U.S. patent application number 17/658048 was filed with the patent office on 2022-07-21 for refractive index modulation modification in a holographic grating.
The applicant listed for this patent is Facebook Technologies, LLC. Invention is credited to Wanli Chi, Austin Lane, Hee Yoon Lee, Matthieu Charles Raoul Leibovici.
Application Number | 20220229396 17/658048 |
Document ID | / |
Family ID | 1000006243648 |
Filed Date | 2022-07-21 |
United States Patent
Application |
20220229396 |
Kind Code |
A1 |
Leibovici; Matthieu Charles Raoul ;
et al. |
July 21, 2022 |
REFRACTIVE INDEX MODULATION MODIFICATION IN A HOLOGRAPHIC
GRATING
Abstract
Techniques disclosed herein relate to modifying refractive index
modulation in a holographic optical element, such as a holographic
grating. According to certain embodiments, a holographic optical
element or apodized grating includes a polymer layer comprising a
first region characterized by a first refractive index and a second
region characterized by a second refractive index. The holographic
optical element or apodized grating includes a plurality of
nanoparticles dispersed in the polymer layer. The nanoparticles
have a higher concentration in either the first region or the
second region. In some embodiments, the nanoparticles may be
configured to increase the refractive index modulation. In some
embodiments, the nanoparticles may be configured to apodize the
grating by decreasing the refractive index modulation proximate to
sides of the grating. The refractive index may be modulated by
applying a monomer reservoir buffer layer to the polymer layer,
either before or after hologram fabrication.
Inventors: |
Leibovici; Matthieu Charles
Raoul; (Seattle, WA) ; Lane; Austin;
(Snohomish, WA) ; Chi; Wanli; (Sammamish, WA)
; Lee; Hee Yoon; (Kirkland, WA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Facebook Technologies, LLC |
Menlo Park |
CA |
US |
|
|
Family ID: |
1000006243648 |
Appl. No.: |
17/658048 |
Filed: |
April 5, 2022 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16550046 |
Aug 23, 2019 |
11327438 |
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17658048 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G03H 1/0248 20130101;
G02B 2027/0174 20130101; G03H 2001/0439 20130101; G02B 5/0252
20130101; G03H 1/04 20130101; G02B 5/0841 20130101 |
International
Class: |
G03H 1/04 20060101
G03H001/04; G02B 5/02 20060101 G02B005/02; G02B 5/08 20060101
G02B005/08; G03H 1/02 20060101 G03H001/02 |
Claims
1. A holographic grating comprising: a polymer matrix comprising: a
first region characterized by a first refractive index; a second
region characterized by a second refractive index, the second
refractive index being higher than the first refractive index; and
a resin layer disposed on the polymer matrix, the resin layer
comprising: a support layer; and a first plurality of nanoparticles
dispersed in the support layer of the resin layer.
2. The holographic grating of claim 1, wherein the nanoparticles
are monomers.
3. The holographic grating of claim 1, wherein: the polymer matrix
further comprises a second plurality of nanoparticles; the second
plurality of nanoparticles have a higher concentration in the
second region than in the first region; and the second plurality of
nanoparticles have a third refractive index that is higher than the
second refractive index.
4. The holographic grating of claim 1, wherein: the polymer matrix
further comprises a second plurality of nanoparticles; the second
plurality of nanoparticles have a higher concentration in the first
region than in the second region; and the second plurality of
nanoparticles have a third refractive index that is lower than the
first refractive index.
5. The holographic grating of claim 1, wherein the nanoparticles in
a given region have a substantially constant concentration with
respect to a thickness of the polymer matrix.
6. The holographic grating of claim 1, wherein the polymer matrix
comprises a multiplexed volume Bragg grating.
7. A holographic grating fabricated by a process comprising
operations of: obtaining a holographic recording material layer;
exposing the holographic recording material layer to a recording
light pattern, the recording light pattern creating, in the
holographic recording material layer, a first region having a first
refractive index and a second region having second refractive index
that is higher than the first refractive index; and after exposing
the holographic recording material layer to the recording light
pattern, applying a first resin layer comprising a first plurality
of nanoparticles to the holographic recording material layer,
thereby causing preferential diffusion of at least a portion of the
first plurality of nanoparticles into the first region or the
second region of the holographic recording material layer, wherein
the nanoparticles include monomers.
8. The holographic grating of claim 7, wherein: the first plurality
of nanoparticles has a third refractive index that is higher than
the second refractive index; and the first plurality of
nanoparticles preferentially diffuses into the second region.
9. The holographic grating of claim 7, wherein: the first plurality
of nanoparticles has a third refractive index that is lower than
the second refractive index; and the first plurality of
nanoparticles preferentially diffuses so as to be more highly
concentrated in proximity to one or more of a top side or a bottom
side of the second region.
10. The holographic grating of claim 7, wherein: the first
plurality of nanoparticles has a third refractive index lower than
the first refractive index; and the first plurality of
nanoparticles preferentially diffuses into the first region.
11. The holographic grating of claim 7, wherein: the first
plurality of nanoparticles has a third refractive index that is
higher than the first refractive index; and the first plurality of
nanoparticles further diffuses so as to be more highly concentrated
in proximity to one or more of a top side or a bottom side of the
first region.
12. The holographic grating of claim 7, wherein the operations
further comprise: removing the first resin layer; and disposing a
substrate on the holographic recording material layer.
13. The holographic grating of claim 7, wherein the operations
further comprise: applying a second resin layer comprising a second
plurality of nanoparticles to the holographic recording material
layer, thereby causing diffusion of at least a portion of the
second plurality of nanoparticles into the holographic recording
material layer.
14. The holographic grating of claim 7, wherein the nanoparticles
in a given region have a substantially constant concentration with
respect to a thickness of the holographic recording material
layer.
15. A holographic grating fabricated by a process comprising
operations of: obtaining a holographic recording material layer;
applying a first resin layer comprising a first plurality of
nanoparticles to the holographic recording material layer; and
after applying the first resin layer, exposing the holographic
recording material layer to a recording light pattern, the
recording light pattern creating, in the holographic recording
material layer, a first region having a first refractive index and
a second region having second refractive index that is higher than
the first refractive index, wherein at least a portion of the first
plurality of nanoparticles diffuses from the first resin layer into
the holographic recording material layer.
16. The holographic grating of claim 15, wherein: the first
plurality of nanoparticles has a third refractive index that is
higher than the second refractive index; and the first plurality of
nanoparticles preferentially diffuses into the second region.
17. The holographic grating of claim 15, wherein: the first
plurality of nanoparticles has a third refractive index that is
lower than the second refractive index; and the first plurality of
nanoparticles diffuse so as to be more highly concentrated in
proximity to a top side or a bottom side of the second region.
18. The holographic grating of claim 15, wherein: the first
plurality of nanoparticles has a third refractive index lower than
the first refractive index; and the first plurality of
nanoparticles preferentially diffuses into the first region.
19. The holographic grating of claim 15, wherein: the first
plurality of nanoparticles has a third refractive index that is
higher than the first refractive index; and the first plurality of
nanoparticles diffuse so as to be more highly concentrated in
proximity to a top side or a bottom side of the first region.
20. The holographic grating of claim 15, wherein the operations
further comprise: applying a second resin layer comprising a second
plurality of nanoparticles to the holographic recording material
layer, thereby causing diffusion of at least a portion of the
second plurality of nanoparticles into the holographic recording
material layer.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This patent application is a divisional of U.S.
Non-Provisional patent application Ser. No. 16/550,046, filed Aug.
23, 2019, entitled "REFRACTIVE INDEX MODULATION MODIFICATION IN A
HOLOGRAPHIC GRATING," which is herein incorporated by reference in
its entirety for all purposes.
BACKGROUND
[0002] An artificial reality system, such as a head-mounted display
(HMD) or heads-up display (HUD) system, generally includes a
near-eye display system in the form of a headset or a pair of
glasses and 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 system 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).
[0003] 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
a diffractive optical element, such as a holographic grating. In
some implementations, the artificial reality systems may employ
eye-tracking subsystems that can track the user's eye (e.g., gaze
direction) to modify or generate content based on the direction in
which the user is looking, thereby providing a more immersive
experience for the user. The eye-tracking subsystems may be
implemented using various optical components, such as holographic
optical elements.
SUMMARY
[0004] This disclosure relates generally to holographic optical
elements. According to certain embodiments, a holographic grating
may include a polymer layer. The polymer layer includes a first
region characterized by a first refractive index, a second region
characterized by a second refractive index, the second refractive
index being higher than the first refractive index, and a plurality
of nanoparticles dispersed in the polymer layer, the nanoparticles
having a higher concentration in either the first region or the
second region.
[0005] According to some embodiments, in the holographic grating,
the nanoparticles are monomers. In some embodiments, the
nanoparticles have the higher concentration in the second region
and the nanoparticles have a third refractive index that is higher
than the second refractive index. In some embodiments, the
nanoparticles have the higher concentration in the first region and
the nanoparticles have a third refractive index that is lower than
the first refractive index. In some embodiments, the nanoparticles
in the first region or the second region have a substantially
constant concentration with respect to a thickness of the polymer
layer. In some embodiments, the polymer layer comprises a
multiplexed volume Bragg grating.
[0006] According to certain embodiments, a grating includes a
polymer layer. The polymer layer includes a first region
characterized by a first refractive index, a second region
characterized by a second refractive index, the second refractive
index being higher than the first refractive index, and a plurality
of nanoparticles dispersed in the polymer layer, the nanoparticles
having a higher concentration in proximity to a surface of the
polymer layer in one or more of the first region or the second
region, such that a refractive index modulation of the grating is
apodized.
[0007] According to certain embodiments, in the grating, the
nanoparticles are monomers. In some embodiments, the nanoparticles
have the higher concentration in the first region and the
nanoparticles have a third refractive index that is higher than the
first refractive index In some embodiments, the nanoparticles have
the higher concentration in the second region and the nanoparticles
have a third refractive index that is lower than the second
refractive index. In some embodiments, the polymer layer comprises
a multiplexed volume Bragg grating.
[0008] According to certain embodiments, a holographic grating may
include a polymer matrix. The polymer matrix includes a first
region characterized by a first refractive index and a second
region characterized by a second refractive index, the second
refractive index being higher than the first refractive index. The
holographic grating further includes a resin layer disposed on the
polymer matrix, the resin layer comprising a support layer and a
first plurality of nanoparticles dispersed in the support layer of
the resin layer.
[0009] According to certain embodiments, in the holographic
grating, the nanoparticles are monomers. In some embodiments, the
polymer matrix further comprises a second plurality of
nanoparticles, the second plurality of nanoparticles have a higher
concentration in the second region than in the first region, and
the second plurality of nanoparticles have a third refractive index
that is higher than the second refractive index. In some
embodiments, the polymer matrix further comprises a second
plurality of nanoparticles, the second plurality of nanoparticles
have a higher concentration in the first region than in the second
region, and the second plurality of nanoparticles have a third
refractive index that is lower than the first refractive index. In
some embodiments, the nanoparticles in a given region have a
substantially constant concentration with respect to a thickness of
the polymer matrix. In some embodiments, the polymer matrix
comprises a multiplexed volume Bragg grating.
