U.S. patent application number 15/097661 was filed with the patent office on 2017-10-19 for waveguides with extended field of view.
This patent application is currently assigned to MICROSOFT TECHNOLOGY LICENSING, LLC. The applicant listed for this patent is MICROSOFT TECHNOLOGY LICENSING, LLC. Invention is credited to Jani Tervo, Tuomas Vallius.
Application Number | 20170299864 15/097661 |
Document ID | / |
Family ID | 58549313 |
Filed Date | 2017-10-19 |
United States Patent
Application |
20170299864 |
Kind Code |
A1 |
Vallius; Tuomas ; et
al. |
October 19, 2017 |
WAVEGUIDES WITH EXTENDED FIELD OF VIEW
Abstract
An input-coupler of an optical waveguide couples light
corresponding to the image and having a corresponding FOV into the
optical waveguide, and the input-coupler splits the FOV of the
image coupled into the optical waveguide into first and second
portions by diffracting a portion of the light corresponding to the
image in a first direction toward a first intermediate-component,
and diffracting a portion of the light corresponding to the image
in a second direction toward a second intermediate-component. An
output-coupler of the waveguide combines the light corresponding to
the first and second portions of the FOV, and couples the light
corresponding to the combined first and second portions of the FOV
out of the optical waveguide so that the light corresponding to the
image and the combined first and second portions of the FOV is
output from the optical waveguide. The intermediate-components and
the output-coupler also provide for pupil expansion.
Inventors: |
Vallius; Tuomas; (Espoo,
FI) ; Tervo; Jani; (Espoo, FI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MICROSOFT TECHNOLOGY LICENSING, LLC |
Redmond |
WA |
US |
|
|
Assignee: |
MICROSOFT TECHNOLOGY LICENSING,
LLC
Redmond
WA
|
Family ID: |
58549313 |
Appl. No.: |
15/097661 |
Filed: |
April 13, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 27/0172 20130101;
G02B 30/35 20200101; G02B 6/005 20130101; H04N 13/344 20180501;
G02B 27/4205 20130101; G02F 1/292 20130101; G02B 5/1819 20130101;
G02B 6/0026 20130101; H04N 13/332 20180501; G02B 5/18 20130101;
G02B 27/0081 20130101; G02B 2005/1804 20130101; G02B 2027/013
20130101; G02B 2027/0174 20130101; G02B 5/1814 20130101; G02B 27/44
20130101; G02B 2027/0123 20130101; G02F 1/295 20130101; G02B
2027/0125 20130101 |
International
Class: |
G02B 27/01 20060101
G02B027/01; G02B 5/18 20060101 G02B005/18; G02B 27/22 20060101
G02B027/22; G02B 27/44 20060101 G02B027/44; G02F 1/29 20060101
G02F001/29; G02B 27/00 20060101 G02B027/00; F21V 8/00 20060101
F21V008/00; F21V 8/00 20060101 F21V008/00; G02B 5/18 20060101
G02B005/18; H04N 13/04 20060101 H04N013/04; G02F 1/295 20060101
G02F001/295; H04N 13/04 20060101 H04N013/04 |
Claims
1. An apparatus for use in replicating an image associated with an
input-pupil to an output-pupil, the apparatus comprising: an
optical waveguide including an input-coupler, first and second
intermediate-components and an output-coupler; the input-coupler
comprising a diffraction grating and configured to: couple light
corresponding to the image associated with the input-pupil, and
having a corresponding field of view (FOV), into the optical
waveguide; diffract a portion of the light corresponding to the
image in a first direction toward the first intermediate-component
such that a first portion of the FOV travels through the optical
waveguide from the input-coupler to the first
intermediate-component; and diffract a portion of the light
corresponding to the image in a second direction toward the second
intermediate-component such that a second portion of the FOV
travels through the optical waveguide from the input-coupler to the
second intermediate-component; wherein the first and second
directions differ from one another; and wherein the first and
second portions of the FOV differ from one another; the first
intermediate-component configured to diffract light corresponding
to the first portion of the FOV, which travels through the optical
waveguide from the input-coupler to the first
intermediate-component, toward the output coupler; the second
intermediate-component configured to diffract light corresponding
to the second portion of the FOV, which travels through the optical
waveguide from the input-coupler to the second
intermediate-component, toward the output coupler; and the
output-coupler configured to: combine the light corresponding to
the first and second portions of the FOV, which travel through the
optical waveguide from the first and second intermediate-components
to the output-coupler; and couple the light corresponding to the
combined first and second portions of the FOV out of the optical
waveguide so that the light corresponding to the image and the
combined first and second portions of the FOV is output from the
optical waveguide and viewable from the output-pupil.
2. The apparatus of claim 1, wherein: the input-coupler, by
diffracting the portion of the light corresponding to the image in
the first direction toward the first intermediate-component, and
diffracting the portion of the light corresponding to the image in
the second direction toward the second intermediate-component,
splits the FOV into the first and second portions; the
output-coupler, by combining the light corresponding to the first
and second portions of the FOV, unifies the FOV that was split by
the input-coupler; and a unified FOV associated with the light
coupled out of the optical waveguide, by the output-coupler, is
greater than a maximum FOV that each of the first and second
intermediate-components can support on their own.
3. The apparatus of claim 1, wherein: each of the first and second
intermediate-components is configured to perform one of horizontal
or vertical pupil expansion; and the output-coupler is configured
to perform the other one of horizontal or vertical pupil
expansion.
4. The apparatus of claim 1, wherein: one of the first and second
directions comprises a leftward direction; and the other one of the
first and second directions comprises a rightward direction.
5. The apparatus of claim 1, wherein the first portion of the FOV
partially overlaps with the second portion of the FOV.
6. The apparatus of claim 1, wherein: the optical waveguide
includes a first major surface and a second major surface opposite
to the first major surface; and the diffraction grating of the
input-coupler comprises a surface relief grating (SRG) that is
located in or on a single one of the first and second major
surfaces of the optical waveguide.
7. The apparatus of claim 1, wherein: the optical waveguide
includes a first major surface and a second major surface opposite
to the first major surface; and the diffraction grating of the
input-coupler comprises: a first surface relief grating (SRG) that
is located in or on one of the first and second major surfaces of
the optical waveguide and is configured to diffract the light
corresponding to the first portion of the FOV in the first
direction toward the first intermediate-component; and a second SRG
that is located in or on the other one of the first and second
major surfaces of the optical waveguide and is configured to
diffract the light corresponding to the second portion of the FOV
in the second direction toward the second
intermediate-component.
8. The apparatus of claim 1, further comprising one or more further
intermediate-components, which is/are in addition to the first and
second intermediate-components, wherein: the input-coupler is also
configured to diffract light corresponding to at least a portion of
the FOV to each of the one or more further intermediate-components;
and the one or more further intermediate-components is/are each
configured to diffract light, corresponding to at least a portion
of the FOV that is incident on the further intermediate-component,
toward the output-coupler.
9. The apparatus of claim 1, further comprising: a display engine
configured to produce an image; wherein the light corresponding to
the image that is coupled into the optical waveguide by the
input-coupler comprises the light corresponding to the image that
is produced by the display engine.
10. The apparatus of claim 1, wherein each of the input-coupler,
the first and second intermediate-components and the output-coupler
comprises a separate diffractive optical element (DOE).
11. The apparatus of claim 1, wherein the apparatus is part of a
head-mounted display (HMD) or a heads-up display (HUD).
12. A method for using an optical waveguide to replicate an image
associated with an input-pupil to an output-pupil, the method
comprising: coupling light corresponding to the image associated
with the input-pupil, and having a corresponding field of view
(FOV), into the optical waveguide; splitting the FOV of the image
coupled into the optical waveguide into first and second portions
by diffracting a portion of the light corresponding to the image in
a first direction, and diffracting a portion of the light
corresponding to the image in a second direction, wherein the first
and second directions differ from one another, and wherein the
first and second portions of the FOV differ from one another; and
after the light corresponding to the image has travelled through
portions of the optical waveguide by way of total internal
reflection, combining the light corresponding to the first and
second portions of the FOV, and coupling the light corresponding to
the combined first and second portions of the FOV out of the
optical waveguide so that the light corresponding to the image and
the combined first and second portions of the FOV is output from
the optical waveguide and viewable from the output-pupil.
