U.S. patent number 10,393,930 [Application Number 15/639,163] was granted by the patent office on 2019-08-27 for large-field-of-view waveguide supporting red, green, and blue in one plate.
This patent grant is currently assigned to Microsoft Technology Licensing, LLC. The grantee listed for this patent is Microsoft Technology Licensing, LLC. Invention is credited to Jani Kari Tapio Tervo.
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United States Patent |
10,393,930 |
Tervo |
August 27, 2019 |
Large-field-of-view waveguide supporting red, green, and blue in
one plate
Abstract
An optical device for combining RGB optical signals in a single
waveguide. The device includes a plurality of DOEs. A first DOE is
configured to receive an optical signal at input propagation angles
and to diffract the optical signal based on spectrum such that
predominately one spectrum of light is diffracted in a first
direction and path and predominately a second spectrum of light is
diffracted in a second different direction and path. The first DOE
is configured to diffract light into a second DOE. The second DOE
is configured to diffract light into a third DOE. The third DOE is
configured to diffract light into an eye box keeping output
propagation angles substantially parallel to the input propagation
angles. A summation of grating vectors for each of the paths is
substantially equal to zero.
Inventors: |
Tervo; Jani Kari Tapio (Espoo,
FI) |
Applicant: |
Name |
City |
State |
Country |
Type |
Microsoft Technology Licensing, LLC |
Redmond |
WA |
US |
|
|
Assignee: |
Microsoft Technology Licensing,
LLC (Redmond, WA)
|
Family
ID: |
62621040 |
Appl.
No.: |
15/639,163 |
Filed: |
June 30, 2017 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20190004219 A1 |
Jan 3, 2019 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B
27/0172 (20130101); G02B 27/0101 (20130101); G02B
5/18 (20130101); G02B 27/0081 (20130101); G02B
5/1842 (20130101); G02B 2027/0123 (20130101) |
Current International
Class: |
G02B
5/18 (20060101); G02B 27/01 (20060101); G02B
27/00 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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3339936 |
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Jun 2018 |
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EP |
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2008110659 |
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Sep 2008 |
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WO |
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2016020643 |
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Feb 2016 |
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WO |
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Other References
"International Search Report and Written Opinion Issued in PCT
Application No. PCT/US18/034518", dated Aug. 30, 2018, 13 Pages.
cited by applicant .
Guo, et al., "Design of a multiplexing grating for color
holographic waveguide", In Journal of Optical Engineering, vol. 54,
Issue 12, Dec. 22, 2015, 2 pages. cited by applicant.
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Primary Examiner: Kakalec; Kimberly N.
Attorney, Agent or Firm: Workman Nydegger
Claims
What is claimed is:
1. An optical device for combining RGB optical signals in a single
waveguide, the device comprising a plurality of DOEs including: a
first DOE comprising a first linear grating having a first grating
period and a second linear grating having a second grating period,
the first DOE being configured to receive an optical signal at
input propagation angles and to diffract the optical signal based
on spectrum such that a +1 diffraction order of a predominately
first spectrum of light is diffracted by the first linear grating
in a first direction and a -1 diffraction order of the
predominantly first spectrum of light is diffracted in a second
direction by the first linear grating and a +1 diffraction order of
a predominately a second spectrum of light is diffracted in a third
direction by the second linear grating and a -1 diffraction order
of the predominantly second spectrum of light is diffracted in a
fourth direction by the second linear grating, such that different
portions of optical signal take different paths, including at least
four different paths; a second DOE comprising at least four wings
with different grating orientations, each grating orientation being
oriented to diffract light toward a third DOE, wherein the first
DOE is configured to diffract the optical signal diffracted in the
first direction toward a first wing, the optical signal diffracted
in the second direction toward a second wing, the optical signal
diffracted in the third direction toward a third wing, and the
optical signal diffracted in the fourth direction toward a fourth
wing; the third DOE configured to diffract light into an eye box
keeping output propagation angles within some predetermined
threshold of the input propagation angles; wherein the second and
third DOE are configured to cause expansions that are substantially
non-parallel; and wherein the plurality of DOEs are associated with
grating vectors and wherein a summation of grating vectors for each
of the paths in the at least two different paths is substantially
equal to zero.
2. The optical device of claim 1, wherein at least one of the first
DOE and the third DOE comprise a linear grating associated with a
first grating vector on the front of the waveguide and a second
grating vector on a back of the waveguide.
3. The optical device of claim 1, wherein the second DOE comprises
a linear grating with a first wing on the front and a second wing
on a back of the waveguide, wherein the first wing and the second
wing overlap.
4. The optical device of claim 1, wherein at least one of the at
least four wings of the second DOE comprises a linear grating.
5. The optical device of claim 1, wherein the first wing and the
second wing of the second DOE comprise linear gratings on a back of
the waveguide.
6. The optical device of claim 1, wherein the second DOE comprises
a cross grating associated with two distinct grating vectors.
7. The optical device of claim 1, wherein the third DOE comprises a
cross grating associated with two distinct grating vectors.
8. A method of combining RGB optical signals in a single waveguide,
the waveguide comprising a plurality of DOEs, the method
comprising: directing an optical signal at a first DOE at input
propagation angles, wherein the first DOE comprises a first linear
grating having a first grating period and a second linear grating
having a second grating period; at the first DOE, diffracting the
optical signal based on spectrum such that a +1 diffraction order
of a predominately first spectrum of light is diffracted by the
first linear grating in a first direction and a -1 diffraction
order of the predominantly first spectrum of the light is
diffracted in a second direction by the first linear grating and a
+1 diffraction order of a predominately second spectrum of light is
diffracted in a third direction by the second linear grating and a
-1 diffraction order of the predominantly second spectrum of light
is diffracted in a fourth direction by the second linear grating,
such that different portions of optical signal take different
paths, including at least four different paths; at the first DOE,
diffracting the different portions into a second DOE, wherein the
second DOE comprises at least four wings with different grating
orientations, each grating orientation being oriented to diffract
light toward a third DOE, and wherein the first DOE diffracts light
in the first direction toward a first wing, light in the second
direction toward a second wing, light in the third direction toward
a third wing, and light in the fourth direction toward the third
wing; at the second DOE, diffracting the different portions into
the third DOE; at the second DOE and the third DOE expanding the
optical signal in a substantially non-parallel fashion; at the
third DOE, diffracting the different portions into an eye box
keeping output propagation angles within some predetermined
threshold of the input propagation angles; and wherein the
plurality of DOEs are associated with grating vectors and wherein
the acts are performed such that a summation of grating vectors for
each of the paths in the at least two different paths is
substantially equal to zero.
