U.S. patent application number 16/224637 was filed with the patent office on 2020-06-18 for waveguide with coherent interference mitigation.
The applicant listed for this patent is Facebook Technologies, LLC. Invention is credited to Babak Amirsolaimani, Giuseppe Calafiore, Wanli Chi, Ningfeng Huang, Alexander Koshelev, Wai Sze Tiffany Lam, Hee Yoon Lee, Gang Li, Lu Lu, Stephan Lutgen, Andrew Maimone, David Massoubre, Scott Charles McEldowney, Francois Olivier, Andrew Ouderkirk, Maxwell Parsons, Pasi Saarikko, Barry David Silverstein.
Application Number | 20200192130 16/224637 |
Document ID | / |
Family ID | 69182636 |
Filed Date | 2020-06-18 |
![](/patent/app/20200192130/US20200192130A1-20200618-D00000.png)
![](/patent/app/20200192130/US20200192130A1-20200618-D00001.png)
![](/patent/app/20200192130/US20200192130A1-20200618-D00002.png)
![](/patent/app/20200192130/US20200192130A1-20200618-D00003.png)
![](/patent/app/20200192130/US20200192130A1-20200618-D00004.png)
![](/patent/app/20200192130/US20200192130A1-20200618-D00005.png)
![](/patent/app/20200192130/US20200192130A1-20200618-D00006.png)
![](/patent/app/20200192130/US20200192130A1-20200618-D00007.png)
![](/patent/app/20200192130/US20200192130A1-20200618-D00008.png)
United States Patent
Application |
20200192130 |
Kind Code |
A1 |
Maimone; Andrew ; et
al. |
June 18, 2020 |
WAVEGUIDE WITH COHERENT INTERFERENCE MITIGATION
Abstract
A pupil-replicating waveguide suitable for operation with a
coherent light source is disclosed. A waveguide body has opposed
surfaces for guiding a beam of image light. An out-coupling element
is disposed in an optical path of the beam for out-coupling
portions of the beam at a plurality of spaced apart locations along
the optical path. Electrodes are coupled to at least a portion of
the waveguide body for modulating an optical path length of the
optical path of the beam to create time-varying phase delays
between the portions of the beam out-coupled by the out-coupling
element.
Inventors: |
Maimone; Andrew; (Duvall,
WA) ; Ouderkirk; Andrew; (Redmond, WA) ; Lee;
Hee Yoon; (Redmond, WA) ; Huang; Ningfeng;
(Redmond, WA) ; Parsons; Maxwell; (Berkley,
CA) ; McEldowney; Scott Charles; (Redmond, WA)
; Amirsolaimani; Babak; (Redmond, WA) ; Saarikko;
Pasi; (Kirkland, WA) ; Chi; Wanli; (Sammamish,
WA) ; Calafiore; Giuseppe; (Redmond, WA) ;
Koshelev; Alexander; (Redmond, WA) ; Silverstein;
Barry David; (Kirkland, WA) ; Lu; Lu;
(Kirkland, WA) ; Lam; Wai Sze Tiffany; (Redmond,
WA) ; Li; Gang; (Seattle, WA) ; Lutgen;
Stephan; (Dresden, DE) ; Olivier; Francois;
(Cork, IE) ; Massoubre; David; (Cork, IE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Facebook Technologies, LLC |
Menlo Park |
CA |
US |
|
|
Family ID: |
69182636 |
Appl. No.: |
16/224637 |
Filed: |
December 18, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 27/0172 20130101;
G02F 1/011 20130101; G02B 27/0081 20130101; G02F 2201/305 20130101;
G02B 2027/0178 20130101; G02F 1/035 20130101; G02B 6/0035 20130101;
G02F 1/0128 20130101; G02B 6/34 20130101; G02F 1/065 20130101; G02F
1/1326 20130101; G02B 2027/0152 20130101; G02F 1/0134 20130101;
G02B 6/0038 20130101; G02B 2027/0123 20130101; G02B 6/005
20130101 |
International
Class: |
G02F 1/01 20060101
G02F001/01; G02F 1/13 20060101 G02F001/13; G02F 1/065 20060101
G02F001/065; G02B 27/01 20060101 G02B027/01 |
Claims
1. A pupil-replicating waveguide comprising: a waveguide body
having opposed surfaces for guiding a beam of image light
therebetween; an out-coupling element in an optical path of the
beam for out-coupling a plurality of portions of the beam at a
plurality of spaced apart locations along the optical path; and
electrodes coupled to at least a portion of the waveguide body for
modulating an optical path length of the optical path of the beam
to provide time-varying phase delays between different portions of
the plurality of portions of the beam out-coupled by the
out-coupling element.
2. The pupil-replicating waveguide of claim 1, wherein the
out-coupling element and one of the electrodes comprise a same
electrically conductive diffraction grating.
3. The pupil-replicating waveguide of claim 1, wherein the
waveguide body comprises: a substrate for propagating the beam of
image light therein; and an electrically responsive layer disposed
between the electrodes and configured to modulate the optical path
length of the beam upon application of an electrical signal to the
electrodes.
4. The pupil-replicating waveguide of claim 3, wherein the
electrical signal comprises voltage, and wherein the electrically
responsive layer comprises an elastic polymer material deformable
by an electrostatic attraction force between the electrodes upon
application of the voltage.
