U.S. patent application number 16/731275 was filed with the patent office on 2020-04-30 for head-mounted display eyeball tracker integrated system.
The applicant listed for this patent is LUMUS LTD.. Invention is credited to Yaakov AMITAI.
Application Number | 20200133008 16/731275 |
Document ID | / |
Family ID | 46614987 |
Filed Date | 2020-04-30 |
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United States Patent
Application |
20200133008 |
Kind Code |
A1 |
AMITAI; Yaakov |
April 30, 2020 |
HEAD-MOUNTED DISPLAY EYEBALL TRACKER INTEGRATED SYSTEM
Abstract
Head-mounted display with an eye-tracking system and including a
light-transmitting substrate (20) having two major surfaces and
edges, optical means for coupling light into said substrate (20) by
total internal reflection, partially-reflecting surfaces (22a-22c)
carried by the substrate (20) that are not parallel with the major
surfaces of the substrate (20), a near-infrared light source (78)
and a display source (92) projecting within the photopic spectrum,
wherein light from the light source (78) and light from the display
source (92) are coupled into the substrate (20) by total internal
reflection.
Inventors: |
AMITAI; Yaakov; (Rehovot,
IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LUMUS LTD. |
Ness Ziona |
|
IL |
|
|
Family ID: |
46614987 |
Appl. No.: |
16/731275 |
Filed: |
December 31, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15680028 |
Aug 17, 2017 |
10520732 |
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16731275 |
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14399113 |
Nov 5, 2014 |
9804396 |
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PCT/IL2013/050428 |
May 19, 2013 |
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15680028 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 2027/0178 20130101;
G02B 27/0081 20130101; G02B 2027/0187 20130101; A61B 3/113
20130101; G02B 27/0172 20130101; G02B 27/145 20130101; G02B 27/0093
20130101; G02B 27/0179 20130101; G02B 27/286 20130101; G02B
2027/0125 20130101; G02B 27/141 20130101 |
International
Class: |
G02B 27/01 20060101
G02B027/01; G02B 27/14 20060101 G02B027/14; G02B 27/00 20060101
G02B027/00; A61B 3/113 20060101 A61B003/113 |
Foreign Application Data
Date |
Code |
Application Number |
May 21, 2012 |
IL |
219907 |
Claims
1. A see-through optical system for vehicle safety, comprising: a
transparent substrate having at least two major surfaces and edges;
an image projector configured to project an image made up of light
waves of at least a second optical spectrum, said image projector
being optically coupled to the substrate so as to inject the image
into the substrate so that the image propagates within the
substrate by internal reflection at the two major surfaces; an
array of partially-reflective surfaces carried by said substrate
and obliquely angled relative to said major surfaces, said array of
partially-reflective surfaces coupling out the image from the
substrate so as to be viewable by the eye of a viewer; an
illumination source generating illumination light waves within a
first optical spectrum distinct from said second optical spectrum;
a chromatically-selective reflector carried by the substrate and
configured for coupling-in light waves generated by said
illumination source reflected from the eye of the viewer; a
detector arrangement deployed to derive an image of at least part
of the eye of the viewer from said light waves reflected from the
eye of the viewer; and a processing system associated with said
detector arrangement and configured to process said image of at
least part of the eye of the viewer to detect an open/closed state
of the eye and to derive an indication of driver drowsiness.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to integrated head-mounted
display (HMD) systems, and in particular, to systems that include
two combined units: a head-mounted unit and an eyeball tracking
unit.
[0002] The invention can be implemented to advantage in a large
number of imaging applications, such as portable DVDs, cellular
phones, mobile TV receivers, video games, portable media players or
other mobile display devices.
BACKGROUND OF THE INVENTION
[0003] One important application for compact optical elements, is
in HMDs wherein an optical module serves both as an imaging lens
and a combiner, in which a two-dimensional image source is imaged
to infinity and reflected into an eye of an observer. The display
source can be obtained directly from, e.g., a spatial light
modulator (SLM) such as a cathode ray tube (CRT), a liquid crystal
display (LCD), an organic light emitting diode array (OLED), a
scanning source, or indirectly, by means of a relay lens, or an
optical fiber bundle. The display source comprises an array of
elements (pixels) imaged to infinity by a collimating lens and
transmitted into the eye of a viewer by means of a reflecting or
partially reflecting surface acting as a combiner for
non-see-through and see-through applications, respectively.