13. The method of claim 12, wherein: one of the first and second
directions comprises a leftward direction; and the other one of the
first and second directions comprises a rightward direction.
14. The method of claim 12, wherein: the coupling light
corresponding to the image associated with the input-pupil, and
having the corresponding FOV, into the optical waveguide, and the
splitting the FOV of the image coupled into the optical waveguide
into the first and second portions, by diffracting the portion of
the light corresponding to the image in the first direction, and
diffracting the portion of the light corresponding to the image in
the second direction, are performed by an input-coupler of the
optical waveguide; prior to the combining the light corresponding
to the first and second portions of the FOV to thereby unify the
FOV that was split, transferring the light corresponding to the
first and second portions of the FOV from the input-coupler,
respectively, to first and second intermediate-components of the
optical waveguide by way of total internal reflection (TIR), and
using the first and second intermediate-components of the optical
waveguide to perform one of horizontal or vertical pupil expansion;
and the combining the light corresponding to the first and second
portions of the FOV, and the coupling the light corresponding to
the combined first and second portions of the FOV out of the
optical waveguide, are performed by an output-coupler of the
optical waveguide.
15. The method of claim 14, further comprising, using the
output-coupler to perform the other one of horizontal or vertical
pupil expansion.
16. A head-mounted display (HMD) or a heads-up display (HUD)
system, comprising: a display engine configured to produce an
image; an optical waveguide including an input-coupler, first and
second intermediate-components, and an output-coupler; the input
coupler configured to: couple light corresponding to the image
produced by the display engine, and having a corresponding field of
view (FOV), into the optical waveguide; and split the FOV of the
image coupled into the optical waveguide into first and second
portions by diffracting a portion of the light corresponding to the
image in a first direction toward the first intermediate-component,
and diffracting a portion of the light corresponding to the image
in a second direction toward the second-intermediate component,
wherein the first and second directions differ from one another,
and wherein the first and second portions of the FOV differ from
one another; and the output-coupler configured to combine the light
corresponding to the first and second portions of the FOV, which
travel from the first and second intermediate-components to the
output-coupler by way of total internal reflection, and couple the
light corresponding to the combined first and second portions of
the FOV out of the optical waveguide so that the light
corresponding to the image and having the combined first and second
portions of the FOV is output from the optical waveguide.
17. The system of claim 16, wherein: the input-coupler, by
diffracting the portion of the light corresponding to the image in
the first direction toward the first intermediate-component, and
diffracting the portion of the light corresponding to the image in
the second direction toward the second intermediate-component,
splits the FOV into the first and second portions; the
output-coupler, by combining the light corresponding to the first
and second portions of the FOV, unifies the FOV that was split by
the input-coupler; and a unified FOV associated with the light
coupled out of the optical waveguide, by the output-coupler, is
greater than a maximum FOV that each of the first and second
intermediate-components can support on their own.
18. The system of claim 16, wherein the first portion of the FOV
partially overlaps with the second portion of the FOV.
19. The system of claim 16, wherein: the optical waveguide includes
a first major surface and a second major surface opposite to the
first major surface; and a diffraction grating of the input-coupler
comprises a surface relief grating (SRG) that is located in or on a
single one of the first and second major surfaces of the optical
waveguide.
20. The system of claim 16, wherein: the optical waveguide includes
a first major surface and a second major surface opposite to the
first major surface; and a diffraction grating of the input-coupler
comprises: a first surface relief grating (SRG) that is located in
or on one of the first and second major surfaces of the optical
waveguide and that is configured to diffract the light
corresponding to the first portion of the FOV in the first
direction toward the first intermediate-component; and a second SRG
that is located in or on the other one of the first and second
major surfaces of the optical waveguide and that is configured to
diffract the light corresponding to the second portion of the FOV
in the second direction toward the second intermediate-component.
Description
BACKGROUND
[0001] Various types of computing, entertainment, and/or mobile
devices can be implemented with a transparent or semi-transparent
display through which a user of a device can view the surrounding
environment. Such devices, which can be referred to as see-through,
mixed reality display device systems, or as augmented reality (AR)
systems, enable a user to see through the transparent or
semi-transparent display of a device to view the surrounding
environment, and also see images of virtual objects (e.g., text,
graphics, video, etc.) that are generated for display to appear as
a part of, and/or overlaid upon, the surrounding environment. These
devices, which can be implemented as head-mounted display (HMD)
glasses or other wearable display devices, but are not limited
thereto, often utilize optical waveguides to replicate an image,
e.g., produced by a display engine, to a location where a user of a
device can view the image as a virtual image in an augmented
reality environment. As this is still an emerging technology, there
are certain challenges associated with utilizing waveguides to
display images of virtual objects to a user.
[0002] In HMDs and other types of imaging devices that utilize
optical waveguides, such as heads up displays (HUDs), light
propagates through the optical waveguide only over a limited range
of internal angles. Light propagating parallel to the surface will,
by definition, travel along the waveguide without bouncing. Light
not propagating parallel to the surface will travel along the
waveguide bouncing back and forth between the surfaces, so long as
the angle of incidence with respect to the surface normal is
greater than some critical angle associated with the material from
which the optical waveguide is made. For example, for BK-7 glass,
this critical angle is about 42 degrees. This critical can be
lowered slightly by using a reflective coating, or by using a
material having a higher index of refraction, which is typically
more expensive. Regardless, the range of internal angles over which
light will propagate through an optical waveguide does not vary
very much, and for glass, the maximum range of internal angles is
typically below 50 degrees. This typically results in a range of
angles exiting the waveguide (i.e., angles in air) of less than 40
degrees, and typically even less when other design factors are
taken into account. For example, in optical waveguides that include
an intermediate-component used for pupil expansion, which is
distinct from the input-coupler and output-coupler of the
waveguide, the intermediate-component typically limits the diagonal
field-of-view (FOV) that can be supported by an optical waveguide
based display to no more than 35 degrees.
SUMMARY
[0003] Certain embodiments of the present technology relate to an
apparatus for use in replicating an image associated with an
input-pupil to an expanded output-pupil. In accordance with an
embodiment, the apparatus comprises an optical waveguide including
an input-coupler, first and second intermediate-components and an
output-coupler. The input-coupler comprises a diffraction grating
and is configured to couple light corresponding to the image
associated with the input-pupil, and having a corresponding field
of view (FOV), into the optical waveguide, diffract a portion of
the light corresponding to the image in a first direction toward
the first intermediate-component such that a first portion of the
FOV travels through the optical waveguide from the input-coupler to
the first intermediate-component, and diffract a portion of the
light corresponding to the image in a second direction toward the
second intermediate-component such that a second portion of the FOV
travels through the optical waveguide from the input-coupler to the
second intermediate-component, wherein the first and second
directions differ from one another, and wherein the first and
second portions of the FOV differ from one another. The first
intermediate-component is configured to diffract light
corresponding to the first portion of the FOV, which travels
through the optical waveguide from the input-coupler to the first
intermediate-component, toward the output coupler. The second
intermediate-component is configured to diffract light
corresponding to the second portion of the FOV, which travels
through the optical waveguide from the input-coupler to the second
intermediate-component, toward the output coupler. The
output-coupler is configured to combine the light corresponding to
the first and second portions of the FOV, which travel through the
optical waveguide from the first and second intermediate-components
to the output-coupler, and couple the light corresponding to the
combined first and second portions of the FOV out of the optical
waveguide so that the light corresponding to the image and the
combined first and second portions of the FOV is output from the
optical waveguide and viewable from the output-pupil. Additionally,
each of the first and second intermediate-components is configured
to perform one of horizontal or vertical pupil expansion, and the
output-coupler is configured to perform the other one of horizontal
or vertical pupil expansion. This way, the output-pupil (also known
as an exit-pupil) is expanded, and thus larger, than the
input-pupil (also known as an entrance-pupil). The input-coupler,
by diffracting a portion of the light corresponding to the image in
the first direction toward the first intermediate-component, and
diffracting a portion of the light corresponding to the image in
the second direction toward the second intermediate-component,
splits the FOV into the first and second portions. The
output-coupler, by combining the light corresponding to the first
and second portions of the FOV, unifies the FOV that was split by
the input-coupler. Beneficially, a unified FOV associated with the
light coupled out of the optical waveguide, by the output-coupler,
is greater than a maximum FOV that each of the first and second
intermediate-components can support on their own. The unified FOV
can also be referred to as a combined FOV.
