Note: Descriptions are shown in the official language in which they were submitted.
CA 02828407 2013-08-27
WO 2012/118573
PCT/US2012/022492
LIGHT CONTROL IN HEAD MOUNTED DISPLAYS
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation-in-part of and claims
priority to
U.S. Pat. Appl. 13/037,324, filed 28 February 2011, now U.S. Pat. No. ,
and to
U.S. Pat. Appl. 13/037,335, also filed on 28 February 2011, now U.S. Pat. No.
_____ , both of which are hereby incorporated by reference in their entirety.
FIELD OF THE INVENTION
[0002] The present disclosure pertains to see-through head mounted displays
and
the control of light entering and exiting the head mounted display.
BACKGROUND
[0003] See-through head mounted displays allow a user to view a displayed
image or a see-through view of the scene in front of the user. See-through
head
mounted displays can also allow the user to view a combined image comprised of
a
displayed image and a see-through view of the scene in front of the user in
which the
displayed image is overlaid on the see-through view. In different modes of
operation,
the see-through head mounted display can present the displayed image so that
the area
of the displayed image is transparent, semitransparent or opaque. In the
transparent
mode, the see-through view of the scene is unblocked and an overlaid displayed
image can be provided with low contrast. In the semitransparent mode, the see-
through view of the scene is partially blocked and an overlaid displayed image
can be
provided with higher contrast. In the opaque mode, the se-through view of the
scene
is fully blocked and an overlaid displayed image can be provided with high
contrast.
[0004] Alternatively, some head-mounted displays provide a see-through
display
for an augmented reality view in which real-world scenes are visible to a user
but
additional image information is overlaid on the real-world scenes. Such an
augmented
reality view is provided by helmet mounted see-through displays found in
military
applications and by heads-up displays (HUDs) in the windshields of
automobiles. In
this case, there can be multiple areas for displaying images over the see-
through view.
[0005] U.S. Pat. No. 5151722 describes a head mounted display with a folded
optical path and a beam splitter with a curved mirror to present an image from
a CRT
image source to the user's eye. The image source is positioned on the side of
the
- 1 -
CA 02828407 2013-08-27
WO 2012/118573
PCT/US2012/022492
user's head with the optical path multiply folded to present the image light
from the
image source into the user's eye. The curved mirror is positioned between the
user's
eye and the scene in front of the user. A see-through version of the head
mounted
display is also discussed wherein the curved mirror is a partially reflective
mirror so
the user can see through the curved mirror to view the scene in front of the
user.
However, the CRT image source is large and heavy so that it is not well suited
for
head mounted displays. The multiply folded geometry with the image source
located
on the side of the user's head makes for a larger beam splitter and a thicker
geometry
in front of the user's eye so that the overall size of the head mounted
display is larger.
Image light that passes through the partially reflecting mirror is
uncontrolled and as
such, a portion of the image light escapes through the front of the see-
through head
mounted display and is seen externally as eyeglow.
[0006] U.S. Pat. No. 5699194 discloses a see-through head mounted display
with
a waveguide wherein the outer surface is a partially reflecting mirror. In
this see-
through head mounted display, image light from the image source is reflected
multiple times from different areas of the partially reflecting mirror before
the image
light is presented to the user's eye. In addition, a corrective lens is
provided so that
distortions of the see-through view of the scene are reduced. And, a liquid
crystal
shutter is provided to block incoming light from the scene so that the see-
through
headmounted display can be operated in an opaque mode. Image light that passes
through the partially reflecting mirror is uncontrolled and as such, a portion
of the
image light escapes through the front of the see-through head mounted display
and is
seen externally as eyeglow.
[0007] U.S. Pat. No. 6693749 describes a head mounted display with a
polarizing
beam splitter cube to reduce light losses and improve efficiency. An image
source is
positioned above the user's eye and the optical path is folded once to present
the
image light from the image source to the user's eye. A curved fully reflecting
mirror
is positioned below the user's eye to focus the image light at the user's eye.
