U.S. patent application number 17/640004 was filed with the patent office on 2022-08-25 for optical system.
The applicant listed for this patent is Lumus Ltd.. Invention is credited to Ronen CHRIKI, Yochay DANZIGER, Shimon GRABARNIK, Eitan RONEN, Elad SHARLIN.
Application Number | 20220269098 17/640004 |
Document ID | / |
Family ID | |
Filed Date | 2022-08-25 |
United States Patent
Application |
20220269098 |
Kind Code |
A1 |
DANZIGER; Yochay ; et
al. |
August 25, 2022 |
Optical System
Abstract
An optical system employs a waveguide including a first set of
partially-reflecting surfaces ("facets") for progressively
redirecting image illumination propagating from a coupling-in
region towards a second region, and a second set of facets in the
second region for progressively coupling-out the redirected image
illumination towards the eye of a viewer. The first set of facets
includes at least a first facet close to the coupling-in region, a
third facet fare from the coupling-in region, and a second facet
located on a medial plane between the first and the third facets.
The second facet is located in a subregion of the medial plane such
that image illumination propagating from the coupling-in region to
the third facet passes through the medial plane without passing
through the second facet.
Inventors: |
DANZIGER; Yochay; (Kfar
Vradim, IL) ; GRABARNIK; Shimon; (Rehovot, IL)
; CHRIKI; Ronen; (Lod, IL) ; RONEN; Eitan;
(Rehovot, IL) ; SHARLIN; Elad; (Mishmar David,
IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Lumus Ltd. |
Ness Ziona |
|
IL |
|
|
Appl. No.: |
17/640004 |
Filed: |
August 23, 2021 |
PCT Filed: |
August 23, 2021 |
PCT NO: |
PCT/IL2021/051034 |
371 Date: |
March 3, 2022 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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63069059 |
Aug 23, 2020 |
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63072174 |
Aug 30, 2020 |
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63076971 |
Sep 11, 2020 |
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International
Class: |
G02B 27/14 20060101
G02B027/14; G02B 27/01 20060101 G02B027/01 |
Claims
1. An optical system for directing image illumination injected at a
coupling-in region to an eye-motion box for viewing by an eye of a
user, the optical system comprising a light-guide optical element
(LOE) formed from transparent material, said LOE comprising: (a) a
first region containing a first set of planar, mutually-parallel,
partially-reflecting surfaces having a first orientation; (b) a
second region containing a second set of planar, mutually-parallel,
partially-reflecting surfaces having a second orientation
non-parallel to said first orientation; (c) a set of
mutually-parallel major external surfaces, said major external
surfaces extending across said first and second regions such that
both said first set of partially-reflecting surfaces and said
second set of partially-reflecting surfaces are located between
said major external surfaces, wherein said second set of
partially-reflecting surfaces are at an oblique angle to said major
external surfaces so that a part of image illumination propagating
within said LOE by internal reflection at said major external
surfaces from said first region into said second region is coupled
out of said LOE towards the eye-motion box, and wherein said first
set of partially-reflecting surfaces are oriented so that a part of
image illumination propagating within said LOE by internal
reflection at said major external surfaces from said coupling-in
region is deflected towards said second region, wherein said first
set of partially-reflecting surfaces comprises a first
partially-reflecting surface proximal to the coupling-in region so
as to contribute to a first part of a field of view of the user as
viewed at the eye-motion box, a third partially-reflecting surface
distal to the coupling-in region so as to contribute to a third
part of a field of view of the user as viewed at the eye-motion
box, and a second partially-reflecting surface lying in a medial
plane between said first and said third partially-reflecting
surfaces so as to contribute to a second part of a field of view of
the user as viewed at the eye-motion box, wherein said second
partially-reflecting surface is deployed in a subregion of said
medial plane such that image illumination propagating from said
coupling-in region to said third partially-reflecting surface and
contributing to the third part of the field of view of the user as
viewed at the eye-motion box passes through said medial plane
without passing through said second partially-reflecting
surface.
2. The optical system of claim 1, wherein said coupling-in region
comprises a coupling-in prism having a first planar surface that is
a continuation of one of said major external surfaces in said first
region, said coupling-in prism having a thickness dimension
measured perpendicular to said major external surfaces that is
greater than a thickness of said LOE.