9. The method of claim 8, wherein diffracting the different
portions into an eye box keeping output propagation angles within
some predetermined threshold of the input propagation angles is
performed by the third DOE being a linear grating with a first
grating vector on the front of the waveguide and a second grating
vector on a back of the waveguide.
10. The method of claim 8, wherein expanding the optical signal in
a substantially non-parallel fashion and diffracting the different
portions into a third DOE is performed by at least two of the at
least four wings of the second DOE having linear gratings disposed
on opposite sides of the waveguide such that the linear gratings
overlap.
11. The method of claim 8, wherein expanding the optical signal in
a substantially non-parallel fashion and diffracting the different
portions into a third DOE is performed by the first wing and the
second wing of the second DOE having linear gratings on the front
of the waveguide.
12. The method of claim 8, wherein expanding the optical signal in
a substantially non-parallel fashion and diffracting the different
portions into a third DOE is performed by the first wing and the
second wing of the second DOE having linear gratings on a back of
the waveguide.
13. The method of claim 8, wherein diffracting the optical signal
based on spectrum such that a +1 diffraction order of a
predominately first spectrum of light is diffracted by the first
linear grating in a first direction and a -1 diffraction order of
the predominantly first spectrum of the light is diffracted in a
second direction by the first linear grating and a +1 diffraction
order of a predominately second spectrum of light is diffracted in
a third direction by the second linear grating and a -1 diffraction
order of the predominantly second spectrum of light is diffracted
in a fourth direction by the second linear grating, such that
different portions of optical signal take different paths,
including at least four different paths is performed by the first
DOE having a cross grating associated with two distinct grating
vectors.
14. The method of claim 8, wherein expanding the optical signal in
a substantially non-parallel fashion and diffracting the different
portions into a third DOE is performed by the second DOE having a
cross grating associated with two distinct grating vectors.
15. The method of claim 8, wherein diffracting the different
portions into an eye box keeping output propagation angles within
some predetermined threshold of the input propagation angles is
performed by the third DOE having a cross grating associated with
two distinct grating vectors.
16. A near eye optical device, comprising: a light engine; a
waveguide coupled to the light engine; wherein the waveguide
comprises: a first DOE comprising a first linear grating having a
first grating period and a second linear grating having a second
grating period, the first DOE being configured to receive an
optical signal from the light engine at input propagation angles
and to diffract the optical signal based on spectrum such that a +1
diffraction order of a predominately first spectrum of light is
diffracted by the first linear grating in a first direction and a
-1 diffraction order of the predominantly first spectrum of light
is diffracted in a second direction by the first linear grating and
a +1 diffraction order of a predominately second spectrum of light
is diffracted in a third direction by the second linear grating and
a -1 diffraction order of the predominantly second spectrum of
light is diffracted in a fourth direction by the second linear
grating, such that different portions of optical signal take
different paths, including at least four different paths; a second
DOE comprising at least four wings with different grating
orientations, each grating orientation being oriented to diffract
light toward a third DOE, wherein the first DOE is configured to
diffract the optical signal diffracted in the first direction
toward a first wing, the optical signal diffracted in the second
direction toward a second wing, the optical signal diffracted in
the third direction toward a third wing, and the optical signal
diffracted in the fourth direction toward a fourth wing; the third
DOE configured to diffract light into an eye box keeping output
propagation angles within some predetermined threshold of the input
propagation angles; wherein the second and third DOEs are
configured to cause expansions that are substantially non-parallel;
and wherein the first, second, and third plurality of DOEs are
associated with grating vectors and wherein a summation of grating
vectors for each of the paths in the at least two different paths
is substantially equal to zero.
17. The near-eye optical device of claim 16, wherein at least some
gratings of the first DOE, the second DOE, or the third DOE are
positioned on a back of the waveguide.
18. The near-eye optical device of claim 16, wherein at least some
gratings of the first DOE, the second DOE, or the third DOE
comprise a cross grating associated with two distinct grating
vectors.
Description
BACKGROUND
Background and Relevant Art
Recently, there has been a resurgence in the interest in virtual
reality (VR) and augmented reality (AR) devices and other such near
eye devices. These devices typically include a video transmitter of
some sort, such as a light engine, and optics couple to the video
transmitter configured to transmit images to the eyes of the user
using the devices. In particular, a user will wear a headset or
similar device that includes a video transmitter optically coupled
to one or more waveguides where the waveguides are configured to
optically couple images out to a user.
One problem that has needed to addressing by manufacturers of such
devices is a problem related to limited Field of View (FoV). In the
contexts illustrated herein, the FoV is the number of degrees of
visual high angle assuming a fixed eye position. Horizontally, the
FoV for a human is around 135.degree.. However, often virtual
reality and augmented reality devices will have a much lower FoV
available. The lower the FoV available from the device, the less
realistic the experience with the device.
Technologies have been implemented which attempt to widen the FoV.
One such technology is the use of diffraction gratings which spread
the light by wavelength to increase the FoV. That is, a diffraction
grating is dispersive, which means that it creates diffraction
orders such that the colors of all non-zero orders propagate in
different directions. While this behavior is highly beneficial,
e.g., in spectroscopic applications, in AR/VR devices based on
diffractive waveguides it is unwanted, since carrying and expanding
the image content in the waveguide requires three (or in some cases
two) separate waveguides unless the FoV is very small.
