structure
1740 may include a layer 1725 including a high refractive index
material and an overcoat layer 1735 including a lower refractive
index material. Layer 1725 may have a refractive index higher than
that of substrate 1715 and may be deposited on substrate 1715. A
grating or another subwavelength structure may be etched in layer
1725, and then overcoat layer 1735 may be formed on the grating or
subwavelength structure. The grating or another subwavelength
structure etched in layer 1725 may change the polarization state of
incident light in a certain wavelength range and incident angle
range. Overcoat layer 1724 may have a refractive index lower than
the refractive index of substrate 1710. Thus, the effective
refractive index of phase structure 1740 that includes layer 1725
and overcoat layer 1735 may be close to the refractive index of
substrate 1715 such that a difference between the refractive index
of substrate 1715 and the effective refractive index of phase
structure 1740 may be less than about 0.35, less than about 0.2,
less than about 0.1, or less than about 0.05. Therefore, the loss
due to the refractive index discontinuity may be reduced. Grating
coupler 1745 may be formed on or coupled to overcoat layer
1735.
[0173] The phase structures described above may be placed at
various locations of an SRG-based waveguide display where it may be
desirable or beneficial to change the polarization state of the
light beam for improved system efficiency. For example, one or more
phase structures can be positioned at the input coupler region,
between the input coupler and the output coupler, at the output
coupler region, or any combinations. The one or more phase
structures at different locations can have the same or different
configurations and polarization characteristics, such as the same
or different waveplate thicknesses. The one or more phase
structures may convert s-polarized light to p-polarized light or
circularly polarized light, convert p-polarized light to
s-polarized light or circularly polarized light, convert circularly
polarized light to s-polarized light or p-polarized light, or the
like.
[0174] The phase structures described above may also be used to
improve the efficiency of a volume Bragg grating-based waveguide
display, such as reducing the undesired outcoupling by the input
grating described above. In addition, a VBG in a VBG-based
waveguide display may function as multilayer reflectors that may
strongly reflect light of a specific wavelength and at a specific
incident angle that meets the Bragg condition. The reflectivity of
the VBG for p-polarized light may be very low when the incident
angle is at or near the Brewster's angle. Thus, it may also be
desirable to change the polarization state of the incident light to
increase the desired diffraction by the VBG or to reduce the
undesired diffraction by the VBG.
[0175] FIG. 18A illustrates an example of a waveguide display 1800
including volume Bragg grating couplers. In the illustrated
example, waveguide display 1800 may include a first assembly 1810
and a second assembly 1820 that are separated by a spacer 1830.
First assembly 1810 may include a first substrate 1812, a second
substrate 1816, and one or more holographic grating layers 1814
between first substrate 1812 and second substrate 1816. Holographic
grating layers 1814 may include multiplexed reflective VBGs,
transmissive VBGs, or both. Similarly, second assembly 1820 may
include a first substrate 1822, a second substrate 1826, and one or
more holographic grating layers 1824 between first substrate 1822
and second substrate 1826. Holographic grating layers 1824 may
include multiplexed reflective VBGs, transmissive VBGs, or
both.
[0176] FIG. 18B illustrates an example of an assembly 1840 of a
waveguide display. Assembly 1840 may be an example of first
assembly 1810 or second assembly 1820, and may include a VBG 1860
within a substrate 1850 or between two substrates. As illustrated,
VBG 1860 may function as multiple reflectors that strongly reflect
light of a specific wavelength and at a specific angle that
satisfies the Bragg condition. Depending on the slant angle of the
multiple reflectors in VBG 1860, the reflected light may pass
through VBG 1860 such that VBG 1860 may transmissively diffract
incident light 1870 as shown in FIG. 18B. The transmissively
diffracted light may be reflected at a bottom surface 1852 of
substrate 1850 and may reach VBG 1860 again. VBG 1860 may at least
partially diffract the light out of substrate 1850 and thus may
decrease the input coupling efficiency of assembly 1840.
[0177] FIG. 19A illustrates an example of a waveguide display 1900
including volume Bragg grating couplers. Waveguide display 1900 may
include a VBG layer 1920 within a substrate 1910 or between two
substrates. VBG layer 1920 may include an input VBG 1922 and an
output VBG 1924. In the illustrated example, input VBG 1922 may
reflectively diffract incident light, and thus may function as a
reflective VBG. Output VBG 1924 may partially reflectively diffract
the light from input VBG 1922 out of substrate 1910 towards an
eyebox of waveguide display 1900.