An
unpolarized image source is used so that half of the image light from the
image source
passes through the polarizing beam splitter while the other half of the light
is reflected
away from the user's eye and toward the scene in front of the user. A
polarizer is
positioned in front of the polarizing beam splitter cube to block the half of
the light
that is reflected away from the user's eye and thereby make the user less
observable
by others in the neighboring environment. However, the polarizing beam
splitter cube
- 2 -
CA 02828407 2013-08-27
WO 2012/118573
PCT/US2012/022492
is large and heavy, so that it is not well suited for use in a head mounted
display.
Further, the curved mirror is also relatively large so that by locating the
mirror below
the user's eye, the thickness of the see-through head mounted display is
necessarily
larger.
[0008] There is a need, therefore, for an improved see-through head-mounted
display that provides a thinner, lighter weight display which also controls
escaping
light to reduce eyeglow.
SUMMARY
[0009] The present disclosure provides a see-through head mounted display
that
is thin and light in weight with a light control element to selectively block
escaping
image light and thereby reduce eyeglow.
[0010] In one embodiment, a see-through head mounted display apparatus is
provided. The see-through head mounted display apparatus includes a see-
through
display assembly including an image source and a partially reflecting mirror.
The
partially reflecting mirror reflects and transmits respective portions of
image light
from the image source and scene light from a see-through view of an external
environment. A combined image comprised of portions of the reflected image
light
and the transmitted scene light is provided to a user's eye. A light control
element is
provided to block escaping light comprised of the transmitted portion of image
light
and the reflected portion of scene light, while allowing a portion of incoming
scene
light to be transmitted from the external environment to the see-through
display
assembly. The light control element transmits a higher percentage of incoming
scene
light than the percentage of escaping light that is not blocked.
[0011] In another embodiment, a method for viewing an image with reduced
eyeglow on a see-through head mounted display having a front and a back is
provided. The method includes steps of providing image light to a partially
reflecting
mirror from an image displayed on an image source and reflecting a first
portion of
the image light from the partially reflecting mirror while transmitting a
second portion
of the image light through the partially reflecting mirror. The method also
includes
steps of transmitting a first portion of scene light from the external
environment
through a light control element at the front of the see-through head mounted
display.
Additional steps include transmitting a second portion of the scene light
through the
partially reflecting mirror while reflecting a third portion of the scene
light from the
- 3 -
CA 02828407 2013-08-27
WO 2012/118573
PCT/US2012/022492
partially reflecting mirror, and combining the first portion of the image
light with the
second portion of the scene light to provide a combined image to a viewer's
eye at the
back of the see-through head mounted display comprised of the image displayed
on
the image source overlaid on a view of the external environment. The method
also
includes a step of using the light control element to block the transmitted
second
portion of the image light and the reflected third portion of the scene light
to reduce
eyeglow.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is an illustration of a see-through head mounted display
device;
[0013] FIG. lA is an illustration of a user with a see-through head mounted
display device wherein eyeglow is depicted;
[0014] FIG. 2 is an illustration of a combination image as seen by a user
when
the see-through display device is operated in a transparent mode;
[0015] FIG. 3 is an illustration of a combination image as seen by a user
when
the see-through display device is operated in a semi-transparent mode;
[0016] FIG. 4 is a schematic view of a cross-section of a see-through
display
assembly;
[0017] FIG. 5 is a schematic view of a cross-section of a see-through
display
assembly;
[0018] FIG. 6 is an illustration of an example of the polarization control
used to
reduce eyeglow;
[0019] FIG. 7 is a schematic cross-section of a light control element;
[0020] FIG. 8 is a schematic cross-section of a see-through display
assembly
with a light control element mounted in a glasses frame; and
[0021] FIG. 9 is a flowchart describing a method disclosed herein.
DETAILED DESCRIPTION
[0022] In a see-through head mounted display, a displayed image can be
viewed
by a user at the same time that a see-through view of the scene from the
surrounding
environment can be viewed. The displayed image and the see-through view can be
viewed as a combined image where the displayed image is overlaid on the see-
through view or the displayed image and the see-through view can be
simultaneously
viewed in different portions of the see-through display that are viewable by
the user.