5. The pupil-replicating waveguide of claim 4, wherein the elastic
polymer material comprises a nanovoided polymer.
6. The pupil-replicating waveguide of claim 5, wherein the
nanovoided polymer has a thickness of between 0.1 micrometers and
20 micrometers.
7. The pupil-replicating waveguide of claim 3, wherein the
electrical signal comprises voltage, and wherein the electrically
responsive layer comprises a liquid crystal layer.
8. The pupil-replicating waveguide of claim 1, wherein the
waveguide body comprises an electro-optic substrate disposed
between the electrodes, and wherein the electro-optic substrate has
a refractive index responsive to electric field between the
electrodes upon application of voltage thereto.
9. The pupil-replicating waveguide of claim 8, wherein the at least
a portion of the waveguide body comprises a piezoelectric material
for modulating a physical length of the optical path of the beam of
image light.
10. The pupil-replicating waveguide of claim 1, wherein the
waveguide body comprises: a substrate for propagating the beam of
image light therein; and an acoustic actuator coupled to the
substrate and comprising an electrically responsive layer between
the electrodes, wherein a thickness of the electrically responsive
layer is variable by applying an electrical signal to the
electrodes.
11. The pupil-replicating waveguide of claim 10, wherein the
acoustic actuator is coupled at a side of the substrate and
configured to provide a volume acoustic wave in the substrate.
12. The pupil-replicating waveguide of claim 10, wherein the
acoustic actuator is mechanically coupled to one of the surfaces
and configured to provide a surface acoustic wave in that
surface.
13. A wearable display comprising: a light source for providing a
beam of image light carrying a plurality of image frames at a frame
rate; a pupil-replicating waveguide comprising: a waveguide body
having opposed surfaces for guiding the beam of image light
therebetween; an out-coupling element in an optical path of the
beam for out-coupling a plurality of portions of the beam at a
plurality of spaced apart locations along the optical path; and
electrodes coupled to at least a portion of the waveguide body for
modulating an optical path length of the optical path of the beam
to create time-varying phase delays between different portions of
the plurality of portions of the beam out-coupled by the
out-coupling element; and a controller operably coupled to the
electrodes of the pupil-replicating waveguide and configured to
apply an electrical signal to the electrodes to modulate the
optical path length.
14. The wearable display of claim 13, wherein a rate of modulation
of the optical path length is higher than the frame rate.
15. The wearable display of claim 14, wherein each image frame
comprises a time sequence of frame lines at a line rate higher than
the frame rate, and wherein the rate of modulation of the optical
path length is higher than the line rate.
16. The wearable display of claim 14, wherein each frame line
comprises a time sequence of line pixels at a pixel rate higher
than the line rate, and wherein the rate of modulation of the
optical path length is higher than the pixel rate.
17. The wearable display of claim 14, wherein a rate of modulation
of the optical path length is randomly varying relative to a rate
at which individual pixels of an image frame are updated.
18. A method for expanding a beam of image light, the method
comprising: propagating the beam along an optical path in a
pupil-replicating waveguide; out-coupling, using an out-coupling
element in an optical path of the beam, a plurality of portions of
the beam at a plurality of spaced apart locations along the optical
path; and modulating, by applying an electrical signal to
electrodes coupled to at least a portion of the pupil-replicating
waveguide, an optical path length of the optical path of the beam
to create time-varying phase delays between different portions of
the plurality of portions of the beam out-coupled by the
out-coupling element.
19. The method of claim 18, wherein the electrical signal comprises
voltage, and wherein the optical path length is modulated using an
electrically responsive layer between the electrodes, by applying
the voltage thereto.
20. The method of claim 18, wherein the beam of image light carries
a plurality of image frames at a frame rate, and wherein a rate of
modulation of the optical path length is randomly varying relative
to the frame rate.
Description
TECHNICAL FIELD
[0001] The present disclosure relates to visual displays and
display systems, and in particular to wearable displays,
components, modules, and related methods.
BACKGROUND
[0002] Head-mounted displays (HMDs), near-eye displays (NEDs), and
other wearable display systems can be used to present virtual
scenery to a user, or to augment real scenery with dynamic
information, data, or virtual objects. The virtual or augmented
scenery can be three-dimensional (3D) to enhance the experience and
to match virtual objects to real objects observed by the user. Eye
position and gaze direction, and/or orientation of the user may be
tracked in real time, and the displayed scenery may be dynamically
adjusted depending on the user's head orientation and gaze
direction, to provide a better experience of immersion into a
simulated or augmented environment.