[0004] 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.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIGS. 1A, 1B and 10 are front, top and side views,
respectively, of an exemplary waveguide that can be used to
replicate an image associated with an input-pupil to an expanded
output-pupil.
[0006] FIG. 2 is side view of the exemplary waveguide introduced
with reference to FIGS. 1A, 1B and 1C, and also shows a display
engine that generates an image including angular content that is
coupled into the waveguide by an input-coupler, and also shows an
eye that is viewing the image within an eye box that is proximate
the output-coupler.
[0007] FIG. 3 is a front view of an optical waveguide, according to
an embodiment of the present technology.
[0008] FIG. 4 is a front view of an optical waveguide, according to
another embodiment of the present technology.
[0009] FIG. 5 is a front view of an optical waveguide, according to
a further embodiment of the present technology.
[0010] FIG. 6 is a front view of an optical waveguide, according to
still another embodiment of the present technology.
[0011] FIG. 7 is a high level flow diagram that is used to
summarize methods according to embodiments of the present
technology.
DETAILED DESCRIPTION
[0012] Certain embodiments of the present technology can be used to
increase (also referred to as expand) the field of view (FOV) that
can be supported by an optical waveguide that includes one or more
intermediate-components that are used to perform pupil expansion,
wherein the intermediate component(s) is/are typically what limit
how large of a FOV can be supported by such an optical waveguide.
Before providing details of such embodiments, FIGS. 1A, 1B and 1C
are first used to describe an exemplary optical waveguide and its
components, as well as its limitations. In the description that
follows, like numerals or reference designators will be used to
refer to like parts or elements throughout. In addition, the first
digit of each reference number identifies the drawing in which the
reference number first appears.
[0013] FIGS. 1A, 1B and 1C are front, top and side views,
respectively, of an exemplary optical waveguide 100 that can be
used to replicate an image associated with an input-pupil to an
expanded output-pupil. The term "input-pupil," as used herein,
refers to an aperture through which light corresponding to an image
is overlaid on an input-coupler of a waveguide. The term
"output-pupil," as used herein, refers to an aperture through which
light corresponding to an image exits an output-coupler of a
waveguide. An input-pupil is sometimes also referred to as an
entrance-pupil, and an output-pupil is sometimes also referred to
as an exit-pupil. The optical waveguide 100 will often be referred
to hereafter more succinctly simply as a waveguide 100. As will be
discussed in further detail below with reference to FIG. 2, the
image that the waveguide 100 is being used to replicate, and likely
also expand, can be generated using a display engine.
[0014] Referring to FIGS. 1A, 1B and 10, the optical waveguide 100
includes a bulk-substrate 106 having an input-coupler 112 and an
output-coupler 116. The input-coupler 112 is configured to couple
light corresponding to an image associated with an input-pupil into
the bulk-substrate 106 of the waveguide. The output-coupler 116 is
configured to couple the light corresponding to the image
associated with the input-pupil, which travels in the optical
waveguide 100 from the input-coupler 112 to the output-coupler 116,
out of the waveguide 100 so that the light is output and viewable
from the output-pupil.
[0015] The bulk-substrate 106, which can be made of glass or
optical plastic, but is not limited thereto, includes a first major
planar surface 108 and a second major planar surface 110 opposite
and parallel to the first major planar surface 108. The first major
planar surface 108 can alternatively be referred to as the
front-side major surface 108 (or more simply the front-side surface
108), and the second major planar surface 110 can alternatively be
referred to as the back-side major surface 110 (or more simply the
back-side surface 110). As the term "bulk" is used herein, a
substrate is considered to be "bulk" substrate where the thickness
of the substrate (between its major surfaces) is at least ten times
(i.e., 10.times.) the wavelength of the light for which the
substrate is being used as an optical transmission medium. For an
example, where the light (for which the substrate is being used as
an optical transmission medium) is red light having a wavelength of
620 nm, the substrate will be considered a bulk-substrate where the
thickness of the substrate (between its major surfaces) is at least
6200 nm, i.e., at least 6.2 .mu.m. In accordance with certain
embodiments, the bulk-substrate 106 has a thickness of at least 25
.mu.m between its major planar surfaces 108 and 110. In specific
embodiments, the bulk-substrate 106 has a thickness (between its
major surfaces) within a range of 100 .mu.m to 1500 .mu.m, with a
likely thickness of about 1000 .mu.m. The bulk-substrate 106, and
more generally the waveguide 100, is transparent, meaning that it
allows light to pass through it so that a user can see through the
waveguide 100 and observe objects on an opposite side of the
waveguide 100 than the user's eye(s).
[0016] The optical waveguide 100 in FIGS. 1A, 1B and 10 is also
shown as including an intermediate-component 114, which can
alternatively be referred to as an intermediate-zone 114. Where the
waveguide 100 includes the intermediate-component 114, the
input-coupler 112 is configured to couple light into the waveguide
100 (and more specifically, into the bulk-substrate 106 of the
waveguide 100) and in a direction of the intermediate-component
114. The intermediate-component 114 is configured to redirect such
light in a direction of the output-coupler 116. Further, the
intermediate-component 114 is configured to perform one of
horizontal or vertical pupil expansion, and the output-coupler 116
is configured to perform the other one of horizontal or vertical
pupil expansion. For example, the intermediate-component 114 can be
configured to perform horizontal pupil expansion, and the
output-coupler 116 can be configured to vertical pupil expansion.
Alternatively, if the intermediate-component 114 were repositioned,
e.g., to be below the input-coupler 112 and to the left of the
output-coupler 116 shown in FIG. 1A, then the
intermediate-component 114 can be configured to perform vertical
pupil expansion, and the output-coupler 116 can be configured to
perform horizontal pupil expansion.
[0017] The input-coupler 112, the intermediate-component 114 and
the output-coupler 116 can be referred to collectively herein as
optical components 112, 114 and 116 of the waveguide, or more
succinctly as components 112, 114 and 116.
[0018] It is possible that a waveguide includes an input-coupler
and an output-coupler, without including an
intermediate-components. In such embodiments, the input-coupler
would be configured to couple light into the waveguide and in a
direction toward the output-coupler. In such embodiments, the
output-coupler can provide one of horizontal or vertical pupil
expansion, depending upon implementation.
[0019] In FIG. 1A, the input-coupler 112, the
intermediate-component 114 and the output-coupler 116 are shown as
having rectangular outer peripheral shapes, but can have
alternative outer peripheral shapes. For example, the input-coupler
112 can alternatively have a circular outer peripheral shape, but
is not limited thereto. For another example, the
intermediate-component can have a triangular or hexagonal outer
peripheral shape, but is not limited thereto. Further, it is noted
that the corners of each of the peripheral shapes, e.g., where
generally rectangular or triangular, can be chamfered or rounded,
but are not limited thereto. These are just a few exemplary outer
peripheral shapes for the input-coupler 112, the
intermediate-component 114 and the output-coupler 116, which are
not intended to be all encompassing.
[0020] As can best be appreciated from FIGS. 1B and 10, the
input-coupler 112, the intermediate-component 114 and the
output-coupler 116 are all shown as being provided in or on a same
surface (i.e., the back-side surface 110) of the waveguide 100. In
such a case, the input-coupler 112 can be transmissive (e.g., a
transmission grating), the intermediate-component 114 can be
reflective (e.g., a reflective grating), and the output-coupler 116
can also be reflective (e.g., a further reflective grating). The
input-coupler 112, the intermediate-component 114 and the
output-coupler 116 can alternatively all be provided in the
front-side surface 110 of the waveguide 100. In such a case, the
input-coupler 112 can be reflective (e.g., a reflective grating),
the intermediate-component 114 can be reflective (e.g., a further
reflective grating), and the output-coupler 116 can also be
transmissive (e.g., a transmission grating).