Typically, a conventional, free-space optical module is used for
these purposes. As the desired field-of-view (FOV) of a HMD system
increases, however, such a conventional optical module becomes
larger, heavier and bulkier, and therefore, even for a
moderate-performance device, is impractical. This is a major
drawback for all kinds of displays and especially in head-mounted
applications, wherein the system should necessarily be as light and
compact as possible.
[0004] The strive for compactness has led to several different
complex optical solutions, all of which, on the one hand, are still
not sufficiently compact for most practical applications and, on
the other hand, suffer major drawbacks in terms of
manufacturability. Furthermore, the eye-motion-box (EMB) of the
optical viewing angles resulting from these designs is usually very
small, typically less than 8 mm. Hence, the performance of the
optical system is very sensitive, even for small movements of the
optical system relative to the eye of a viewer, and does not allow
sufficient pupil motion for comfortable reading of text from such
displays.
[0005] The teachings included in Publication Nos. WO01/95027,
WO03/081320, WO2005/024485, WO2005/024491, WO2005/024969,
WO2005/124427, WO2006/013565, WO2006/085309, WO2006/085310,
WO2006/087709, WO2007/054928, WO2007/093983, WO2008/023367,
WO2008/129539 and WO2008/149339, all in the name of Applicant, are
herein incorporated by references.
DISCLOSURE OF THE INVENTION
[0006] The present invention facilitates the exploitation of very
compact light-guide optical elements (LOEs) for, amongst other
applications, HMDs. The invention allows for relatively wide FOVs
together with relatively large EMB values. The resulting optical
system offers a large, high-quality image, which also accommodates
large movements of the eye. The optical system offered by the
present invention is particularly advantageous because it is
substantially more compact than the state-of-the-art
implementations and yet, it can be readily incorporated even into
optical systems having specialized configurations.
[0007] Another optical function which could prove to be useful for
HMD designs is eyeball tracking, or sensing the direction the
eyeball is looking at, relative to the direction of the head. A
typical eye tracker will combine a miniature CCD camera and an
infrared LED to illuminate the pupil. By measuring the changes in
shape and position of the pupil, it is possible to perceive the
direction in which the viewer's eye is looking, with very
reasonable accuracy once calibrated. Combining measurements of head
position and eye position would solve the problems inherent in
existing HMD technology, since the projected symbols and boresight
could be slaved to the direction in which the viewer is looking,
thus retaining existing human tracking behavior. It will be useful
to combine the HMD and the eyeball tracker in the same optical
module.
[0008] A broad object of the present invention is therefore to
alleviate the drawbacks of prior art compact optical display
devices and to provide other optical components and systems having
improved performance, according to specific requirements.
[0009] In accordance with the invention there is therefore provided
an optical system, comprising a light-transmitting substrate having
at least two major surfaces and edges, at least one optical means
for coupling light waves into the substrate by total internal
reflection, at least two partially reflecting surfaces carried by
the substrate wherein the partially reflecting surfaces are not
parallel to the main surfaces of the substrate, at least one light
source projecting light waves located within a first optical
spectrum, and at least one display source projecting light waves
located within a second optical spectrum, characterized in that the
light waves from the light source and light waves from the display
source are coupled into the substrate by total internal
reflection.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The invention is described in connection with certain
preferred embodiments, with reference to the following illustrative
figures so that it may be more fully understood.
[0011] With specific reference to the figures in detail, it is
stressed that the particulars shown are by way of example and for
purposes of illustrative discussion of the preferred embodiments of
the present invention only, and are presented in the cause of
providing what is believed to be the most useful and readily
understood description of the principles and conceptual aspects of
the invention. In this regard, no attempt is made to show
structural details of the invention in more detail than is
necessary for a fundamental understanding of the invention. The
description taken with the drawings are to serve as direction to
those skilled in the art as to how the several forms of the
invention may be embodied in practice.