[0003] Lightweight and compact near-eye displays reduce strain on
the user's head and neck, and are generally more comfortable to
wear. The optics block of such displays can be the heaviest part of
the entire system. Compact planar optical components, such as
waveguides, gratings, Fresnel lenses, etc., may be employed to
reduce size and weight of an optics block. However, compact planar
optics may have limitations related to image quality, exit pupil
size and uniformity, pupil swim, field of view of the generated
imagery, visual artifacts, etc.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] Exemplary embodiments will now be described in conjunction
with the drawings, in which:
[0005] FIG. 1 is a schematic cross-sectional view of a
pupil-replicating waveguide of the present disclosure coupled to a
coherent light source;
[0006] FIG. 2 is a side cross-sectional view of the
pupil-replicating waveguide of FIG. 1 showing optical path length
difference between out-coupled portions of the beam;
[0007] FIG. 3 is a side cross-sectional view of a pupil-replicating
waveguide including a nanovoided electroactive polymer layer;
[0008] FIG. 4 is a side cross-sectional view of a pupil-replicating
waveguide including a liquid crystal layer;
[0009] FIG. 5A is a side cross-sectional view of a
pupil-replicating waveguide including an acoustic actuator for
creating a volume acoustic wave in the pupil-replicating
waveguide;
[0010] FIG. 5B is a side cross-sectional view of a
pupil-replicating waveguide including an acoustic actuator for
creating a surface acoustic wave in the pupil-replicating
waveguide;
[0011] FIG. 6 is a side cross-sectional view of a wearable display
of the present disclosure;
[0012] FIG. 7 is a flow chart of a method for expanding a beam of
image light;
[0013] FIG. 8A is an isometric view of an eyeglasses form factor
near-eye augmented reality (AR)/virtual reality (VR) display
incorporating a pupil-replicating waveguide of the present
disclosure;
[0014] FIG. 8B is a side cross-sectional view of the AR/VR display
of FIG. 8A; and
[0015] FIG. 9 is an isometric view of a head-mounted display (HMD)
incorporating a pupil-replicating waveguide of the present
disclosure.
DETAILED DESCRIPTION
[0016] While the present teachings are described in conjunction
with various embodiments and examples, it is not intended that the
present teachings be limited to such embodiments. On the contrary,
the present teachings encompass various alternatives and
equivalents, as will be appreciated by those of skill in the art.
All statements herein reciting principles, aspects, and embodiments
of this disclosure, as well as specific examples thereof, are
intended to encompass both structural and functional equivalents
thereof. Additionally, it is intended that such equivalents include
both currently known equivalents as well as equivalents developed
in the future, i.e., any elements developed that perform the same
function, regardless of structure.
[0017] As used herein, the terms "first", "second", and so forth
are not intended to imply sequential ordering, but rather are
intended to distinguish one element from another, unless explicitly
stated. Similarly, sequential ordering of method steps does not
imply a sequential order of their execution, unless explicitly
stated. In FIGS. 1 to 4, 5A and 5B, and FIG. 6, similar reference
numerals denote similar elements.
[0018] Pupil-replicating waveguides are often used in wearable
displays due to their compactness and suitability for augmented
reality (AR) applications. It may be desirable to use a high
coherence light source, such as a laser source, in a wearable
display with pupil-replicating waveguide(s). High degree of
coherence of light source enables highly efficient beam redirection
and delivery. Laser beam scanned displays can have good power
efficiency, low cost, compact size, bright color gamut, and may
enable resolution scaling. However, in a pupil-replicating
waveguide display, each coherently replicated beam has a different
optical path length, and therefore a different optical phase. When
the eye receives and focuses multiple replicated out-of-phase
beams, constructive or destructive interference may result. This
causes the intensity of the image to spatially vary in an
uncontrollable manner. In accordance with the present disclosure,
time-varying phase delays may be imparted on different coherently
replicated beams to smooth or average out undesired interference
effects. The time-varying phase delays may be created by varying
optical path length of the beam propagating along the optical path
in the waveguide. The optical path length may be varied by varying
physical path length, refractive index, or both.
[0019] In accordance with the present disclosure, there is provided
a pupil-replicating waveguide comprising a waveguide body having
opposed surfaces for guiding a beam of image light therebetween. An
out-coupling element is disposed in an optical path of the beam for
out-coupling portions of the beam at a plurality of spaced apart
locations along the optical path. Electrodes are coupled to at
least a portion of the waveguide body for modulating an optical
path length of the optical path of the beam to provide time-varying
phase delays between the portions of the beam out-coupled by the
out-coupling element.
[0020] The out-coupling element and one of the electrodes may
include a same electrically conductive diffraction grating. The
waveguide body may include a substrate for propagating the beam of
image light therein, and an electrically responsive layer disposed
between the electrodes and configured to modulate the optical path
length of the beam upon application of an electrical signal to the
electrodes.
[0021] In some embodiments, the electrical signal comprises
voltage, and the electrically responsive layer comprises an elastic
polymer material deformable by an electrostatic attraction force
between the electrodes upon application of the voltage. The elastic
polymer material may include a nanovoided polymer having a
thickness of e.g. between 0.1 micrometers and 20 micrometers. In
some embodiments, the electrical signal comprises voltage, and the
electrically responsive layer comprises a liquid crystal layer.
[0022] In some embodiments, the waveguide body comprises an
electro-optic substrate disposed between the electrodes, and the
electro-optic substrate has a refractive index responsive to
electric field between the electrodes upon application of voltage
to the electrodes. The electrode-coupled portion of the waveguide
body may include a piezoelectric material for modulating a physical
length of the optical path of the beam of image light.