[0178] FIG. 19B illustrates an example of an input coupler 1930
including a volume Bragg grating 1950 in a substrate 1940. VBG 1950
may be an example of input VBG 1922. As illustrated, VBG 1950 may
function as multiple reflectors that strongly reflect light of a
specific wavelength and at a specific angle that satisfies the
Bragg condition. Depending on the slant angle of the multiple
reflectors in VBG 1950, the reflected light may not pass through
VBG 1950 such that VBG 1950 may reflectively diffract incident
light 1960 as shown in FIG. 19B. The reflectively diffracted light
may be reflected at a top surface 1942 of substrate 1940 and may
reach VBG 1950 again. VBG 1950 may at least partially diffract the
reflected light out of substrate 1940 and thus may decrease the
input coupling efficiency of input coupler 1930.
[0179] Thus, both transmissive VBGs and reflective VBGs may
function as multilayer reflectors. The reflectivity of each of the
multiple reflectors may depend on the polarization state and the
incident angle of the incident light, and the base refractive index
and the refractive index modulation (.DELTA.n) of the VBG.
[0180] FIG. 20A illustrates examples of reflection coefficients of
s-polarized and p-polarized light with different incident angles at
an interface between a low refractive index material and a high
refractive index material. In the illustrated example, the
refractive index of the first medium is 1.0, the refractive index
of the second medium is 1.5, and the s-polarized or p-polarized
light reaches the interface between the two media from the first
medium. A curve 2010 in FIG. 20A shows the reflection coefficients
for s-polarized light with different incident angles. A curve 2020
shows the reflection coefficients for p-polarized light with
different incident angles. Curve 2020 shows that, when the incident
angle is equal to or close to the Brewster's angle, the reflection
coefficient for p-polarized light is about or close to zero. Thus,
the reflectivity at the interface between the two media can be very
low for p-polarized light from certain incident angles.
[0181] FIG. 20B illustrates examples of reflection coefficients of
s-polarization and p-polarization light with different incident
angles at an interface between a high refractive index material and
a low refractive index material. In the illustrated example, the
refractive index of the first medium is 1.5, the refractive index
of the second medium is 1.0, and the s-polarized or p-polarized
light reaches the interface between the two media from the first
medium. A curve 2012 in FIG. 20B shows the reflection coefficients
for s-polarized light with different incident angles. A curve 2022
shows the reflection coefficients for p-polarized light with
different incident angles. As shown by curves 2012 and 2022, the
incident light may be totally reflected when the incident angle is
greater than the critical angle. When the incident angle is less
than the critical angle, the reflection coefficients for
p-polarized light with incident angles at or near the Brewster's
angle may be close to zero. Thus, the reflectivity at the interface
between the two media can be very low for p-polarized light from
certain incident angles. Thus, in a VBG-based waveguide display, it
may be desirable to alter the polarization state of the incident
light to preferentially diffract or transmit the incident light in
order to achieve a high efficiency of the VBG-based waveguide
display
[0182] FIG. 21A illustrates an example of an optical see-through
waveguide display 2100 including volume Bragg gratings for exit
pupil expansion according to certain embodiments. Waveguide display
2100 may be an example of waveguide display 1000 described above.
Waveguide display 2100 may include a first grating 2110, a second
grating 2120, a third grating 2130, and a fourth grating 2140
coupled to one or more substrates. As described above with respect
to FIG. 10, display light may be coupled into a substrate by first
grating 2110. Second grating 2120 may direct the coupled display
light towards third grating 2130. Third grating 2130 may replicate
the input pupil in one direction and direct the display light
towards fourth grating 2140. Fourth grating 2140 may replicate the
input pupil in a second direction and direct the display light
towards an eyebox 2150. First grating 2110 and fourth grating 2140
may compensate for the dispersion caused by each other. Similarly,
second grating 2120 and third grating 2130 may compensate for the
dispersion caused by each other. In order to achieve a wide field
of view and a wide spectral range, the grating vectors of the four
gratings may not be aligned. As such, a light beam may be
s-polarized light for one grating, but may be p-polarized light for
another grating that has a different grating vector.
[0183] FIG. 21B illustrates examples of polarization states of
light beams in an example of a waveguide display 2105. In the
illustrated example, a first grating 2160 and a second grating 2170
may have high diffraction efficiencies for s-polarized light but
low diffraction efficiencies for p-polarized light. However, due to
the different orientations and grating vectors of first grating
2160 and second grating 2170, s-polarized light diffracted by first
grating 2160 may become p-polarized for second grating 2170. As
such, only a small portion of the p-polarized light may be
diffracted by second grating 2170. Therefore, the overall
efficiency of waveguide display 2105 may be low.