- 4 -
CA 02828407 2013-08-27
WO 2012/118573
PCT/US2012/022492
[0023] FIG. 1 shows an illustration of a see-through head mounted display
device 100. The device includes a frame 105 with lenses 110 that have display
areas
115 and clear areas 102. The device also has image sources and associated
optics (not
shown) to present image light from the image source to the display areas 115,
wherein
the image sources and associated optics can be located at the top, bottom or
side of
the display areas 115. The frame 105 is supported on the viewer's head with
arms
130. The arms 130 also contain electronics 125 including a processor to drive
the
displays and peripheral electronics 127 including batteries and wireless
connection(s)
to other information sources such as can be obtained on the intern& or from
localized
servers through Wi-Fi, Bluetooth, cellular or other wireless technologies. A
camera
120 can be included to capture images of the surrounding environment. The
locations
of the various components in the see-through head mounted display device 100
are
shown as an example, other locations are possible.
[0024] The see-through head-mounted display device 100 can further include
controllable darkening layers in the display areas 115 wherein the
controllable
darkening layers can change opacity behind the respective portions of the
display area
115 to enable changes in operating mode between transparent, semi-transparent
and
opaque in the areas where images are displayed. The controllable darkening
layers
can be segmented so that images can be displayed over different areas of the
lenses
110. FIG. 2 shows an example of a combined image as seen by a user using a see-
through head mounted display device 100 wherein the see-through head mounted
display device 100 is operating in a transparent mode. As can be seen in FIG.
2, the
displayed image seen by the user has a low contrast and objects from the see-
through
view are easily seen in the display area 115. FIG. 3 shows an example of a
combined
image as seen by a user using a see-through head mounted display device 100
wherein
the see-through head mounted display device 100 is operating in a semi-
transparent
mode. As can be seen in FIG. 3, the displayed image seen by the user has a
higher
contrast and objects from the see-through view are very dim in the display
area 115.
[0025] A wide variety of see-through head mounted display devices 100 are
known in the art. See-through head-mounted display devices 100 can provide
image
information to one eye of the user or both eyes of the user. See-through head
mounted display devices 100 that present image information to both eyes of the
user
can have one or two image sources. Monoscopic viewing in which the same image
information is presented to both eyes is done with see-through head mounted
display
- 5 -
CA 02828407 2013-08-27
WO 2012/118573
PCT/US2012/022492
devices 100 that have one or two image sources. Stereoscopic viewing typically
requires a head-mounted display device 100 that has two image sources with
different
images being presented to the user's eyes wherein the different images have
different
perspectives of the same scene.
[0026] A variety of image sources to provide images for display are known
in the
art including, for example, organic light-emitting diode (OLED) displays,
quantum
dot based light emitting diodes (QLED) displays, liquid crystal displays
(LCDs), or
liquid crystal on silicon (LCOS) displays. In addition, the image sources can
be
microprojectors or microdisplays with associated optics to present the image
light to
the display areas 115 so that the user can view the displayed images with
his/her eyes.
[0027] The optics associated with the image sources relay the image light
from
the image sources to the display areas 115. The optics can comprise refractive
lenses,
reflective lenses, mirrors, diffractive lenses, holographic lenses or
waveguides. For a
see-through head mounted display device 100, the user should be provided with
at
least a partial view of the scene in front of the see-through head-mounted
display
device 100 within the user's field of view. The present disclosure concerns
see-
through head mounted display devices 100 that have optics associated with the
image
source that include a partially reflective mirror for simultaneously
presenting image
light and scene light to the user so that the user is provided with a
displayed image
overlaid on at least a partial see-through view of the scene in front of the
user.
Wherein the partially reflective mirror can be any type of reflecting mirror
surface
that also allows some portion of the incident light to be transmitted such as
for
example a partially metalized coated surface or a dielectric multilayer mirror
coated
surface.