[0012] In the drawings:
[0013] FIG. 1 is a side view of an exemplary, prior art, LOE;
[0014] FIGS. 2A and 2B illustrate desired reflectance and
transmittance characteristics of selectively reflecting surfaces,
used in the present invention, for two ranges of incident
angles;
[0015] FIG. 3 illustrates a reflectance curve as a function of the
incident angle for an exemplary dielectric coating;
[0016] FIG. 4 is a schematic diagram illustrating a detailed
sectional view of an exemplary array of selectively reflective
surfaces;
[0017] FIG. 5 illustrates a prior art eyeglass HMD device;
[0018] FIG. 6 illustrates a side view of an LOE showing light waves
scattered from an eye and coupled back into the LOE;
[0019] FIG. 7 illustrates a reflectance curve as a function of the
wavelength for a specific partially reflecting surface;
[0020] FIG. 8 illustrates a reflectance curve as a function of the
wavelength for another partially reflecting surface;
[0021] FIG. 9 illustrates reflectance curves as a function of the
incident angle for two different partially reflecting surfaces;
[0022] FIG. 10 illustrates a side view of an LOE, showing light
waves coupled out through an exit aperture, which are scattered
from the eye and coupled back into the LOE;
[0023] FIG. 11 illustrates a side view of an LOE, showing light
waves which are scattered from an eye and coupled back into the
LOE, wherein only part of the rays are coupled out through an exit
aperture;
[0024] FIG. 12 illustrates reflectance curves as a function of the
wavelength for a reflection filter at two different incident
angles;
[0025] FIG. 13 illustrates reflectance curves as a function of the
wavelength for a transmission filter at two different incident
angles;
[0026] FIG. 14 illustrates an optical system combining light waves
from a display source and a light source;
[0027] FIG. 15 illustrates a reflectance curve as a function of the
wavelength for a polarizing beam splitter, and
[0028] FIG. 16 illustrates a side view of still another embodiment
of an LOE having two adjacent partially reflecting surfaces for
coupling out light waves into the viewer's eye.
[0029] FIG. 17 illustrates a side view of another embodiment of an
LOE having two separate coupling in elements.
[0030] FIG. 18 illustrates a reflective pattern of the polarizing
beam splitter of FIG. 17.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0031] FIG. 1 illustrates a sectional view of a prior art substrate
20 and associated components (hereinafter also "an LOE"),
utilizable in the present invention. An optical means, e.g., a
reflecting surface 16, is illuminated by a collimated display 18,
emanating from a light source (not shown) located behind the LOE.
The reflecting surface 16 reflects incident light from the source,
such that the light is trapped inside a planar substrate 20 of the
LOE, by total internal reflection. After several reflections off
the major lower and upper surfaces 26, 27 of the substrate 20, the
trapped waves reach an array of selective reflecting surfaces 22,
which couple the light out of the substrate into an eye 24, having
a pupil 25, of a viewer. Herein, the input surface of the LOE will
be regarded as the surface through which the input waves enter the
LOE and the output surface of the LOE will be regarded as the
surface through which the trapped waves exit the LOE. In the case
of the LOE illustrated in FIG. 1, both the input and the output
surfaces are on the lower surface 26. Other configurations,
however, are envisioned in which the input and the image waves
could be located on opposite sides of the substrate 20. Assuming
that the central wave of the source is coupled out of the substrate
20 in a direction normal to the substrate surface 26, the
reflecting surfaces 22 are flat, and the off-axis angle of the
coupled waves inside the substrate 20 is .alpha..sub.in, then the
angle .alpha..sub.sur2 between the reflecting surfaces and the
normal to the substrate plane is:
.alpha. sur 2 = .alpha. in 2 . ( 1 ) ##EQU00001##
[0032] As seen in FIGS. 1 and 2A, the trapped rays arrive at the
reflecting surfaces from two distinct directions 28, 30. In this
particular embodiment, the trapped rays arrive at the reflecting
surface from one of these directions 28 after an even number of
reflections from the substrate surfaces 26 and 27, wherein the
incident angle .beta..sub.ref (see FIG. 2A) between the trapped ray
and the normal to the reflecting surface is:
.beta. ref = 90 .degree. - ( .alpha. in - .alpha. sur 2 ) = 90
.degree. - .alpha. in 2 . ( 2 ) ##EQU00002##
[0033] The trapped rays arrive at the reflecting surface from the
second direction 30 after an odd number of reflections from the
substrate surfaces 26 and 27, where the off-axis angle is a
.alpha.'.sub.in=180.degree.-.alpha..sub.in and the incident angle
between the trapped ray and the normal to the reflecting surface is
as indicated in FIG. 2B:
.beta. ref ' = 90 .degree. - ( .alpha. in ' - .alpha. sur 2 ) = 90
.degree. - ( 180 .degree. - .alpha. in - .alpha. sur 2 ) = - 90
.degree. + 3 .alpha. in 2 . ( 3 ) ##EQU00003##
[0034] As further illustrated in FIG. 1, for each reflecting
surface, each ray first arrives at the surface from the direction
30, wherein some of the rays again impinge on the surface from
direction 28. In order to prevent undesired reflections and ghost
images, it is important that the reflectance be negligible for the
rays that impinge on the surface having the second direction
28.