[0023] In some embodiments, the waveguide body includes a substrate
for propagating the beam of image light therein, and an acoustic
actuator coupled to the substrate and comprising an electrically
responsive layer between the electrodes. A thickness of the
electrically responsive layer is variable by applying an electrical
signal to the electrodes. The acoustic actuator may be coupled at a
side of the substrate and configured to provide a volume acoustic
wave in the substrate. Alternatively, the acoustic actuator may be
mechanically coupled to one of the surfaces and configured to
provide a surface acoustic wave in that surface.
[0024] In accordance with the present disclosure, there is provided
a wearable display comprising a light source for providing a beam
of image light carrying a plurality of image frames at a frame
rate, a pupil-replicating waveguide, and a controller. The
pupil-replicating waveguide may include a waveguide body having
opposed surfaces for guiding the beam of image light therebetween,
an out-coupling element in an optical path of the beam for
out-coupling portions of the beam at a plurality of spaced apart
locations along the optical path, and electrodes coupled to at
least a portion of the waveguide body for modulating an optical
path length of the optical path of the beam to create time-varying
phase delays between the portions of the beam out-coupled by the
out-coupling element. The controller may be operably coupled to the
electrodes of the pupil-replicating waveguide and configured to
apply an electrical signal to the electrodes to modulate the
optical path length.
[0025] A rate of modulation of the optical path length may be
higher than the frame rate. In embodiments where each image frame
comprises a time sequence of frame lines at a line rate higher than
the frame rate, the rate of modulation of the optical path length
may be higher than the line rate. In embodiments where each frame
line comprises a time sequence of line pixels at a pixel rate
higher than the line rate, the rate of modulation of the optical
path length may be higher than the pixel rate. A rate of modulation
of the optical path length may be made to randomly vary relative to
a rate at which individual pixels of an image frame are
updated.
[0026] In accordance with the present disclosure, there is further
provided a method for expanding a beam of image light. The method
includes propagating the beam along an optical path in a
pupil-replicating waveguide, out-coupling, using an out-coupling
element in an optical path of the beam, portions of the beam at a
plurality of spaced apart locations along the optical path, and
modulating, by applying an electrical signal to electrodes coupled
to at least a portion of the pupil-replicating waveguide, an
optical path length of the optical path of the beam to create
time-varying phase delays between the portions of the beam
out-coupled by the out-coupling element. In some embodiments, the
electrical signal comprises voltage, and the optical path length is
modulated using an electrically responsive layer between the
electrodes, by applying the voltage thereto. In some embodiments,
the beam of image light carries a plurality of image frames at a
frame rate, and a rate of modulation of the optical path length is
randomly varying relative to the frame rate.
[0027] Referring now to FIG. 1, a pupil-replicating waveguide 100
is optically coupled to a coherent light source 102, which provides
a cone of beams of image light carrying an image in angular domain
to be displayed to an eye 105. Only one beam 104 is shown for
brevity; it is to be understood that the image light comprises
beams at multiple angles within a field of view observable by the
eye 105. An in-coupler 103, e.g. a diffraction grating, may be
provided to in-couple the beam 104 for propagation in a waveguide
body 106 of the pupil-replicating waveguide. The waveguide body 106
has opposed top 115 and bottom 116 surfaces for guiding the beam
104 between the surfaces 115,116 by reflection, e.g. total internal
reflection (TIR), from the surfaces 115,116. An out-coupling
element 110 such as a surface-relief diffraction grating, a volume
Bragg grating (VBG), a hologram, etc., can be disposed in an
optical path of the beam 104 for out-coupling portions
111,112,113,114 of the beam 104 at a plurality of spaced apart
locations 121,122,123,124 along the optical path. Electrodes
107,108 can be coupled to at least a portion of the waveguide body
106 for modulating optical path length of the optical path of the
beam 104 to create time-varying phase delays between the portions
111,112,113,114 of the beam 104 out-coupled by the out-coupling
element 110. It is noted that, although the out-coupling element
110 is shown in FIG. 1 on the outside, that is, supported by the
bottom electrode 107, the order, i.e. relative position, of the
out-coupling element 110 and the bottom electrode 107 may be
reversed.
[0028] The electrodes 107,108 can modify some property of at least
a portion of the waveguide body 106, e.g. geometrical dimensions,
index of refraction, etc., via a suitable mechanism such as
electro-optic effect, piezo effect, thermo-optic effect,
magneto-optic effect, acousto-optic effect, photoelasticity, etc.,
to modulate the optical path length of the beam 104 to modulate,
i.e. vary in time domain, optical path difference between the
different beam portions 111,112,113,114. When the optical path
length difference is varied, the interference effects between the
different beam portions 111,112,113,114 wash out, i.e. are averaged
out, reducing or even completely eliminating undesirable spatial
modulation of optical power density of the image to be
displayed.
[0029] To employ an electro-optic effect, such as Pockels or Kerr
effect, the waveguide body 106 may include an electro-optic
substrate between the electrodes 107,108. The electro-optic
substrate may have a refractive index responsive to electric field
between the electrodes 107,108 generated by applying a voltage
(i.e. electric potential difference) to the electrodes 107,108. The
electro-optic substrate may be made of lithium niobate, for
example. To employ piezo effect, the waveguide body 106 may be made
of a transparent material exhibiting a piezo effect, e.g. a
suitable crystal such as quartz, lithium tantalate, lithium
niobate, etc. When the waveguide body 106 is made out of a
transparent piezoelectric material, a physical length of the
waveguide body 106 changes upon application of the voltage to the
electrodes 107,108, which causes the optical path length change of
the beam 104. In some embodiments, the diffraction grating 110 may
be made conductive, and thus serve as one of the electrodes, e.g.
the electrode 107. In other words, the diffraction grating 110 may
combine the functions of the out-coupling element and one of the
electrodes.