Having multiple waveguides greatly complicates the manufacturing
process. Not only one must manufacture several waveguides but
manufacturing tolerances become much tighter. In addition, one must
accurately put the multiple plates in a grating stack, which adds
additional manufacturing steps which require high accuracy, and
increased cost.
The subject matter claimed herein is not limited to embodiments
that solve any disadvantages or that operate only in environments
such as those described above. Rather, this background is only
provided to illustrate one exemplary technology area where some
embodiments described herein may be practiced.
BRIEF SUMMARY
One embodiment illustrated herein includes an optical device for
combining RGB optical signals in a single waveguide. The device
includes a plurality of DOEs. The device includes a first DOE
configured to receive an optical signal at input propagation angles
and to diffract the optical signal based on spectrum such that
predominately one spectrum of light is diffracted in a first
direction and predominately a second spectrum of light is
diffracted in a second different direction such that different
portions of optical signal take different paths, including at least
two different paths. The device includes a second DOE. The first
DOE is configured to diffract light into the second DOE. The device
includes a third DOE. The second DOE is further configured to
diffract light into the third DOE. The second and third DOE are
configured to cause expansions that are substantially non-parallel.
The third DOE is configured to diffract light into an eye box
keeping output propagation angles within some predetermined
threshold of the input propagation angles. The plurality of DOEs
are associated with grating vectors. A summation of grating vectors
for each of the paths in the at least two different paths is
substantially equal to zero.
This Summary is provided to introduce a selection of concepts in a
simplified form that are further described below in the Detailed
Description. This Summary is not intended to identify key features
or essential features of the claimed subject matter, nor is it
intended to be used as an aid in determining the scope of the
claimed subject matter.
Additional features and advantages will be set forth in the
description which follows, and in part will be obvious from the
description, or may be learned by the practice of the teachings
herein. Features and advantages of the invention may be realized
and obtained by means of the instruments and combinations
particularly pointed out in the appended claims. Features of the
present invention will become more fully apparent from the
following description and appended claims, or may be learned by the
practice of the invention as set forth hereinafter.
BRIEF DESCRIPTION OF THE DRAWINGS
In order to describe the manner in which the above-recited and
other advantages and features can be obtained, a more particular
description of the subject matter briefly described above will be
rendered by reference to specific embodiments which are illustrated
in the appended drawings. Understanding that these drawings depict
only typical embodiments and are not therefore to be considered to
be limiting in scope, embodiments will be described and explained
with additional specificity and detail through the use of the
accompanying drawings in which:
FIG. 1 illustrates an example of a near-eye display device;
FIG. 2 illustrates various display elements;
FIG. 3 illustrates a waveguide;
FIG. 4A illustrates a wave vector space representation;
FIG. 4B illustrates a wave vector space representation;
FIG. 4C illustrates a wave vector space representation;
FIG. 5 illustrates an output waveguide;
FIG. 6A illustrates a waveguide with odd-order expansion;
FIG. 6B illustrates a waveguide with odd-order expansion;
FIG. 7 illustrates a waveguide with even-order expansion; and
FIG. 8 illustrates a method of combining RGB optical signals in a
single waveguide.
DETAILED DESCRIPTION
Some embodiments illustrated herein may include or may be used to
implement a diffractive waveguide based AR/VR device that 1)
carries virtual content from a light engine to the front of a
user's eye and 2) expands the pupil, thus enlarging the eye box. In
particular, some embodiments, can support a large FoV (e.g.,
45.times.30.degree.) in a single waveguide plate for multiple
different wavelengths. For example, embodiments may be configured
to support red, green, and blue (RGB) wavelengths with a large FoV,
in a single waveguide. Thus, embodiments may carry large FoV RGB
content through a single waveguide. This can be accomplished in
some embodiments as now illustrated.
Some embodiments include various diffractive optical elements
(DOEs) in a waveguide to accomplish the functionality described
herein. In one example embodiment an incoupling grating (referred
to herein as DOE1) diffracts light into two or more directions such
that one spectrum of wavelengths, e.g., the red light, is
diffracted primarily in a different direction(s) than another
spectrum of wavelengths e.g., blue light. In the illustrated
example, green light is split between these directions. This can be
accomplished for example, by using a single-sided crossed grating
(doubly-periodic grating) or by using linear gratings on the two
surfaces of the waveguide. While the examples illustrated herein
refer to the two (or more) paths through the waveguide as the red
path and the blue path, it should be appreciated that other color
spectrum paths may be implemented. Further, it should be
appreciated that in practice, part of red light (or other colors)
naturally goes through the blue path (or other colors), and vice
versa.
As will be illustrated in further detail below, there are different
expansion gratings (illustrated herein as DOE2) for the blue path
and the red path. Both have at least one distinct wing of DOE2 but
may also have more. The number of wings for DOE2 can also be
unequal for these two paths.
The out-coupling grating (illustrated herein as DOE3) has two
different periods and orientations (or more if multiple colors are
handled separately) for the red and blue. Again, this can be done
by crossed grating on one side of a grating or "crossed" linear
gratings, one on each of the different surfaces of the
waveguide.
Note that in components where light reaches DOE3 by multiple
possible paths, each path obeys a zero summation rule separately
such that the summations of vectors for each path sums to
approximately zero, as illustrated in more detail below.
Thus, in general, embodiments may split the FoV of different colors
into two (or more) paths, carry the partial FoVs to DOE3 while
expanding the pupil by pupil replication, and at DOE3 recombining
the different contributions of each color.
Additional details are now illustrated.
FIG. 1 shows an example of a near-eye display device in which
embodiments can be practiced. The near-eye display device 100 may
be a virtual reality (VR) and/or augmented reality (AR) device that
can provide a VR or AR experience with the user. In a VR
experience, essentially the entire visual experience is provided by
the VR device's light engine. In an AR experience, the light engine
is used to transmit images onto a transparent protective visor. In
this way, the visual experience includes elements provided by the
light engine of the VR device as well as objects that can be seen
visually by the user through the transparent protective visor. In
the examples illustrated herein, the near-eye display device 100 is
designed for AR visualization, but VR devices can be implemented
using the principles illustrated.