[0010] According to certain embodiments, a holographic grating may
be fabricated by the following process. A holographic recording
material layer is obtained. The holographic recording material
layer is exposed to a recording light pattern, the recording light
pattern creating, in the holographic recording material layer, a
first region having a first refractive index and a second region
having second refractive index that is higher than the first
refractive index. After exposing the holographic recording material
layer to the recording light pattern, a first resin layer
comprising a first plurality of nanoparticles is applied to the
holographic recording material layer, thereby causing diffusion of
at least a portion of the first plurality of nanoparticles into the
holographic recording material layer.
[0011] According to certain embodiments, in the fabricated
holographic grating, the first plurality of nanoparticles has a
third refractive index that is higher than the second refractive
index and the first plurality of nanoparticles preferentially
diffuses into the second region. In some embodiments, the first
plurality of nanoparticles has a third refractive index that is
lower than the second refractive index and the first plurality of
nanoparticles preferentially diffuses so as to be more highly
concentrated in proximity to one or more of a top side or a bottom
side of the second region. In some embodiments, the first plurality
of nanoparticles has a third refractive index lower than the first
refractive index and the first plurality of nanoparticles
preferentially diffuses into the first region. In some embodiments,
the first plurality of nanoparticles has a third refractive index
that is higher than the first refractive index; and the first
plurality of nanoparticles further diffuses so as to be more highly
concentrated in proximity to one or more of a top side or a bottom
side of the first region. In some embodiments, the steps further
comprise removing the first resin layer and disposing a substrate
on the holographic recording material layer. In some embodiments,
the steps further include applying a second resin layer comprising
a second plurality of nanoparticles to the holographic recording
material layer, thereby causing diffusion of at least a portion of
the second plurality of nanoparticles into the holographic
recording material layer. In some embodiments, the nanoparticles in
a given region have a substantially constant concentration with
respect to a thickness of the holographic recording material
layer.
[0012] According to certain embodiments, a holographic grating may
be fabricated by the following process. A holographic recording
material layer is obtained. A first resin layer comprising a first
plurality of nanoparticles is applied to the holographic recording
material layer. After applying the first resin layer, the
holographic recording material layer is exposed to a recording
light pattern, the recording light pattern creating, in the
holographic recording material layer, a first region having a first
refractive index and a second region having second refractive index
that is higher than the first refractive index, wherein at least a
portion of the first plurality of nanoparticles diffuses from the
first resin layer into the holographic recording material
layer.
[0013] According to certain embodiments, in the fabricated
holographic grating, the first plurality of nanoparticles has a
third refractive index that is higher than the second refractive
index and the first plurality of nanoparticles preferentially
diffuses into the second region. In some embodiments, the first
plurality of nanoparticles has a third refractive index that is
lower than the second refractive index and the first plurality of
nanoparticles diffuse so as to be more highly concentrated in
proximity to a top side or a bottom side of the second region. In
some embodiments, the first plurality of nanoparticles has a third
refractive index lower than the first refractive index and the
first plurality of nanoparticles preferentially diffuses into the
first region. In some embodiments, the first plurality of
nanoparticles has a third refractive index that is higher than the
first refractive index and the first plurality of nanoparticles
diffuse so as to be more highly concentrated in proximity to a top
side or a bottom side of the first region. In some embodiments, the
steps further include applying a second resin layer comprising a
second plurality of nanoparticles to the holographic recording
material layer, thereby causing diffusion of at least a portion of
the second plurality of nanoparticles into the holographic
recording material layer. In some embodiments, the nanoparticles in
a given region have a substantially constant concentration with
respect to a thickness of the holographic recording material
layer.
[0014] 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
[0015] Illustrative embodiments are described in detail below with
reference to the following figures.
[0016] 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.
[0017] 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.
[0018] 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.
[0019] FIG. 4 illustrates an example of an optical see-through
augmented reality system using a waveguide display that includes an
optical combiner according to certain embodiments.
[0020] FIG. 5A illustrates an example of a volume Bragg grating
(VBG). FIG. 5B illustrates the Bragg condition for the volume Bragg
grating shown in FIG. 5A.
[0021] FIG. 6 illustrates an example of a holographic recording
material including two-stage photopolymers.
[0022] FIG. 7A illustrates the recording light beams for recording
a volume Bragg grating and the light beam reconstructed from the
volume Bragg grating.
[0023] FIG. 7B is an example of a holography momentum diagram
illustrating the wave vectors of recording beams and reconstruction
beams and the grating vector of the recorded volume Bragg
grating.
[0024] FIG. 8 illustrates an example of a holographic recording
system for recording holographic optical elements.
[0025] FIG. 9 illustrates an example of a grating including regions
of different refractive index.
[0026] FIGS. 10A-10B illustrate an example of modifying refractive
index modulation in a holographic grating.
[0027] FIGS. 11A-11C illustrate an example technique for modifying
the refractive index modulation in a holographic grating.
[0028] FIGS. 12A-12D illustrate examples of refractive index
modulation modification, according to some embodiments.
[0029] FIGS. 13A-13B illustrate variations in refractive index
modulation modification in a grating, according to some
embodiments.
[0030] FIG. 14 illustrates a grating with tapered refractive index
modification.
[0031] FIGS. 15A-15B illustrate an example of a refractive index
modulation profile in an apodized grating.
[0032] FIGS. 16A-16B illustrate sidelobe reduction using an
apodized grating in accordance with some embodiments.
[0033] FIG. 17 is a simplified flow chart illustrating an example
of a method of fabricating a holographic optical element according
to certain embodiments.
[0034] FIG. 18 is a schematic diagram showing another holographic
optical element fabrication method according to some
embodiments.
[0035] FIG. 19 is a simplified block diagram of an example of an
electronic system of a near-eye display system (e.g., HMD device)
for implementing some of the examples disclosed herein according to
certain embodiments.
[0036] 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.
[0037] 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
[0038] Techniques disclosed herein relate generally to holographic
optical elements. More specifically, and without limitation, this
disclosure relates to modifying the refractive index of recorded
holographic optical elements (HOEs) to enhance the refractive index
modulation or apodize the recorded holographic optical elements, in
order to improve the diffraction efficiency and/or the contrast of
the displayed images by, for example, increasing the number of
gratings in the multiplexed grating and reducing the sidelobes of a
grating (and thus crosstalk between gratings in a multiplexed
grating). Various inventive embodiments are described herein,
including materials, systems, modules, devices, components,
methods, compositions, and the like.
[0039] In various optical systems, such as artificial reality
systems including virtual reality, augmented reality (AR), and
mixed reality (MR) systems, to improve the performance of the
optical systems, such as improving the brightness of the displayed
images, expanding the eyebox, reducing artifacts, increasing the
field of view, and improving user interaction with presented
content, various holographic optical elements may be used for light
beam coupling and shaping, such as coupling light into or out of a
waveguide display or tracking the motion of the user's eyes. These
holographic optical elements may need to have a high refractive
index modulation, a small pitch or feature size, high clarity, high
diffraction efficiency, and the like.
[0040] The diffraction efficiency of a holographic optical element
is related to the difference in refractive index in different
regions of a grating. Given the relatively small range of
refractive index modulation available in materials suitable for
recording a holographic grating, there is a limit on the
diffraction efficiency achievable using traditional methods.
Another limitation in these gratings is sidelobes in the
diffraction pattern, which may affect image quality. In the case of
multiplexed gratings, the sidelobes of a grating may overlap with
the main lobes of other gratings, resulting in crosstalk. To reduce
crosstalk, one option is to reduce the number of gratings
multiplexed, which can be undesirable in many applications.
Techniques described herein can be applied to increase the
refractive index modulation in an HOE to improve diffraction
efficiency, and/or to apodize a grating to eliminate or reduce
sidelobes/crosstalk without limiting the number of gratings that
may be multiplexed in a holographic material layer.
[0041] According to certain embodiments, a layer of resin material
including a support matrix and monomers (or other nanoparticles)
dispersed in the support matrix, such as a monomer reservoir buffer
layer, may be formed on a photopolymer layer, either before or
after the holographic recording in the photopolymer layer.
Depending on, for example, the sizes of the monomers and the
affinity between the monomers and the polymers in the recorded
holographic optical elements, the monomers in the layer of resin
material may more preferentially diffuse to the high refractive
index regions of the HOE than to the low refractive index regions
of the HOE, or more preferentially diffuse to the low refractive
index regions than to the high refractive index regions. As such,
the refractive index in the high refractive index regions (or the
low refractive regions) may be changed more than the low refractive
index regions (or the high refractive index regions). The changes
may include increasing the refractive index in the diffused regions
if the monomers in the layer of resin material have a higher
refractive index than the refractive index in the diffused regions,
or decreasing the refractive index in the diffused regions if the
monomers in the layer of resin material have a lower refractive
index than the refractive index in the diffused regions. Thus, the
refractive index may be selectively increased or decreased in
different regions to increase or decrease the refractive index
modulation.
[0042] In some embodiments, the refractive index in the low
refractive index regions of the HOE may be decreased by
preferentially diffusing lower refractive index monomers to the low
refractive index regions. In some embodiments, the refractive index
in the high refractive index regions of the HOE may be increased by
preferentially diffusing higher refractive index monomers to the
high refractive index regions. In some embodiments, the refractive
index in both the high and low refractive index regions of the HOE
may be increased, but the refractive index in the high refractive
index regions of the HOE may be increased more due to the
preferential diffusion of higher index monomers. In some
embodiments, the refractive index in both the high and low
refractive index regions of the HOE may be decreased, but the
refractive index in the low refractive index regions of the HOE may
be decreased more due to the preferential diffusion of lower index
monomers. Thus, the refractive index modulation of the HOE can be
increased to increase the diffraction efficiency and/or to
multiplex more gratings in a photopolymer material layer.
[0043] In some embodiments, the layer of resin material may include
a lower concentration of monomers or the diffusion may be
controlled to occur in limited time, and thus the monomers may not
diffuse through the full depth of the HOE. As a result, the HOE may
have different refractive index modulations at different depths.
For example, the monomers in the layer of resin material may have a
lower refractive index and may more preferentially diffuse into the
high refractive index regions through a certain thickness of the
HOE such that the refractive index modulation may taper from the
center of the HOE in the thickness direction. In some embodiments,
the layer of resin material including the support matrix and
monomers may be formed on opposite sides of the photopolymer layer,
such that the refractive index modulation may taper from the center
of the HOE in the thickness direction to the opposite sides,
forming a bell-shaped refractive index modulation profile. Thus,
the HOE may be apodized to reduce sidelobes in the diffraction
efficiency curves and thus crosstalk between gratings in a
multiplexed grating.
[0044] In some embodiments, the layer of resin material including
the support matrix and monomers (or other nanoparticles) dispersed
in the support matrix may be formed after the HOE is recorded and a
cover layer is removed, and may or may not remain in the final
device after the diffusion of the monomers in the layer of resin
material. In some embodiments, the layer of resin material (e.g.,
the monomer reservoir buffer layer) may be formed on the
photopolymer layer before the holographic recording and may or may
not remain in the final device. For example, the support matrix of
the monomer reservoir buffer layer may be similar to a substrate
and may remain in the final device after the monomers diffuse into
the HOE.