[0030] Referring to FIG. 2, an optical path length difference d
between two 112,113 of the out-coupled portions of the beam 104 is
further illustrated. The waveguide body 106 has a refractive index
n and thickness t, and the beam 104 propagates in the waveguide
body 106 at an angle .theta.. The optical path length difference d
consists of two equal halves d/2, as shown, each half d/2=nt/sin
.theta., and the optical phase difference .PHI. accordingly is
.PHI.=4.pi.nt/(.lamda. sin .theta.) (1) [0031] where .lamda. is the
wavelength of the beam 104.
[0032] For a given angle .theta. and wavelength .lamda., one can
change the relative phase shift by varying thickness t, refractive
index n, or both. At a reasonable waveguide body 106 thickness,
e.g. 1-2 mm, refractive index of 1.5-2.2, and angles .theta., e.g.
40-65 degrees, very small changes in thickness (tens of nanometers)
or refractive index n (of the order of 10.sup.-5) are required to
produce the maximum phase difference amplitude of .pi.. When
relative phases of the beam portions 122,123 change, different
interference patterns will result. By changing the phase difference
.PHI. rapidly over time, one can visually average out interference
effects. For example, one may sweep phase difference .PHI. over the
.pi. magnitude between adjacent replicated beam portions
111,112,113,114 at a rate comparable to, or higher than, the frame
rate of the light source 102 (FIG. 1).
[0033] Referring now to FIG. 3, a pupil-replicating waveguide 300
of the present disclosure includes a waveguide body 306 having two
portions: a substrate 328 for propagating the beam 104, and a thin
electrically responsive layer 330 disposed between electrodes
307,308. An out-coupling diffraction grating 310 is disposed on the
opposite side of the substrate 328 as the electrically responsive
layer 330. The out-coupling diffraction grating 310 may also be
disposed on a same side of the substrate 328 as the electrically
responsive layer 330. The electrically responsive layer 330 can be
configured to modulate the optical path length of the beam 104 upon
application of an electrical signal, such as electric current (when
the electrically responsive layer responds to electric current) or
voltage, i.e. difference of electric potentials (when the
electrically responsive layer responds to electric field), to the
electrodes 307,308. Herein, the term "electrically responsive
layer" means a layer having a thickness or an optical thickness
(the thickness multiplied by refractive index) dependent on the
electrical signal. One advantage is that electrically responsive
materials exist which create a large change in optical path length
with moderate voltages, increasing the magnitude of the
corresponding optical response of the electrically responsive layer
330.
[0034] In some embodiments of the present disclosure, the
electrically responsive layer 330 includes an electroactive polymer
material, that is, a polymer material that may change its size or
shape in the presence of an electric field, thus changing the
optical path length within the material. One type of electroactive
polymers is dielectric electroactive polymer, which is an elastic
polymer material deformable by an electrostatic attraction force
between the electrodes when the voltage is applied to the
electrodes. Other types of suitable electroactive polymers may be
used, including e.g. ferroelectric electroactive polymers which
maintain a permanent electric polarization that can be reversed or
switched by an external electric field.
[0035] One drawback of a dielectric polymer is a comparatively
large actuation voltage. In accordance with the present disclosure,
the actuation voltage of a dielectric polymer of the electrically
responsive layer 330 may be reduced by providing a plurality of
voids 332 throughout the dielectric polymer material. Only several
voids 332 are shown in FIG. 3 for brevity. The voids 332 may be
approximately 7 nm to 70 nm in size and may occupy between 10% and
90% of the polymer volume, or, in another embodiment, between 30%
and 70% of the polymer volume. The thickness of the electrically
responsive layer 330 comprising a nanovoided dielectric polymer may
be between 0.1 micrometers and 20 micrometers, for example. The
presence of the voids 332 improves electromechanical response of
the polymer layer and considerably reduces the required maximum
driving voltage. As low voltage as 3-5V may be enough to produce a
significant phase difference (e.g., .pi.) between the replicated
beam portions in the nanovoided polymer material. The driving
voltage range may accordingly be 0V-3V; 0V-5V; 0V-12V; or in some
embodiments, 0V to 30V. In some embodiments, the diffraction
grating 310 may be disposed not on an opposite side as shown in
FIG. 3 but on a same side of the substrate 328 as the electrically
responsive layer 330, e.g. resting on the top electrode 308, for
example. In some embodiments, the diffraction grating 310 may be
made out of a conductive material and therefore may act as one of
the electrodes 307,308.