In the illustrated embodiment, the near-eye display device 100
includes a chassis 101, a transparent protective visor 102 mounted
to the chassis 101, and left and right side arms 104 mounted to the
chassis 101. The visor 102 forms a protective enclosure for various
display elements shown in FIG. 2.
A display assembly 200 (see FIG. 2) that can generate images for
AR/VR visualization is also mounted to the chassis 101 and enclosed
within the protective visor 102. The visor assembly 102 and/or
chassis 101 may also house electronics to control the functionality
of the display assembly 200 and other functions of the near-eye
display device 100. The near-eye display device 100 further
includes an adjustable headband 105 attached to the chassis 101, by
which the near-eye display device 100 can be worn on a user's
head.
FIG. 2 shows a side view of display components that may be
contained within the visor 102 of the near-eye display device 100,
in some embodiments of the invention. During operation of the
near-eye display device 100, the display components are positioned
relative to the user's left eye 206.sub.L or right eye 206.sub.R.
The display components are mounted to the interior surface of the
chassis 101. The chassis 101 is shown in cross-section in FIG.
2.
In an AR application, the display components are designed to
overlay three-dimensional images on the user's view of a real-world
environment viewable through the transparent protective visor 102,
e.g., by projecting light into the user's eyes. Accordingly, the
display components include a display module 204 that houses a light
engine including components such as: one or more light sources
(e.g., one or more light emitting diodes (LEDs)); one or more
microdisplay imagers, such as liquid crystal on silicon (LCOS),
liquid crystal display (LCD), digital micromirror device (DMD); and
one or more lenses, beam splitters and/or waveguides. The
microdisplay imager(s) (not shown) within the display module 204
may be connected via a flexible circuit connector 205 to a printed
circuit board 208 that has image generation/control electronics
mounted on it.
The display components further include a transparent waveguide
carrier 201 to which the display module 204 is mounted, and one or
more output waveguides 202 on the user's side of the waveguide
carrier 201, for each of the left eye and right eye of the user.
Note that, ideally, embodiments are able to use a single waveguide
to implement the functionality described herein. The waveguide
carrier 201 has a central nose bridge portion 210, from which its
left and right waveguide mounting surfaces extend. Waveguides 202
are implemented on each of the left and right waveguide mounting
surfaces of the waveguide carrier 201, to project light emitted
from the display module and representing images into the left eye
206.sub.L and right eye 206.sub.R, respectively, of the user. The
display assembly 200 can be mounted to the chassis 101 through a
center tab 207 located at the top of the waveguide carrier 201 over
the central nose bridge section 210.
The near-eye display device can provide light representing an image
to an optical receptor (e.g., an eye) of a user. The user may be,
e.g., a human, an animal or a machine.
FIG. 3 shows an example of an output waveguide that can be mounted
on the waveguide carrier 201 to convey light to one eye of the
user. A similar waveguide can be designed for the other eye (or
eyes), for example, as a (horizontal) mirror image of the waveguide
shown in FIG. 3. The waveguide 310 is transparent (although
diffractive) and, as can be seen from FIG. 2, would normally be
disposed directly in front of the eye of the user during operation
of the near-eye display device, e.g., as one of the waveguides 202
in FIG. 2. The waveguide 310 is, therefore, shown from the user's
perspective during operation of the near-eye display device
100.
The waveguide 310 includes a single input port 311, which is a DOE
indicated as DOE1 (also called in-coupling element). The input port
311 may be formed from, for example, a surface diffraction grating,
volume diffraction grating, or a reflective component.
In the example illustrated herein, the input port 311 is configured
to diffract input light into two or more spectra (with some leakage
of the other specta) and to diffract those two or more spectra in
different directions. This causes the different spectra to take
different paths on the transmission channel 312 illustrated in FIG.
3.
This is illustrated in one detailed example illustrated in FIG. 4A.
FIG. 4A illustrates a wave vector space representation. FIG. 4A
shows a transverse wave vector space representation of light waves
being diffracted by DOE1, input port 311 in the waveguide 310. The
inner solid circle 401 represents the border of total internal
refraction (TIR) condition. The outer solid circle 402 represents
the border of evanescent waves.
Therefore, any light waves in the doughnut shaped portion between
concentric circles 401 and 402 propagate in the waveguide 310 by
total internal reflection (TIR). Any light waves in the inner
circle 401 are waves propagate in the waveguide and then exit into
the air. In other words, those light waves propagate in the
waveguide and then exit from the waveguide. Any light waves outside
of the outer circle 402 are evanescent waves that are not coupled
into the waveguide.
FIG. 4A shows two grating vectors for DOE1 and the FOVs diffracted
by DOE1 of the waveguide 310. In particular, FIG. 4A shows a DOE1
blue path, -1 order, a DOE1 red path, -1 order, a DOE1 red path, +1
order and a DOE1 blue path, +1 order.
In some embodiments, DOE1 may include a linear grating with a first
grating orientation and period on the front surface of the grating
and a second grating orientation and period on the back of the
grating. The first grating can diffract one spectrum of light, and
the second grating can diffract a second spectrum of light.
Alternatively, DOE1 may include a cross grating on one side of a
waveguide. The grating vectors of the cross grating may have
different orientations and lengths, and they may be non-orthogonal
to each other.
Referring once again to FIG. 3, the waveguide 310 includes a
transmission channel 312. The transmission channel includes a DOE,
referred to herein as DOE2. Note that DOE2 has several different
wings, including DOE2 top left, DOE2 top right, DOE2 bottom left
and DOE2 bottom right. As noted previously, DOE2 comprises a number
of expansion gratings. The functionality of DOE2, will be explained
in more detail below in conjunction with the description of FIGS. 5
through 7.
However, reference is now made to FIG. 4B which illustrates DOE2
grating vectors and FOVs diffracted by DOE2.