[0045] As used herein, visible light may refer to light with a
wavelength between about 380 nm and about 750 nm, between about 400
nm and about 700 nm, or between about 440 nm and about 650 nm. Near
infrared (NIR) light may refer to light with a wavelength between
about 750 nm to about 2500 nm. The desired infrared (IR) wavelength
range may refer to the wavelength range of IR light that can be
detected by a suitable IR sensor (e.g., a complementary metal-oxide
semiconductor (CMOS), a charge-coupled device (CCD) sensor, or an
InGaAs sensor), such as between 830 nm and 860 nm, between 930 nm
and 980 nm, or between about 750 nm to about 1000 nm.
[0046] As also used herein, a substrate may refer to a medium
within which light may propagate. The substrate may include one or
more types of dielectric materials, such as glass, quartz, plastic,
polymer, poly(methyl methacrylate) (PMMA), crystal, or ceramic. At
least one type of material of the substrate may be transparent to
visible light and NIR light. A thickness of the substrate may range
from, for example, less than about 1 mm to about 10 mm or more. As
used herein, a material may be "transparent" to a light beam if the
light beam can pass through the material with a high transmission
rate, such as larger than 60%, 75%, 80%, 90%, 95%, 98%, 99%, or
higher, where a small portion of the light beam (e.g., less than
40%, 25%, 20%, 10%, 5%, 2%, 1%, or less) may be scattered,
reflected, or absorbed by the material. The transmission rate
(i.e., transmissivity) may be represented by either a photopically
weighted or an unweighted average transmission rate over a range of
wavelengths, or the lowest transmission rate over a range of
wavelengths, such as the visible wavelength range.
[0047] As also used herein, the term "support matrix" refers to the
material, medium, substance, etc., in which the polymerizable
component is dissolved, dispersed, embedded, enclosed, etc. In some
embodiments, the support matrix is typically a low T.sub.g polymer.
The polymer may be organic, inorganic, or a mixture of the two.
Without being particularly limited, the polymer may be a thermoset
or thermoplastic.
[0048] As also used herein, the term "polymerizable component"
refers to one or more photoactive polymerizable materials, and
possibly one or more additional polymerizable materials, e.g.,
monomers and/or oligomers, that are capable of forming a
polymer.
[0049] As also used herein, the term "photoactive polymerizable
material" refers to a monomer, an oligomer and combinations thereof
that polymerize in the presence of a photoinitiator that has been
activated by being exposed to a photoinitiating light source, e.g.,
recording light. In reference to the functional group that
undergoes curing, the photoactive polymerizable material comprises
at least one such functional group. It is also understood that
there exist photoactive polymerizable materials that are also
photoinitiators, such as N-methylmaleimide, derivatized
acetophenones, etc., and that in such a case, it is understood that
the photoactive monomer and/or oligomer of the present disclosure
may also be a photoinitiator.
[0050] As also used herein, the term "photopolymer" refers to a
polymer formed by one or more photoactive polymerizable materials,
and possibly one or more additional monomers and/or oligomers.
[0051] In the following description, 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.
[0052] FIG. 1 is a simplified block diagram of an example of an
artificial reality system environment 100 including a near-eye
display system 120 in accordance with certain embodiments.
Artificial reality system environment 100 shown in FIG. 1 may
include near-eye display system 120, an optional imaging device
150, and an optional input/output interface 140 that may each be
coupled to an optional console 110. While FIG. 1 shows example
artificial reality system environment 100 including one near-eye
display system 120, one 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 display
systems 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 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. In some configurations, near-eye display systems 120 may
include imaging device 150, which may be used to track one or more
input/output devices (e.g., input/output interface 140), such as a
handhold controller.
[0053] Near-eye display system 120 may be a head-mounted display
that presents content to a user. Examples of content presented by
near-eye display system 120 include one or more of images, videos,
audios, or some combination thereof. In some embodiments, audios
may be presented via an external device (e.g., speakers and/or
headphones) that receives audio information from near-eye display
system 120, console 110, or both, and presents audio data based on
the audio information. Near-eye display system 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
system 120 may be implemented in any suitable form factor,
including a pair of glasses. Some embodiments of near-eye display
system 120 are further described below. 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 system 120 and artificial reality content (e.g.,
computer-generated images). Therefore, near-eye display system 120
may augment images of a physical, real-world environment external
to near-eye display system 120 with generated content (e.g.,
images, video, sound, etc.) to present an augmented reality to a
user.
[0054] In various embodiments, near-eye display system 120 may
include one or more of display electronics 122, display optics 124,
and an eye-tracking system 130. In some embodiments, near-eye
display system 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 system 120 may omit any of these
elements or include additional elements in various embodiments.
Additionally, in some embodiments, near-eye display system 120 may
include elements combining the function of various elements
described in conjunction with FIG. 1.
[0055] 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
system 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
stereo 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 (i.e., a perception of image depth by a user
viewing the image).
[0056] In certain embodiments, display optics 124 may display image
content optically (e.g., using optical waveguides and couplers),
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 system 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.
[0057] 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.
[0058] 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
system 120/
[0059] 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 a 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.
[0060] Locators 126 may be objects located in specific positions on
near-eye display system 120 relative to one another and relative to
a reference point on near-eye display system 120. In some
implementations, console 110 may identify locators 126 in images
captured by imaging device 150 to determine the artificial reality
headset's position, orientation, or both. A locator 126 may be a
light emitting diode (LED), a corner cube reflector, a reflective
marker, a type of light source that contrasts with an environment
in which near-eye display system 120 operates, or some combinations
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.
[0061] Imaging device 150 may be part of near-eye display system
120 or may be external to near-eye display system 120. Imaging
device 150 may generate slow calibration data based on calibration
parameters received from console 110. Slow calibration data may
include one or more images showing observed positions of locators
126 that are detectable by imaging device 150. 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 some combinations thereof. Additionally, imaging
device 150 may include one or more filters (e.g., to increase
signal to noise ratio). Imaging device 150 may be configured to
detect light emitted or reflected from locators 126 in a field of
view of imaging device 150. In embodiments where locators 126
include passive elements (e.g., retroreflectors), 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 imaging device 150. Slow calibration data may be communicated
from imaging device 150 to console 110, and 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.).
[0062] Position sensors 128 may generate one or more measurement
signals in response to motion of near-eye display system 120.
Examples of position sensors 128 may include accelerometers,
gyroscopes, magnetometers, other motion-detecting or
error-correcting sensors, or some combinations 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.
[0063] 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 some 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 system
120 relative to an initial position of near-eye display system 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 system 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 system 120 (e.g., a
center of IMU 132).
[0064] Eye-tracking system 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 system 120. An eye-tracking system may include an imaging
system to image one or more eyes and may generally 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 system 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 system 130 may capture reflected radio waves
emitted by a miniature radar unit. Eye-tracking system 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 system 130 may be arranged to increase
contrast in images of an eye captured by eye-tracking system 130
while reducing the overall power consumed by eye-tracking system
130 (e.g., reducing power consumed by a light emitter and an
imaging system included in eye-tracking system 130). For example,
in some implementations, eye-tracking system 130 may consume less
than 100 milliwatts of power.
[0065] Eye-tracking system 130 may be configured to estimate the
orientation of the user's eye. The orientation of the eye may
correspond to the direction of the user's gaze within near-eye
display system 120. The orientation of the user's eye may be
defined as the direction of the foveal axis, which is the axis
between the fovea (an area on the retina of the eye with the
highest concentration of photoreceptors) and the center of the
eye's pupil. In general, when a user's eyes are fixed on a point,
the foveal axes of the user's eyes intersect that point. The
pupillary axis of an eye may be defined as the axis that passes
through the center of the pupil and is perpendicular to the corneal
surface. In general, even though the pupillary axis and the foveal
axis intersect at the center of the pupil, the pupillary axis may
not directly align with the foveal axis. For example, the
orientation of the foveal axis may be offset from the pupillary
axis by approximately -1.degree. to 8.degree. laterally and about
.+-.4.degree. vertically (which may be referred to as kappa angles,
which may vary from person to person). Because the foveal axis is
defined according to the fovea, which is located in the back of the
eye, the foveal axis may be difficult or impossible to measure
directly in some eye-tracking embodiments. Accordingly, in some
embodiments, the orientation of the pupillary axis may be detected
and the foveal axis may be estimated based on the detected
pupillary axis.
[0066] In general, the movement of an eye corresponds not only to
an angular rotation of the eye, but also to a translation of the
eye, a change in the torsion of the eye, and/or a change in the
shape of the eye. Eye-tracking system 130 may also be configured to
detect the translation of the eye, which may be a change in the
position of the eye relative to the eye socket. In some
embodiments, the translation of the eye may not be detected
directly, but may be approximated based on a mapping from a
detected angular orientation. Translation of the eye corresponding
to a change in the eye's position relative to the eye-tracking
system due to, for example, a shift in the position of near-eye
display system 120 on a user's head, may also be detected.
Eye-tracking system 130 may also detect the torsion of the eye and
the rotation of the eye about the pupillary axis. Eye-tracking
system 130 may use the detected torsion of the eye to estimate the
orientation of the foveal axis from the pupillary axis. In some
embodiments, eye-tracking system 130 may also track a change in the
shape of the eye, which may be approximated as a skew or scaling
linear transform or a twisting distortion (e.g., due to torsional
deformation). In some embodiments, eye-tracking system 130 may
estimate the foveal axis based on some combinations of the angular
orientation of the pupillary axis, the translation of the eye, the
torsion of the eye, and the current shape of the eye.
[0067] In some embodiments, eye-tracking system 130 may include
multiple emitters or at least one emitter that can project a
structured light pattern on all portions or a portion of the eye.
The structured light pattern may be distorted due to the shape of
the eye when viewed from an offset angle. Eye-tracking system 130
may also include at least one camera that may detect the
distortions (if any) of the structured light pattern projected onto
the eye. The camera may be oriented on a different axis to the eye
than the emitter. By detecting the deformation of the structured
light pattern on the surface of the eye, eye-tracking system 130
may determine the shape of the portion of the eye being illuminated
by the structured light pattern. Therefore, the captured distorted
light pattern may be indicative of the 3D shape of the illuminated
portion of the eye. The orientation of the eye may thus be derived
from the 3D shape of the illuminated portion of the eye.
Eye-tracking system 130 can also estimate the pupillary axis, the
translation of the eye, the torsion of the eye, and the current
shape of the eye based on the image of the distorted structured
light pattern captured by the camera.
[0068] Near-eye display system 120 may use the orientation of the
eye to, e.g., determine an inter-pupillary distance (IPD) of the
user, determine gaze directions, 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 some combination
thereof. Because the orientation may be determined for both eyes of
the user, eye-tracking system 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.
[0069] 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, 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 (e.g., imaging device 150) 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.
[0070] Console 110 may provide content to near-eye display system
120 for presentation to the user in accordance with information
received from one or more of imaging device 150, near-eye display
system 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
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.
[0071] 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
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.
[0072] 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.
[0073] Headset tracking module 114 may track movements of near-eye
display system 120 using slow calibration information from imaging
device 150. For example, headset tracking module 114 may determine
positions of a reference point of near-eye display system 120 using
observed locators from the slow calibration information and a model
of near-eye display system 120. Headset tracking module 114 may
also determine positions of a reference point of near-eye display
system 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 some combination thereof, to
predict a future location of near-eye display system 120. Headset
tracking module 114 may provide the estimated or predicted future
position of near-eye display system 120 to artificial reality
engine 116.