[0036] Turning to FIG. 4, a pupil-replicating waveguide 400 of the
present disclosure includes a waveguide body 406 having two
portions, a substrate 428 for propagating the beam 104, and a
liquid crystal layer 430 disposed between electrodes 407,408. An
out-coupling diffraction grating 410 is disposed on the opposite
side of the substrate 428 from the liquid crystal layer 330. The
out-coupling diffraction grating 410 may also be disposed on a same
side of the substrate 428 as the liquid crystal layer 430. Upon
application of voltage, i.e. a difference of electric potentials,
between the electrodes 307,308, liquid crystal molecules change
their orientation e.g. due to dipole interaction with the resulting
electric field, thereby changing birefringence of the liquid
crystal layer 430. In one embodiment, the liquid crystal molecules
are oriented generally in X-direction, by corresponding alignment
layers, not shown. The optical beam 104 is linearly polarized such
that it generally propagates in the XY plane as shown at 440. Upon
application of voltage between the electrodes 407,408, the liquid
crystal molecules become predominantly oriented in the direction of
the electric field, that is, in Y-direction. In such example
configuration, the changed birefringence will result in a
corresponding change of the optical phase of the optical beam 104,
creating optical phase variations between beam portions 112,113.
Different types of crystal layer materials and configurations may
be used including without limitation nematic, cholesteric, or
ferroelectric liquid crystals. Spacer-filled gasket 442 may be
provided to seal the liquid crystal layer 430 and define the
thickness of the liquid crystal layer 430. In some embodiments, a
ferroelectric liquid crystal material may be used due to
sub-millisecond switching speed of ferroelectric liquid
crystals.
[0037] Referring to FIG. 5A, a pupil-replicating waveguide 500A of
the present disclosure includes a waveguide body 506A having two
portions, a substrate 528 for propagating the beam 104, and a
volume-wave acoustic actuator 530A mechanically coupled at a side
of the substrate 528 joining its top 515 and bottom 516 reflective
surfaces. A diffraction grating 510 out-couples the portions
112,113 of the beam 104. In the embodiment shown, the volume-wave
acoustic actuator 530A includes an electrically responsive layer
532A, e.g. a piezoelectric layer, disposed between electrodes
507A,508A. In operation, an electrical signal at a high frequency,
typically in the range of 1 MHz to 100 MHz or higher, is applied to
the electrodes 507A,508A causing the electrically responsive layer
532A to oscillate, typically at a frequency of a mechanical
resonance of the electrically responsive layer 532A. The
oscillating thickness of the electrically responsive layer 532A
creates a volume acoustic wave 534A propagating in the substrate
528 in a direction 535, i.e. along the X-axis. The volume acoustic
wave 534A modulates optical path length by changing the substrate
528 index of refraction due to the effect of photoelasticity, the
geometrical shape of the substrate 528, or both. In some
embodiments, an acoustic wave terminator 536A can be coupled to an
opposite side of the substrate 528 to absorb the volume acoustic
wave 534A and thus prevent a standing acoustic wave formation in
the substrate 528. A standing volume acoustic wave may be
undesirable in that it may create distortions in the image being
carried by the beam 104 towards a user's eye.
[0038] Turning to FIG. 5B, a pupil-replicating waveguide 500B of
the present disclosure includes a waveguide body 506B having two
portions, the substrate 528 for propagating the beam 104, and a
surface-wave acoustic actuator 530B mechanically coupled at the top
reflective surface 515. Alternatively, the surface-wave acoustic
actuator 530B may also be coupled at the bottom reflective surface
516. In the embodiment shown, the surface-wave acoustic actuator
530B includes an electrically responsive layer 532B, e.g. a
piezoelectric layer, disposed between electrodes 507B,508B. In
operation, an electrical signal at a high frequency, typically in
the range of 1 MHz to 100 MHz or higher, is applied to the
electrodes 507B,508B causing the electrically responsive layer 532B
to oscillate. The oscillation of the electrically responsive layer
532A creates a surface acoustic wave 534B propagating in the
substrate 528 in the direction 535, i.e. along the X-axis. The
surface acoustic wave 534B modulates optical path length by
changing the substrate 528 index of refraction due to the effect of
photoelasticity, the geometrical shape of the substrate 528, or
both. When the index of refraction or the geometrical shape or size
of the substrate are changed, the optical path length of the beam
104 changes. In some embodiments, an acoustic wave terminator 536B
can be coupled to an opposite side of the substrate 528 at the same
surface, i.e. at the top surface 515 in FIG. 5B, to absorb the
surface acoustic wave 534B and thus prevent a standing acoustic
wave formation. A standing surface acoustic wave may be undesirable
in that it may create distortions in the image being carried by the
beam 104 towards a user's eye.
[0039] Referring now to FIG. 6, a wearable display 680, e.g. a
near-eye display (NED) or a head-mounted display (HMD), includes a
light source 602 providing a beam 604 of image light carrying a
plurality of image frames to be displayed to a user's eye 605 at a
fixed or variable frame rate. In the embodiment shown, the light
source 602 includes a linear laser diode array 601 optically
coupled to a linear scanner 609. Each image frame may include a
time sequence of frame lines generated by the linear laser diode
array 601, which are shifted by the linear scanner 609 in
synchronism with the generated lines of the image to form an image
frame line by line, at a line rate N times higher than the frame
rate, where N is the number of lines in a frame being generated. A
single laser diode light source coupled to a two-dimensional
scanner for scanning the beam 604 in X and Y planes may also be
used. For the single scanned laser diode source, each frame line
includes a time sequence of line pixels at a pixel rate higher than
the line rate. The line rate is the frequency of a scanning line,
e.g. in X plane, and the frame rate is the frequency of the
scanning in Y plane.