Note that the various wings of DOE2 may be implemented on a grating
with a first wing on the front of the grating, and a second wing on
the back of the grating. In some embodiments, these first and
second wings can overlap. In some embodiments, DOE2 may be a linear
grating with first and second wings on the front of the waveguide.
In some embodiments, DOE2 may be a linear grating with first and
second wings on the back of the waveguide.
Referring once again to FIG. 3, The waveguide 310 further includes
a single output port 313, which is a DOE indicated as DOE3 (also
called out-coupling element).
Referring now to FIG. 4C, DOE3 grating vectors and FOVs diffracted
by DOE3 are shown.
During operation, the display module 204 (see FIG. 2) outputs light
representing an image for an eye from its output port into the
input port 311 of the waveguide 310.
The transmission channel 312 conveys light from the input port 311
to the output port 313 and may be, for example, a surface
diffraction grating, polarization grating, volume diffraction
grating, or a reflective component. The transmission channel 312
may be designed to accomplish this by use of total internal
reflection (TIR). Light representing the image is then projected
from the output port 313 to the user's eye.
Thus, in general, embodiments may split the FoV of different colors
into two (or more) paths, carry the partial FoVs to DOE3 while
expanding the pupil by pupil replication, and at DOE3 recombining
the different contributions of each color. Two or more paths may be
identical in some parts of the path.
The grating vectors of DOEs 1, 2 and 3 satisfy
D.sub.1+D.sub.2+D.sub.2=0.
Specifically, the two grating vectors of DOE1 (for the +1 order)
are denoted by D1r and D1b for "red" and "blue" paths as
illustrated in the Figures above.
DOE2 grating vectors are denoted by D2tr, D2br, D2tl, D2bl for
top-right, bottom-right, top-left, bottom-left, respectively
Grating vectors of DOE3 are denoted by D3b and D3r
Then the path equations are: D1r+D2bl+D3r=0 -D1r+D2tr+D3r=0
D1b+D2br+D3b=0 -D1b+D2tl+D3b=0
FIG. 4A-4Cc presents an example of a k-vector map enabling this
type of solution. Note that in FIG. 3, a part of both red and blue
FoV appear to be leaky but this is not necessary the case in all
embodiments.
The waveguide 310 may include multiple diffraction optical elements
(DOEs), in order to control the directions of the light propagating
in the near-eye display device via multiple occurrences of optical
diffraction. The DOEs may be, for example, surface diffraction
gratings or volume diffraction gratings. Various components of the
waveguide 310 can be designed to contain one or more of the
DOEs.
For example, the waveguide 310 may include three DOEs. The input
port 311 of the waveguide 310 is a DOE1 for coupling light into the
waveguide 310 and controlling the direction of light path after the
light reaches the input port 311.
The transmission channel 312 of the waveguide 310 is a DOE2 for
controlling the direction of light path in the transmission channel
312 and ensuring the light propagating inside of the transmission
channel 312 through total internal reflection (TIR). Further, DOE2
is configured homogenize light signals in a horizontal
direction
The output port 313 is a DOE3 for controlling the direction of the
light path after the light exits the output port 313. DOE3
configured to diffract light into an eye box keeping output
propagation angles within some predetermined threshold of the input
propagation angle
The propagation directions of the expanded light waves are
substantially parallel to each other (within some predetermined
threshold). The expanded light waves are spaced or distributed
along the particular direction.
In other words, the expanded light waves are translated along the
particular direction (or coordinate axis) in an output waveguide
before exiting the output waveguide. Each of the expanded light
waves has a relatively narrow range of propagation angles or FoV.
Each expanded light wave has a "propagation vector" representing
the average propagation direction of the light wave and denoting a
center axis of the prorogation energy of the expanded light wave.
Translation of a light wave means shifting the corresponding
propagation vector of the light wave along a particular direction
(or coordinate axis) that is not parallel to the propagation vector
itself.
Thus, the light waves exiting the output waveguide have the same
direction as (i.e., are substantially parallel, within some
threshold, to) the light waves entering the output waveguide for
light of any given wavelength, to have the light waves follow the
desired path to the optical receptor of a user. This condition is
called achromatic imaging.
The following illustrates details with respect to expanding light
and is directed to a single light path. However, it should be
appreciated that the concepts illustrated can be applied to the
different paths described above, such that expansion and the
summation rules apply for each distinct path of light.
The waveguide including three DOEs can expand the light waves in
two dimensions. The expansion process is also referred to as exit
pupil expansion. FIG. 5 shows an example of an output waveguide
that expands the exit pupil of a near-eye display device. The
waveguide 510 includes three DOEs 515, 520 and 525 to expand the
exit pupil. The DOEs 515, 520 and 525 are successive in a common
light path. The DOEs 515, 520 and 525 can be, e.g., arranged on a
planar substrate.
The imager 505 (e.g., an LCOS device) outputs a light wave 550 that
is incident upon the first DOE 515 in a Z direction. The DOE 515
directs the light wave 552 toward the second DOE 520. As shown in
FIG. 5, the DOE 520 expands the light wave 554 in a first dimension
(X dimension). As shown in FIG. 5, during the expansion, each
propagation vector of the expanded light waves 554 is shifted along
the X coordinate axis such that the expanded light waves are spaced
or distributed in the X dimension.
The DOE 520 further redirects the expanded light wave 554 to a
third DOE 525. The third DOE 525 further expands the light wave 554
in a second dimension (Y dimension), and redirects the expanded
light wave 556 outward in the Z direction.
Thus, the waveguide 510 receives the input light wave 550 incident
in the Z direction, expands the light wave in both X and Y
dimensions, and redirects the expanded light waves in the same
Z-direction. In other words, the waveguide 510 expanded light
distribution in two dimensions while maintains the direction of the
light wave. Thus, the waveguide 510 can be referred to as a
beam-expanding device or an exit pupil expander.
The waveguide, as a beam-expanding device, can expand light waves
in, e.g., an odd-order expansion process or an even-order process.
FIG. 6A shows an output waveguide conducting an odd-order
expansion. The waveguide 600 includes DOEs 615, 620 and 625.