[0028] When using a see-through head mounted display, light losses from the
display areas 115 and from light reflected or scattered from the image source
or
associated optics or light reflected or scattered from the user, contribute
light that
passes from the see-through head mounted display into the environment. These
light
losses are perceived by external viewers as eyeglow where portions of the
lenses 110
or the areas surrounding the see-through head mounted display device 100
appear to
be glowing when viewed in a dimly lit environment. In certain cases of eyeglow
as
shown in FIG. 1A, the displayed image can be seen as an observable image 190
in the
display areas 115 when viewed externally by external viewers. To maintain
privacy
of the viewing experience for the user both in terms of maintaining privacy of
the
- 6 -
CA 02828407 2013-08-27
WO 2012/118573
PCT/US2012/022492
images being viewed and in terms of making the user less noticeable when using
the
see-through head mounted display device 100 in a dimly lit environment, it is
preferable to reduce eyeglow. This disclosure provides methods and apparatus
that
reduce eyeglow in see-through head mounted displays such as the see-through
head
mounted display devices 100 which include a partially reflective mirror in the
optics
associated with the image source.
[0029] FIGS. 4 and 5 provide examples of optics associated with image
sources
for see-through head mounted display devices 100 that include partially
reflective
mirrors 440 and 540. Light control elements 480 and 580 block image light that
passes through the partially reflective mirrors 440 and 540 respectively to
reduce
escaping light that contributes to eyeglow.
[0030] Turning first to FIG. 4, the optics associated with the image source
in this
example will be described. In this example, the image source includes a
projection
system (not shown) to provide image light with an optical layout that includes
a first
horizontal optical axis located in or along the upper portion of the frame 105
in the
see-through head mounted display device 100. The optics along this first
horizontal
axis can include lenses to focus the image light 470 to provide a focused
displayed
image from the image source to the user's eye 410. A folding mirror 460 then
redirects the image light 470 from the first horizontal axis to a non-vertical
optical
axis 452 that proceeds to a see-through display assembly 400 with a beam
splitter
layer 420 and a second horizontal optical axis 450. The beam splitter layer
420 can
be a partially reflecting mirror or a polarizing beam splitter layer. The beam
splitter
layer 420 in the see-through display assembly 400 is oriented at an angle to
the non-
vertical optical axis and the second horizontal optical axis 450 to provide a
thinner
see-through display assembly 400. The beam splitter layer 420 reflects and
redirects
at least a portion of the image light 470 along the second horizontal optical
axis 450 in
a direction away from the user's eye 410. A first portion of the image light
470 that
has been reflected by the beam splitter layer 420, is then reflected back
toward the
user's eye 410 by a partially reflecting mirror 440. The partially reflecting
mirror 440
can be spherical or aspheric as appropriate to present a focused image to the
user's
eye 410. The reflected first portion of the image light 470 then passes back
through
the beam splitter and is focused at the user's eye 410.
[0031] At the same time, a second portion of the image light 470 that has
been
reflected by the beam splitter layer 420, is transmitted through the partially
reflecting
- 7 -
CA 02828407 2013-08-27
WO 2012/118573
PCT/US2012/022492
mirror 440. It is this second portion of image light 470 that escapes from the
see-
through display assembly 400 to contribute to eyeglow in the form of an
observable
image 190 that can be seen by external viewers. Light control element 480
blocks
the second portion of the image light 470 thereby reducing escaping light and
reducing eyeglow. In one embodiment, the light control element 480, the
partially
reflecting mirror 440, the beam splitter layer 420 and the user's eye 410 are
all located
along a common optical axis, the second horizontal optical axis 450.
Simultaneously,
a first portion of scene light from the external environment 465 passes
through the
light control element 480. A second portion of the scene light 465 then passes
through the partially reflective mirror 440 and the beam splitter layer 420 to
combine
with the first portion of the image light 470 to present a combined image to
the user's
eye 410. The combined image includes the displayed image from the image source
overlaid onto at least a partial see-through view of the external environment
in front
of the user.
[0032] At the same time, a third portion of the scene light 465 is
reflected by the
partially reflecting mirror 440. This third portion of scene light 465 also
contributes
to eyeglow since it escapes from the see-through display assembly 400.