[0184] FIG. 22A illustrates a cross-sectional view of an example of
a waveguide display 2200 including VBG couplers and a phase
structure 2230 according to certain embodiments. Waveguide display
2200 may be similar to waveguide display 1900 and may additionally
include phase structure 2230. As illustrated, waveguide display
2200 may include VBGs 2220 and 2222 in a substrate 2210 or between
two substrates. VBG 2220 may reflectively diffract incident display
light (e.g., s-polarized light) towards a top surface 2212 of
substrate 2210. Top surface 2212 may reflect the display light
towards a bottom surface 2214 of substrate 2210. Phase structure
2230 at bottom surface 2214 of substrate 2210 may receive the
reflected display light and change the polarization state of the
display light, for example, to p-polarized light. The display light
may be reflected at bottom surface 2214 of substrate 2210 or a
bottom surface of phase structure 2230. The reflected display light
may incident on VBG 2222 as s-polarized light due to the different
orientation and different grating vector of VBG 2222 compared to
VBG 2220, and may be diffracted out of substrate 2210 towards an
eyebox at a higher diffraction efficiency by VBG 2222.
[0185] FIG. 22B illustrates a top view of an example of a waveguide
display 2202 including VBGs and a phase structure 2290 according to
certain embodiments. As in waveguide display 2100, waveguide
display 2202 may include a first grating 2240, a second grating
2250, a third grating 2260, and a fourth grating 2270 coupled to
one or more substrates 2205. Each of gratings 2240-2270 may be a
reflective VBG or a transmissive VBG. As described above with
respect to FIG. 10, display light may be coupled into a substrate
2205 by first grating 2240. Second grating 2250 may direct the
coupled display light towards third grating 2260. Third grating
2260 may replicate the input pupil in one direction and direct the
display light towards fourth grating 2270. Fourth grating 2270 may
replicate the input pupil in a second direction and direct the
display light towards an eyebox 2280. Phase structure 2290 may be
at a region where first grating 2240 and/or second grating 2250 are
located, and may be used to change the polarization state of the
display light coupled into substrate 2205, for example, from
p-polarized to s-polarized or from s-polarized to p-polarized.
[0186] FIG. 23A illustrates a cross-sectional view of an example of
a waveguide display 2300 including volume Bragg gratings 2320 and
2322 and phase structures 2330 and 2332 according to certain
embodiments. As illustrated, waveguide display 2300 may include
VBGs 2320 and 2322 in a substrate 2310 or between two substrates.
VBG 2320 may reflectively diffract incident display light (e.g.,
s-polarized light) towards a top surface of substrate 2310. Phase
structure 2332 may be coupled to the top surface of substrate 2310,
and may change the polarization state of the incident display
light. The top surface of substrate 2310 or phase structure 2332
may reflect the display light towards the bottom surface of
substrate 2310. Phase structure 2330 at the bottom surface of
substrate 2310 may change the polarization state of the incident
display light. The display light may be reflected at the bottom
surface of substrate 2310 or phase structure 2330. The reflected
display light may incident on VBG 2322, and may be diffracted by
VBG 2322 out of substrate 2310 towards an eyebox at a high
diffraction efficiency.
[0187] In some embodiments, phase structures 2330 and 2332 may be
only at selected locations on the top and bottom surfaces of
substrate 2310. In some embodiments, either phase structure 2330 or
phase structure 2332 may be used in a waveguide display. In some
embodiments, both phase structure 2330 and phase structure 2332 may
be used in a waveguide display, where the desired phase change or
retardation may be achieved by the combination of the two phase
structures. For example, to convert s-polarized light to
p-polarized light, a first phase structure may convert the
s-polarized light to circularly polarized light, and a second phase
structure may convert the circularly polarized light to p-polarized
light. In some embodiments, the polarization alteration
characteristics of phase structure 2330 or phase structure 2332 may
vary at different locations.
[0188] FIG. 23B illustrates a top view of an example of a waveguide
display 2302 including volume Bragg gratings and a phase structure
2390 according to certain embodiments. Waveguide display 2302 may
include a first grating 2340, a second grating 2350, a third
grating 2360, and a fourth grating 2370 coupled to one or more
substrates 2305. As described above, display light may be coupled
into a substrate 2305 by first grating 2340. Second grating 2350
may direct the coupled display light towards third grating 2360.
Third grating 2360 may replicate the input pupil in one direction
and direct the display light towards fourth grating 2370. Fourth
grating 2370 may replicate the input pupil in a second direction
and direct the display light towards an eyebox 2380. Phase
structure 2390 may be on one or two surface of a substrate 2305,
and may be used to change polarization state of the display light,
for example, from p-polarized to s-polarized or from s-polarized to
p-polarized. Phase structure 2390 may cover the areas of waveguide
display 2302 where gratings 2340-2370 are located.