[0035] A solution for this requirement that exploits the angular
sensitivity of thin film coatings was previously proposed in the
Publications referred-to above. The desired discrimination between
the two incident directions can be achieved if one angle is
significantly smaller than the other one. It is possible to provide
a coating with very low reflectance at high incident angles, and a
high reflectance for low incident angles. This property can be
exploited to prevent undesired reflections and ghost images by
eliminating the reflectance in one of the two directions. For
example choosing .beta..sub.ref.about.25.degree., then it can be
calculated that:
.beta.'.sub.ref=105.degree.;.alpha..sub.in=50.degree.;.alpha.'.sub.in=13-
0.degree.;.alpha..sub.sur2=25.degree.. (4)
[0036] If a reflecting surface is now determined for which
.beta.'.sub.ref is not reflected but .beta..sub.ref is, then the
desired condition is achieved.
[0037] Referring now specifically to FIGS. 2A and 2B, these figures
illustrate desired reflectance behavior of selectively reflecting
surfaces. While the ray 32 (FIG. 2A), having an off-axis angle of
.beta..sub.ref.about.25.degree., is partially reflected and is
coupled out of the substrate 34, the ray 36 (FIG. 2B), which
arrives at an off-axis angle of .beta..sub.ref'.about.75.degree. to
the reflecting surface (which is equivalent to
.beta..sub.ref'.about.105.degree., is transmitted through the
reflecting surface 34, without any notable reflection. An LOE is
usually exploited not only for a single wave, but for an optical
system having a wide FOV. Assuming a system having a FOV of
30.degree. and an LOE having a refractive index of 1.517, then the
FOV inside the substrate is .about.20.degree.. As a result, there
are two angular regions which are defined for this specific LOE: a
first region of 75.degree..+-.10.degree. where .beta.'.sub.ref is
located, and a second region of 25.degree..+-.10.degree. where
.beta..sub.ref is located.
[0038] FIG. 3 illustrates the reflectance curve of a typical
partially reflecting surface of this specific LOE, as a function of
the incident angle for S-polarized light with the wavelength
.lamda.=550 nm. For a full-color display, similar reflectance
curves should be achieved for all the other wavelengths in the
photopic region. There are two significant regions in this graph:
between 65.degree. and 85.degree., where the reflectance is very
low, and between 10.degree. and 40.degree., where the reflectance
increases monotonically with increasing incident angles. Hence, as
long as, for a given FOV and for a given spectral region, it can
ensured that the entire angular spectrum of .beta.'.sub.ref, where
very low reflections are desired, will be located inside the first
region, while the entire angular spectrum of .beta..sub.ref, where
higher reflections are required, will be located inside the second
region, the reflection into the viewer's eye of an embodiment
having only one substrate can be ensured, thus ensuring a
ghost-free image.
[0039] FIG. 4 is a schematic sectional view of an array of
selectively reflecting surfaces which couple light rays trapped
inside the substrate out and into an eye of a viewer. As can be
seen, in each cycle, the coupled rays pass through reflecting
surfaces 38, having a direction of .alpha.'.sub.in=130.degree.,
whereby the angle between the rays and the normal to the reflecting
surfaces, is .about.75.degree., and the reflections from these
surfaces are negligible. In addition, in each cycle, the rays 39
pass through the reflecting surface 22 twice in a direction of
.alpha..sub.in=50.degree., where the incident angle is 25.degree.
and part of the energy of the ray is coupled out of the
substrate.