3. The optical system of claim 2, wherein said coupling-in prism
presents a coupling-in surface and a transition line between said
coupling-in prism as said LOE, said coupling-in surface defining an
optical aperture of said coupling-in prism in a dimension parallel
to said major external surfaces and said transition line defining
an optical aperture of said coupling-in prism in a dimension
perpendicular to said major external surfaces.
4. The optical system of claim 2, wherein said first set of
partially-reflecting surfaces further comprises at least one
partially-reflecting surface located within a volume of said
coupling-in prism.
5. An optical system for directing image illumination injected at a
coupling-in region to an eye-motion box for viewing by an eye of a
user, the optical system comprising a light-guide optical element
(LOE) formed from transparent material, said LOE comprising: (a) a
first region containing a first set of planar, mutually-parallel,
partially-reflecting surfaces having a first orientation; (b) a
second region containing a second set of planar, mutually-parallel,
partially-reflecting surfaces having a second orientation
non-parallel to said first orientation; (c) a set of
mutually-parallel major external surfaces, said major external
surfaces extending across said first and second regions such that
both said first set of partially-reflecting surfaces and said
second set of partially-reflecting surfaces are located between
said major external surfaces, wherein said second set of
partially-reflecting surfaces are at an oblique angle to said major
external surfaces so that a part of image illumination propagating
within said LOE by internal reflection at said major external
surfaces from said first region into said second region is coupled
out of said LOE towards the eye-motion box, and wherein said first
set of partially-reflecting surfaces are oriented so that a part of
image illumination propagating within said LOE by internal
reflection at said major external surfaces from said coupling-in
region is deflected towards said second region, wherein said
coupling-in region comprises a coupling-in prism having a first
planar surface that is a continuation of one of said major external
surfaces in said first region, said coupling-in prism having a
thickness dimension measured perpendicular to said major external
surfaces that is greater than a thickness of said LOE, and wherein
said coupling-in prism presents a coupling-in surface and a
transition line between said coupling-in prism as said LOE, said
coupling-in surface defining an optical aperture of said
coupling-in prism in a dimension parallel to said major external
surfaces and said transition line defining an optical aperture of
said coupling-in prism in a dimension perpendicular to said major
external surfaces.
6. The optical system of claim 5, wherein said first set of
partially-reflecting surfaces further comprises at least one
partially-reflecting surface located within a volume of said
coupling-in prism.
7. An optical system for directing image illumination injected at a
coupling-in region to an eye-motion box for viewing by an eye of a
user, the optical system comprising a light-guide optical element
(LOE) formed from transparent material, said LOE comprising: (a) a
first region containing a first set of planar, mutually-parallel,
partially-reflecting surfaces having a first orientation; (b) a
second region containing a second set of planar, mutually-parallel,
partially-reflecting surfaces having a second orientation
non-parallel to said first orientation; (c) a set of
mutually-parallel major external surfaces, said major external
surfaces extending across said first and second regions such that
both said first set of partially-reflecting surfaces and said
second set of partially-reflecting surfaces are located between
said major external surfaces, wherein said second set of
partially-reflecting surfaces are at an oblique angle to said major
external surfaces so that a part of image illumination propagating
within said LOE by internal reflection at said major external
surfaces from said first region into said second region is coupled
out of said LOE towards the eye-motion box, and wherein said first
set of partially-reflecting surfaces are oriented so that a part of
image illumination propagating within said LOE by internal
reflection at said major external surfaces from said coupling-in
region is deflected towards said second region, wherein said
coupling-in region comprises a coupling-in prism having a first
planar surface that is a continuation of one of said major external
surfaces in said first region, said coupling-in prism having a
thickness dimension measured perpendicular to said major external
surfaces that is greater than a thickness of said LOE, and wherein
said first set of partially-reflecting surfaces further comprises
at least one partially-reflecting surface located within a volume
of said coupling-in prism.
8. The optical system of claim 7, wherein said coupling-in prism
presents a coupling-in surface and a transition line between said
coupling-in prism as said LOE, said coupling-in surface defining an
optical aperture of said coupling-in prism in a dimension parallel
to said major external surfaces and said transition line defining
an optical aperture of said coupling-in prism in a dimension
perpendicular to said major external surfaces.
9. The optical system of claim 2, wherein said coupling-in prism is
bonded to said LOE at an edge surface of said LOE.
10. The optical system of claim 2, wherein said coupling-in prism
is bonded to one of said major external surfaces of said LOE.