Each of the DOEs 615, 620 and 625 has a diffraction grating. A
diffraction grating is an optical component with a periodic
structure, which splits and diffracts an incident light beam into
several beams travelling in different directions. The periodic
structure can include linear grooves arranged in a periodic
pattern. The distance between nearby grooves is called grating
period d.
The diffraction grating has a property of grating vector D (also
referred to as diffraction pattern vector). The grating vector D
represents the direction and spacing of the grating pattern (also
referred to as periodic diffraction pattern). The length of a
grating vector is D=2.pi./d. The direction of the grating vector D
is perpendicular to ("normal to" or "orthogonal to") center axes of
the periodic linear grooves, where the center axes are
perpendicular to the cross sections of the periodic linear
grooves.
Light is incident upon the waveguide 600 in a Z direction, which is
perpendicular to the X and Y directions. The first DOE 615 couples
light from an imager (not shown) into the waveguide 600. The second
DOE 620 expands the light in the X direction. The third DOE 625
further expands the light in the Y direction and couples the
expanded light out from the waveguide 600 in the same Z
direction.
As shown in FIG. 6A, the second DOE 620 receives the light wave
from the first DOE 615 at a left edge (as the reader views the
figure) of the DOE 620. The light wave is reflected by the grating
pattern in the DOE 620 for one or more times before the light wave
exits the DOE 620 at a bottom edge of the DOE 620. Because the
odd-order expansion enables the second DOE 620 to receive the light
wave at a side edge, a waveguide of an odd-order expansion
configuration usually occupies less space than a waveguide of an
even-order expansion configuration (which is discussed later).
During the odd-order expansion process, the second DOE 620 reflects
(i.e., changes the direction of) the light for an odd number of
times before redirecting the light into the third DOE 625. Over the
process of multiple reflections between 0 and +1 diffraction
orders, a greater portion of the light energy is converted to +1
order, which is redirected toward the third DOE 625.
FIG. 6B shows the wave vectors of light propagating in the
waveguide and grating vectors of DOEs of the waveguide. The
incident light has a pair of transverse wave vector components
k.sub.x0 and k.sub.y0. The magnitude of the wave vector is the wave
number k=2.pi./.lamda., where .lamda. is the wavelength of the
light. The wave number of the incident light in the air is denoted
as k.sub.0. The wave number of the light propagating in the
waveguide is denoted as k=k.sub.0*n, where n is the refractive
index of the waveguide material.
The grating vectors of the DOE1, 2, and 3 (616, 620 and 625 in FIG.
6B) are denoted as D.sub.j=(D.sub.xj, D.sub.yj). The DOE 615 with a
wave vector of (D.sub.x1, D.sub.y1) redirects the incident light
(k.sub.x0, k.sub.y0) toward the second DOE 620. Therefore,
(k.sub.x1, k.sub.y1)=(k.sub.x0+D.sub.x1, k.sub.y0+D.sub.y1).
The DOE 620 with a wave vector of (D.sub.x2, D.sub.y2) receives
light (k.sub.x1, k.sub.y1) and redirects the light (k.sub.x1,
k.sub.y1) toward the third DOE 625. Therefore, (k.sub.x2,
k.sub.y2)=(k.sub.x1+D.sub.x2,
k.sub.y1+D.sub.y2)=(k.sub.x0+D.sub.x1+D.sub.x2+D.sub.x3,
k.sub.y0+D.sub.y1+D.sub.y2+D.sub.x3).
The DOE 625 with a wave vector of (D.sub.x3, D.sub.y3) receives
light (k.sub.x2, k.sub.y2) and couples the light (k.sub.x2,
k.sub.y2) out in a Z direction. Therefore, (k.sub.x3,
k.sub.y3)=(k.sub.x2+D.sub.x3,
k.sub.y2+D.sub.y3)=(k.sub.x0+D.sub.x1+D.sub.x2+D.sub.x3,
k.sub.y0+D.sub.y1+D.sub.y2+D.sub.x3).
The waveguide 600 satisfies the achromatic imaging condition, which
means that when the light waves with different wavelengths are
expanded by the waveguide 600 and exit the waveguide 600, the exit
directions of the light waves are the same as the input directions
in which the light waves enter the waveguide 600. In other words,
the incident light wave number (k.sub.x0, k.sub.y0) matches the
out-coupled light wave number (k.sub.x3, k.sub.y3): (k.sub.x0,
k.sub.y0)=(k.sub.x3, k.sub.y3). Therefore, the grating vectors of
the waveguide 600 satisfy
D.sub.x1+D.sub.x2+D.sub.x3=D.sub.y1+D.sub.y2+D.sub.x3)=0.
Alternatively, in a vector form, a vector summation of the grating
vectors equals zero:
D.sub.1+D.sub.2+D.sub.2=0 (also referred to as the "summation
rule").
Note that the grating vectors D.sub.1, D.sub.2, D.sub.2 depend on
grating periods but do not depend on wavelengths of the light
waves. Therefore, once the grating vectors satisfy the summation
rule, the achromatic imaging condition is satisfied for light waves
with any wavelengths (hence the term "achromatic imaging").
To satisfy the achromatic imaging condition, it is not necessary to
restrict the diffraction gratings of first DOE 615 and the DOE 625
to have the same grating period. The summation rule relaxes the
design limitations of those diffraction gratings. The relaxed
design limitations enable a waveguide 600 to have a larger FoV.
Furthermore, the waveguide 600 keeps the light diffracted by DOEs
615 and 620 inside the waveguide 600. Thus, the light propagating
inside of the waveguide 600 is not evanescent and satisfies
condition of total internal reflection (TIR). In other words, light
diffracted by DOE 615 satisfies the TIR condition inside of the
waveguide: k.sub.x1.sup.2+k.sub.y1.sup.2>k.sub.0.sup.2. Light
diffracted by DOE 615 is not evanescent:
k.sub.x1.sup.2+k.sub.y1.sup.2<k.sup.2. Light diffracted by DOE
620 also satisfies the TIR condition inside of the waveguide:
k.sub.x2.sup.2+k.sub.y2.sup.2>k.sub.0.sup.2. Light diffracted by
DOE 620 is not evanescent:
k.sub.x2.sup.2+k.sub.y2.sup.2<k.sup.2.