[0040] In general, all the potential configurations of the LOEs
considered in the Publications referred-to above, offer several
important advantages over alternative compact optics for display
applications, which include that:
[0041] 1) the input display source can be located very close to the
substrate, so that the overall optical system is compact and
lightweight, offering an unparalleled form-factor;
[0042] 2) in contrast to other compact display configurations, the
LOE technology offers flexibility as to location of the input
display source relative to the eyepiece. This flexibility, combined
with the ability to locate the display source close to the
expanding substrate, alleviates the need to use an off-axis optical
configuration that is common to other display systems. In addition,
since the input aperture of the LOE is much smaller than the active
area of the output aperture, the numerical aperture of the
collimating lens is much smaller than required for a comparable
conventional imaging system. Consequently, a significantly more
convenient optical system can be implemented and the many
difficulties associated with off-axis optics and high
numerical-aperture lenses, such as field or chromatic aberrations,
can be compensated-for relatively easily and efficiently;
[0043] 3) the reflectance coefficients of the selectively
reflecting surfaces in the present invention, are essentially
identical over the entire relevant spectrum. Hence, both
monochromatic and polychromatic light sources may be used as
display sources. The LOE has a negligible wavelength-dependence,
ensuring high-quality color images with high resolutions;
[0044] 4) since each point from the input image is transformed into
a plane light wave that is reflected into the eye of a viewer from
a large part of the reflecting array, the tolerances on the exact
location of the eye can be significantly relaxed. As such, the
viewer can see the entire FOV, and the EMB can be significantly
larger than in other compact display configurations, and
[0045] 5) since a large part of the intensity from the display
source is coupled into the substrate, and since a large portion of
this coupled energy is "recycled" and coupled out into an eye of a
viewer, a display of comparatively high brightness can be achieved
even with display sources having low-power consumption.
[0046] FIG. 5 illustrates a prior art embodiment in which the LOE
is embedded in eyeglass frames 40. The display source 42 and the
collimating device 44, which includes a light waves folding
element, are assembled inside arm portions 46 of the eyeglass
frames 40 next to the edge of the LOE. In a case where the display
source is an electronic element, such as a small CRT, LCD or OLED,
driving electronics 48 for the display source, may be assembled
with the back portion of the arm 46. A handheld unit 50 comprising
a power supply, a video source and control interface is connected
to arm 46 by a cable 52, which is used for transmitting power,
video signals, audio signals and control commands. Earphones can
also be installed in the eyeglasses to enable the exploitation of
audio channels. The handheld unit 50 can be a portable DVD, a
cellular phone, a mobile TV receiver, a video games console, a
portable media player, or any other mobile display device. The unit
50 is referred to as "handheld", since it is usually operated by
the user's hand, but it can be any other portable device, and it
can be affixed to the user's belt or located in a pocket, a pouch,
a purse or hung on the user's neck. In addition to the components
which are embedded in the eyeglass frame, a miniature video camera
54 with, optional optical zoom capability, can be installed e.g.,
in the front region of the frame 40. The camera captures images
from the external scene, transfers the video signal to an
image-processing unit 56, which can be installed inside the
electronics unit 48, and controlled in real-time by the user. The
processed image signal is then transferred to the display source 42
which projects the image through the LOE into the eye of a viewer.
Other potential elements that can be installed on the frame are a
GPS receiver, an orientation sensor and a coordinate position
sensor, wherein the processor 56 receiving an input from these
sensors is providing a visually sensible output for displaying on
the eyeglass.
[0047] Some of the current HMD technology uses head position
measurements to approximate line-of-sight, which may cause
significant disparity between what a viewer is intended to look at,
and what the viewer is actually looking at, as a result of at least
.+-.20.degree. eye movement. Therefore, it is necessary to
integrate eyeball tracking capability into HMDs in some
applications. Eyeball tracking is the process of measuring either
the point of gaze or the motion of an eye relative to the head. An
eyeball tracker is a device for measuring eye positions and eye
movement. The most popular method for operating this device is by
utilizing an optical method for measuring eye motion. Light from an
external source, typically infrared, is reflected from the eye and
sensed by a video camera, or some other specially designed optical
sensors. The information is then analyzed to extract eye rotation
from changes in reflections. Video-based eye trackers typically use
corneal reflection and the center of the pupil as features to track
over time. As a result, an HMD-eyeball tracker integrated system
would be able to display stereoscopic virtual images as would a
classical HMD, and also be able to track the `direction of gaze` of
a viewer.