[0189] FIG. 24A illustrates a simulation result for an example of a
volume Bragg grating-based waveguide display 2400 according to
certain embodiments. Waveguide display 2400 may be an example of
waveguide display 2100. FIG. 24A shows a display light beam coupled
into a waveguide by a first grating (e.g., first grating 2110) and
then directed by a second grating (e.g., second grating 2120) to
output gratings. The input coupling efficiency of waveguide display
2400 may be measured after the display light is diffracted by the
second grating and before the display light reaches the output
gratings.
[0190] FIG. 24B illustrates a simulation result of an example of a
waveguide display 2405 including volume Bragg gratings and a phase
structure according to certain embodiments. Waveguide display 2405
may be an example of waveguide display 2202, where a phase
structure (e.g., phase structure 2290) may be located at a region
where a first grating (e.g., first grating 2240) and a second
grating (e.g., second grating 2250) are located. FIG. 24B shows a
display light beam coupled into a waveguide by the first grating
and then directed by the second grating to output gratings. The
input coupling efficiency of waveguide display 2405 may be measured
after the display light is diffracted by the second grating and
before the display light reaches the output gratings. FIG. 24B
shows that the intensity of the display light beam after the second
grating may be much higher than that shown in FIG. 24A.
[0191] FIG. 25 illustrates simulated input coupling efficiencies of
examples of waveguide displays including various phase structures
according to certain embodiments. The waveguide displays used for
the simulations may have a configuration as shown in FIG. 22B. The
input coupling efficiencies of the waveguide displays may be
measured after the display light is diffracted by the second
grating (e.g., second grating 2250) and before the display light
reaches the output gratings (e.g., third grating 2260). In the
simulations, phase structures (e.g., waveplates) with different
thicknesses and orientations with respect to the first grating
(e.g., first grating 2240) are placed at a region where the first
grating and the second grating are located as shown in FIG. 22B.
For each phase structure configuration (e.g., a unique combination
of thickness and orientation of the waveplate), the average input
coupling efficiency for light from different regions in a field of
view is measured.
[0192] In FIG. 25, the horizontal axis corresponds to the thickness
of the waveplate (in .mu.m for physical thickness and in
wavelengths for waveplate thickness), where the waveplate has a
birefringence characterized by a .DELTA.n about 0.145. The
waveplate thickness of the waveplate may vary between 0 and about
one wavelength. The vertical axis corresponds to the average input
coupling efficiency for each phase structure configuration and the
corresponding change of the average input coupling efficiency with
respect to a baseline efficiency measured without using a phase
structure. Each curve in FIG. 25 corresponds to a different
orientation of the fast axis of the phase structure with respect to
the grating ridges of the first grating, where the angle between
the fast axis of the waveplate and the grating ridges may vary from
about 0.degree. to about 170.degree..
[0193] FIG. 25 shows that the maximum input coupling efficiency may
be achieved when the phase structure has a waveplate thickness
about 0.4 wavelengths (e.g., with a physical thickness about 1.54
.mu.m) and is oriented such that the fast axis of the phase
structure is at about 130.degree. with respect to the grating
ridges. The maximum input coupling efficiency may be about 42%
higher than the baseline efficiency.
[0194] FIGS. 26A-26C illustrate simulated input coupling
efficiencies of an example of a VBG-based waveguide display (e.g.,
waveguide display 2100) for light from different regions of a field
of view and in red, green, and blue colors, respectively. FIG. 26A
shows that the average input coupling efficiency of the VBG-based
waveguide display with no phase structures is about 0.725% for red
light. FIG. 26B shows that the average input coupling efficiency of
the VBG-based waveguide display with no phase structures is about
0.62% for green light. FIG. 26C shows that the average input
coupling efficiency of the VBG-based waveguide display with no
phase structures is about 1.246% for blue light.
[0195] FIGS. 26D-26F illustrate simulated input coupling
efficiencies of an example of a VBG-based waveguide display (e.g.,
waveguide display 2202) including a phase structure (e.g., a zeroth
order phase plate) for light from different regions in a field of
view and in red, green, and blue colors, respectively. FIG. 26D
shows that the average input coupling efficiency of the VBG-based
waveguide display with the phase structure is about 0.996% for red
light, which is about 37% higher than the baseline result shown in
FIG. 26A. FIG. 26E shows that the average input coupling efficiency
of the VBG-based waveguide display with the phase structure is
about 0.871% for green light, which is about 40% higher than the
baseline result shown in FIG. 26B. FIG. 26F shows that the average
input coupling efficiency of the VBG-based waveguide display with
the phase structure is about 1.486% for blue light, which is about
40% higher than the baseline result shown in FIG. 26C.