11. The optical system of claim 3, wherein said coupling-in prism
is bonded to said LOE at an edge surface of said LOE.
12. The optical system of claim 3, wherein said coupling-in prism
is bonded to one of said major external surfaces of said LOE.
13. The optical system of claim 4, wherein said coupling-in prism
is bonded to said LOE at an edge surface of said LOE.
14. The optical system of claim 4, wherein said coupling-in prism
is bonded to one of said major external surfaces of said LOE
15. The optical system of claim 5, wherein said coupling-in prism
is bonded to said LOE at an edge surface of said LOE.
16. The optical system of claim 5, wherein said coupling-in prism
is bonded to one of said major external surfaces of said LOE.
17. The optical system of claim 6, wherein said coupling-in prism
is bonded to said LOE at an edge surface of said LOE.
18. The optical system of claim 6, wherein said coupling-in prism
is bonded to one of said major external surfaces of said LOE.
19. The optical system of claim 7, wherein said coupling-in prism
is bonded to said LOE at an edge surface of said LOE.
20. The optical system of claim 7, wherein said coupling-in prism
is bonded to one of said major external surfaces of said LOE.
Description
FIELD AND BACKGROUND OF THE INVENTION
[0001] The present invention relates to optical systems and, in
particular, it concerns an optical system for two-dimensional
expansion of an image from an image projector for display to a
user.
[0002] A near eye display optical engine is shown in FIG. 1A,
including an image projector 200 that projects image light having
an angular field through transmissive coupling prism 202T and
through vertical aperture 203V into waveguide 204. The light
propagates in the waveguide, being reflected by total internal
reflection. Partial reflectors 206 embedded in the waveguide
reflect the image out of the waveguide (dashed arrows) towards the
observer having eyeball center 208.
[0003] FIG. 1B shows an alternative way of coupling into the
waveguide by using reflective coupling prism 202R having mirror on
its back side.
[0004] FIG. 1C shows schematically a front view of a 2D aperture
expansion waveguide. Here image projector 200 injects an image
through coupling prism 202 through lateral aperture 203L (203V is
also present, but not visible from this orientation) into waveguide
204. The image light ray 220A propagates laterally in the waveguide
as it reflects by TIR between the waveguide faces. Here two sets of
facets are used: set 206L expand the aperture laterally by
reflecting the guided image progressively to a different guided
direction 220B while facets set 206V expand the aperture vertically
by progressively coupling the image out from area 210 on the
waveguide onto the observer's eye.
SUMMARY OF THE INVENTION
[0005] The present invention is an optical system for directing
image illumination injected at a coupling-in region to an
eye-motion box for viewing by a user.
[0006] According to the teachings of an embodiment of the present
invention there is provided, an optical system for directing image
illumination injected at a coupling-in region to an eye-motion box
for viewing by an eye of a user, the optical system comprising a
light-guide optical element (LOE) formed from transparent material,
the LOE comprising: (a) a first region containing a first set of
planar, mutually-parallel, partially-reflecting surfaces having a
first orientation; (b) a second region containing a second set of
planar, mutually-parallel, partially-reflecting surfaces having a
second orientation non-parallel to the first orientation; (c) a set
of mutually-parallel major external surfaces, the major external
surfaces extending across the first and second regions such that
both the first set of partially-reflecting surfaces and the second
set of partially-reflecting surfaces are located between the major
external surfaces, wherein the second set of partially-reflecting
surfaces are at an oblique angle to the major external surfaces so
that a part of image illumination propagating within the LOE by
internal reflection at the major external surfaces from the first
region into the second region is coupled out of the LOE towards the
eye-motion box, and wherein the first set of partially-reflecting
surfaces are oriented so that a part of image illumination
propagating within the LOE by internal reflection at the major
external surfaces from the coupling-in region is deflected towards
the second region, wherein the first set of partially-reflecting
surfaces comprises a first partially-reflecting surface proximal to
the coupling-in region so as to contribute to a first part of a
field of view of the user as viewed at the eye-motion box, a third
partially-reflecting surface distal to the coupling-in region so as
to contribute to a third part of a field of view of the user as
viewed at the eye-motion box, and a second partially-reflecting
surface lying in a medial plane between the first and the third
partially-reflecting surfaces so as to contribute to a second part
of a field of view of the user as viewed at the eye-motion box,
wherein the second partially-reflecting surface is deployed in a
subregion of the medial plane such that image illumination
propagating from the coupling-in region to the third
partially-reflecting surface and contributing to the third part of
the field of view of the user as viewed at the eye-motion box
passes through the medial plane without passing through the second
partially-reflecting surface.