However, the
third portion of scene light 465 contributes a generally reflected light from
the
environment and as such does not contribute to the observable image 190 that
can be
seen by external viewers. The eyeglow produced by the third portion of scene
light
465 is seen by external viewers as a general brightness in the lenses 110 or
as a
reflected image of the external scene in front of the user.
[0033] In an embodiment, the image source provides linearly polarized image
light 470 and the beam splitter layer 420 is a partially reflective mirror.
Linearly
polarized image light can be provided by various means including microdisplays
with
linearly polarized illumination such as LCOS displays or LCD displays,
alternately
self-luminous displays (such as OLED, QLED and transmissive LCOS) with a
linear
polarizer can be used to provide linearly polarized image light 470. With
linearly
polarized image light 470 and a partially reflective mirror as the beam
splitter layer
420, the light control element 480 is a linear polarizer. Wherein the linear
polarizer in
the light control element 480 is oriented relative to the linearly polarized
image light
470 so that the second portion of the linearly polarized image light 470 that
passes
through the partially reflecting mirror 440 is blocked and eyeglow is reduced.
- 8 -
CA 02828407 2013-08-27
WO 2012/118573
PCT/US2012/022492
[0034] In a further embodiment, the beam splitter layer 420 is a polarizing
beam
splitter, or the image source provides polarized image light 470 and the beam
splitter
layer 420 is a polarizing beam splitter, so that the reflected image light 470
is linearly
polarized light, this embodiment and the associated polarization control is
shown in
FIG. 6. For the case where the image source provides linearly polarized image
light
and the beam splitter layer 420 is a polarizing beam splitter, the
polarization state of
the image light is aligned to the polarizing beam splitter so that the image
light 470 is
reflected by the polarizing beam splitter. FIG. 6 shows the reflected image
light as
having S state polarization. In cases where the beam splitter layer 420 is a
polarizing
beam splitter, a first quarter wave film 430 is provided between the beam
splitter layer
420 and the partially reflecting mirror 440.
[0035] The first quarter wave film 430 converts the linearly polarized
image light
to circularly polarized image light (shown as S being converted to CR in FIG.
6). The
reflected first portion of image light 470 is then also circularly polarized
where the
circular polarization state is reversed (shown as CL in FIG. 6) so that after
passing
back through the quarter wave film, the polarization state of the reflected
first portion
of image light 470 is reversed (to P polarization) compared to the
polarization state of
the image light 470 provided by the image source (shown as S). As a result,
the
reflected first portion of the image light 470 passes through the polarizing
beam
splitter without reflection losses. When the beam splitter layer 420 is a
polarizing
beam splitter and the see-through display assembly 400 includes a first
quarter wave
film 430, the light control element 480 is a second quarter wave film 653 and
a linear
polarizer 654. Wherein the second quarter wave film 653 converts the second
portion
of the circularly polarized image light 470 into linearly polarized image
light 470
(shown as CR being converted to S) with a polarization state that is blocked
by the
linear polarizer 654 in the light control element 480 so that eyeglow is
reduced.
[0036] When the light control element 480 includes a linear polarizer 654
and a
quarter wave film 653, incoming unpolarized scene light 465 from the external
environment in front of the user is converted to linearly polarized light
(shown as P
polarization state in FIG. 6) while 50% of the light is blocked. The first
portion of
scene light 465 that passes through the linear polarizer 654 is linearly
polarized light
which is converted by the quarter wave film to circularly polarized light
(shown as P
being converted to CL in FIG. 6). The third portion of scene light that is
reflected
from the partially reflecting mirror 440 has reversed circular polarization
(shown as
- 9 -
CA 02828407 2013-08-27
WO 2012/118573
PCT/US2012/022492
converting from CL to CR in FIG. 6) which is then converted to linearly
polarized
light by the second quarter wave film 653 (shown as CR converting to S
polarization
in FIG. 6). The linear polarizer 654 then blocks the reflected third portion
of the
scene light thereby reducing escaping light and reducing eyeglow.