[0196] FIGS. 26G-26I illustrate simulated input coupling
efficiencies of an example of a VBG-based waveguide display (e.g.,
waveguide display 2202) including a phase structure (e.g., an
achromatic phase plate) for light from different regions in a field
of view and in red, green, and blue colors, respectively. FIG. 26G
shows that the average input coupling efficiency of the VBG-based
waveguide display with the phase structure is about 1.022% for red
light, which is about 41% higher than the baseline result shown in
FIG. 26A. FIG. 26H shows that the average input coupling efficiency
of the VBG-based waveguide display with the phase structure is
about 0.871% for green light, which is about 40% higher than the
baseline result shown in FIG. 26B. FIG. 26I shows that the average
input coupling efficiency of the VBG-based waveguide display with
the phase structure is about 1.623% for blue light, which is about
30% higher than the baseline result shown in FIG. 26C.
[0197] The phase structures described above (e.g., phase structure
2230, 2290, 2330, 2332, or 2390) may include any birefringent
materials (e.g., birefringent crystals, liquid crystals, or
polymers) or structures (e.g., gratings, meta-gratings,
nano-structures, or other subwavelength structures) that can cause
a desired phase delay between two orthogonal linear polarization
components (e.g., s-polarized light and p-polarized light), such
that the incident light beam may be changed to an s-polarized,
p-polarized, circularly polarized, or elliptically polarized
beam
[0198] In some embodiments, in order to reduce the loss (e.g., due
to undesired Fresnel reflection) at the interfaces between the
phase structures and the adjacent components of the waveguide
display, such as the substrate, it may be desirable to use a phase
structure that has an effective refractive index close to the
refractive index of the adjacent component. In some embodiments
where the substrate has a high refractive index (e.g., >2.0,
such as 2.5), it may be difficult to find a birefringent material
that has a matching refractive index. In such cases, gratings or
other subwavelength structures may be used to achieve the phase
delay, polarization conversion, and refractive index matching as
described above with respect to, for example, FIGS. 17A and 17B,
such that a difference between the refractive index of the
substrate and the effective refractive index of the phase structure
may be less than about 0.35, less than about 0.2, less than about
0.1, or less than about 0.05.
[0199] Embodiments of the invention may be used to implement
components of an artificial reality system or may be implemented in
conjunction with an artificial reality system. Artificial reality
is a form of reality that has been adjusted in some manner before
presentation to a user, which may include, for example, a virtual
reality (VR), an augmented reality (AR), a mixed reality (MR), a
hybrid reality, or some combination and/or derivatives thereof.
Artificial reality content may include completely generated content
or generated content combined with captured (e.g., real-world)
content. The artificial reality content may include video, audio,
haptic feedback, or some combination thereof, and any of which may
be presented in a single channel or in multiple channels (such as
stereo video that produces a three-dimensional effect to the
viewer). Additionally, in some embodiments, artificial reality may
also be associated with applications, products, accessories,
services, or some combination thereof, that are used to, for
example, create content in an artificial reality and/or are
otherwise used in (e.g., perform activities in) an artificial
reality. The artificial reality system that provides the artificial
reality content may be implemented on various platforms, including
a head-mounted display (HMD) connected to a host computer system, a
standalone HMD, a mobile device or computing system, or any other
hardware platform capable of providing artificial reality content
to one or more viewers.
[0200] FIG. 27 is a simplified block diagram of an example of an
electronic system 2700 of an example near-eye display (e.g., HMD
device) for implementing some of the examples disclosed herein.
Electronic system 2700 may be used as the electronic system of an
HMD device or other near-eye displays described above. In this
example, electronic system 2700 may include one or more
processor(s) 2710 and a memory 2720. Processor(s) 2710 may be
configured to execute instructions for performing operations at a
number of components, and can be, for example, a general-purpose
processor or microprocessor suitable for implementation within a
portable electronic device. Processor(s) 2710 may be
communicatively coupled with a plurality of components within
electronic system 2700. To realize this communicative coupling,
processor(s) 2710 may communicate with the other illustrated
components across a bus 2740. Bus 2740 may be any subsystem adapted
to transfer data within electronic system 2700. Bus 2740 may
include a plurality of computer buses and additional circuitry to
transfer data.
[0201] Memory 2720 may be coupled to processor(s) 2710. In some
embodiments, memory 2720 may offer both short-term and long-term
storage and may be divided into several units. Memory 2720 may be
volatile, such as static random access memory (SRAM) and/or dynamic
random access memory (DRAM) and/or non-volatile, such as read-only
memory (ROM), flash memory, and the like. Furthermore, memory 2720
may include removable storage devices, such as secure digital (SD)
cards. Memory 2720 may provide storage of computer-readable
instructions, data structures, program modules, and other data for
electronic system 2700. In some embodiments, memory 2720 may be
distributed into different hardware modules. A set of instructions
and/or code might be stored on memory 2720. The instructions might
take the form of executable code that may be executable by
electronic system 2700, and/or might take the form of source and/or
installable code, which, upon compilation and/or installation on
electronic system 2700 (e.g., using any of a variety of generally
available compilers, installation programs,
compression/decompression utilities, etc.), may take the form of
executable code.