[0007] According to a further feature of an embodiment of the
present invention, the coupling-in region comprises a coupling-in
prism having a first planar surface that is a continuation of one
of the major external surfaces in the first region, the coupling-in
prism having a thickness dimension measured perpendicular to the
major external surfaces that is greater than a thickness of the
LOE.
[0008] According to a further feature of an embodiment of the
present invention, the coupling-in prism presents a coupling-in
surface and a transition line between the coupling-in prism as the
LOE, the coupling-in surface defining an optical aperture of the
coupling-in prism in a dimension parallel to the major external
surfaces and the transition line defining an optical aperture of
the coupling-in prism in a dimension perpendicular to the major
external surfaces.
[0009] According to a further feature of an embodiment of the
present invention, the first set of partially-reflecting surfaces
further comprises at least one partially-reflecting surface located
within a volume of the coupling-in prism.
[0010] There is also provided according to the teachings of an
embodiment of the present invention, an optical system for
directing image illumination injected at a coupling-in region to an
eye-motion box for viewing by an eye of a user, the optical system
comprising a light-guide optical element (LOE) formed from
transparent material, the LOE comprising: (a) a first region
containing a first set of planar, mutually-parallel,
partially-reflecting surfaces having a first orientation; (b) a
second region containing a second set of planar, mutually-parallel,
partially-reflecting surfaces having a second orientation
non-parallel to the first orientation; (c) a set of
mutually-parallel major external surfaces, the major external
surfaces extending across the first and second regions such that
both the first set of partially-reflecting surfaces and the second
set of partially-reflecting surfaces are located between the major
external surfaces, wherein the second set of partially-reflecting
surfaces are at an oblique angle to the major external surfaces so
that a part of image illumination propagating within the LOE by
internal reflection at the major external surfaces from the first
region into the second region is coupled out of the LOE towards the
eye-motion box, and wherein the first set of partially-reflecting
surfaces are oriented so that a part of image illumination
propagating within the LOE by internal reflection at the major
external surfaces from the coupling-in region is deflected towards
the second region, wherein the coupling-in region comprises a
coupling-in prism having a first planar surface that is a
continuation of one of the major external surfaces in the first
region, the coupling-in prism having a thickness dimension measured
perpendicular to the major external surfaces that is greater than a
thickness of the LOE, and wherein the coupling-in prism presents a
coupling-in surface and a transition line between the coupling-in
prism as the LOE, the coupling-in surface defining an optical
aperture of the coupling-in prism in a dimension parallel to the
major external surfaces and the transition line defining an optical
aperture of the coupling-in prism in a dimension perpendicular to
the major external surfaces.
[0011] According to a further feature of an embodiment of the
present invention, the first set of partially-reflecting surfaces
further comprises at least one partially-reflecting surface located
within a volume of the coupling-in prism.
[0012] There is also provided according to the teachings of an
embodiment of the present invention, an optical system for
directing image illumination injected at a coupling-in region to an
eye-motion box for viewing by an eye of a user, the optical system
comprising a light-guide optical element (LOE) formed from
transparent material, the LOE comprising: (a) a first region
containing a first set of planar, mutually-parallel,
partially-reflecting surfaces having a first orientation; (b) a
second region containing a second set of planar, mutually-parallel,
partially-reflecting surfaces having a second orientation
non-parallel to the first orientation; (c) a set of
mutually-parallel major external surfaces, the major external
surfaces extending across the first and second regions such that
both the first set of partially-reflecting surfaces and the second
set of partially-reflecting surfaces are located between the major
external surfaces, wherein the second set of partially-reflecting
surfaces are at an oblique angle to the major external surfaces so
that a part of image illumination propagating within the LOE by
internal reflection at the major external surfaces from the first
region into the second region is coupled out of the LOE towards the
eye-motion box, and wherein the first set of partially-reflecting
surfaces are oriented so that a part of image illumination
propagating within the LOE by internal reflection at the major
external surfaces from the coupling-in region is deflected towards
the second region, wherein the coupling-in region comprises a
coupling-in prism having a first planar surface that is a
continuation of one of the major external surfaces in the first
region, the coupling-in prism having a thickness dimension measured
perpendicular to the major external surfaces that is greater than a
thickness of the LOE, and wherein the first set of
partially-reflecting surfaces further comprises at least one
partially-reflecting surface located within a volume of the
coupling-in prism.