[0037] As shown in FIG. 6, the reflected first portion of image light 470
and the
transmitted second portion of scene light have the same circular polarization
state
(shown as CL) so that they combine and are converted by the first quarter wave
film
430 into linearly polarized light (shown as P) which passes through the beam
splitter
when the beam splitter layer 420 is a polarizing beam splitter. The linearly
polarized
combined light 690 then provides a combined image to the user's eye 410
located at
the back of the see-through display assembly 400, where the combined image is
comprised of overlaid portions of the displayed image from the image source
and the
see-through view of the external environment in front of the user.
[0038] The example optics associated with image sources for see-through
head
mounted display devices 100 shown in FIG. 5 as see-through display assembly
500
will now be addressed. In this example, an image source 520 that provides
linearly
polarized image light 570 is used. The linearly polarized image light 570
enters a
waveguide 555 wherein the light is first reflected by total internal
reflection from the
back surface 530, a first portion of the image light 570 is reflected from a
partially
reflecting mirror 540 and then transmitted through surface 530 to present an
image
from the image source 520 to the user's eye 410. The user looks through the
waveguide 555 and the partially reflecting mirror 540 to obtain a see-through
view of
the external scene in front of the user. Due to distortions imparted by the
thick layers
of optical material in the waveguide 555, a corrective element 560 is provided
to
reduce distortions in the see-through view seen by the user. The combined
image
presented to the user's eye 410, comprised of the displayed image from the
image
source 520 overlaid on at least a portion of a see-through view of the
external scene,
is formed from the image light 570 and the scene light 565. In this example,
eyeglow
comes from a second portion of image light 570 that is transmitted through the
partially reflecting mirror 540 where it passes through the corrective element
560 and
escapes from the see-through display assembly 500.
[0039] In this case, the linear polarization of the image light 570 is
maintained
so that the second portion of image light 570 that escapes from the see-
through
display assembly 500 has the same linear polarization as the image light 570
provided
- 10 -
CA 02828407 2013-08-27
WO 2012/118573
PCT/US2012/022492
by the image source 520. The light control element 580 for this embodiment
comprises a linear polarizer that is oriented along with the image source 520
so that
escaping light is blocked. The polarization state of the image light 570 and
the
orientation of the linear polarizer in the light control element 580 are
chosen together
to block escaping light. As an example, if the image source 520 provides S
polarized
image light 570, the linear polarizer in the light control element 580 is
oriented to
block S polarized light. As shown in FIG. 5, the light control element 580,
the
corrective element 560, the partially reflective mirror 540, the waveguide 555
and the
user's eye 410 are all located on a common optical axis 550. In addition,
while FIG. 5
shows image light 570 being reflected once on surface 530 and once on
partially
reflecting mirror 540, waveguides can be used where multiple reflections of
the image
light 570 occur on either the surface 530 or the partially reflective mirror
540.
[0040] It should be noted, that the embodiments may include see-through
display
assemblies 400 and 500 where partially reflective mirrors 440 and 540
respectively
are located on common optical axes with the user's eye 410 and light control
elements
480 and 580 respectively. This optical layout has been selected to provide the
additional benefit of providing a thin see-through display assembly with a
large
displayed field of view overlaid onto the see-through field of view. To
provide a
large displayed field of view, the portion of the partially reflective mirror
where the
image is displayed must be relatively large. By including an angled beam
splitter
layer as shown in FIG. 4, it is possible to locate the partially reflective
mirror above or
below the see-through field of view. However, if the partially reflective
mirror is
located with an optical axis that is perpendicular to the optical axis
associated with the
see-through field of view, the lateral dimension of the partially reflective
mirror
increases the thickness of the see-through display assembly substantially.