Although FIGS. 6A, 6B and 6C shows a waveguide including three
DOEs, a waveguide according to the disclosed technology can have
any arbitrary number of DOEs. For example, if a waveguide includes
N number of DOEs, the condition of achromatic imaging is
D.sub.x1+D.sub.x2+D.sub.x3+ . . .
+D.sub.xN=D.sub.y1+D.sub.y2+D.sub.x3+ . . . +D.sub.yN=0.
Alternatively, in a vector form: D.sub.1+D.sub.2+D.sub.2+ . . .
+D.sub.N=0. The DOEs also satisfy the conditions for TIR and
non-evanescence.
In some embodiments, the achromatic imaging condition can be
expressed as a weighted vector summation of the grating vectors:
mD.sub.1+nD.sub.2+lD.sub.3=0, where the values m, n, and l in the
addends are integer weight values that represent diffraction orders
to which the periodic diffraction patterns are designed to
concentrate light energy. In some embodiments, the integer weight
values can be 0, negative, or positive.
Furthermore, the waveguide, as a beam-expanding device, can expand
light waves in an even-order expansion process as well. FIG. 7
shows an output waveguide conducting an even-order expansion. The
waveguide 700 includes DOEs 715, 720 and 725.
Light is incident upon the waveguide 700 in a Z direction, which is
perpendicular to the X and Y directions. The first DOE 715 couples
light into the waveguide 700, and redirects the light wave into the
second DOE 720 at a top edge of DOE 720. The second DOE 720 expands
the light in the X direction. The third DOE 725 further expands the
light in the Y direction and couples the expanded light out from
the waveguide 700 in the same Z direction.
As shown in FIG. 7, the second DOE 720 receives the light wave from
the first DOE 715 at the top edge of the DOE 520. Note that in the
odd-order expansion illustrated in FIG. 6A, the second DOE 520
receives the light wave at the left side edge. The choice of either
odd-order expansion or even-order expansion depends on various
design factors for the waveguide. Typically, a waveguide of
odd-order expansion configuration tends to be smaller. An
even-order expansion configuration, on the other hand, enables
supplying the light wave at the top edge of the second DOE, which
may be advantageous when there is a limitation on the width of the
waveguide.
The light wave is reflected by the grating pattern in the DOE 720
multiple times before the light wave exits the DOE 720 at a bottom
edge of the DOE 720. During the even-order expansion process, the
second DOE 720 reflects the light an even number of times
(including zero time) before redirecting the light into the third
DOE 525. Similar to the odd-order expansion, over the process of
multiple reflections between 0 and +1 orders, more of the light
energy is converted to +1 order, which is redirected toward the
third DOE 725.
As shown in FIG. 7, the second DOE 720 expands the light wave in
the X direction. However, the second DOE 720 maintains the
direction of its output light as the same of the direction of its
input light. In other words, in the even-order expansion, the wave
vectors of light waves before and after second DOE 720 are
identical. Thus, the grating vector for the diffraction grating of
the second DOE 720 does not impose limitation to diffraction
vectors of other DOEs in the waveguide 700.
In the even-order expansion, the first DOE 715 can have, e.g.,
linear diffraction gratings on two sides of the DOE 715 (also
referred to as "dual-sided linear grating"). The first diffraction
grating on a first side (e.g., top side) of DOE 715 has a grating
vector of D.sub.1a=(D.sub.x1a, D.sub.y1a). The second diffraction
grating on a second side (e.g., bottom side) of DOE 715 has a
grating vector of D.sub.1b=(D.sub.x1b, D.sub.y1b). The diffraction
grating of the third DOE 725 has a grating vector of
D.sub.3=(D.sub.x3, D.sub.y3)
The waveguide 700 satisfies the achromatic imaging condition, which
means the incident light (k.sub.x0, k.sub.y0) matches the
out-coupled light (k.sub.x3, k.sub.y3). The achromatic imaging
condition is satisfied, if mD.sub.1a+nD.sub.1b=.+-.D.sub.3, wherein
m and n are integer order numbers.
In some embodiments, the achromatic imaging condition can be
expressed as a weighted vector summation of the grating vectors:
mD.sub.1a+nD.sub.1b+lD.sub.3=0, where the values m, n and l in the
addends are integer weight values that represent diffraction orders
to which the periodic diffraction patterns are designed to
concentrate light energy (also referred to as "weighted summation
rule"). In some embodiments, the integer weight values can be 0, -1
or +1. Higher diffraction orders, corresponding to integer numbers
whose absolute values are larger than 1, are usually suppressed by
the grating patterns.
In some embodiments, m=1 and n=0, or m=0 and n=1. Thus, the first
DOE 715 has one diffraction grating with a wave vector
D.sub.1=.+-.D.sub.3. In other words, if the first DOE 715 and the
third DOE 725 have the same length for the grating vectors (or the
same grating period), the achromatic imaging condition is
satisfied.
The design limitation of the grating vectors can be further
relaxed, because the grating periods for first DOE 715 and third
DOE 725 do not need to be equal. In some embodiments, m=1 and n=1,
which means the first diffraction grating of the first DOE 715
reflects the light wave to +1 diffraction order, and then the
second diffraction grating of the first DOE 715 reflects the light
wave again to +1 diffraction order. Diffraction orders higher than
the +1 diffraction order usually are less efficient and can create
ghost image effects. Thus, when m=1 and n=1, a vector sum of the
grating vectors of the diffraction gratings of the first DOE 715
either equals the grating vector of the third DOE 725, or is the
exact opposite to the grating vector of the third DOE 725:
D.sub.1a+D.sub.1b=.+-.D.sub.3. Particularly, in case of -D.sub.3,
the first and second diffraction gratings of the first DOE 715 and
the diffraction grating of the third DOE 725 satisfy the summation
rule: D.sub.1a+D.sub.1b+D.sub.3=0.