[0013] According to a further feature of an embodiment of the
present invention, the coupling-in prism presents a coupling-in
surface and a transition line between the coupling-in prism as the
LOE, the coupling-in surface defining an optical aperture of the
coupling-in prism in a dimension parallel to the major external
surfaces and the transition line defining an optical aperture of
the coupling-in prism in a dimension perpendicular to the major
external surfaces.
[0014] According to a further feature of an embodiment of the
present invention, the coupling-in prism is bonded to the LOE at an
edge surface of the LOE. Alternatively, the coupling-in prism may
be bonded to one of the major external surfaces of the LOE.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The invention is herein described, by way of example only,
with reference to the accompanying drawings, wherein:
[0016] FIGS. 1A and 1B, described above, are schematic side views
of a conventional near-eye waveguide-based display illustrating two
geometries for coupling-in of image illumination into the
waveguide;
[0017] FIG. 1C, described above, is a front view of a conventional
near-eye waveguide-based display illustrating the use of first and
second sets of partially-reflecting internal surfaces to expand an
optical aperture of an image projector in two dimensions;
[0018] FIG. 1D is a schematic isometric view of a waveguide similar
to that of FIG. 1C and corresponding to FIG. 5A of publication WO
2020/049542 A1;
[0019] FIGS. 2A-2C are isometric, top and side views, respectively,
of an angular representation of the image propagation through an
optical system according to the teachings of the present
invention;
[0020] FIG. 3A is a schematic front view of a light-guide optical
element (LOE, or waveguide), constructed and operative according to
the teachings of an aspect of the present invention, illustrating
propagation of image illumination from a coupling-in region to a
first set of partially-reflecting surfaces (facets), and from the
first set of facets to a second set of facets;
[0021] FIG. 3B is a view similar to FIG. 3A illustrating a
theoretical locus of facet locations required for providing a field
of view (FOV) to a single viewing point;
[0022] FIG. 3C is a view similar to FIG. 3B illustrating a
corresponding set of loci for facet locations to provide a FOV
across an "eye-motion box" (EMB) of permitted viewing
locations;
[0023] FIG. 3D is a view similar to FIG. 3A illustrating the
required facet positions and dimensions in order to span the loci
illustrated in FIG. 3C;
[0024] FIG. 3E is a view similar to FIG. 3C where the loci are
further increased according to the geometrical requirements
resulting from using an obliquely-angled first set of facets;
[0025] FIG. 3F is a schematic representation of the LOE of FIG. 3D
where the facet-containing regions are demarcated by corresponding
polygons, with the first set of facets demarcated by a concave
polygon;
[0026] FIG. 3G is a view similar to FIG. 3F in which the concave
polygon containing the first set of facets is subdivided into a
number of non-concave blocks or slices;
[0027] FIG. 3H is a schematic isometric view illustrating how such
blocks can be assembled to produce the structure of FIG. 3G, for
subsequent slicing to form a plurality of LOEs;
[0028] FIG. 4A is a view similar to FIG. 3A illustrating exemplary
dimensions for an implementation generating a rectangular field of
view with angular dimensions as illustrated in FIG. 4B;
[0029] FIG. 4C is a view similar to FIG. 3A illustrating exemplary
dimensions for an implementation generating a trapezoidal field of
view with angular dimensions as illustrated in FIG. 4D;
[0030] FIG. 5A is a view similar to FIG. 4A illustrating an image
projector and a coupling-in prism for introducing image
illumination into the LOE;
[0031] FIG. 5B is a schematic isometric view of the coupling-in
prism of FIG. 5A;
[0032] FIG. 5C is a side view of the coupling-in prism of FIG. 5A
illustrating the required dimensions for an exemplary
implementation of the present invention;
[0033] FIG. 5D illustrates a variant implementation of the present
invention employing a coupling-in prism which is attached to a
major external surface of the LOE;
[0034] FIG. 6A is a schematic front view similar to FIG. 5A