[0202] In some embodiments, memory 2720 may store a plurality of
application modules 2722 through 2724, which may include any number
of applications. Examples of applications may include gaming
applications, conferencing applications, video playback
applications, or other suitable applications. The applications may
include a depth sensing function or eye tracking function.
Application modules 2722-2724 may include particular instructions
to be executed by processor(s) 2710. In some embodiments, certain
applications or parts of application modules 2722-2724 may be
executable by other hardware modules 2780. In certain embodiments,
memory 2720 may additionally include secure memory, which may
include additional security controls to prevent copying or other
unauthorized access to secure information.
[0203] In some embodiments, memory 2720 may include an operating
system 2725 loaded therein. Operating system 2725 may be operable
to initiate the execution of the instructions provided by
application modules 2722-2724 and/or manage other hardware modules
2780 as well as interfaces with a wireless communication subsystem
2730 which may include one or more wireless transceivers. Operating
system 2725 may be adapted to perform other operations across the
components of electronic system 2700 including threading, resource
management, data storage control and other similar
functionality.
[0204] Wireless communication subsystem 2730 may include, for
example, an infrared communication device, a wireless communication
device and/or chipset (such as a Bluetooth.RTM. device, an IEEE
802.11 device, a Wi-Fi device, a WiMax device, cellular
communication facilities, etc.), and/or similar communication
interfaces. Electronic system 2700 may include one or more antennas
2734 for wireless communication as part of wireless communication
subsystem 2730 or as a separate component coupled to any portion of
the system. Depending on desired functionality, wireless
communication subsystem 2730 may include separate transceivers to
communicate with base transceiver stations and other wireless
devices and access points, which may include communicating with
different data networks and/or network types, such as wireless
wide-area networks (WWANs), wireless local area networks (WLANs),
or wireless personal area networks (WPANs). A WWAN may be, for
example, a WiMax (IEEE 802.16) network. A WLAN may be, for example,
an IEEE 802.11x network. A WPAN may be, for example, a Bluetooth
network, an IEEE 802.15x, or some other types of network. The
techniques described herein may also be used for any combination of
WWAN, WLAN, and/or WPAN. Wireless communications subsystem 2730 may
permit data to be exchanged with a network, other computer systems,
and/or any other devices described herein. Wireless communication
subsystem 2730 may include a means for transmitting or receiving
data, such as identifiers of HMD devices, position data, a
geographic map, a heat map, photos, or videos, using antenna(s)
2734 and wireless link(s) 2732. Wireless communication subsystem
2730, processor(s) 2710, and memory 2720 may together comprise at
least a part of one or more of a means for performing some
functions disclosed herein.
[0205] Embodiments of electronic system 2700 may also include one
or more sensors 2790. Sensor(s) 2790 may include, for example, an
image sensor, an accelerometer, a pressure sensor, a temperature
sensor, a proximity sensor, a magnetometer, a gyroscope, an
inertial sensor (e.g., a module that combines an accelerometer and
a gyroscope), an ambient light sensor, or any other similar module
operable to provide sensory output and/or receive sensory input,
such as a depth sensor or a position sensor. For example, in some
implementations, sensor(s) 2790 may include one or more inertial
measurement units (IMUs) and/or one or more position sensors. An
IMU may generate calibration data indicating an estimated position
of the HMD device relative to an initial position of the HMD
device, based on measurement signals received from one or more of
the position sensors. A position sensor may generate one or more
measurement signals in response to motion of the HMD device.
Examples of the position sensors may include, but are not limited
to, one or more accelerometers, one or more gyroscopes, one or more
magnetometers, another suitable type of sensor that detects motion,
a type of sensor used for error correction of the IMU, or some
combination thereof. The position sensors may be located external
to the IMU, internal to the IMU, or some combination thereof. At
least some sensors may use a structured light pattern for
sensing.
[0206] Electronic system 2700 may include a display module 2760.
Display module 2760 may be a near-eye display, and may graphically
present information, such as images, videos, and various
instructions, from electronic system 2700 to a user. Such
information may be derived from one or more application modules
2722-2724, virtual reality engine 2726, one or more other hardware
modules 2780, a combination thereof, or any other suitable means
for resolving graphical content for the user (e.g., by operating
system 2725). Display module 2760 may use liquid crystal display
(LCD) technology, light-emitting diode (LED) technology (including,
for example, OLED, ILED, .mu.LED, AMOLED, TOLED, etc.), light
emitting polymer display (LPD) technology, or some other display
technology.