[0074] Headset tracking module 114 may calibrate the artificial
reality system environment 100 using one or more calibration
parameters, and may adjust one or more calibration parameters to
reduce errors in determining the position of near-eye display
system 120. For example, headset tracking module 114 may adjust the
focus of imaging device 150 to obtain a more accurate position for
observed locators on near-eye display system 120. Moreover,
calibration performed by headset tracking module 114 may also
account for information received from IMU 132. Additionally, if
tracking of near-eye display system 120 is lost (e.g., imaging
device 150 loses line of sight of at least a threshold number of
locators 126), headset tracking module 114 may re-calibrate some or
all of the calibration parameters.
[0075] Artificial reality engine 116 may execute applications
within artificial reality system environment 100 and receive
position information of near-eye display system 120, acceleration
information of near-eye display system 120, velocity information of
near-eye display system 120, predicted future positions of near-eye
display system 120, or some 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 system 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 system 120 that reflects 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 system 120 or
haptic feedback via input/output interface 140.
[0076] Eye-tracking module 118 may receive eye-tracking data from
eye-tracking system 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 system 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.
[0077] In some embodiments, eye-tracking module 118 may store a
mapping between images captured by eye-tracking system 130 and eye
positions to determine a reference eye position from an image
captured by eye-tracking system 130. Alternatively or additionally,
eye-tracking module 118 may determine an updated eye position
relative to a reference eye position by comparing an image from
which the reference eye position is determined to an image from
which the updated eye position is to be determined. Eye-tracking
module 118 may determine eye position using measurements from
different imaging devices or other sensors. For example,
eye-tracking module 118 may use measurements from a slow
eye-tracking system to determine a reference eye position, and then
determine updated positions relative to the reference eye position
from a fast eye-tracking system until a next reference eye position
is determined based on measurements from the slow eye-tracking
system.
[0078] Eye-tracking module 118 may also determine eye calibration
parameters to improve precision and accuracy of eye tracking. Eye
calibration parameters may include parameters that may change
whenever a user dons or adjusts near-eye display system 120.
Example eye calibration parameters may include an estimated
distance between a component of eye-tracking system 130 and one or
more parts of the eye, such as the eye's center, pupil, cornea
boundary, or a point on the surface of the eye. Other example eye
calibration parameters may be specific to a particular user and may
include an estimated average eye radius, an average corneal radius,
an average sclera radius, a map of features on the eye surface, and
an estimated eye surface contour. In embodiments where light from
the outside of near-eye display system 120 may reach the eye (as in
some augmented reality applications), the calibration parameters
may include correction factors for intensity and color balance due
to variations in light from the outside of near-eye display system
120. Eye-tracking module 118 may use eye calibration parameters to
determine whether the measurements captured by eye-tracking system
130 would allow eye-tracking module 118 to determine an accurate
eye position (also referred to herein as "valid measurements").
Invalid measurements, from which eye-tracking module 118 may not be
able to determine an accurate eye position, may be caused by the
user blinking, adjusting the headset, or removing the headset,
and/or may be caused by near-eye display system 120 experiencing
greater than a threshold change in illumination due to external
light. In some embodiments, at least some of the functions of
eye-tracking module 118 may be performed by eye-tracking system
130.
[0079] 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
200 for implementing some of the examples disclosed herein. HMD
device 200 may be a part of, e.g., a virtual reality (VR) system,
an augmented reality (AR) system, a mixed reality (MR) system, or
some combinations 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 right 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
temples tips as shown in, for example, FIG. 2, rather than head
strap 230.
[0080] 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),
audios, or some combinations 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, a
liquid crystal display (LCD), an organic light emitting diode
(.mu.LED OLED) display, an inorganic light emitting diode (ILED)
display, a micro light emitting diode ( ) display, an active-matrix
organic light emitting diode (AMOLED) display, a transparent
organic light emitting diode (TOLED) display, some other display,
or some combinations thereof. HMD device 200 may include two eye
box regions.
[0081] 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 some 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.
[0082] FIG. 3 is a perspective view of an example of a near-eye
display system 300 in the form of a pair of glasses for
implementing some of the examples disclosed herein. Near-eye
display system 300 may be a specific implementation of near-eye
display system 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 system 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 system 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).
[0083] Near-eye display system 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 fields 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
system 300, and/or to provide an interactive VR/AR/MR experience to
a user of near-eye display system 300. In some embodiments, sensors
350a-350e may also be used for stereoscopic imaging.
[0084] In some embodiments, near-eye display system 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.
[0085] In some embodiments, near-eye display system 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.
[0086] FIG. 4 illustrates an example of an optical see-through
augmented reality system 400 using a waveguide display according to
certain embodiments. Augmented reality system 400 may include a
projector 410 and a combiner 415. Projector 410 may include a light
source or image source 412 and projector optics 414. In some
embodiments, image source 412 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 412 may
include a light source that generates coherent or partially
coherent light. For example, image source 412 may include a laser
diode, a vertical cavity surface emitting laser, and/or a light
emitting diode. In some embodiments, image source 412 may include a
plurality of light sources each emitting a monochromatic image
light corresponding to a primary color (e.g., red, green, or blue).
In some embodiments, image source 412 may include an optical
pattern generator, such as a spatial light modulator. Projector
optics 414 may include one or more optical components that can
condition the light from image source 412, such as expanding,
collimating, scanning, or projecting light from image source 412 to
combiner 415. The one or more optical components may include, for
example, one or more lenses, liquid lenses, mirrors, apertures,
and/or gratings. In some embodiments, projector optics 414 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 412.
[0087] Combiner 415 may include an input coupler 430 for coupling
light from projector 410 into a substrate 420 of combiner 415.
Combiner 415 may transmit at least 50% of light in a first
wavelength range and reflect at least 25% of light in a second
wavelength range. For example, the first wavelength range may be
visible light from about 400 nm to about 650 nm, and the second
wavelength range may be in the infrared band, for example, from
about 800 nm to about 1000 nm. Input coupler 430 may include a
volume holographic grating, a diffractive optical elements (DOE)
(e.g., a surface-relief grating), a slanted surface of substrate
420, or a refractive coupler (e.g., a wedge or a prism). Input
coupler 430 may have a coupling efficiency of greater than 30%,
50%, 75%, 90%, or higher for visible light. Light coupled into
substrate 420 may propagate within substrate 420 through, for
example, total internal reflection (TIR). Substrate 420 may be in
the form of a lens of a pair of eyeglasses. Substrate 420 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, or ceramic. A thickness
of the substrate may range from, for example, less than about 1 mm
to about 10 mm or more. Substrate 420 may be transparent to visible
light.
[0088] Substrate 420 may include or may be coupled to a plurality
of output couplers 440 configured to extract at least a portion of
the light guided by and propagating within substrate 420 from
substrate 420, and direct extracted light 460 to an eye 490 of the
user of augmented reality system 400. As input coupler 430, output
couplers 440 may include grating couplers (e.g., volume holographic
gratings or surface-relief gratings), other DOEs, prisms, etc.
Output couplers 440 may have different coupling (e.g., diffraction)
efficiencies at different locations. Substrate 420 may also allow
light 450 from environment in front of combiner 415 to pass through
with little or no loss. Output couplers 440 may also allow light
450 to pass through with little loss. For example, in some
implementations, output couplers 440 may have a low diffraction
efficiency for light 450 such that light 450 may be refracted or
otherwise pass through output couplers 440 with little loss, and
thus may have a higher intensity than extracted light 460. In some
implementations, output couplers 440 may have a high diffraction
efficiency for light 450 and may diffract light 450 to 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 415 and virtual objects projected
by projector 410.
[0089] In addition, as described above, in an artificial reality
system, to improve user interaction with presented content, the
artificial reality system may track the user's eye and modify or
generate content based on a location or a direction in which the
user is looking at. Tracking the eye may include tracking the
position and/or shape of the pupil and/or the cornea of the eye,
and determining the rotational position or gaze direction of the
eye. One technique (referred to as Pupil Center Corneal Reflection
or PCCR method) involves using NIR LEDs to produce glints on the
eye cornea surface and then capturing images/videos of the eye
region. Gaze direction can be estimated from the relative movement
between the pupil center and glints. Various holographic optical
elements may be used in an eye-tracking system for illuminating the
user's eyes or collecting light reflected by the user's eye.
[0090] One example of the holographic optical elements used in an
artificial reality system for eye tracking or image display may be
a holographic volume Bragg grating, which may be recorded on a
holographic material layer by exposing the holographic material
layer to light patterns generated by the interference between two
or more coherent light beams.
[0091] FIG. 5A illustrates an example of a volume Bragg grating
(VBG) 500. Volume Bragg grating 500 shown in FIG. 5A may include a
transmission holographic grating that has a thickness D. The
refractive index n of volume Bragg grating 500 may be modulated at
an amplitude n.sub.1, and the grating period of volume Bragg
grating 500 may be .LAMBDA.. Incident light 510 having a wavelength
.lamda. may be incident on volume Bragg grating 500 at an incident
angle .theta., and may be refracted into volume Bragg grating 500
as incident light 520 that propagates at an angle .theta..sub.n in
volume Bragg grating 500. Incident light 520 may be diffracted by
volume Bragg grating 500 into diffraction light 530, which may
propagate at a diffraction angle .theta..sub.d in volume Bragg
grating 500 and may be refracted out of volume Bragg grating 500 as
diffraction light 540.
[0092] FIG. 5B illustrates the Bragg condition for volume Bragg
grating 500 shown in FIG. 5A. Vector 505 represents the grating
vector {right arrow over (G)}, where |{right arrow over
(G)}|=2.pi./.LAMBDA.. Vector 525 represents the incident wave
vector {right arrow over (k.sub.l)}, and vector 535 represents the
diffract wave vector {right arrow over (k.sub.d)}, where |{right
arrow over (k.sub.l)}|=|{right arrow over
(k.sub.d)}|=2.pi.n/.lamda.. Under the Bragg phase-matching
condition, {right arrow over (k.sub.l)}-{right arrow over
(k.sub.d)}={right arrow over (G)}. Thus, for a given wavelength
.lamda., there may only be one pair of incident angle .theta. (or
.theta..sub.n) and diffraction angle .theta..sub.d that meets the
Bragg condition perfectly. Similarly, for a given incident angle
.theta., there may only be one wavelength .lamda. that meets the
Bragg condition perfectly. As such, the diffraction may only occur
in a small wavelength range and a small incident angle range. The
diffraction efficiency, the wavelength selectivity, and the angular
selectivity of volume Bragg grating 500 may be functions of
thickness D of volume Bragg grating 500. For example, the
full-width-half-magnitude (FWHM) wavelength range and the FWHM
angle range of volume Bragg grating 500 at the Bragg condition may
be inversely proportional to thickness D of volume Bragg grating
500, while the maximum diffraction efficiency at the Bragg
condition may be a function sin.sup.2(a.times.n.sub.1.times.D),
where a is a coefficient. For a reflection volume Bragg grating,
the maximum diffraction efficiency at the Bragg condition may be a
function of tan h.sup.2(a.times.n.sub.1.times.D).
[0093] In some embodiments, a multiplexed Bragg grating may be used
to achieve the desired optical performance, such as a high
diffraction efficiency and a large field of view (FOV) for the full
visible spectrum (e.g., from about 400 nm to about 700 nm, or from
about 440 nm to about 650 nm). Each part of the multiplexed Bragg
grating may be used to diffract light from a respective FOV range
and/or within a respective wavelength range. Thus, in some designs,
multiple volume Bragg gratings each recorded under a respective
recording condition may be used.