illustrating the use of an integrated laser-scanning image
projector integrated with a coupling-in prism;
[0035] FIG. 6B is a schematic side view of the integrated
laser-scanning image projector integrated with a coupling-in prism
of FIG. 6A;
[0036] FIG. 7A is a schematic side view of a coupling-in
arrangement employing an inclined reflector coupling arrangement
and a coupling-in prism, and employing external collimating
optics;
[0037] FIG. 7B is a view similar to FIG. 7A in which the inclined
reflector coupling arrangement and the coupling-in prism are
combined and reduced in size;
[0038] FIG. 7C is a view similar to FIG. 7A employing a polarized
beam splitter and integrating reflective collimating optics into
the reflective coupling-in arrangement;
[0039] FIG. 7D is a view similar to FIG. 7C but using external
collimating optics;
[0040] FIG. 8A is a view similar to FIG. 5A, but where a
coupling-in prism is integrated with part of the waveguide;
[0041] FIG. 8B is a schematic isometric view of the coupling-in
prism of FIG. 8A;
[0042] FIG. 9A is a schematic side view of the coupling-in prism of
FIG. 8A implemented as a coupling-in prism bonded to the LOE at an
edge surface of the LOE;
[0043] FIGS. 9B and 9C are schematic isometric views of the
coupling-in prism of FIG. 9A showing inclusion of full or partial
partially-reflective facets, respectively, within the prism;
[0044] FIG. 9D is a schematic side view of the coupling-in prism of
FIG. 8A implemented as a coupling-in prism bonded to one of the
major external surfaces of the LOE;
[0045] FIGS. 9E and 9F are schematic isometric views of the
coupling-in prism of FIG. 9D showing inclusion of full or partial
partially-reflective facets, respectively, within the prism;
[0046] FIG. 10A is a side view of an angular representation similar
to FIG. 2C illustrating two specific points within a field of view
of the projected image;
[0047] FIG. 10B is a partial view similar to FIG. 4A illustrating
the image light propagation paths corresponding to the two points
of FIG. 10A;
[0048] FIGS. 10C and 10D are side views of a coupling-in prism
indicating the injection angle of these two field point,
respectively, and the corresponding desired location of the first
reflective facet they should encounter;
[0049] FIGS. 11A-11C are views similar to FIGS. 7A, 7C and 7D,
respectively, illustrating implementations of these geometries with
partially-reflective facets within the coupling prisms;
[0050] FIG. 11D is a view similar to FIG. 6B illustrating an
implementation of this geometry with partially-reflective facets
within the coupling prism;
[0051] FIG. 12A is a schematic isometric view of a series of plates
with selectively-deployed partially-reflecting coatings, each
according to a pattern required for a different plane of the LOE of
FIG. 3D, for assembly according to a production method of the
present invention;
[0052] FIG. 12B is a schematic isometric view of a stack of plates
formed by bonding together the series of plates of FIG. 12A;
[0053] FIG. 12C is a schematic isometric view of a block formed by
slicing the stack of FIG. 12B along the indicated dashed lines;
[0054] FIG. 12D is a schematic isometric view of (a part of) an LOE
formed by slicing the block of FIG. 12C along the indicated dashed
lines;
[0055] FIG. 13 is a schematic side view of a coupling-in
configuration employing an air gap and a mirror surface;
[0056] FIGS. 14A and 14B are views similar to FIGS. 2A and 2C,
respectively, showing the image propagation through the optical
system in the case of an obliquely oriented first set of
partially-reflecting surfaces;
[0057] FIG. 14C is a view similar to FIG. 3F for an implementation
of the LOE optimized for the image propagation described in FIGS.
14A and 14B;
[0058] FIG. 15 is a schematic side view of a side coupling-in
configuration employing a beam-splitter to fill the waveguide with
the injected image and its conjugate;
[0059] FIG. 16A is a side view of an angular representation of the
image propagation through the second region of an LOE according to
a variant implementation of the present invention employing a
high-inclination second set of partially-reflecting surfaces;
[0060] FIG. 16B is a schematic side view of the second region of
the LOE implemented according to the optical geometry of FIG.