[0207] Electronic system 2700 may include a user input/output
module 2770. User input/output module 2770 may allow a user to send
action requests to electronic system 2700. An action request may be
a request to perform a particular action. For example, an action
request may be to start or end an application or to perform a
particular action within the application. User input/output module
2770 may include one or more input devices. Example input devices
may include a touchscreen, a touch pad, microphone(s), button(s),
dial(s), switch(es), a keyboard, a mouse, a game controller, or any
other suitable device for receiving action requests and
communicating the received action requests to electronic system
2700. In some embodiments, user input/output module 2770 may
provide haptic feedback to the user in accordance with instructions
received from electronic system 2700. For example, the haptic
feedback may be provided when an action request is received or has
been performed.
[0208] Electronic system 2700 may include a camera 2750 that may be
used to take photos or videos of a user, for example, for tracking
the user's eye position. Camera 2750 may also be used to take
photos or videos of the environment, for example, for VR, AR, or MR
applications. Camera 2750 may include, for example, a complementary
metal-oxide-semiconductor (CMOS) image sensor with a few millions
or tens of millions of pixels. In some implementations, camera 2750
may include two or more cameras that may be used to capture 3-D
images.
[0209] In some embodiments, electronic system 2700 may include a
plurality of other hardware modules 2780. Each of other hardware
modules 2780 may be a physical module within electronic system
2700. While each of other hardware modules 2780 may be permanently
configured as a structure, some of other hardware modules 2780 may
be temporarily configured to perform specific functions or
temporarily activated. Examples of other hardware modules 2780 may
include, for example, an audio output and/or input module (e.g., a
microphone or speaker), a near field communication (NFC) module, a
rechargeable battery, a battery management system, a wired/wireless
battery charging system, etc. In some embodiments, one or more
functions of other hardware modules 2780 may be implemented in
software.
[0210] In some embodiments, memory 2720 of electronic system 2700
may also store a virtual reality engine 2726. Virtual reality
engine 2726 may execute applications within electronic system 2700
and receive position information, acceleration information,
velocity information, predicted future positions, or some
combination thereof of the HMD device from the various sensors. In
some embodiments, the information received by virtual reality
engine 2726 may be used for producing a signal (e.g., display
instructions) to display module 2760. For example, if the received
information indicates that the user has looked to the left, virtual
reality engine 2726 may generate content for the HMD device that
mirrors the user's movement in a virtual environment. Additionally,
virtual reality engine 2726 may perform an action within an
application in response to an action request received from user
input/output module 2770 and provide feedback to the user. The
provided feedback may be visual, audible, or haptic feedback. In
some implementations, processor(s) 2710 may include one or more
GPUs that may execute virtual reality engine 2726.
[0211] In various implementations, the above-described hardware and
modules may be implemented on a single device or on multiple
devices that can communicate with one another using wired or
wireless connections. For example, in some implementations, some
components or modules, such as GPUs, virtual reality engine 2726,
and applications (e.g., tracking application), may be implemented
on a console separate from the head-mounted display device. In some
implementations, one console may be connected to or support more
than one HMD.
[0212] In alternative configurations, different and/or additional
components may be included in electronic system 2700. Similarly,
functionality of one or more of the components can be distributed
among the components in a manner different from the manner
described above. For example, in some embodiments, electronic
system 2700 may be modified to include other system environments,
such as an AR system environment and/or an MR environment.
[0213] The methods, systems, and devices discussed above are
examples. Various embodiments may omit, substitute, or add various
procedures or components as appropriate. For instance, in
alternative configurations, the methods described may be performed
in an order different from that described, and/or various stages
may be added, omitted, and/or combined. Also, features described
with respect to certain embodiments may be combined in various
other embodiments. Different aspects and elements of the
embodiments may be combined in a similar manner. Also, technology
evolves and, thus, many of the elements are examples that do not
limit the scope of the disclosure to those specific examples.
[0214] Specific details are given in the description to provide a
thorough understanding of the embodiments. However, embodiments may
be practiced without these specific details. For example,
well-known circuits, processes, systems, structures, and techniques
have been shown without unnecessary detail in order to avoid
obscuring the embodiments. This description provides example
embodiments only, and is not intended to limit the scope,
applicability, or configuration of the invention. Rather, the
preceding description of the embodiments will provide those skilled
in the art with an enabling description for implementing various
embodiments. Various changes may be made in the function and
arrangement of elements without departing from the spirit and scope
of the present disclosure.