[0094] The holographic optical elements described above may be
recorded in a holographic material (e.g., photopolymer) layer. In
some embodiments, the HOEs can be recorded first and then laminated
on a substrate in a near-eye display system. In some embodiments, a
holographic material layer may be coated or laminated on the
substrate and the HOEs may then be recorded in the holographic
material layer.
[0095] In general, to record a holographic optical element in a
photosensitive material layer, two coherent beams may interfere
with each other at certain angles to generate a unique interference
pattern in the photosensitive material layer, which may in turn
generate a unique refractive index modulation pattern in the
photosensitive material layer, where the refractive index
modulation pattern may correspond to the light intensity pattern of
the interference pattern. The photosensitive material layer may
include, for example, silver halide emulsion, dichromated gelatin,
photopolymers including photo-polymerizable monomers suspended in a
polymer matrix, photorefractive crystals, and the like. One example
of the photosensitive material layer for holographic recording is
two-stage photopolymers.
[0096] FIG. 6 illustrates an example of a holographic recording
material including two-stage photopolymers. The raw material 610 of
the two-stage photopolymers may be a resin including matrix
precursors 612 and imaging components 614. Matrix precursors 612 in
raw material 610 may include monomers that may be thermally or
otherwise cured at the first stage to polymerize and to form a
photopolymer film 620 that includes a cross-linked matrix formed by
polymeric binders 622. Imaging components 614 may include writing
monomers and polymerization initiating agents, such as
photosensitizing dyes, initiators, and/or chain transfer agents.
Thus, photopolymer film 620 may include polymeric binders 622,
writing monomers (e.g., acrylate monomers), and initiating agents,
such as photosensitizing dyes, initiators, and/or chain transfer
agents. Polymeric binders 622 may act as the backbone or the
support matrix for the writing monomers and initiating agents. For
example, in some embodiments, polymeric binders 622 may include a
low refractive index (e.g., <1.5) rubbery polymer (e.g., a
polyurethane), which may provide mechanical support during the
holographic exposure and ensure the refractive index modulation by
the light pattern is permanently preserved.
[0097] Imaging components 614 including the writing monomers and
the polymerization initiating agents may be dispersed in the
support matrix. The writing monomers may serve as refractive index
modulators. For example, the writing monomers may include high
refractive index acrylate monomers which can react with the
initiators and polymerize. The photosensitizing dyes may be used to
absorb light and interact with the initiators to produce active
species, such as radicals, cations (e.g., acids), or anion (e.g.,
bases). The active species (e.g., radicals) may initiate the
polymerization by attacking a monomer. For example, in some
monomers, one electron pair may be held securely between two
carbons in a sigma bond and another electron pair may be more
loosely held in a pi bond, and the free radical may use one
electron from the pi bond to form a more stable bond with a first
carbon atom in the two carbon atoms. The other electron from the pi
bond may return to the second carbon atom in the two carbon atoms
and turn the whole molecule into another radical. Thus, a monomer
chain (e.g., a polymer) may be formed by adding additional monomers
to the end of the monomer chain and transferring the radical to the
end of the monomer chain to attack and add more monomers to the
chain.
[0098] During the recording process (e.g., the second stage), an
interference pattern generated by the interference between two
coherent beams may cause the photosensitizing dyes and the
initiators in the bright fringes to generate active species, such
as radicals, cations (e.g., acids), or anion (e.g., bases), from
the initiators, where the active species (e.g., radicals) may
transfer from the initiators to monomers and cause the
polymerization of the monomers in the bright fringes as described
above. The initiators or radicals may be bound to the polymer
matrix when abstracting the hydrogen atoms on the polymer matrix.
The radicals may be transferred to the ends of the chains of
monomers to add more monomers to the chains. While the monomers in
the bright fringes are attached to chains of monomers, monomers in
the unexposed dark regions may diffuse to the bright fringes to
enhance the polymerization. As a result, polymerization
concentration and density gradients may be formed in photopolymer
film 620, resulting in refractive index modulation in photopolymer
film 620 due to the higher refractive index of the writing
monomers. For example, areas with a higher concentration of
monomers and polymerization may have a higher refractive index.
Thus, a hologram or a holographic optical element 630 may be formed
in photopolymer film 620.
[0099] During the exposure, a radical at the end of one monomer
chain may combine with a radical at the end of another monomer
chain to form a longer chain and terminate the polymerization. In
addition to the termination due to radical combination, the
polymerization may also be terminated by disproportionation of
polymers, where a hydrogen atom from one chain may be abstracted to
another chain to generate a polymer with a terminal unsaturated
group and a polymer with a terminal saturated group. The
polymerization may also be terminated due to interactions with
impurities or inhibitors (e.g., oxygen). In addition, as the
exposure and polymerization proceed, fewer monomers may be
available for diffusion and polymerization, and thus the diffusion
and polymerization may be suppressed. The polymerization may stop
until there are no more monomers or until the monomer chains
terminate for an exposure. After all or substantially all monomers
have been polymerized, no more new holographic optical elements 630
(e.g., gratings) may be recorded in photopolymer film 620.
[0100] In some embodiments, the recorded holographic optical
elements in the photosensitive material layer may be UV cured or
thermally cured or enhanced, for example, for dye bleaching,
completing polymerization, permanently fixing the recorded pattern,
and enhancing the refractive index modulation. At the end of the
process, a holographic optical element, such as a holographic
grating, may be formed. The holographic grating may be a volume
Bragg grating with a thickness of, for example, a few, or tens, or
hundreds of microns.
[0101] To generate the desired light interference pattern for
recording the HOEs, two or more coherent beams may generally be
used, where one beam may be a reference beam and another beam may
be an object beam that may have a desired wavefront profile. When
the recorded HOEs are illuminated by the reference beam, the object
beam with the desired wavefront profile may be reconstructed.
[0102] In some embodiments, the holographic optical elements may be
used to diffract light outside of the visible band. For example, IR
light or NIR light (e.g., at 940 nm or 850 nm) may be used for
eye-tracking. Thus, the holographic optical elements may need to
diffract IR or NIR light, but not the visible light. However, there
may be very few holographic recording materials that are sensitive
to infrared light. As such, to record a holographic grating that
can diffract infrared light, recording light at a shorter
wavelength (e.g., in visible or UV band, such as at about 660 nm,
about 532 nm, about 514 nm, or about 457 nm) may be used, and the
recording condition (e.g., the angles of the two interfering
coherent beams) may be different from the reconstruction
condition.
[0103] FIG. 7A illustrates the recording light beams for recording
a volume Bragg grating 700 and the light beam reconstructed from
volume Bragg grating 700. In the example illustrated, volume Bragg
grating 700 may include a transmission volume hologram recorded
using a reference beam 720 and an object beam 710 at a first
wavelength, such as 660 nm. When a light beam 730 at a second
wavelength (e.g., 940 nm) is incident on volume Bragg grating 700
at a 0.degree. incident angle, the incident light beam 730 may be
diffracted by volume Bragg grating 700 at a diffraction angle as
shown by a diffracted beam 740.
[0104] FIG. 7B is an example of a holography momentum diagram 705
illustrating the wave vectors of recording beams and reconstruction
beams and the grating vector of the recorded volume Bragg grating.
FIG. 7B shows the Bragg matching conditions during the holographic
grating recording and reconstruction. The length of wave vectors
750 and 760 of the recording beams (e.g., object beam 710 and
reference beam 710) may be determined based on the recording light
wavelength .lamda..sub.c (e.g., 660 nm) according to
2.pi.n/.lamda..sub.c, where n is the average refractive index of
holographic material layer. The directions of wave vectors 750 and
760 of the recording beams may be determined based on the desired
grating vector K (770) such that wave vectors 750 and 760 and
grating vector K (770) can form an isosceles triangle as shown in
FIG. 7B. Grating vector K may have an amplitude 2.pi./.LAMBDA.,
where .LAMBDA. is the grating period. Grating vector K may in turn
be determined based on the desired reconstruction condition. For
example, based on the desired reconstruction wavelength
.lamda..sub.r (e.g., 940 nm) and the directions of the incident
light beam (e.g., light beam 730 at 0.degree.) and the desired
diffracted light beam (e.g., diffracted beam 740), grating vector K
(770) of volume Bragg grating 700 may be determined based on the
Bragg condition, where wave vector 780 of the incident light beam
(e.g., light beam 730) and wave vector 790 of the diffracted light
beam (e.g., diffracted beam 740) may have an amplitude
2.pi.n/.lamda..sub.r, and may form an isosceles triangle with
grating vector K (770) as shown in FIG. 7B.
[0105] As described above, for a given wavelength, there may only
be one pair of incident angle and diffraction angle that meets the
Bragg condition perfectly. Similarly, for a given incident angle,
there may only be one wavelength that meets the Bragg condition
perfectly. When the incident angle of the reconstruction light beam
is different from the incident angle that meets the Bragg condition
of the volume Bragg grating or when the wavelength of the
reconstruction light beam is different from the wavelength that
meets the Bragg condition of the volume Bragg grating, the
diffraction efficiency may be reduced as a function of the Bragg
mismatch factor caused by the angular or wavelength detuning from
the Bragg condition. As such, the diffraction may only occur in a
small wavelength range and a small incident angle range.
[0106] FIG. 8 illustrates an example of a holographic recording
system 800 for recording holographic optical elements. Holographic
recording system 800 includes a beam splitter 810 (e.g., a beam
splitter cube), which may split an incident collimated laser beam
802 into two light beams 812 and 814 that are coherent and have
similar intensities. Light beam 812 may be reflected by a first
mirror 820 towards a plate 830 as shown by the reflected light beam
822. On another path, light beam 814 may be reflected by a second
mirror 840. The reflected light beam 842 may be directed towards
plate 830, and may interfere with light beam 822 at plate 830 to
generate an interference pattern that may include bright fringes
and dark fringes. In some embodiments, plate 830 may also be a
mirror. A holographic recording material layer 850 may be formed on
plate 830 or on a substrate mounted on plate 830. The interference
pattern may cause the holographic optical element to be recorded in
holographic recording material layer 850 as described above.
[0107] In some embodiments, a mask 860 may be used to record
different HOEs at different regions of holographic recording
material layer 850. For example, mask 860 may include an aperture
862 for the holographic recording and may be moved to place
aperture 862 at different regions on holographic recording material
layer 850 to record different HOEs at the different regions under
different recording conditions (e.g., recording beams with
different angles).
[0108] Holographic recording materials can be selected for specific
applications based on some parameters of the holographic recording
materials, such as the spatial frequency response, dynamic range,
photosensitivity, physical dimensions, mechanical properties,
wavelength sensitivity, and development or bleaching method for the
holographic recording material.
[0109] The dynamic range indicates the refractive index change that
can be achieved in a holographic recording material. The dynamic
range may affect, for example, the thickness of the device to
achieve a high efficiency, and the number of holograms that can be
multiplexed in a holographic material layer. The dynamic range may
be represented by the refractive index modulation (RIM), which may
be one half of the total change in refractive index. In generally,
a large refractive index modulation in the holographic optical
elements is desired in order to improve the diffraction efficiency
and record multiple holographic optical elements in a same
holographic material layer. However, for holographic photopolymer
materials, due to the solubility limitation of the monomers in the
holographic photopolymer materials, the maximum achievable
refractive index modulation or dynamic range may be limited.