[0041] As a result, the embodiments may include partially reflective
mirrors that
share an optical axis with the see-through field of view so that the large
dimension of
the partially reflective mirror that is associated with the large displayed
field of view
is vertical and as such does not contribute to the thickness of the see-
through display
assembly. However, since the partially reflective mirror is located on the
optical axis
of the see-through field of view, the partially reflective mirror must be both
partially
reflective to provide the displayed image and partially transparent to provide
the see-
through view. As an example, a see-through display assembly was designed
similar
to that shown in FIG. 4 for a 30 degree field of view displayed image. The
partially
- 11 -
CA 02828407 2013-08-27
WO 2012/118573
PCT/US2012/022492
reflective mirror was then 15 mm high. By positioning the partially reflective
mirror
in front of the user, the thickness of the see-through display assembly from
the front
of the partially reflective mirror to the back of the beam splitter layer was
reduced to
mm.
[0042] In a further embodiment, the light control layer includes an
electrically
controllable darkening layer to reduce the amount of scene light entering the
see-
through head mounted display. The controllable darkening layer is controlled
in
response to detected changes in the environment, changes in the user's
movements or
changes in the type of images being displayed. In one embodiment, the
controllable
darkening layer is segmented to provide differential control in the display
areas and
the clear areas of the lens to provide a displayed image with higher contrast.
Examples of controllable darkening layers include various types of liquid
crystal
layers, electrowetting layers or electrochromic layers.
[0043] FIG. 7 shows a cross-sectional view of a light control element 700.
Light
control element 700 includes a controllable darkening layer 652, a quarter
wave film
653, a linear polarizer 654 and a support layer 740. In another embodiment,
light
control element 700 can be a separate replaceable element in the see-through
head
mounted display device 100. In this way, different levels of functionality can
be built
into the light control element 700 such as different color tints or thicker
support layers
740 to provide increased impact resistance, ballistic protection or laser
protection.
Impact resistance can be provided with a high impact plastic such as
polycarbonate
and ballistic protection can be provided with a laminated component, as in
bullet
proof glass. Laser protection can also be provided, for example, with cut
filters to
block laser wavelengths. In a further example, the support layer 740 can
include
photochromic materials which automatically darken when in bright environments
to
block a portion of the scene light thereby making it easier to view displayed
images.
[0044] In another example, the controllable darkening layer 652 can be
included
in some versions of the light control element 700 to block a portion of the
scene light
to provide improved viewing conditions with higher contrast displayed images
in
portions of the combined image Simpler versions of light control element 700
may
simply omit the controllable darkening layer 652. As previously discussed, the
quarter wave film 653 should be left out of the light control element 700 when
used
with certain types of see-through display assemblies 400 such as when the
image
- 12 -
CA 02828407 2013-08-27
WO 2012/118573
PCT/US2012/022492
source provides linearly polarized image light 470 and the beam splitter layer
420 is a
partially reflective mirror or when a see-through display assembly 500 is
used.
[0045] FIG. 8 shows an example of a see-through display assembly with a
light
control element 480 in a glasses frame. The glasses cross-section 800 shows
the
components of see-through display assembly 400 in a glasses frame 805.
Wherein,
the light control element 480 covers the entire see-through view seen by the
user.
Supporting members 887 and 885 are shown supporting the partially reflecting
mirror
440 and the beam splitter layer 420 respectively in the field of view of the
user's eye
410. The supporting members 885 and 887 along with the light control element
700
are connected to the glasses frame 805. The other components such as the
folding
mirror 460 and the first quarter wave film 430 are also connected to the
supporting
members 887 and 885 so that the combined assembly is structurally sound.
[0046] FIG. 9 describes a method of using the present disclosure. In step
910,
image light is provided by an image source, such as a microdisplay, to a
partially
reflecting mirror. In step 920, the partially reflecting mirror reflects a
first portion of
the image light while transmitting a second portion of image light. In step
930, a first
portion of scene light is transmitted through a light control element. A
second portion
of the scene light is transmitted through the partially reflecting mirror
while a third
portion of the scene light is reflected from the partially reflecting mirror
in step 940.