[0215] Also, some embodiments were described as processes depicted
as flow diagrams or block diagrams. Although each may describe the
operations as a sequential process, many of the operations may be
performed in parallel or concurrently. In addition, the order of
the operations may be rearranged. A process may have additional
steps not included in the figure. Furthermore, embodiments of the
methods may be implemented by hardware, software, firmware,
middleware, microcode, hardware description languages, or any
combination thereof. When implemented in software, firmware,
middleware, or microcode, the program code or code segments to
perform the associated tasks may be stored in a computer-readable
medium such as a storage medium. Processors may perform the
associated tasks.
[0216] It will be apparent to those skilled in the art that
substantial variations may be made in accordance with specific
requirements. For example, customized or special-purpose hardware
might also be used, and/or particular elements might be implemented
in hardware, software (including portable software, such as
applets, etc.), or both. Further, connection to other computing
devices such as network input/output devices may be employed.
[0217] With reference to the appended figures, components that can
include memory can include non-transitory machine-readable media.
The term "machine-readable medium" and "computer-readable medium"
may refer to any storage medium that participates in providing data
that causes a machine to operate in a specific fashion. In
embodiments provided hereinabove, various machine-readable media
might be involved in providing instructions/code to processing
units and/or other device(s) for execution. Additionally or
alternatively, the machine-readable media might be used to store
and/or carry such instructions/code. In many implementations, a
computer-readable medium is a physical and/or tangible storage
medium. Such a medium may take many forms, including, but not
limited to, non-volatile media, volatile media, and transmission
media. Common forms of computer-readable media include, for
example, magnetic and/or optical media such as compact disk (CD) or
digital versatile disk (DVD), punch cards, paper tape, any other
physical medium with patterns of holes, a RAM, a programmable
read-only memory (PROM), an erasable programmable read-only memory
(EPROM), a FLASH-EPROM, any other memory chip or cartridge, a
carrier wave as described hereinafter, or any other medium from
which a computer can read instructions and/or code. A computer
program product may include code and/or machine-executable
instructions that may represent a procedure, a function, a
subprogram, a program, a routine, an application (App), a
subroutine, a module, a software package, a class, or any
combination of instructions, data structures, or program
statements.
[0218] Those of skill in the art will appreciate that information
and signals used to communicate the messages described herein may
be represented using any of a variety of different technologies and
techniques. For example, data, instructions, commands, information,
signals, bits, symbols, and chips that may be referenced throughout
the above description may be represented by voltages, currents,
electromagnetic waves, magnetic fields or particles, optical fields
or particles, or any combination thereof.
[0219] Terms, "and" and "or" as used herein, may include a variety
of meanings that are also expected to depend at least in part upon
the context in which such terms are used. Typically, "or" if used
to associate a list, such as A, B, or C, is intended to mean A, B,
and C, here used in the inclusive sense, as well as A, B, or C,
here used in the exclusive sense. In addition, the term "one or
more" as used herein may be used to describe any feature,
structure, or characteristic in the singular or may be used to
describe some combination of features, structures, or
characteristics. However, it should be noted that this is merely an
illustrative example and claimed subject matter is not limited to
this example. Furthermore, the term "at least one of" if used to
associate a list, such as A, B, or C, can be interpreted to mean
any combination of A, B, and/or C, such as A, AB, AC, BC, AA, ABC,
AAB, AABBCCC, etc.
[0220] Further, while certain embodiments have been described using
a particular combination of hardware and software, it should be
recognized that other combinations of hardware and software are
also possible. Certain embodiments may be implemented only in
hardware, or only in software, or using combinations thereof. In
one example, software may be implemented with a computer program
product containing computer program code or instructions executable
by one or more processors for performing any or all of the steps,
operations, or processes described in this disclosure, where the
computer program may be stored on a non-transitory computer
readable medium. The various processes described herein can be
implemented on the same processor or different processors in any
combination.
[0221] Where devices, systems, components or modules are described
as being configured to perform certain operations or functions,
such configuration can be accomplished, for example, by designing
electronic circuits to perform the operation, by programming
programmable electronic circuits (such as microprocessors) to
perform the operation such as by executing computer instructions or
code, or processors or cores programmed to execute code or
instructions stored on a non-transitory memory medium, or any
combination thereof. Processes can communicate using a variety of
techniques, including, but not limited to, conventional techniques
for inter-process communications, and different pairs of processes
may use different techniques, or the same pair of processes may use
different techniques at different times.
[0222] The specification and drawings are, accordingly, to be
regarded in an illustrative rather than a restrictive sense. It
will, however, be evident that additions, subtractions, deletions,
and other modifications and changes may be made thereunto without
departing from the broader spirit and scope as set forth in the
claims. Thus, although specific embodiments have been described,
these are not intended to be limiting. Various modifications and
equivalents are within the scope of the following claims.
* * * * *