Besides dual-sided linear grating, the first DOE 715 can have,
e.g., crossed diffraction gratings on two sides of the DOE 715
(also referred to as "dual-sided crossed grating"). Thus, the first
DOE 715 effectively have four diffraction gratings with four
grating vectors. On a first side (e.g., top side) of the first DOE
715, there are two diffraction gratings that are crossed to each
other and have grating vectors of D.sub.1a=(D.sub.x1a, D.sub.y1a)
and D.sub.1b=(D.sub.x1b, D.sub.y1b). In other words, the grating
pattern is periodic in two directions on the first side. On a
second side (e.g., bottom side) of the first DOE 715, there are two
diffraction gratings that are crossed to each other and have
grating vectors of D.sub.1c=(D.sub.x1c, D.sub.y1c) and
D.sub.1d=(D.sub.x1d, D.sub.y1d).
The waveguide 700 satisfies the achromatic imaging condition, which
means the incident light matches the out-coupled light. The
achromatic imaging condition is satisfied, if
mD.sub.1a+nD.sub.1b+oD.sub.1a+pD.sub.1b=.+-.D.sub.3, wherein m, n,
o, and p are integer order numbers.
Therefore, the weighted vector summation rule can be used to design
DOEs of output waveguides. The diffraction gratings of DOEs follow
the summation rule or the weighted summation rule, and therefore
satisfies the achromatic imaging order. The summation rule or the
weighted summation rule enables relaxed degrees of freedom for
designing the configuration of the output waveguides with various
properties of DOEs.
The following discussion now refers to a number of methods and
method acts that may be performed. Although the method acts may be
discussed in a certain order or illustrated in a flow chart as
occurring in a particular order, no particular ordering is required
unless specifically stated, or required because an act is dependent
on another act being completed prior to the act being
performed.
Referring now to FIG. 8, a method 800 is illustrated. The method
800 includes acts for combining RGB optical signals in a single
waveguide. The waveguide includes a plurality of DOEs. The method
incudes directing an optical signal at a first DOE at input
propagation angles (act 802).
The method 800 further includes at the first DOE, diffracting the
optical signal based on spectrum such that predominately one
spectrum of light is diffracted in a first direction and
predominately a second spectrum of light is diffracted in a second
different direction such that different portions of optical signal
take different paths, including at least two different paths (act
804).
The method 800 further includes at the first DOE, diffracting the
different portions into a second DOE (act 806).
The method 800 further includes at the second DOE, diffracting the
different portions into a third DOE (808).
The method 800 further includes at the second DOE and the third DOE
expanding the optical signal in a substantially non-parallel
fashion; Expansions at DOE2 and DOE3 are substantially
non-parallel. For example, embodiments may expand the pupil at DOE2
essentially in the vertical direction, and then at DOE3 in the
horizontal direction during the outcoupling process (act 810).
The method 800 further includes at the third DOE, diffracting the
different portions into an eye box keeping output propagation
angles within some predetermined threshold of the input propagation
angles. That is, an attempt is made to keep the output propagation
angles substantially parallel to the input propagation angles to
prevent distortion and/or other side-effects (act 812).
The plurality of DOEs are associated with grating vectors. The acts
of method 800 are performed such that a summation of grating
vectors for each of the paths in the at least two different paths
is substantially equal to zero (act 814).
Note that being `substantially equal to zero` is dependent on the
display resolution of a device. In particular, the summation is
substantially equal to zero so long as some predefined resolution
is maintained. In some embodiments, this may mean that the output
resolution of an outgoing optical signal must be the same as the
input resolution of an incoming optical signal.
The method 800 may be practiced where diffracting the optical
signal based on spectrum such that predominately one spectrum of
light is diffracted in a first direction and predominately a second
spectrum of light is diffracted in a second different direction
such that different portions of optical signal take different
paths, including at least two different paths is performed by the
first DOE having a linear grating associated with a first grating
vector on the front of the grating and a second grating vector on
the back of the waveguide.
The method 800 may be practiced where diffracting the different
portions into an eye box keeping output propagation angles within
some predetermined threshold of the input propagation angles is
performed by the third DOE being a linear grating with a first
grating vector on the front of the waveguide and a second grating
vector on the back of the waveguide.
The method 800 may be practiced where expanding the optical signal
in a substantially non-parallel fashion and diffracting the
different portions into a third DOE is performed by the second DOE
having a linear grating with a first wing on the front and a second
wing on the back of the waveguide, wherein the first wing and the
second wings overlap.
The method 800 may be practiced where expanding the optical signal
in a substantially non-parallel fashion and diffracting the
different portions into a third DOE is performed by the second DOE
having a linear grating with a first wing and a second wing on the
front of the waveguide.
The method 800 may be practiced where expanding the optical signal
in a substantially non-parallel fashion and diffracting the
different portions into a third DOE is performed by the second DOE
having a linear grating with a first wing and a second wing on the
back of the waveguide.
The method 800 may be practiced where diffracting the optical
signal based on spectrum such that predominately one spectrum of
light is diffracted in a first direction and predominately a second
spectrum of light is diffracted in a second different direction
such that different portions of optical signal take different
paths, including at least two different paths is performed by the
first DOE having a cross grating associated with two distinct
grating vectors.
The method 800 may be practiced where expanding the optical signal
in a substantially non-parallel fashion and diffracting the
different portions into a third DOE is performed by the second DOE
having a cross grating associated with two distinct grating
vectors.
The method 800 may be practiced where diffracting the different
portions into an eye box keeping output propagation angles within
some predetermined threshold of the input propagation angles is
performed by the third DOE having a cross grating associated with
two distinct grating vectors.
The present invention may be embodied in other specific forms
without departing from its spirit or characteristics. The described
embodiments are to be considered in all respects only as
illustrative and not restrictive. The scope of the invention is,
therefore, indicated by the appended claims rather than by the
foregoing description. All changes which come within the meaning
and range of equivalency of the claims are to be embraced within
their scope.
* * * * *