[0048] In accordance with the present invention, it would be
advantageous to physically combine the two optical units, the HMD
and the eyeball tracker. Moreover, it would be beneficial to
utilize the same LOE for projecting the light from the display
source into a viewer's eye, as described above, as well as for
illuminating the eye with light from the eye tracker source, and to
collect light which reflects from the eye into the detector. These
two optical units should work properly without interfering with
each other. To achieve this goal, two main characteristics of the
combined optical system are exploited in the present invention: a
separate partially reflecting surface or facet, dedicated for
transferring light from a light source to the inspected eye and
backwards, and a light having a wavelength substantially different
from the photopic region utilized for the eye tracking.
[0049] FIG. 6 schematically illustrates how one of the surfaces of
an LOE can be utilized to illuminate the viewer's eye 24 for
eye-tracking purposes. As illustrated, light rays from an eyeball
tracker 64 having a wavelength of .lamda.tr, which is substantially
different than the photopic region, usually in the near IR region
and preferably at the range of 850-900 nm, are coupled into the LOE
by total internal reflection through the light waves coupling
surface 16. In this embodiment, the input and the image waves are
located on opposite sides of the LOE. The light waves are
coupled-out of the LOE by the partially reflecting surface 22a and
are directed to illuminate the viewer's eye 24. After reflecting
from the eye 24, rays 60 and 62 are coupled back into the LOE by
the same partially reflecting surface 22a and then coupled-out of
the LOE by the surface 16, back into the eye tracker 64, wherein
light waves are imaged by a detector 66, which analyzes the
incoming rays to track the position of the eye-pupil 25.
[0050] In order to avoid ghost images, it is important that only
one of the facets of the surfaces of the LOE (partially reflecting
surface 22a in the shown Figure) will reflect light waves in the
range of about .lamda.ir. Otherwise, light waves from other
surfaces will also be reflected from the eye and cause a noise on
the detector 66, thus severely degrading the quality of the imaged
eyeball. In addition, reflecting surface 22a should be transparent
to the photopic range in the relevant angular spectra of the LOE,
in the lower region, as well as the upper one.
[0051] FIGS. 7 and 8 illustrate the reflectance curve of partially
reflecting surfaces 22a and 22b, respectively, at incident angles
of 35.degree. and 75.degree. as a function of the wavelength. As
shown in FIG. 7, reflecting surface 22a reflects light waves having
a wavelength of 850 nm with a reflectance of 20% at an incident
angle of 35.degree., while it is actually transparent for the
entire photopic range at both incident angles. At an incident angle
of 35.degree., reflecting surface 22b partially reflects the light
waves in the photopic range while it is actually transparent at an
incident angle of 75.degree. in the photopic range, as well as at
both angles, in the region of 850 nm.
[0052] FIG. 9 illustrates the reflectance curve of partially
reflecting surfaces 22a and 22b at a wavelength of 550 nm as a
function of the incident angle. As illustrated, for surface 22b
there are two significant regions in this graph: between 65.degree.
and 85.degree., where the reflectance is very low, and between
10.degree. and 40.degree., where the reflectance increases
monotonically with increasing incident angles, as required for the
regular operation of an LOE. For partially reflecting surface 22a
the reflectance is negligible at both lower and higher relevant
angular regions. The actual interpretation of FIGS. 7 to 9 is that
reflecting surface 22a is solely dedicated for eyeball tracking and
does not at all interfere with the usual operation of the LOE at
the photopic region. In addition, reflecting surface 22b is
substantially transparent to the spectral region of around 850 nm,
and hence, does not interfere with the optical operation of eyeball
tracking. All the other partially reflecting surfaces are designed
to behave in a similar manner to that of reflecting surface 22b.
That is, the other facets are also transparent to the spectral
region of 850 nm and have optical performance in the photopic
region, as required by the optical design of the LOE acting as a
combiner for HMD.
[0053] Another problem that should be addressed is the possibility
that a ghost image might also for a single surface. As illustrated
in FIG. 10, two different rays from a single point in the eye 24
are imaged through the LOE. Their optical behavior is, however,
different: while ray 68 is reflected only once from each of the
external surfaces 28 and 30 of the LOE, the ray 70 is reflected
twice from each surface. As a result, these two rays have different
optical pathways from partially reflecting surface 22a to
reflecting surface 16, and hence, they cannot be utilized together
to form the image of wavelength .lamda.out at the detector 66.
Therefore, the rays that are reflected twice from the external
surfaces 28, 30 must be blocked from the detector 66.