[0110] The spatial frequency response is a measure of the feature
size that the holographic material can record and may dictate the
types of Bragg conditions that can be achieved. The spatial
frequency response can be characterized by a modulation transfer
function, which may be a curve depicting the sinusoidal waves of
varying frequencies. In general, a single spatial frequency value
may be used to represent the frequency response, which may indicate
the spatial frequency value at which the refractive index
modulation begins to drop or at which the refractive index
modulation is reduced by 3 dB. The spatial frequency response may
also be represented by lines/mm, line pairs/mm, or the period of
the sinusoid.
[0111] The photosensitivity of the holographic recording material
may indicate the photo-dosage used to achieve a certain efficiency,
such as 100% (or 1% for photo-refractive crystals). The physical
dimensions that can be achieved in a particular holographic
material may affect the aperture size as well as the spectral
selectivity of the HOE device. Physical parameters of holographic
recording materials may include, for example, damage thresholds and
environmental stability. The wavelength sensitivity may be used to
select the light source for the recording setup and may also affect
the minimum achievable period. Some materials may be sensitive to
light in a wide wavelength range. Many holographic materials may
need post-exposure development or bleaching. Development
considerations may include how the holographic material is
developed or otherwise processed after the recording.
[0112] To record holographic optical elements for artificial
reality system, it may be desirable that the photopolymer material
is sensitive to visible light, can produce a large refractive index
modulation .DELTA.n (e.g., high dynamic range), and have temporally
and spatially controllable reaction and/or diffusion of the
monomers and/or polymers such that chain transfer and termination
reactions can be suppressed.
[0113] FIG. 9 illustrates an example of a grating 900. The grating
900 includes two substrate layers 910, 915 and a polymer layer 920.
The grating 900 may correspond to a volume Bragg grating and/or a
multiplexed volume Bragg grating.
[0114] In some embodiments, the first substrate 910 is disposed on
a first side of the polymer layer 920. The first substrate 910 may
be composed of, for example, glass, quartz, plastic, polymer, or
any other suitable material which is transparent to visible light
and NIR light. A thickness of the first substrate 910 may range
from about 0.1 mm to about 10 mm. In some embodiments, the first
substrate 910 may not be included and/or may be substituted with
another component.
[0115] In some embodiments, second substrate 915 is disposed on a
second side of the polymer layer 920. The second substrate 915 may
be composed of, for example, glass, quartz, plastic, polymer, or
any other suitable material which is transparent to visible light
and NIR light. A thickness of the second substrate 915 may range
from about 0.1 mm to about 10 mm. In some embodiments, the second
substrate 915 may not be included and/or may be substituted with
another component.
[0116] The polymer layer 920 includes first regions 922 having a
first refractive index (n1), and second regions 924 having a second
refractive index (n2). The second regions may have a refractive
index higher than the first regions (or vice versa). The refractive
index difference between the regions (e.g., |n1-n2|) may be between
approximately 0 and about 0.2.
[0117] In addition to the refractive indexes of the regions 922,
924, the grating 900 is characterized by the slant angle .theta.
(940) of the fringes and the pitch 950. The slant angle .theta.
(940) of the fringes may be between approximately 0 degrees and
about 90 degrees. The pitch 950, may be between approximately 0.1
and about 1.5 .mu.m.
[0118] The parameters .theta. (940) and pitch 950 may affect the
behavior of incident light 960 approaching the grating 900. Based
on these parameters, along with other parameters such as the
relative refractive indexes in the grating, diffracted light 970
may have certain power and may be in a certain direction. The
diffraction efficiency of the grating 900 is the ratio between
power of diffracted light and power of incident light.
[0119] FIGS. 10A-10B illustrate examples of gratings with a
modified refractive index modulation according to some embodiments.
The diffractive efficiency may increase as the refractive index
difference between regions in the grating increases within a
certain range. Similarly, the diffractive efficiency may decrease
as the refractive index difference between regions in the grating
decreases within a certain range. In some cases, it may be
desirable to increase the refractive index difference between the
regions. This can be achieved by modifying the refractive indexes
in the regions, as illustrated in FIGS. 10A and 10B.
[0120] FIG. 10A illustrates a grating 1000 with a certain initial
refractive index modulation and diffraction efficiency. The grating
1000 includes two substrate layers 1010 and 1020 and a polymer
layer 1030 which includes regions 1032 and 1034. Each region 1032
is a region of relatively high refractive index (as compared to
each region 1034). Each region 1034 is a region of relatively low
refractive index (as compared to each region 1032). When incident
light 1040 passes through the grating 1000, some percentage of the
incident light 1040 is diffracted as diffracted light 1045,
according to the diffraction efficiency of the grating 1000.
[0121] FIG. 10B illustrates a grating 1050 with a modified
refractive index modulation and increased diffraction efficiency.
The grating 1050 includes two substrate layers 1060, 1070 and a
polymer layer 1080 which includes regions 1082 and 1084. Each
region 1082 is a region of relatively high refractive index (as
compared to each region 1084). Each region 1084 is a region of
relatively low refractive index (as compared to the first region
1082).
[0122] There are several ways to modify the refractive index
modulation of the grating 1050 by modifying the refractive index of
the polymer layer 1080, in whole or in part. For example, the
refractive index modulation of the grating 1050 can be increased by
decreasing the refractive index in region 1084 while the refractive
index of region 1082 remains substantially constant. The refractive
index modulation of the grating 1050 can alternatively be increased
by increasing the refractive index in region 1082 while the
refractive index of region 1084 remains substantially constant. The
refractive index modulation of the grating 1050 can also be
increased by decreasing the refractive index in both regions, but
decreasing the refractive index more in region 1084. The refractive
index modulation of the grating 1050 can be increased by increasing
the refractive index in both regions, but increasing the refractive
index more in region 1082.
[0123] When incident light 1090 passes through the grating 1050,
some percentage of the incident light 1090 is diffracted as
diffracted light 1095, according to the diffraction efficiency of
the grating 1050. As the diffraction efficiency of the grating 1050
in FIG. 10B has been increased, as compared to the diffraction
efficiency of grating 1000 of FIG. 10A, a larger fraction of the
incident light is diffracted in diffracted light 1095 in comparison
to diffracted light 1045.
[0124] FIGS. 11A-11C illustrate an example technique for modifying
the refractive index modulation in a holographic grating. FIG. 11A
illustrates the grating after recording, FIG. 11B illustrates the
grating with a substrate replaced by a resin layer that includes
nanoparticles (e.g., monomers), and FIG. 11C illustrates the
grating after the nanoparticles diffuse into the grating from the
resin layer.
[0125] FIG. 11A illustrates a recorded holographic grating 1100.
The grating 1100 includes a first substrate 1102 disposed on a
bottom side of a polymer layer. The polymer layer includes regions
of relatively high refractive index 1104 and regions of relatively
low refractive index 1106. The polymer layer may, for example, have
been exposed to a holographic recording light pattern to record a
refractive index modulation pattern in the polymer layer. The
grating 1100 further includes a second substrate 1103 disposed on a
top side of the polymer layer.
[0126] FIG. 11B illustrates a grating 1120 including a resin layer
1123 that includes nanoparticles. Similarly to the grating 1100 of
FIG. 11A, the grating 1120 includes a first substrate 1122 disposed
on a bottom side of a polymer layer and regions of differing
refractive index 1124 and 1126. The second substrate (e.g., second
substrate 1103 shown in FIG. 11A) has been removed and replaced
with resin layer 1123. The resin layer 1123 includes a support
layer or matrix, filled with high refractive index nanoparticles
(e.g., with a higher refractive index than the high refractive
index region of the polymer layer). The resin layer filled with
nanoparticles is also referred to herein as a "monomer reservoir
buffer layer." Alternatively, low or moderate refractive index
nanoparticles may be used, depending on the modification desired.
In some embodiments, the nanoparticles may be monomers. In some
embodiments, the nanoparticles may be in the form of a liquid. The
resin layer 1123 is disposed on the top side of the polymer layer,
such that the resin layer 1123 and the polymer layer are in contact
with one another. The sponge layer may be a polymer film, typically
an elastomer. Typical elastomers include crosslinked films of
polyesters, polyethers, polyurethanes, or polysiloxanes.
[0127] When the resin layer 1123 and the polymer layer are placed
in contact, the nanoparticles may diffuse from the resin layer 1123
into the polymer layer. As indicated by the gradients in regions
1124, 1126, the introduction of the nanoparticles in the polymer
layer modifies the refractive index of regions 1124, 1126.
[0128] FIG. 11C illustrates a grating 1140 with modified refractive
index modulation. Grating 1140 includes a substrate 1142, a
nanoparticle-filled resin layer 1143, and a polymer layer which
includes regions of different refractive index 1144, 1146. The
nanoparticles have further diffused into the polymer layer,
creating a change in the refractive indexes in regions 1144,
1146.
[0129] FIGS. 12A-12D illustrate an example of refractive index
modulation modification in a holographic grating, according to some
embodiments. Depending on the properties of the nanoparticles in
the resin layer, the diffusion of the nanoparticles and the
resulting refractive index modulation modification may vary. The
diffusion properties may be controlled based on the properties of
the nanoparticles in the resin layer, such as the refractive index
and the solubility in the different regions of the polymer layer.
The solubility of the nanoparticles in a given region may be
controlled, e.g., based on the size of the nanoparticle and/or the
affinity between the nanoparticle and the material in the region of
interest.
[0130] FIG. 12A illustrates a first example of a grating 1200 with
refractive index modulation modification using a monomer (or other
nanoparticles) reservoir buffer layer 1202. The grating 1200
includes a polymer layer which includes regions of relatively low
refractive index 1204 (with initial refractive index n1) and
regions of relatively high refractive index 1206 (with initial
refractive index n2). A substrate layer 1201 is disposed on a
bottom side of the polymer layer. Monomer reservoir buffer layer
1202 is disposed on a top side of the polymer layer.
[0131] In FIG. 12A, the monomer reservoir buffer layer 1202
includes a monomer with a relatively large refractive index n3
(>n2). Further, the monomer is more soluble in low refractive
index fringes (e.g., in regions 1204) than in high refractive index
fringes (e.g., in regions 1206). Accordingly, the impact on the
refractive index modulation is most pronounced with respect to dips
in the initial refractive index modulation profile, as indicated in
refractive index modulation plot 1208. The plot 1208 shows the
refractive index of the grating 1200 as a function of position from
left to right across the polymer layer. Initially, before addition
of the monomer reservoir buffer layer 1202, the refractive index of
the grating 1200 varies between n1 and n2 (as shown by a curve
1209A). With the refractive index modification introduced by the
monomer reservoir buffer layer, the refractive index modulation
profile changes as shown by a curve 1209B, due to the increase in
the refractive index of low refractive index regions 1204
(corresponding to the dips in the refractive index modulation
profile).
[0132] FIG. 12B illustrates a second example of a grating 1210 with
refractive index modulation modification using a monomer reservoir
buffer layer 1212. The grating 1210 includes a polymer layer which
includes regions of relatively low refractive index 1214 (with
refractive index n1) and regions of relatively high refractive
index 1216 (with a refractive index n2). A substrate layer 1211 is
disposed on a bottom side of the polymer layer. The monomer
reservoir buffer layer 1212 is disposed on a top side of the
polymer layer.