[0021] Alternatively, the input-coupler 112, the
intermediate-component 114 and the output-coupler 116 can all be
embedded (also referred to as immersed) in the bulk-substrate 106.
For example, the bulk-substrate 106 can be separated into two
halves (that are parallel to the major surfaces 108 and 110), and
the input-coupler 112, the intermediate-component 114 and the
output-coupler 116 can be provided in (e.g., etched into) one of
the inner surfaces of the two halves, and the inner surfaces of the
two halves can be adhered to one another. Alternatively, the
bulk-substrate 106 can be separated into two halves (that are
parallel to the major surfaces 108 and 110), and the input-coupler
112, the intermediate-component 114 and the output-coupler 116 can
be provided between the inner surfaces of the two halves. Other
implementations for embedding the input-coupler 112, the
intermediate-component 114 and the output-coupler 116 in the
bulk-substrate 106 are also possible, and within the scope of the
embodiments described herein. It is also possible that one of the
input-coupler 112, the intermediate-component 114 and the
output-coupler 116 is provided in or on the front-side surface 108
of the waveguide 108, another one of the components 112, 114 and
116 is provided in or on the back-side surface 110, and the last
one of the components 112, 114 and 116 is embedded or immersed in
the bulk-substrate 106. More generally, unless stated otherwise,
any individual one of the input-coupler 112, the
intermediate-component 114 and the output-coupler 116 can be
provided in or on either one of the major planar surfaces 108 or
110 of the bulk-substrate 106, or embedded therebetween.
[0022] The input-coupler 112, the intermediate-component 114 and
the output-coupler 116 can each be implemented as a diffraction
grating, or more generally, as a diffractive optical element (DOE).
A diffraction grating is an optical component that may contain a
periodic structure that causes incident light to split and change
direction due to an optical phenomenon known as diffraction. The
splitting (known as optical orders) and angle change depend on the
characteristics of the diffraction grating. When the periodic
structure is on the surface of an optical component, it is referred
to a surface grating. When the periodic structure is due to varying
of the surface itself, it is referred to as a surface relief
grating (SRG). For example, an SRG can include uniform straight
grooves in a surface of an optical component that are separated by
uniform straight groove spacing regions. Groove spacing regions can
be referred to as "lines", "grating lines" or "filling regions".
The nature of the diffraction by an SRG depends on the wavelength,
polarization and angle of light incident on the SRG and various
optical characteristics of the SRG, such as refractive index, line
spacing, groove depth, groove profile, groove fill ratio and groove
slant angle. An SRG can be fabricated by way of a suitable
microfabrication process, which may involve etching of and/or
deposition on a substrate to fabricate a desired periodic
microstructure on the substrate to form an optical component, which
may then be used as a production master such as a mold or mask for
manufacturing further optical components. An SRG is an example of a
Diffractive Optical Element (DOE). When a DOE is present on a
surface (e.g. when the DOE is an SRG), the portion of that surface
spanned by that DOE can be referred to as a DOE area. A diffraction
grating, instead of being a surface grating, can alternatively be a
volume grating, such as a Bragg diffraction grating. It is also
possible that one or more of the couplers are manufactured as SRGs
and then covered within another material, e.g., using an atomic
layer deposition process or an aluminum deposition process, thereby
essentially burying the SRGs such that the major planar waveguide
surface(s) including the SRG(s) is/are substantially smooth. Such a
coupler is one example of a hybrid of a surface and volume
diffraction grating. Any one of the input-coupler 112, the
intermediate-component 114 and the output-coupler 116 can be, e.g.,
a surface diffraction grating, or a volume diffraction grating, or
a hybrid of a surface and volume diffraction grating. In accordance
with embodiments described herein, each diffraction grating can
have a preferential linear polarization orientation specified by a
direction of the grating lines of the diffraction grating, wherein
the coupling efficiency for light having the preferential linear
polarization orientation will be higher than for light having a
non-preferential linear polarization orientation.
[0023] Where the input-coupler 112, the intermediate-component 114
and/or the output-coupler 116 is an SRG, each such SRG can be
etched into one of the major planar surfaces 108 or 110 of the
bulk-substrate 106. In such embodiments, the SRG can be said to be
formed "in" the bulk-substrate 106. Alternatively, each SRG can be
physically formed in a coating that covers one of the major planar
surfaces 108 or 110 of the bulk-substrate 106, in which case each
such SRG can be said to be formed "on" the bulk-substrate 106.
Either way, the components 112,114 and 116 are considered parts of
the waveguide 100.
[0024] Referring specifically to FIG. 1A, in an exemplary
embodiment, the input-coupler 112 can have surface gratings that
extend in a vertical (y) direction, the output-coupler 116 can have
surface gratings that extend in a horizontal (x) direction, and the
intermediate-component 114 can have surface gratings that extend
diagonal (e.g., .about.45 degrees) relative to the horizontal and
vertical directions. This is just an example. Other variations are
also possible.
[0025] More generally, the input-coupler 112, the
intermediate-component 114 and the output-coupler 116 can have
various different outer peripheral geometries, can be provided in
or on either of the major planar surfaces of the bulk-substrate, or
can be embedded in the bulk-substrate 106, and can be implemented
using various different types of optical structures, as can be
appreciated from the above discussion, and will further be
appreciated from the discussion below.
[0026] In general, light corresponding to an image, which is
coupled into the waveguide via the input-coupler 112, can travel
through the waveguide from the input-coupler 112 to the
output-coupler 114, by way of total internal refection (TIR). TIR
is a phenomenon which occurs when a propagating light wave strikes
a medium boundary (e.g., of the bulk-substrate 106) at an angle
larger than the critical angle with respect to the normal to the
surface. In other words, the critical angle (.theta..sub.c) is the
angle of incidence above which TIR occurs, which is given by
Snell's Law, as is known in the art. More specifically, Snell's law
specifies that the critical angle (.theta..sub.c) is specified
using the following equation:
.theta..sub.c=sin.sup.-1 (n2/n1)
where [0027] .theta..sub.c the critical angle for two optical
mediums (e.g., the bulk-substrate 106, and air or some other medium
that is adjacent to the bulk-substrate 106) that meet at a medium
boundary, [0028] n1 is the index of refraction of the optical
medium in which light is traveling towards the medium boundary
(e.g., the bulk-substrate 106, once the light is couple therein),
and [0029] n2 is the index of refraction of the optical medium
beyond the medium boundary (e.g., air or some other medium adjacent
to the bulk-substrate 106).
[0030] The concept of light traveling through the waveguide 100,
from the input-coupler 112 to the output-coupler 114, by way of
TIR, can be better appreciated from FIG. 2, which is discussed
below. Referring now to FIG. 2, as in FIG. 10, FIG. 2 shows a side
view of the waveguide 100, but also shows a display engine 204 that
generates an image including angular content that is coupled into
the waveguide by the input-coupler 112. Also shown in FIG. 2, is
representation of a human eye 214 that is using the waveguide 100
to observe an image, produced using the display engine 204, as a
virtual image.
[0031] The display engine 204 can include, e.g., an image former
206, a collimating lens 208 and an illuminator 210, but is not
limited thereto. The image former 206 can be implemented using a
transmissive projection technology where a light source is
modulated by an optically active material, and backlit with white
light. These technologies are usually implemented using liquid
crystal display (LCD) type displays with powerful backlights and
high optical energy densities. The illuminator 210 can provide the
aforementioned backlighting. The image former 206 can also be
implemented using a reflective technology for which external light
is reflected and modulated by an optically active material. Digital
light processing (DLP), liquid crystal on silicon (LCOS) and
Mirasol.RTM. display technology from Qualcomm, Inc. are all
examples of reflective technologies. Alternatively, the image
former 206 can be implemented using an emissive technology where
light is generated by a display, see for example, a PicoP.TM.
display engine from Microvision, Inc. Another example of emissive
display technology is a micro organic light emitting diode (OLED)
display. Companies such as eMagin and Microoled provide examples of
micro OLED displays. The image former 206, alone or in combination
with the illuminator 210, can also be referred to as a micro
display. The collimating lens 208 is arranged to receive a
diverging display image from the image former 206, to collimate the
display image, and to direct the collimated image toward the
input-coupler 112 of the waveguide 100. In accordance with an
embodiment, an entry pupil associated with the waveguide may be
approximately the same size as an exit pupil associated with the
image former 206, e.g., 5 mm or less in some embodiments, but is
not limited thereto.