[0040] A pupil-replicating waveguide 600 includes a waveguide body
606 including a substrate 628 having opposed top 615 and bottom 616
surfaces for guiding the beam 604 between the surfaces 615,616 by
reflection, e.g. TIR, from the surfaces 615,616, and an
electrically responsive layer 630. The beam 604 may be coupled into
the waveguide body 606 by using a grating coupler 603, for example.
Using TIR for guiding the beam 604 in the waveguide body 606 has an
advantage of allowing an external light at angles less than a TIR
critical angle to be transmitted through the surfaces 615,616. Any
of the above described pupil-replicating waveguides, i.e. the
pupil-replicating waveguide 100 of FIG. 1, the pupil-replicating
waveguide 300 of FIG. 3, the pupil-replicating waveguide 400 of
FIG. 4, the pupil-replicating waveguide 500A of FIG. 5A, or the
pupil-replicating waveguide 500B of FIG. 5B may be used. An
out-coupling element 610, such as a surface-relief diffraction
grating, a volume Bragg grating (VBG), a hologram, etc., may be
disposed in the optical path of the beam 604 at any one of the
surfaces 615,616, or inside a substrate 628, for out-coupling
portions 611,612,613,614 of the beam 604 at a plurality of spaced
apart locations 621,622,623,624 along the optical path.
[0041] Electrodes 607,608 may be coupled to the waveguide 600, or
to an electrically responsive layer 630 of the waveguide 600. The
electrically responsive layer 630 may include e.g. the nanovoided
elastic polymer layer 330 of FIG. 3 or the liquid crystal layer 430
of FIG. 4. The electrodes 607,608 convey an electrical signal, e.g.
electrical current or voltage, to the electrically responsive layer
630 for modulating an optical path length of the optical path of
the beam 604 to create time-varying phase delays between the
portions 611,612,613,614 of the beam 604 out-coupled by the
out-coupling element 610. A controller 650 can be operably coupled
to the electrodes 607,608 of and configured to apply the electrical
signal to the electrodes 607,608 to modulate the optical path
length. The controller 650 may also be coupled to the light source
602 for providing image frames to be displayed.
[0042] The controller 650 may be configured to have a rate of
modulation of the optical path length rate to be higher than the
frame rate, such that any optical power density non-uniformities
due to interference between different beam portions 611-614 may be
averaged out in a single frame. For embodiments where the light
source 602 includes the linear diode array 601 coupled to a linear
scanner 609, the controller 650 may be configured to have the rate
of modulation of the optical path length rate to be higher than the
line rate, such that any optical power density non-uniformities due
to interference between different beam portions 611-614 may be
averaged out in each image line. For embodiments where a single
diode laser light source is scanned in two dimensions, e.g. in X
and Y planes, the controller 650 may be configured to have the rate
of modulation of the optical path length higher than the pixel
rate. It may also be preferable to configure the controller 650
such that the rate of modulation of the optical path length is
randomly varying relative to the frame rate, or relative to a rate
at which individual pixels of an image frame are updated. In other
words, the phase delays of the beam portions 611-614 may be made
random relative to the time intervals when frames, lines, and/or
individual pixels of the image are being updated. This may prevent
the interference-caused image non-uniformity patterns from staying
steady or drifting across image frames.
[0043] Referring now to FIG. 7, a method 700 for expanding a beam
of image light includes propagating (702) the beam along an optical
path in a pupil-replicating waveguide. Portions of the beam are
out-coupled (704) using an out-coupling element in an optical path
of the beam at a plurality of spaced apart locations along the
optical path. Optical path length of the optical path of the beam
is then modulated (706) by applying an electrical signal to
electrodes coupled to at least a portion of the waveguide, to
create time-varying phase delays between the portions of the beam
out-coupled by the out-coupling element. The modulated optical path
length causes interference patterns of the out-coupled beam
portions to shift, effectively washing them out, or averaging them.
This enables one to use a coherent light source, which may be
well-collimated and may be easier to work with.
[0044] In some embodiments of the method 700, the rate of
modulation of the optical path length is randomly varying relative
to the frame rate of the images displayed, to prevent any
noticeable steady or drifting interference patterns from appearing.
The optical path length modulation may be carried out using any of
the devices/technologies described above, e.g. using an
electrically responsive layer between the electrodes, such as a
nanovoided polymer, a liquid crystal layer, a piezo element,
etc.
[0045] Referring to FIGS. 8A and 8B, a near-eye AR/VR display 800
is an embodiment of the wearable display 680 of FIG. 6, and may
include the pupil-replicating waveguide 100 of FIG. 1, the
pupil-replicating waveguide 300 of FIG. 3, the pupil-replicating
waveguide 400 of FIG. 4, the pupil-replicating waveguide 500A of
FIG. 5A, and/or the pupil-replicating waveguide 500B of FIG. 5B. A
body or frame 802 of the near-eye AR/VR display 800 has a form
factor of a pair of eyeglasses, as shown. A display 804 includes a
display assembly 806 (FIG. 8B), which provides image light 808 to
an eyebox 810, i.e. a geometrical area where a good-quality image
may be presented to a user's eye 812. The display assembly 806 may
include a separate coherent-replication VR/AR display module for
each eye, or one coherent-replication VR/AR display module for both
eyes. For the latter case, an optical switching device may be
coupled to a single electronic display for directing images to the
left and right eyes of the user in a time-sequential manner, one
frame for left eye and one frame for right eye. The images are
presented fast enough, i.e. with a fast enough frame rate, that the
individual eyes do not notice the flicker and perceive smooth,
steady images of surrounding virtual or augmented scenery.