[0133] In FIG. 12B, the monomer reservoir buffer layer 1212
includes a monomer with a relatively large refractive index n3
(>n2). Further, the monomer is more soluble in high refractive
index fringes (e.g., in regions 1216) than in low refractive index
fringes (e.g., in regions 1214). Accordingly, the impact on the
refractive index is most pronounced with respect to peaks in the
refractive index modulation profile, as indicated in refractive
index modulation plot 1218 (showing an initial refractive index
modulation 1219A and a modified refractive index modulation 1219B).
In particular, by introducing a larger refractive index material
into the regions of relatively high refractive index 1216 via the
monomer reservoir buffer layer 1212, the refractive index in the
regions of relatively high refractive index 1216 increases. This
increase in refractive index causes the peaks in refractive index
plot 1219B to increase above the initial level of n2.
[0134] FIG. 12C illustrates a third example of a grating 1220 with
a refractive index modulation modification using a monomer
reservoir buffer layer 1222. Grating 1220 includes a polymer layer
which includes regions of relatively low refractive index 1224
(with refractive index n1) and regions of relatively high
refractive index 1226 (with refractive index n2). A substrate layer
1221 is disposed on a bottom side of the polymer layer. The monomer
reservoir buffer layer 1222 is disposed on a top side of the
polymer layer.
[0135] In FIG. 12C, the monomer reservoir buffer layer 1222
includes a monomer with a relatively small refractive index n4
(<n1). Further, the monomer is more soluble in low refractive
index fringes (e.g., in regions 1224) than in high refractive index
fringes (e.g., in regions 1226). Accordingly, the impact on
refractive index modulation is most pronounced with respect to dips
in the refractive index modulation profile, as indicated in
refractive index modulation plot 1228 (showing initial refractive
index modulation 1229A and modified refractive index modulation
1229B). By introducing a lower refractive index material into the
lower refractive index regions 1224 via the monomer reservoir
buffer layer 1222, the refractive index in the regions of
relatively low refractive index 1224 decreases, causing refractive
index at low points in plot 1229B to dip below n1.
[0136] FIG. 12D illustrates a fourth example of a grating 1230 with
refractive index modulation modification using a monomer reservoir
buffer layer 1232. Grating 1230 includes a polymer layer which
includes regions of relatively low refractive index 1234 (with
refractive index n1) and regions of relatively high refractive
index 1236 (with refractive index n2). A substrate layer 1231 is
disposed on a bottom side of the polymer layer. Monomer reservoir
buffer layer 1232 is disposed on a top side of the polymer
layer.
[0137] In FIG. 12D, the monomer reservoir buffer layer 1232
includes a monomer with a relatively small refractive index n4
(<n1). Further, the monomer is more soluble in high refractive
index fringes (e.g., in regions 1236) than in low refractive index
fringes (e.g., in regions 1234). Accordingly, the impact on the
refractive index is most pronounced with respect to the peaks in
the refractive index modulation profile, as indicated in refractive
index modulation plot 1238 (peaks reduced as-modified 1239B, as
compared to initial refractive index modulation 1239A). By
introducing a lower refractive index material into the higher
refractive index regions 1236 via the monomer reservoir buffer
layer 1232, the refractive index in the higher refractive index
regions 1236 decreases, causing refractive index at high points in
plot 1239B to dip below n2.
[0138] FIGS. 13A-13B illustrate variations on refractive index
modulation modification in a grating, according to some
embodiments. In FIG. 13A, the refractive index modulation
modification is substantially constant across the thickness of a
region of the polymer layer, while in FIG. 13B, the refractive
index modification varies across the thickness of a region of the
polymer layer. The "thickness" represents the z-direction from
bottom to top of the polymer layer.
[0139] FIG. 13A shows a grating 1300 which includes a first region
1302 with an initial refractive index n1 and a second region 1304
with an initial refractive index n2. In the grating 1300, the
refractive index modification has occurred through the whole
thickness of the polymer layer. Refractive index modulation graphs
1306, 1308 illustrate the refractive index modulation across the
polymer layer. Refractive index modulation graph 1306 illustrates
the refractive index modulation as a function of position through a
cross-section 1305 towards the upper side of the polymer layer.
Refractive index modulation graph 1308 illustrates the refractive
index modulation as a function of position through a cross-section
1307 towards the lower side of the polymer layer. In the grating
1300, the refractive index modulation modification profile is
substantially the same at the cross-sections 1305, 1307. This
corresponds to a concentration of nanoparticles (e.g., monomers)
being in a substantially constant concentration across the
thickness of the polymer layer in a given region. Substantially
constant concentration may correspond to some small variations,
such as 0.1%, 0.5%, 1%, or 5%.
[0140] FIG. 13B shows a grating 1350 which includes a first region
1352 with an initial refractive index n1 and a second region 1354
with an initial refractive index n2. In the grating 1350, the
refractive index modulation modification has occurred in a portion
of the polymer layer. Refractive index modulation graphs 1356, 1358
illustrate the refractive index modulation across the polymer
layer. Refractive index modulation graph 1356 illustrates the
refractive index modulation as a function of position through a
cross-section 1355 towards the upper side of the polymer layer.
Refractive index modulation graph 1358 illustrates the refractive
index modulation as a function of position through a cross-section
1357 towards the lower side of the polymer layer. In the grating
1350, the refractive index modulation at cross-section 1355 has
been modified. Monomers of refractive index n3, which is greater
than n1, have diffused preferentially into region 1352 near a top
surface of the polymer layer, which causes the refractive index in
region 1352 to shift upward from n1 in plot 1356. In contrast, at
cross-section 1357, the monomers have not diffused to this point of
the polymer layer, so the refractive index modulation has not been
modified as shown in graph 1358). The refractive index modulation
modification shown in FIG. 13B corresponds to the monomers or other
nanoparticles being more highly concentrated in proximity to the
upper edge of the polymer layer (e.g., the top surface of the
polymer layer shown in FIG. 13B).
[0141] Accordingly, based on the position and contents of the
monomer reservoir buffer layer(s), the refractive index modulation
modification can be customized to taper as a function of the
thickness within the polymer layer. The refractive index modulation
modification may happen only across a certain diffusion depth. The
refractive index modulation may be tapered to smooth the refractive
index modulation from the upper and/or lower edges of the polymer
layer towards the center of the polymer layer. This tapered
refractive index modulation can be used to reduce sidelobes of the
diffracted order and improve performance of the waveguide
display.
[0142] FIG. 14 illustrates a grating 1400 with a refractive index
modulation profile that is tapered on both a top and a bottom edge
of the grating. Region 1402 has an initial refractive index of n1
and region 1402 has an initial refractive index of n2. The
refractive index across the grating has been modulated (e.g., by
affixing monomer reservoir buffer layers to the upper and lower
edges of the polymer layer). The modulation affects the grating
most strongly at the top and the bottom, where the monomer is more
concentrated in proximity to the upper and lower edges of the
polymer layer. Graph 1430 shows the refractive index modulation
across the grating at cross-section 1432 at the center of the
grating 1400 in terms of thickness. The refractive index modulation
modification from the monomer reservoir buffer layers does not
reach to the center. Accordingly, at cross-section 1432 the
refractive index modulation remains at an initial level.
[0143] Graph 1410 shows the refractive index modulation across the
grating at cross-section 1412 near the bottom of the grating 1400.
The refractive index modulation modification from the monomer
reservoir buffer layer at the bottom of the grating has reached the
depth level indicated by cross-section 1412. Accordingly, at
cross-section 1412 the refractive index modulation has been
modified such that the refractive index in regions 1402 is
increased, as indicated in graph 1410. In comparison with graph
1430, in graph 1410, the lowest points in refractive index have
shifted upwards from n1.
[0144] Graph 1420 shows the refractive index modulation across the
grating at cross-section 1422 near the top of the grating 1400. The
refractive index modulation modification from the monomer reservoir
buffer layer at the top of the grating has reached the depth level
indicated by cross-section 1422. Accordingly, at cross-section 1422
the refractive index modulation has been modified such that the
refractive index in regions 1402 is increased, as indicated in
graph 1420. In comparison with graph 1430, in graph 1420, the
lowest points in refractive index have shifted upwards from n1.
[0145] FIGS. 15A-15B illustrate an example of refractive index
modulation in an apodized grating in accordance with some
embodiments. FIG. 15A shows the refractive index modulation as a
function of grating depth z (as illustrated in FIG. 15B), with and
without refractive index modification.
[0146] In FIG. 15A, a refractive index modulation profile in an
apodized grating is shown. This apodized grating may be used in a
1-D or 2-D pupil expander in a waveguide-based near-eye display
system, as shown in FIG. 15B. Refractive index modulation without
index profile modulation 1502 has a constant profile with respect
to normalized grating depth z. A refractive index modulation with
index profile modulation 1504 can be used to reduce or eliminate
sidelobes, as illustrated in FIGS. 16A-16B.
[0147] FIGS. 16A-16B illustrate sidelobe reduction using an
apodized grating in accordance with some embodiments. In FIG. 16A,
normalized diffraction efficiency for a single grating is shown as
a function of wavelength. Plot 1602 may correspond to a grating
without apodization. Sidelobes 1606 are visible. These sidelobes
are undesirable, particularly in multiplexed gratings. In
multiplexed gratings, the sidelobes in diffraction pattern cause
crosstalk, reducing the image contrast. To avoid such crosstalk,
the number of gratings multiplexed may be limited, which limits the
efficiency achievable.
[0148] Plot 1604, on the other hand, corresponds to a grating with
variable refractive index across the thickness of the grating,
reducing the sidelobes. To reduce the sidelobes, the refractive
index of the grating should be modified so that the refractive
index modulation is higher at the center of the grating and lower
at one or more sides of the grating, as illustrated in FIGS. 13B
and 14. In some embodiments, a bell-shaped refractive index
modulation profile across the z-direction in the grating may be
generated, as illustrated in FIGS. 15A-15B. Accordingly, varying
the refractive index across the thickness of the grating can reduce
sidelobes and crosstalk in multiplexed gratings. This improves the
image contrast and enables a larger number of gratings to be
multiplexed, increasing the overall efficiency.
[0149] In FIG. 16B, the normalized diffraction efficiency vs
wavelength plots 1602 and 1604 are shown on a logarithmic scale,
further highlighting the sidelobes 1606 and reduction thereof.
[0150] FIG. 17 is a simplified flow chart 1700 illustrating an
example of a method of fabricating a holographic optical element
according to certain embodiments. The operations described in flow
chart 1700 are for illustration purposes only and are not intended
to be limiting. In various implementations, modifications may be
made to flow chart 1700 to add additional operations, omit some
operations, combine some operations, split some operations, or
reorder some operations.
[0151] At block 1710, a holographic recording material layer may be
obtained. The holographic recording material layer may include a
mixture of matrix monomers and writing monomers. The matrix
monomers may be configured to polymerize (e.g., via thermal
treatment) to form a polymer matrix. The writing monomers may be
dispersed in the matrix monomers and may be configured to
polymerize when the holographic recording material is exposure to
recording light. The matrix monomers may have different refractive
index(es) from the writing monomers. For example, the writing
monomers may have a higher refractive index than the matrix
monomers.