[0032] In FIG. 2, the display engine 204 is shown as facing the
back-side surface 110 of the waveguide 100, and the eye 214 is
shown as facing the front-side surface 108 opposite and parallel to
the back-side surface 110. This provides for a periscope type of
configuration in which light enters the waveguide on one side of
the waveguide 100, and exits the waveguide at an opposite side of
the waveguide 100. Alternatively, the input-coupler 112 and the
output-coupler 116 can be implemented in a manner such that the
display engine 204 and the eye 214 are proximate to and face a same
major planar surface (108 or 110).
[0033] The waveguide 100 can be incorporated into a see-through
mixed reality display device system, but is not limited to use
therewith. A separate instance of the waveguide 100 and the display
engine 204 can be provided for each of the left and right eyes of a
user. In certain embodiments, such waveguide(s) 100 may be
positioned next to or between see-through lenses, which may be
standard lenses used in eye glasses and can be made to any
prescription (including no prescription). Where a see-through mixed
reality display device system is implemented as head-mounted
display (HMD) glasses including a frame, the display engine 204 can
be located to the side of the frame so that it sits near to a
user's temple. Alternatively, the display engine 204 can be located
in a central portion of the HMD glasses that rests above a nose
bridge of a user. Other locations for the display engine 204 are
also possible. In these instances, the user can also be referred to
as a wearer. Where there is a separate waveguide for each of the
left and right eyes of a user, there can be a separate display
engine for each of the waveguides, and thus, for each of the left
and right eyes of the user. One or more further adjacent waveguides
can be used to perform eye tracking based on infrared light that is
incident on and reflected from the user's eye(s) 214, as is known
in the art.
[0034] The exemplary optical waveguide 100, described above with
reference to FIGS. 1A, 1B, 10 and 2, can support a diagonal
field-of-view (FOV) of only about 35 degrees, where the index of
refraction of the bulk-substrate 106 is about 1.7 (i.e.,
n1.about.1.7). The optical component that limits the diagonal FOV
to about 35 degrees is the intermediate-component 112, since the
input-coupler 112 and the output-coupler 116 can each handle much
larger diagonal FOVs than the intermediate-component 112. One way
to attempt to increase (also referred to as extend) the diagonal
FOV is to increase the index of refraction of the bulk-substrate
106 of the optical waveguide 100, which would enable the
intermediate-component 112 to support a larger diagonal FOV.
However, materials (e.g., glass) having such a high index of
refraction are very expensive. Further, suitable materials for
producing bulk-substrates having such a high index of refraction in
large quantities are not readily available. Accordingly, literature
about waveguide based displays that include
intermediate-components, for use in pupil expansion, typically
specify that the upper limit for the diagonal FOV is about 35
degrees.
[0035] In accordance with certain embodiments of the present
technology, an optical waveguide includes at least two
intermediate-components, each of which is used to support a
different part of a FOV. More specifically, the input-coupler is
designed to diffract light in at least two different (e.g.,
opposite) directions in order to guide light corresponding to an
image to different intermediate-components. For example, by
appropriately tuning the grating periods of the input-coupler,
light corresponding to a left portion of a FOV is steered to a left
intermediate-component, and light corresponding to a right portion
of the FOV is steered to a right intermediate-component.
Additionally, grating periods can be appropriately tuned so that
part of the FOV (e.g., a central portion of the FOV) that is not to
be steered to either of the left and right intermediate-components
goes to an evanescent diffraction order that does not carry any
power. More generally, through proper design and placement of an
input-coupler and proper placement and design of two or more
intermediate-components, different parts of a FOV can be guided in
different directions. Such embodiments can provide two significant
advantages. First, such embodiments can provide for a total
diagonal FOV that is very large, even though each of the
intermediate-components individually support a relatively smaller
FOV (e.g., a diagonal FOV of no more than about 35 degrees).
Additionally, since only a desired part of a FOV is guided in each
of the different directions, there can be significant power savings
(e.g., of up to 50%). Demonstrations of embodiments of the present
technology have shown that such embodiments can be used to obtain a
diagonal FOV of up to about 70 degrees, where the index of
refraction of the bulk-substrate of the optical waveguide is about
1.7 (i.e., n1.about.1.7). Accordingly, it has been demonstrated
that embodiments of the present technology can be used to double
the diagonal FOV, compared to the FOV that could be achieved using
the exemplary waveguide 100 described above with references to
FIGS. 1A, 1B, 10 and 2. Through proper design, embodiments
described herein can be used to provide even larger FOVs of up to
about 90 degrees. It is noted that the term FOV, as used herein,
refers to the diagonal FOV, unless stated otherwise.
[0036] FIG. 3 is a front view of an optical waveguide 300,
according to an embodiment of the present technology. Referring to
FIG. 3, the optical waveguide 300 is shown as including an
input-coupler 312, two intermediate-components 314a and 314b, and
an output-coupler 316. The input-coupler 312 includes a diffraction
grating and is configured to couple light corresponding to an image
associated with an input-pupil, and having a corresponding FOV,
into the optical waveguide 300 (and more specifically into the
bulk-substrate of the optical waveguide). The input-coupler 312 is
also configured to diffract a portion of the light corresponding to
the image in a first direction toward the first
intermediate-component 314a such that a first portion of the FOV
travels through the optical waveguide 300 from the input-coupler
312 to the first intermediate-component 314a, and diffract a
portion of the light corresponding to the image in a second
direction toward the second intermediate-component 314b such that a
second portion of the FOV travels through the optical waveguide 300
from the input-coupler 312 to the second intermediate-component
314b. The first and second portions of the FOV differ from one
another, and depending upon implementation, may (or may not)
partially overlap one another. The first and second directions, in
which the input-coupler 212 diffracts light, also differ from one
another. In the configuration shown, the first direction is a
leftward direction, and the second direction is a rightward
direction. More specifically, the first direction is both leftward
and acutely angled downward, and the second direction is both
rightward and acutely angled downward.
[0037] In the configuration shown, the intermediate-component 314a
is configured to perform horizontal pupil expansion, and to
diffract light corresponding to the first portion of the FOV, which
travels through the optical waveguide from the input-coupler 312 to
the first intermediate-component 314a, toward the output coupler
316. The intermediate-component 314b is configured to perform
horizontal pupil expansion, and to diffract light corresponding to
the second portion of the FOV, which travels through the optical
waveguide from the input-coupler 312 to the second
intermediate-component 314b, toward the output coupler 316. The
intermediate-components 314a and 314b can individually be referred
to as an intermediate-component 314, or collectively as
intermediate-components 314. In alternative embodiments, the layout
and optical components can be rearranged and reconfigured (e.g., by
rotating the layout by 90 degrees) such that the
intermediate-components 314 are configured to perform vertical
pupil expansion, and the output-coupler 316 is configured to
perform horizontal pupil expansion. More generally, the
intermediate-components can be configured to perform one of
horizontal or vertical pupil expansion, and the output-coupler can
be configured to perform the other one of horizontal or vertical
pupil expansion.
[0038] In the configuration shown, the output-coupler 316 is
configured to combine the light corresponding to the first and
second portions of the FOV, which travel through the optical
waveguide from the first and second intermediate-components 314a
and 314b to the output-coupler 316. The output-coupler 316 is also
configured to couple the light corresponding to the combined first
and second portions of the FOV out of the optical waveguide 300 so
that the light corresponding to the image and the combined first
and second portions of the FOV is output from the optical waveguide
300 and viewable from an output-pupil.