[0046] An electronic display of the display assembly 806 may
include, for example and without limitation, a liquid crystal
display (LCD), a Liquid Crystal on Silicon (LCoS) display, a
scanned laser beam display, a scanned laser beam array, a phased
array display, a holographic display, or a combination thereof. The
near-eye AR/VR display 800 may also include an eye-tracking system
814 for determining, in real time, the gaze direction and/or the
vergence angle of the user's eyes 812. The determined gaze
direction and vergence angle may also be used for real-time
compensation of visual artifacts dependent on the angle of view and
eye position. Furthermore, the determined vergence and gaze angles
may be used for interaction with the user, highlighting objects,
bringing objects to the foreground, dynamically creating additional
objects or pointers, etc. Furthermore, the near-eye coherent AR/VR
display 800 may include an audio system, such as small speakers or
headphones.
[0047] Turning now to FIG. 9, an HMD 900 is an example of an AR/VR
wearable display system enclosing user's eyes for a greater degree
of immersion into the AR/VR environment. The HMD 900 may be a part
of an AR/VR system including a user position and orientation
tracking system, an external camera, a gesture recognition system,
control means for providing user input and controls to the system,
and a central console for storing software programs and other data
for interacting with the user for interacting with the AR/VR
environment. The functional purpose of the HMD 900 is to augment
views of a physical, real-world environment with computer-generated
imagery, and/or to generate entirely virtual 3D imagery. The HMD
900 may include a front body 902 and a band 904. The front body 902
is configured for placement in front of eyes of the user in a
reliable and comfortable manner, and the band 904 may be stretched
to secure the front body 902 on the user's head. A display system
980 may include any of the waveguide assemblies described herein.
The display system 980 may be disposed in the front body 902 for
presenting AR/VR images to the user. Sides 906 of the front body
902 may be opaque or transparent.
[0048] In some embodiments, the front body 902 includes locators
908, an inertial measurement unit (IMU) 910 for tracking
acceleration of the HMD 900 in real time, and position sensors 912
for tracking position of the HMD 900 in real time. The locators 908
may be traced by an external imaging device of a virtual reality
system, such that the virtual reality system can track the location
and orientation of the HMD 900 in real time. Information generated
by the IMU and the position sensors 912 may be compared with the
position and orientation obtained by tracking the locators 908, for
improved tracking of position and orientation of the HMD 900.
Accurate position and orientation is important for presenting
appropriate virtual scenery to the user as the latter moves and
turns in 3D space.
[0049] The HMD 900 may further include an eye tracking system 914,
which determines orientation and position of user's eyes in real
time. The obtained position and orientation of the eyes allows the
HMD 900 to determine the gaze direction of the user and to adjust
the image generated by the display system 980 accordingly. In one
embodiment, the vergence, that is, the convergence angle of the
user's eyes gaze, is determined. The determined gaze direction and
vergence angle may be used for real-time compensation of visual
artifacts dependent on the angle of view and eye position.
Furthermore, the determined vergence and gaze angles may be used
for interaction with the user, highlighting objects, bringing
objects to the foreground, creating additional objects or pointers,
etc. An audio system may also be provided including e.g. a set of
small speakers built into the front body 902.
[0050] The hardware used to implement the various illustrative
logics, logical blocks, modules, and circuits described in
connection with the aspects disclosed herein may be implemented or
performed with a general purpose processor, a digital signal
processor (DSP), an application specific integrated circuit (ASIC),
a field programmable gate array (FPGA) or other programmable logic
device, discrete gate or transistor logic, discrete hardware
components, or any combination thereof designed to perform the
functions described herein. A general-purpose processor may be a
microprocessor, but, in the alternative, the processor may be any
conventional processor, controller, microcontroller, or state
machine. A processor may also be implemented as a combination of
computing devices, e.g., a combination of a DSP and a
microprocessor, a plurality of microprocessors, one or more
microprocessors in conjunction with a DSP core, or any other such
configuration. Alternatively, some steps or methods may be
performed by circuitry that is specific to a given function.
[0051] The present disclosure is not to be limited in scope by the
specific embodiments described herein. Indeed, other various
embodiments and modifications, in addition to those described
herein, will be apparent to those of ordinary skill in the art from
the foregoing description and accompanying drawings. Thus, such
other embodiments and modifications are intended to fall within the
scope of the present disclosure. Further, although the present
disclosure has been described herein in the context of a particular
implementation in a particular environment for a particular
purpose, those of ordinary skill in the art will recognize that its
usefulness is not limited thereto and that the present disclosure
may be beneficially implemented in any number of environments for
any number of purposes. Accordingly, the claims set forth below
should be construed in view of the full breadth and spirit of the
present disclosure as described herein.
* * * * *