[0152] In some embodiments, the layer of the holographic recording
material may be cured, for example, thermally or optically, to
polymerize the matrix monomers and form a polymer matrix. The
writing monomers may not polymerize under the curing condition and
may be dispersed in the formed polymer matrix. The polymer matrix
may function as a support matrix or backbone of the layer of the
holographic recording material.
[0153] At block 1720, the layer of holographic recording material
may be exposed to a recording light pattern to polymerize the
writing monomers in selected regions, such as the bright fringes of
the recording light pattern, as described above with respect to,
for example, FIGS. 7A-8. The recording light pattern may correspond
to a grating, a lens, a diffuser, and the like. The recording light
pattern may cause the polymerization and diffusion of the writing
monomers to form a holographic optical element corresponding to the
recording light pattern. The exposure to the recording light
pattern creates a first region having a first refractive index and
a second region having a second refractive index.
[0154] At block 1730, a resin layer comprising nanoparticles may be
applied to the holographic recording material layer. For example,
the layer of the holographic recording material may be deposited or
laminated on a first resin layer. In some embodiments, the
holographic recording material layer may be laminated on a
substrate, which is removed before applying the resin layer. In
some embodiments, the holographic recording material layer may be
sandwiched between two resin layers. Alternatively, the holographic
recording material layer may be laminated on a substrate (e.g.,
glass or plastic) layer on one side, and a resin layer is applied
to the holographic recording material layer on the other side.
Application of the resin layer causes diffusion of nanoparticles
from the resin layer into the holographic recording material layer.
Particles will further diffuse from the holographic recording
material layer into the resin layer. If unreacted monomer from the
initial holographic film is not present in the resin layer, the
monomer will diffuse from the holographic film to the resin layer
just because there is a natural concentration gradient between the
two films. Accordingly, the refractive index in the holographic
recording material layer is modified due to the diffusion of
particles. The concentration of nanoparticles in the resin layer
may be controlled so that, after a time, no nanoparticles are
available to diffuse into the holographic recording material layer.
Alternatively, or additionally, the removal of the resin layer may
be timed to tailor the nanoparticle concentration in the
holographic recording material layer. The concentration of the
nanoparticles may be tailored to achieve any of the configurations
for increasing the diffractive efficiency or apodizing the grating
described above.
[0155] Optionally, at block 1740, the resin layer(s) may be removed
from the layer of the holographic recording material. The
holographic recording material layer may then be laminated on one
or more substrates. For example, the resin layer may comprise a
flexible polyester film or plastic sheeting. Such a flexible resin
layer may be peeled off of the holographic recording material
layer. The layer of the holographic recording material on one
substrate may then be laminated on a substrate, such as an optical
component (e.g., a quartz, glass, crystal plate, or lens).
[0156] Removal of the resin layer and/or a substrate without
damaging the holographic recording material layer can be achieved
in multiple ways. The use of a pliable material such as flexible
plastic may facilitate low impact layer removal. Alternatively, or
additionally, a resin layer or substrate may be treated with an
anti-adhesion component to make the layer remove easily.
[0157] FIG. 18 is a schematic diagram showing another HOE
fabrication method 1800, according to some embodiments. HOE
fabrication method 1800 is similar to the method described above
with respect to FIG. 7, but the resin layer(s) are applied before
holographic exposure.
[0158] At 1802, a resin layer 1810, filled with nanoparticles such
as monomers with some predetermined refractive index, is applied to
a first substrate 1820. The resin layer 1810 may be bonded to, or
deposited on, the first substrate 1820. A holographic recording
material layer 1830 is applied to a second substrate 1840.
Similarly, the holographic recording material layer 1830 may be
bonded to, or deposited on, the second substrate 1840. In some
embodiments, the resin layer and the holographic recording material
layer have similar properties. For example the resin layer and the
holographic recording material layer may both comprise a polymer
matrix. However, the holographic recording material layer may
differ in the addition of photoinitiators for holographic
recording.
[0159] At 1804, resin layer 1810 and first substrate 1820 are
disposed on the holographic recording material layer 1830 and
second substrate 1840. The resin layer 1810 is placed in contact
with the holographic recording material layer 1830. The resin layer
1810 is laminated or bonded to the holographic recording material
layer 1830. Nanoparticles may diffuse from the resin layer 1810 to
the holographic recording material layer 1830. Species may also
diffuse into the resin layer 1810 from the holographic recording
material layer 1830. The dispersion of the nanoparticles may be
tailored to achieve any of the configurations for increasing the
diffractive efficiency or apodizing the grating described
above.
[0160] At 1806, a hologram is recorded in the holographic recording
material layer 1830. A recoding light pattern is applied to at
least the recording material layer, as described above with respect
to FIG. 17.
[0161] At 1808, the hologram has been recorded in holographic
recording material layer 1830. The resin layer 1810 may remain
affixed to the holographic recording material layer 1830. Diffusion
may continue for a time after the hologram is recorded. As
nanoparticles diffuse from the resin layer 1810 into the
holographic recording material layer 1830, or vice versa, the
refractive index modulation may continue to change. The amount of
diffusion, and the corresponding refractive index change, may be
controlled by controlling the number of nanoparticles in the resin
layer 1810 (e.g., so that only a desired number of nanoparticles
are available). The speed of the diffusion process (and the
solubility of the monomer in the grating) can be controlled by
increasing/decreasing the temperature. In addition, the diffusion
process could be stopped by flood exposing both films to polymerize
the diffused monomer. Further, the support layer of the resin layer
may be selected so as to be transparent to visible light (e.g.,
similar to a substrate layer), to avoid affecting performance of
the holographic optical element.
[0162] Embodiments may be used to fabricate 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.
[0163] FIG. 19 is a simplified block diagram of an example of an
electronic system 1900 of a near-eye display system (e.g., HMD
device) for implementing some of the examples disclosed herein.
Electronic system 1900 may be used as the electronic system of an
HMD device or other near-eye displays described above. In this
example, electronic system 1900 may include one or more
processor(s) 1910 and a memory 1920. Processor(s) 1910 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) 1910 may be
communicatively coupled with a plurality of components within
electronic system 1900. To realize this communicative coupling,
processor(s) 1910 may communicate with the other illustrated
components across a bus 1940. Bus 1940 may be any subsystem adapted
to transfer data within electronic system 1900. Bus 1940 may
include a plurality of computer buses and additional circuitry to
transfer data.
[0164] Memory 1920 may be coupled to processor(s) 1910. In some
embodiments, memory 1920 may offer both short-term and long-term
storage and may be divided into several units. Memory 1920 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 1920
may include removable storage devices, such as secure digital (SD)
cards. Memory 1920 may provide storage of computer-readable
instructions, data structures, program modules, and other data for
electronic system 1900. In some embodiments, memory 1920 may be
distributed into different hardware modules. A set of instructions
and/or code might be stored on memory 1920. The instructions might
take the form of executable code that may be executable by
electronic system 1900, and/or might take the form of source and/or
installable code, which, upon compilation and/or installation on
electronic system 1900 (e.g., using any of a variety of generally
available compilers, installation programs,
compression/decompression utilities, etc.), may take the form of
executable code.
[0165] In some embodiments, memory 1920 may store a plurality of
application modules 1922 through 1924, 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 1922-1924 may include particular instructions
to be executed by processor(s) 1910. In some embodiments, certain
applications or parts of application modules 1922-1924 may be
executable by other hardware modules 1980. In certain embodiments,
memory 1920 may additionally include secure memory, which may
include additional security controls to prevent copying or other
unauthorized access to secure information.
[0166] In some embodiments, memory 1920 may include an operating
system 1925 loaded therein. Operating system 1925 may be operable
to initiate the execution of the instructions provided by
application modules 1922-1924 and/or manage other hardware modules
1980 as well as interfaces with a wireless communication subsystem
1930 which may include one or more wireless transceivers. Operating
system 1925 may be adapted to perform other operations across the
components of electronic system 1900 including threading, resource
management, data storage control and other similar
functionality.
[0167] Wireless communication subsystem 1930 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 1900 may include one or more antennas
1934 for wireless communication as part of wireless communication
subsystem 1930 or as a separate component coupled to any portion of
the system. Depending on desired functionality, wireless
communication subsystem 1930 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 1930 may
permit data to be exchanged with a network, other computer systems,
and/or any other devices described herein. Wireless communication
subsystem 1930 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)
1934 and wireless link(s) 1932. Wireless communication subsystem
1930, processor(s) 1910, and memory 1920 may together comprise at
least a part of one or more of a means for performing some
functions disclosed herein.
[0168] Embodiments of electronic system 1900 may also include one
or more sensors 1990. Sensor(s) 1990 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) 1990 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.
[0169] Electronic system 1900 may include a display module 1960.
Display module 1960 may be a near-eye display, and may graphically
present information, such as images, videos, and various
instructions, from electronic system 1900 to a user. Such
information may be derived from one or more application modules
1922-1924, virtual reality engine 1926, one or more other hardware
modules 1980, a combination thereof, or any other suitable means
for resolving graphical content for the user (e.g., by operating
system 1925). Display module 1960 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.
[0170] Electronic system 1900 may include a user input/output
module 1970. User input/output module 1970 may allow a user to send
action requests to electronic system 1900. 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
1970 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
1900. In some embodiments, user input/output module 1970 may
provide haptic feedback to the user in accordance with instructions
received from electronic system 1900. For example, the haptic
feedback may be provided when an action request is received or has
been performed.
[0171] Electronic system 1900 may include a camera 1950 that may be
used to take photos or videos of a user, for example, for tracking
the user's eye position. Camera 1950 may also be used to take
photos or videos of the environment, for example, for VR, AR, or MR
applications. Camera 1950 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 1950
may include two or more cameras that may be used to capture 3-D
images.
[0172] In some embodiments, electronic system 1900 may include a
plurality of other hardware modules 1980. Each of other hardware
modules 1980 may be a physical module within electronic system
1900. While each of other hardware modules 1980 may be permanently
configured as a structure, some of other hardware modules 1980 may
be temporarily configured to perform specific functions or
temporarily activated. Examples of other hardware modules 1980 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 1980 may be implemented in
software.
[0173] In some embodiments, memory 1920 of electronic system 1900
may also store a virtual reality engine 1926. Virtual reality
engine 1926 may execute applications within electronic system 1900
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 1926 may be used for producing a signal (e.g., display
instructions) to display module 1960. For example, if the received
information indicates that the user has looked to the left, virtual
reality engine 1926 may generate content for the HMD device that
mirrors the user's movement in a virtual environment. Additionally,
virtual reality engine 1926 may perform an action within an
application in response to an action request received from user
input/output module 1970 and provide feedback to the user. The
provided feedback may be visual, audible, or haptic feedback. In
some implementations, processor(s) 1910 may include one or more
GPUs that may execute virtual reality engine 1926.
[0174] 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 1926,
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.
[0175] In alternative configurations, different and/or additional
components may be included in electronic system 1900. 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 1900 may be modified to include other system environments,
such as an AR system environment and/or an MR environment.
[0176] 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.
[0177] 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.
[0178] 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.
[0179] 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.
[0180] 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.
[0181] 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.
[0182] 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.
[0183] 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.
[0184] 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.
[0185] 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.
* * * * *