[0039] The input-coupler 312, the intermediate-component 314 and
the output-coupler 316 can be referred to collectively herein as
optical components 312, 314 and 316 of the waveguide, or more
succinctly as components 312, 314 and 316.
[0040] In the FIGS. (e.g., FIGS. 1, 2 and 3), the waveguides (e.g.,
100 and 300) were typically shown as including a pair of planar
surfaces. In an alternative embodiment, surfaces of a waveguide
(e.g., 100, 300, 400, 500 or 600) could be non-planar, i.e.,
curved. While gratings may be more easily manufacture on or in
planar surfaces, with curved surface(s) it could be possible to
reduce some of the aberrations in a system.
[0041] As noted above, in optical waveguide that include an
intermediate-component used for pupil expansion, which is distinct
from the input-coupler and output-coupler of the waveguide, the
intermediate-component typically limits the diagonal FOV of
waveguide based displays to no more than 35 degrees. In other
words, intermediate-component(s) can typically only support a FOV
up to about 35 degrees. By contrast, the input-coupler and the
output-coupler of an optical waveguide are each able to support a
much larger FOV than an individual intermediate-component. More
specifically, the input-coupler and the output-coupler of an
optical waveguide can each support a FOV that is at least twice as
large as an intermediate component. Accordingly, the
intermediate-component is typically the optical component of an
optical waveguide that limits the total FOV that can be achieved
using the optical waveguide.
[0042] In the embodiments of the present technology described
herein, including the embodiment just described above with
reference to FIG. 3, the input-coupler 312, by diffracting a
portion of the light corresponding to the image in the first
direction toward the first intermediate-component 314a, and
diffracting a portion of the light corresponding to the image in
the second direction toward the second intermediate-component 314b,
splits the FOV into the first and second portions. The
output-coupler 316, by combining the light corresponding to the
first and second portions of the FOV, unifies the FOV that was
split by the input-coupler 312. Beneficially, the FOV associated
with the light coupled out of the optical waveguide 300, by the
output-coupler 312, is greater than a maximum FOV that each of the
first and second intermediate-components 314 can support on their
own.
[0043] Assume that the FOV of the light coupled into the waveguide
300 by the input-coupler 312 is about 70 degrees, and that the each
of the intermediate-component 314a and 314b can individually
support a FOV of only about 35 degrees. In this example, the
input-coupler 312 can split the 70 degree FOV into a first 35
degree FOV portion (which travel by way of TIR to the first
intermediate-component 314a) and a second 35 degree FOV portion
(which travel by way of TIR to the second intermediate-component
314b). For example, the first portion of the FOV can be from 0 to
35 degrees, and the second portion of the FOV can be from 35 to 70
degrees. The output-coupler 316 can then combine the light
corresponding to the first 35 degree portion of the FOV (which
travel through the optical waveguide by way of TIR from the first
intermediate-component 314a to the output-coupler 316) and the
light corresponding to the second 35 degree FOV (which travel
through the optical waveguide by way of TIR from the second
intermediate-components 314b to the output-coupler 316), to thereby
unify the two 35 degree FOV portions into the original FOV of about
70 degrees. The output-coupler 316 couples the light corresponding
to the combined first and second portions of the FOV, i.e.,
combined to have the FOV of about 70 degrees, out of the optical
waveguide 300 so that the light corresponding to the image and the
combined first and second portions of the FOV is output from the
optical waveguide 300 and viewable from an output-pupil.
Accordingly, the about 70 degree FOV associated with the light
coupled out of the optical waveguide 300, by the output-coupler
312, is greater than the about 35 degree FOV that each of the first
and second intermediate-components 314a and 314b can support on
their own.
[0044] As noted above, the first and second portions of the FOV
differ from one another, and depending upon implementation, may (or
may not) partially overlap one another. Accordingly, where first
and second portions of the FOV partially overlap one another, the
first portion of the FOV may be, e.g., from 2 to 37 degrees, and
the second portion of the FOV may be from 33 to 68 degrees. This is
just one example, which is not intended to be limiting.
[0045] In accordance with certain embodiments, the input-coupler
312, the intermediate-components 314 and the output-coupler 316 can
each be implemented as a DOE. In accordance with certain
embodiments, the input-coupler 312, the intermediate-components 314
and the output-coupler 316 are implemented as SRG type DOEs that
are in or on one (or both) of the major surfaces of the waveguide
300. In certain embodiments, each of the SRGs can include uniform
straight grooves in or on only one of the major surfaces of the
waveguide 300, which grooves are separated by uniform straight
groove spacing regions. The nature of the diffraction by each SRG
depends both on the wavelength of light incident on the grating and
various optical characteristics of the SRG, such as line spacing,
groove depth and groove slant angle. Each SRG can be fabricated by
way of a suitable microfabrication process, which may involve
etching of and/or deposition on a substrate to fabricate a desired
periodic microstructure in or on the substrate to form an optical
component, which may then be used as a production master such as a
mold or mask for manufacturing further optical components.
[0046] In accordance with certain embodiments, the input-coupler
312 is implemented as an SRG in or one only one of the major
surfaces of the waveguide 300, wherein the line spacing of the
gratings of the input-coupler 312 is constant, but the slant angle
of a first half the gratings is optimized to direct a portion of
the light incident on the input-coupler 312 in the direction of the
first intermediate-component 314a, and the slant angle of a second
half the gratings is optimized to direct a portion of the light
incident on the input-coupler 312 in the direction of the second
intermediate-component 314b.
[0047] In accordance with other embodiments, the input-coupler 312
is implemented as an SRG in or one both of the major surfaces of
the waveguide 300. In such an embodiment, a first SRG is located in
or on one the major surfaces of the optical waveguide 300 and is
configured to diffract the light corresponding to a first portion
of the FOV in a first direction toward the first
intermediate-component 314a, and a second SRG is located in or on
the other one of the major surfaces of the optical waveguide 300
and is configured to diffract the light corresponding to a second
portion of the FOV in a second direction toward the second
intermediate-component 314b. In accordance with an embodiment, the
grating period of the first SRG of the input-coupler 312 is the
same as the grating period of the second SRG of the input-coupler
312, but the slant angles differ from one another. In accordance
with another embodiment, the grating period of the first SRG of the
input-coupler 312 differs from the grating period of the second SRG
of the input-coupler 312.
[0048] FIG. 3 illustrates just one exemplary layout for the
input-coupler, intermediate-components and output-coupler. FIG. 4
illustrates an alternative layout for the input-coupler,
intermediate-components and output-coupler. Referring to FIG. 4, an
input-coupler 412 includes a diffraction grating and is configured
to couple light corresponding to an image associated with an
input-pupil, and having a corresponding FOV, into the optical
waveguide 400, diffract a portion of the light corresponding to the
image in a first direction toward a first intermediate-component
414a such that a first portion of the FOV travels through the
optical waveguide 400 from the input-coupler 412 to the first
intermediate-component 414a, and diffract a portion of the light
corresponding to the image in a second direction toward a second
intermediate-component 414b such that a second portion of the FOV
travels through the optical waveguide 400 from the input-coupler
412 to the second intermediate-component 414b. In the configuration
shown, the first direction is a leftward direction, and the second
direction is a rightward direction. An output-coupler 416 is
configured to combine the light corresponding to the first and
second portions of the FOV, which travel through the optical
waveguide from the first and second intermediate-components 414a
and 414b to the output-coupler 416. The output-coupler 416 is also
configured to couple the light corresponding to the combined first
and second portions of the FOV out of the optical waveguide 400 so
that the light corresponding to the image and the combined first
and second portions of the FOV is output from the optical waveguide
400 and viewable from an output-pupil.
[0049] In certain embodiments, the optical waveguide includes one
or more further intermediate-components, which is/are in addition
to the first and second intermediate-components, and the
input-coupler is also configured to diffract light corresponding to
at least a portion of the FOV to each of the one or more further
intermediate-components. In such embodiments, the one or more
further intermediate-components is/are each configured to diffract
light, corresponding to at least a portion of the FOV that is
incident on the further intermediate-component, toward the
output-coupler of the optical waveguide. Examples of such
embodiments are shown in FIGS. 5 and 6.