[0054] FIG. 11 illustrates how a spatial filter 72 which is located
at the reflecting surface 16, blocks these undesired rays. That is,
ray 74 is no longer reflected by surface 16 via tracker 64 into the
detector 66, but rather continues to propagate inside the
substrate, and is eventually absorbed at the edges of the LOE. In
order to avoid disturbance for the incoming light waves from the
display source which creates the image that is projected by the LOE
into a viewer's eye, it is important that the filter 72 should be
transparent to the light waves having a wavelength of .lamda.tr,
while still being reflective to the photopic range.
[0055] FIG. 12 illustrates the reflectance curve of the filter 72
as a function of the wavelength at incident angles of 15.degree.
and 35.degree.. As illustrated, the filter is highly reflective for
the photopic range, while it is substantially transparent for the
spectral range around 850 nm.
[0056] The embodiments described above with regard to the
reflecting surface 16 are examples of a method for coupling the
input waves into the substrate. Input waves could, however, also be
coupled into the substrate by other optical means, including, but
not limited to, folding prisms, fiber optic bundles, diffraction
gratings, and other solutions. In some of these methods, which were
described in the Publications referred to above, the input surface
of the LOE is not a reflecting surface but rather a transparent
aperture. In these cases, it is required that the filter will be
reflective to light waves having a wavelength of .lamda.tr, while
still transparent to the photopic range.
[0057] FIG. 13 illustrates the reflectance curve of filter 72 as a
function of the wavelength at incident angles of 15.degree. and
35.degree.. As illustrated, the filter 72 is substantially
transparent for the photopic range, while it is reflective for the
spectral range of about 850 nm.
[0058] The combination of a display source with a light source for
illuminating an eye tracker utilizing light waves having a
wavelength of .lamda.tr, is illustrated in FIG. 14. As shown, the
s-polarized input light waves 80 emanating from the light source 78
and having wavelengths inside the photopic spectrum, are reflected
by a reflective dichroic surface 82, e.g., a beam splitter,
associated with a light guide 83, and are then coupled into a light
guide 84 of a combiner 85, usually composed of a light waves
transmitting material, through its lower surface 86. Following
reflection of the light waves off of a polarizing beam splitter 88,
the light waves are coupled out of the light guide 84 through
surface 90. The light waves which illuminate bright pixels of the
Liquid Crystal on Silicon (LCOS) 92 then pass through a dynamic
quarter-wavelength retardation plate 94, reflected by a reflecting
surface of the LCOS 92, return to pass again through the
retardation plate 94, and re-enter the light-guide 84 through
surface 90. The now p-polarized light waves pass through the
polarizing beam splitter 88 and are coupled out of the light guide
84 through surface 96. The light waves then pass through a second
quarter-wavelength retardation plate 98, collimated by a component
100, e.g., a lens, at its reflecting surface 102, return to pass
again through the retardation plate 98, and re-enter the
light-guide 84 through surface 96. The now s-polarized light-waves
reflect off the polarizing beam splitter 88 and exit the light
guide through the upper surface 104 of the combiner 85. In
addition, s-polarized input light waves 106 having wavelengths of
the light illuminating source 107, located in the eyeball tracker
108 and have an optical spectrum different than the photopic
spectrum, preferably, in the near IR region, pass through the
dichroic surface 82, are coupled into a light guide 84, pass
directly through the polarizing beam splitter 88 and are then
coupled out of the light-guide 84 through the upper surface 104.
For the relevant angular spectrum, the dichroic surface 82 has high
reflectance for the photopic spectrum and high transmittance for
the spectrum of the light waves 106.
[0059] The two spectrally separated s-polarized input light waves
80 and 106 are now coupled through the reflecting surface 16 of the
LOE, by total internal reflection. The light waves 80 are utilized
for forming a virtual image projected by partially reflecting
surfaces 22a-22e into a viewer's eye 24, while the light waves 106
are utilized to illuminate the eye 24 for eye-tracking. The light
waves 106 having the wavelength of .lamda.tr, are reflected from
the eye 24 coupled again into the LOE by the partially reflecting
surface 22a, coupled out from the LOE through reflecting surface
16, and as seen, pass again through the polarizing beam splitter 88
and through the dichroic surface 82, and coupled into the eyeball
tracker 108, where they are focused onto the detector 110.