In step 950 the first portion of image light and the second portion of scene
light are
combined to provide a combined image to the user's eye wherein the combined
image
is comprised of the displayed image from the image source overlaid on a see-
through
view of the external scene in front of the user. In step 960, the light
control element
blocks escaping light from the second portion of the image light and the third
portion
of the scene light to thereby reduce eyeglow. Wherein the percentage of light
in the
first portion of scene light that is transmitted through the light control
element is
larger than the percentage of escaping light from the second portion of image
light
and the third portion of scene light that is not blocked by the light control
element.
[0047] The partially reflecting mirror included in the apparatus can have a
range
of reflectivity from 20% to 80%. Wherein the lower levels of reflectivity
provide for
more scene light to be presented to the user's eye so that the see-through
view is
brighter but, higher levels of image light will escape so that power usage for
the
image source will be increased to provide a displayed image with a given level
of
brightness. In contrast, higher levels of reflectivity provide for less scene
light to be
- 13 -
CA 02828407 2013-08-27
WO 2012/118573
PCT/US2012/022492
presented to the user's eye so that the see-through view is dimmer and lower
levels of
image light will escape, so that power usage for the image source will be
reduced to
provide a displayed image with a given level of brightness.
[0048] By using polarization based methods to reduce eyeglow, the
efficiency of
the light usage is increased. Linear polarizers typically block 99.9% or
greater of one
linear polarization state while allowing 99.9% of the other linear
polarization state to
pass through. Unpolarized light is comprised of a mixture of the two linear
polarization states so that 50% of the unpolarized light is blocked and 50%
passes
through the linear polarizer. Purely absorbing filters or purely reflecting
filters cannot
block a higher percentage of light than they pass under any circumstances. In
the
embodiments, the polarization states of the various portions of the image
light and the
scene light are controlled in the see-through display assembly and the light
control
element such that a high percentage of scene light is allowed to pass into the
see-
through display assembly while a higher percentage of escaping light is
blocked so
that a bright see-through view is presented to the user and eyeglow is
reduced.
Considering that in some cases, the image light or the scene light may take on
some
elliptical polarization, it is reasonable to expect that the light control
element blocks
greater than 90% of the escaping light while allowing greater than 30% of the
scene
light to be transmitted.
[0049] The polarizing beam splitter in the embodiments discussed herein can
be
of several different types. While the examples shown in FIGS. 4, 6 and 8 show
wiregrid plates or wiregrid films applied to support plates as the polarizing
beam
splitters, MacNeil prism type polarizing beam splitters can also be used.
[0050] In yet another embodiment, light absorbing structures are included
on one
or more of the edges of the frame 105 to absorb light that is reflected or
scattered
from the user's face. Where the light absorbing structures can include black
areas or
textured areas. The light absorbing structures can also be flexible to conform
to the
user's face.
- 14 -
CA 02828407 2013-08-27
WO 2012/118573
PCT/US2012/022492
[0051] Table of numerals for figures
100 see-through head 452 optical axis 653 quarter wave
film
mounted display device
102 clear areas of 460 folding 654 linear polarize
lenses mirror
105 frames 465 scene light 690 combined image light
110 lenses 470 image light 700 light control element
115 display areas 480 light control 740 support layer
element
120 camera 500 see-through 800 glasses cross-section
display assembly
125 electronics 520 image source 805 glasses frame
127 peripheral 530 back surface 885 supporting member
electronics of waveguide
130 arms 540 partially 887 supporting member
reflective mirror
190 externally 550 optical axis 910 step of providing image
observable image light to the partial mirror
400 see-through 555 waveguide 920 step of reflecting and
display assembly transmitting portions of image light
410 user's eye 560 corrective 930 step of transmitting scene
element light through the light control
element
420 beam splitter layer 565 scene light 940 step of
transmitting and
reflecting portions of scene light
430 quarter wave film 570 image light 950 step of
combining image
light and scene light to provide a
combined image to the user
440 partially reflective 580 light control 960 step of using
the light
mirror element control element to block escaping
light
450 optical axis 652 controllable
darkening layer
[0052] The present disclosure has been very detailed with particular
reference to
certain embodiments thereof, but it will be understood that variations and
modifications can be effected within the spirit and scope of the invention.
- 15 -