[0050] Referring to FIG. 5, an optical waveguide 500 is shown as
including an input-coupler 512, four intermediate-components 514a,
514b, 514c and 514d, and an output-coupler 516. The input-coupler
512 includes one or more diffraction gratings and is configured to
couple light corresponding to an image associated with an
input-pupil, and having a corresponding FOV, into the optical
waveguide 500. The input-coupler 514a is also configured to
diffract a portion of the light corresponding to the image in a
first direction toward the intermediate-component 514a such that a
first portion of the FOV travels through the optical waveguide 500
from the input-coupler 512 to the intermediate-component 514a,
diffract a portion of the light corresponding to the image in a
second direction toward the intermediate-component 414b such that a
second portion of the FOV travels through the optical waveguide 500
from the input-coupler 512 to the intermediate-component 514b,
diffract a portion of the light corresponding to the image in a
third direction toward the intermediate-component 514c such that a
third portion of the FOV travels through the optical waveguide 500
from the input-coupler 512 to the intermediate-component 514c, and
diffract a portion of the light corresponding to the image in a
fourth direction toward the fourth intermediate-component 514d such
that a fourth portion of the FOV travels through the optical
waveguide 500 from the input-coupler 512 to the
intermediate-component 514d.
[0051] In the embodiment of FIG. 5, the portion of the FOV provided
to the intermediate-component 514a differs from the portion of the
FOV provided to the intermediate-component 514d, and the portion of
the FOV provided to the intermediate-component 514b differs from
the portion of the FOV provided to the intermediate-component 514c.
Depending upon implementation, the portion of the FOV provided to
the intermediate-component 514b may be the same or different that
the portion of the FOV provided to the intermediate component 514a;
and the portion of the FOV provided to the intermediate-component
514c may be the same or different that the portion of the FOV
provided to the intermediate component 514d. In accordance with an
embodiment, the grating period of the input-coupler 512 is tuned so
that part of the FOV that is not to be steered to either of the
intermediate-components 514a and 514d goes to an evanescent
diffraction order that does not carry any power.
[0052] In the embodiment of FIG. 5, each of the intermediate
components 514a and 514d is configured to perform horizontal pupil
expansion, and diffract light having a respective portion of the
original FOV toward the output-coupler 516. The intermediate
components 514b and 514c can also be configured to perform
horizontal pupil expansion, and diffract light having a respective
portion of the original FOV toward the output-coupler 516.
Alternatively, the intermediate components 514b and 514c can
diffract light having a respective portion of the original FOV
toward the output-coupler 516 without performing any pupil
expansion, in which case the middle portion of the output-coupler
516 can output light corresponding to the image having a FOV coming
straight from the input-coupler 512. The output-coupler 516 is also
configured to combine the FOVs and couple the light corresponding
to the combined FOVs out of the optical waveguide 500 so that the
light corresponding to the image and the combined FOVs is output
from the optical waveguide 500 and viewable from an
output-pupil.
[0053] Referring to FIG. 6, an optical waveguide 600 is shown as
including an input-coupler 612, three intermediate-components 614a,
614b and 614c, and an output-coupler 616. The input-coupler 612
includes one or more diffraction gratings and is configured to
couple light corresponding to an image associated with an
input-pupil, and having a corresponding FOV, into the optical
waveguide 600. The input-coupler 614a is also configured to
diffract a portion of the light corresponding to the image in a
first direction toward the first intermediate-component 614a such
that a first portion of the FOV travels through the optical
waveguide 600 from the input-coupler 612 to the first
intermediate-component 614a, diffract a portion of the light
corresponding to the image in a second direction toward the second
intermediate-component 614b such that a second portion of the FOV
travels through the optical waveguide 600 from the input-coupler
612 to the second intermediate-component 614b, and diffract a
portion of the light corresponding to the image in a third
direction toward the third intermediate-component 614c such that a
third portion of the FOV travels through the optical waveguide 600
from the input-coupler 612 to the third intermediate-component
614c.
[0054] In the embodiment of FIG. 6, the portion of the FOV provided
to the intermediate-component 614a differs from the portion of the
FOV provided to the intermediate-component 614c. The portion of the
FOV provided to the intermediate-component 514b can include part of
the FOV provided to the intermediate-component 614a and part of the
FOV provided to the intermediate-component 614c. The portion of the
FOV provided to the intermediate-component 514b can alternatively
be distinct from the portion of the FOV provided to the
intermediate-component 614a and portion of the FOV provided to the
intermediate-component 614c. In accordance with an embodiment, the
grating period of the input-coupler 612 is tuned so that part of
the FOV that is not to be steered to either of the
intermediate-components 614a and 614c goes to an evanescent
diffraction order that does not carry any power.
[0055] In the embodiment of FIG. 6, each of the intermediate
components 614a and 614c is configured to perform horizontal pupil
expansion, and diffract light having a respective portion of the
original FOV toward the output-coupler 616. The intermediate
component 614b can also be configured to perform horizontal pupil
expansion, and diffract light having a respective portion of the
original FOV toward the output-coupler 616. Alternatively, the
intermediate components 614b can diffract light having a respective
portion of the original FOV toward the output-coupler 616 without
performing any pupil expansion, in which case the middle portion of
the output-coupler 616 can output light corresponding to the image
having a FOV coming straight from the input-coupler 612. The
output-coupler 616 is also configured to combine the FOVs and
couple the light corresponding to the combined FOVs out of the
optical waveguide 600 so that the light corresponding to the image
and the combined FOVs is output from the optical waveguide 600 and
viewable from an output-pupil.
[0056] While not specifically shown in FIGS. 3-6, each of the
optical waveguides (300, 400, 500 and 600) is for use with a
display engine, which can be the same as or similar to the display
engine 204 described above with reference to FIG. 2, but is not
limited thereto. For example, the display engine (e.g., 204) can
face a back-side surface of one of the optical waveguides (300,
400, 500 or 600), and a user's eye (e.g., the eye of a person
wearing HMD glasses) can facing a front-side surface opposite and
parallel to the back-side surface, to provide for a periscope type
of configuration in which light enters the waveguide on one side of
the waveguide, and exits the waveguide at an opposite side of the
waveguide. Alternatively, the input-coupler and the output-coupler
can be implemented in a manner such that the display engine and a
user's eye are proximate to and face a same major surface of the
optical waveguide.
[0057] Where optical waveguides are used to perform pupil
replication (also referred to as image replication),
non-uniformities in local and global intensities may occur, which
may result in dark and light fringes and dark blotches when the
replicated image is viewed, which is undesirable. The embodiments
shown in and described with reference to FIGS. 5 and 6 may provide
for improved intensity distributions, and thereby, can be used to
improve the replicated image when viewed, compared to the
embodiments shown in and described with reference to FIGS. 3 and
4.
[0058] In the embodiments described herein, each of the diffraction
gratings, instead of being a surface grating, can alternatively be
a volume grating, such as a Bragg diffraction grating. It is also
possible that one or more of the couplers are manufactured as SRGs
and then covered within another material, e.g., using an aluminium
deposition process, thereby essentially burying the SRGs such that
the major planar waveguide surface(s) including the SRG(s) is/are
substantially smooth. Such a coupler is one example of a hybrid of
a surface and volume diffraction grating. Any one of the
input-coupler (e.g., 312, 412, 512, 612), the
intermediate-components (e.g., 314, 414, 514, 614) and the
output-coupler (e.g., 316, 416, 516, 616) can be, e.g., a surface
diffraction grating, or a volume diffraction grating, ora hybrid of
a surface and volume diffraction grating. In accordance with
embodiments described herein, each diffraction grating can have a
preferential linear polarization orientation specified by a
direction of the grating lines of the diffraction grating, wherein
the coupling efficiency for light having the preferential linear
polarization orientation will be higher than for light having a
non-preferential linear polarization orientation.