[0060] FIG. 15 illustrates the reflectance pattern of the
polarizing beam splitter 88 of FIG. 14. As shown, the beam splitter
88 has high and low reflectance, for the s- and p-polarization,
respectively, in the photopic range, while having high
transmittance for the s-polarized light having a wavelength of
.lamda.tr.
[0061] In all the configurations described so far, the optical
reflecting 16 is utilized to couple light waves from the display
source having wavelengths in the photopic range, as well as light
waves from the eyeball tracker 108 having wavelength of .lamda.tr,
into the LOE, by total internal reflection. There are, however,
configurations wherein different coupling elements are utilized to
couple separately the light waves from the display source and the
light waves from the eyeball tracker. These configuration include,
but are not limited to, two different elements wherein the first
one is substantially transparent for the photopic range, while it
is reflective for the spectral range wavelength of Air, and the
second element is substantially transparent for the spectral range
wavelength of .lamda.tr, while it is reflective for photopic
range.
[0062] In all the configurations described so far, the two
partially reflecting surfaces, 22a and 22b, are laterally
separated. However, there are configurations wherein, for the sake
of compactness or for enlarging the EMB of the optical system, it
is required that the two surfaces will be adjacent to each
other.
[0063] FIG. 16 illustrates a first partially reflecting surface 22a
which is coated on the surface directed to one side of substrate
20, and a second partially reflecting surface 22b which is coated
on the surface directed towards the other side of substrate 20. The
two surfaces are optically attached and laterally separated by a
cement layer 112. Typically, the thickness of the cement layer 112
is in the order of 10 .mu.m, hence, the two surfaces can be
considered as being optically disposed in one location. As
illustrated, two different rays 116, 118 from the eyeball tracker
108 and the display source 92, respectively, (see FIG. 14) are
coupled into the substrate 20 by the coupling reflecting surface 16
and then coupled out of the substrate 20 towards the viewer's eye
24 by partially reflecting surfaces 22a and 22b, respectively.
[0064] In all the hereinbefore described embodiments, the light
waves from the eyeball tracker, as well as from the display source,
are coupled into the substrate by the same coupling-in element.
However, there are embodiments wherein, for the sake of simplicity
or because of geometrical constraints, it is required that the
eyeball tracker and the display source will be separated, and
hence, the two different light waves will impinge on the substrate
at two different locations.
[0065] FIG. 17 illustrates a system wherein the optical waves 116
and 118 from the eyeball tracker 120 and the display source 122,
are separately coupled into the substrate 20 by two different
coupling-in elements, 124 and 126, respectively. While the
coupling-in element 124 is a simple reflecting surface, the
coupling-in element 126 is a dichroic beam splitter. It is assumed
that the angle between the surfaces 124 and 126 and the major
surface 26 of the substrate 20 is about 30.degree..
[0066] FIG. 18 illustrates a reflection pattern of the polarizing
beam splitter 126 of FIG. 17. As shown, the beam splitter 126 has
high reflectance for the s-polarization in the photopic range at an
incident angle of 30.degree., while having high transmittance for
the s-polarized light having a wavelength of .lamda.tr at the same
angle. As a result, light waves 116, having a wavelength of
.lamda.tr, are coupled into the substrate by the reflecting surface
124 and then pass through the element 126 with negligible
interference.
[0067] In some of methods described in the prior art Publications
referred to above, the input surface of the LOE is not a reflecting
surface, but rather a transparent aperture. In these cases, it is
required that the second aperture will be reflective to light waves
having a wavelength of .lamda.tr while still being transparent to
the photopic range.
[0068] So far, it was assumed that the main purpose of the eyeball
tracker is to measure eye positions and eye movements. When,
however, an eyelid of a viewer's eye is closed, the pattern of the
optical waves which are reflected from the eye, is significantly
changed. The eyeball tracker can easily detect if a viewer's eyelid
is open or closed. Since the LOE-based eyeglasses illustrated in
FIG. 5 have a see-through capability, it is possible to utilize
same for automotive applications where they can potentially assist
a drive in driving and in navigation tasks, or can project a
thermal image in the driver's eyes during low-visibility
conditions. In addition to these tasks, the LOE-based eyeglasses,
combined with an eyeball tracker, can also serve as a drowsy driver
alert unit, that is, the eyeball tracker device can detect the
driver's blinking patterns and determine how long the driver's eyes
stay closed between blinks. Hence, the system can conclude that the
driver is no longer alert and provide a warning concerning this
situation.
* * * * *