[0059] Using embodiments described herein, a large FOV of at least
70 degrees, and potentially up to 90 degrees or even larger can be
achieved by an optical waveguide that utilizes
intermediate-components to provide pupil expansion, even where the
intermediate-components individually can only support of FOV of
about 35 degrees. Additionally, where only a portion of the total
FOV is guided to disparate intermediate-components, a power savings
of up to 50% can be achieved when compared to a situation where the
FOV is not split by the input-coupler.
[0060] In many designs of HMDs, the input-coupler of an optical
waveguide is located near the temple or nose bridge region of a
wearer, when the HMD is being worn. This may be the case with the
embodiments described above with reference to FIGS. 1 and 2. In the
embodiments shown in FIGS. 3-6, by contrast, the input-coupler may
be directly above the eye of the wearer of an HMD, resulting in a
shorter the propagation distance that light corresponding to the
image travels between the input-coupler and the output-coupler,
before the light is output and viewed by the eye of the wearer.
This shorter distance results in a lower cumulative error.
Furthermore, if light corresponding to a portion (e.g., a middle
portion) of the FOV is steered directly from the input-coupler to
the output-coupler, so that light does not interact significantly
with an intermediate-component, then a combination of
two-dimensional and one-dimensional pupil expansion can be
supported by a single optical waveguide.
[0061] The optical waveguides (e.g., 300, 400, 500, 600) described
herein can be incorporated into a see-through mixed reality display
device system. The same waveguide can be used to steer light of
multiple different colors (e.g., red, green and blue) associated
with an image from the input-coupler to the output-coupler.
Alternatively, three waveguides can be stacked adjacent to each
other, with each of the waveguides being used to steer light of a
different color (e.g., red, green or blue) associated with an image
from its respective input-coupler to its output-coupler. It would
also be possible that one waveguide handle light of two colors
(e.g., green and blue) and another waveguide handles light of a
third color (e.g., red). Other variations are also possible.
[0062] The optical waveguides (e.g., 300, 400, 500 or 600)
described herein are for use in steering light from an
input-coupler to an output-coupler, where the light is out-coupled
for viewing or imaging by one of a person's two eyes (i.e., either
their left or right eye). One or more further instances of the
waveguide (e.g., 300, 400, 500 or 600) can be provided for the
other eye. In other words, a separate instance of the waveguide
(e.g., 300, 400, 500 or 600) and the display engine 204 can be
provided for each of the left and right eyes of a user. In certain
embodiments, such waveguide(s) may be positioned next to or between
see-through lenses, which may be standard lenses used in eye
glasses and can be made to any prescription (including no
prescription). Where there is a separate waveguide for each of the
left and right eyes of a user, there can be a separate display
engine for each of the waveguides, and thus, for each of the left
and right eyes of the user. One or more further adjacent waveguides
can be used to perform eye tracking based on infrared light that is
incident on and reflected from the user's eye(s) 214, as is known
in the art.
[0063] In FIGS. 3, 4, 5 and 6, the input-couplers, the
intermediate-components and the output-couplers were are shown as
having specific outer peripheral shapes, but can have alternative
outer peripheral shapes. Similarly, the peripheral shape of the
optical waveguides can also be changed, while still being within
the scope of embodiments described herein.
[0064] In certain embodiments, the input-coupler (e.g., 312, 412,
512, 612) can have surface gratings that extend in a vertical (y)
direction, the output-coupler (e.g., 316, 416, 516, 616) can have
surface gratings that extend in a horizontal (x) direction, and
certain intermediate-components (e.g., 314a, 414a, 514a, 614a) can
have surface gratings that extend diagonal (e.g., .about.45
degrees) relative to the horizontal and vertical directions, and
other intermediate-components (e.g., 314b, 414b, 514d, 614c) can
have surface gratings that extend diagonal (e.g., .about.45
degrees) in the other direction. These are just a few examples.
Other variations are also possible and within the scope of
embodiments of the present technology. Depending upon
implementation, the grating periods of the intermediate-components
of an optical waveguide can all be the same, or can all be
different. Regardless, two or more of the intermediate-components
of an optical waveguide should perform pupil expansion and steer
light toward the output-coupler of the optical waveguide.
[0065] The high level flow diagram of FIG. 7 will now be used to
summarize methods according to certain embodiments of the present
technology. The methods described with reference to FIG. 7 utilize
an optical waveguide to replicate an image associated with an
input-pupil to an output-pupil. Referring to FIG. 7, step 702
involves coupling light corresponding to the image associated with
the input-pupil, and having a corresponding FOV, into the optical
waveguide. Step 704 involves splitting the FOV of the image coupled
into the optical waveguide into first and second portions by
diffracting a portion of the light corresponding to the image in a
first direction, and diffracting a portion of the light
corresponding to the image in a second direction, wherein the first
and second directions differ from one another, and wherein the
first and second portions of the FOV differ from one another. In
accordance with an embodiment, one of the first and second
directions comprises a leftward direction, and the other one of the
first and second directions comprises a rightward direction. Step
706 involves, after the light corresponding to the image has
travelled through portions of the optical waveguide by way of total
internal reflection (TIR) (e.g., from an input-coupler to a
spatially separated output-coupler), combining the light
corresponding to the first and second portions of the FOV, and
coupling the light corresponding to the combined first and second
portions of the FOV out of the optical waveguide so that the light
corresponding to the image and the combined first and second
portions of the FOV is output from the optical waveguide and
viewable from the output-pupil. As can be appreciate from the above
discussion of FIGS. 3-6, steps 702 and 704 can be performed by an
input-coupler (e.g., 312, 412, 512 or 612) of the optical
waveguide, and step 706 can be performed by an output-coupler
(e.g., 316, 416, 516 or 616) of the optical waveguide.
[0066] In accordance with certain embodiments, prior to combining
the light corresponding to the first and second portions of the FOV
to thereby unify the FOV that was split, the light corresponding to
the first and second portions of the FOV is transferred from the
input-coupler, respectively, to first and second
intermediate-components of the optical waveguide by way of total
internal reflection (TIR), and the first and second
intermediate-components of the optical waveguide are used to
perform one of horizontal or vertical pupil expansion. In
accordance with certain embodiments, the output-coupler of the
optical-waveguide is used to perform the other one of horizontal or
vertical pupil expansion.
[0067] In such embodiments, the input-coupler, by diffracting a
portion of the light corresponding to the image in the first
direction toward a first intermediate-component, and diffracting a
portion of the light corresponding to the image in the second
direction toward the second intermediate-component, splits the FOV
into the first and second portions. The output-coupler, by
combining the light corresponding to the first and second portions
of the FOV, unifies the FOV that was split by the input-coupler.
Using such embodiments, a unified FOV associated with the light
coupled out of the optical waveguide, by the output-coupler, is
greater than a maximum FOV that each of the first and second
intermediate-components can support on their own, as was explained
above. As noted above, it is also possible that a FOV associated
with light corresponding to an image that is coupled into a
waveguide by an input-coupler can be split into more than two
portions, and the more than two portions of the FOV can be combined
by the output-coupler of the waveguide.
[0068] Embodiments described herein can be used to increase (also
referred to as extend) the FOV that can be supported by an optical
waveguide, without requiring that image tiling be used, which has
been proposed. Further, embodiments described herein can be used to
increase the FOV that can be supported by an optical waveguide,
without requiring the use of switchable Bragg gratings.
Nevertheless, it is possible that one or more of the input-coupler,
intermediate-components and output-coupler, in the embodiments
described with reference to FIGS. 3-6, can be implemented using a
switchable Bragg grating. However, in such an embodiment, it would
not be the fact the grating is switchable that enables the optical
waveguide to support a large FOV, as was the case in other
proposals that rely only switching and time division multiplexing
of different portions of an image and/or different grating
prescriptions to support a large FOV.
[0069] Although the subject matter has been described in language
specific to structural features and/or methodological acts, it is
to be understood that the subject matter defined in the appended
claims is not necessarily limited to the specific features or acts
described above. Rather, the specific features and acts described
above are disclosed as example forms of implementing the
claims.
* * * * *