16A;
[0061] FIG. 16C is a graph indicating schematically the preferred
angle dependence of reflectance of the facets for the
implementation of FIG. 16B;
[0062] FIG. 17A is a schematic isometric view of a plate with
selectively-deployed partially-reflecting coatings, similar to the
plates of FIG. 12A;
[0063] FIG. 17B is an enlarged schematic side view illustrating a
coated region implemented with an abrupt edge;
[0064] FIG. 17C is a schematic illustration of the use of a raised
mask to generate a coating with a marginal region of
gradually-varying thickness;
[0065] FIG. 17D is a schematic illustration of the use of the
principle of FIG. 17C to deposit a multi-layer coating with a
marginal region of gradually-varying thickness;
[0066] FIG. 17E is a schematic illustration of the use of a second
raised mask to generate a complementary transparent coating in
regions not coated by the first process; and
[0067] FIG. 17F is a schematic side view illustrating a
partially-reflecting region resulting from the sequence of coating
processes described with reference to FIGS. 17D and 17E.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0068] The present invention is an optical system for directing
image illumination injected at a coupling-in region to an
eye-motion box for viewing by a user.
[0069] By way of introduction, in the context of near-eye displays
of the sort illustrated in FIG. 1C, it has been found that
particularly advantageous geometrical properties, and in
particular, minimization of the dimensions required for a given
angular field of view, may be provided by injecting image
illumination into the waveguide at "shallow angles", meaning that
all of the image illumination is incident on only one side of both
the first and the second sets of facets. Typically, in shallow
angle implementations, at least part of each image lies within
about 15 degrees, and more preferably within about 10 degrees, from
the plane of the external surfaces of the waveguide. This results
in a shortened light path from the image projector to the
observer's eye, and hence also enables reduced size of the optical
components for a given angular field of view. The present invention
relates to a number of aspects which facilitate shallow-angle
implementations of such a display, which presents certain design
challenges, particularly with regard to coupling-in configurations.
It should be noted, however, that various aspects of the invention
described herein are not limited to shallow-angle implementations,
and may also be applicable to other implementations.
[0070] FIGS. 2A-2C show an angular polar representation of an image
as it propagates in the waveguide according to present invention.
FIG. 2A shows an isometric view, FIG. 2C a side view and FIG. 2B
shows a top view (relative to FIG. 2A) that corresponds to the view
from the front of the waveguide.
[0071] The waveguide has total-internal-reflection (TIR) boundary
circles 228, indicating that images within these circles are not
subject to TIR, and will be coupled-out so as to escape the
waveguide.
[0072] Image 220A1 is coupled into the waveguide and propagates by
TIR back and forth to 220A2. These images propagate along a very
shallow trajectory along the waveguide where the shallowest part of
the image is only 7 degrees from the waveguide plane (shown as
angle 221 in FIG. 2C). Facets 224 (equivalent to 206L of FIG. 1C)
in this implementation are perpendicular to the waveguide, and
therefore reflect images 220A1 and 220A2 directly onto 220B1 and
220B2, respectively. Images 220B1 and 220B2 are coupled by TIR as
they propagate down the waveguide. In the second portion of the
LOE, facets 226 (equivalent to 206V in FIG. 1C) couple image 220B2
out of the waveguide onto image 220C towards the observer.
[0073] By way of one non-limiting example, the illustrations shown
herein relate primarily to an image having aspect of 4:3 and
diagonal field of 70 degrees injected into a waveguide having
refractive index on 1.6. The design illustrated here generates a
full image at an eyeball center 35 mm away from the waveguide
(including eye-relief, eyeball-radius and margins). Adaptations of
these implementations for different fields of view and aspect
ratios can readily be implemented by a person ordinarily skilled in
the art on the basis of the description herein.
[0074] One aspect of the present invention relates to optimization
of deployment of partially-reflecting surfaces (or "facets") in the
first part of the waveguide responsible for the first dimension of
optical aperture expansion. In an earlier patent application
published as WO 2020/049542 A1 ("the '542 publication"), it has
been suggested to deploy facets selectively within an envelope
encompassing the facets which are needed for delivering image
illumination to the eye-motion box from which the image is to be
viewed.
[0075] An example of the resulting deployment of facets is
illustrated in FIG. 5A of that publication, which is reproduced
here as FIG. 1D. In that implementation, an optical system for
directing image illumination injected at a coupling-in region 15 to
an eye-motion box 26 for viewing by an eye of a user employs a
light-guide optical element (LOE) 12 formed from transparent
material having a first region 16 containing a first set of planar,
mutually-parallel, partially-reflecting surfaces 17 having a first
orientation, and a second region 18 containing a second set of
planar, mutually-parallel, partially-reflecting surfaces 19 having
a second orientation non-parallel to the first orientation. A set
of mutually-parallel major external surfaces 24 extend across the
first and second regions such that both the first set of
partially-reflecting surfaces and the second set of
partially-reflecting surfaces are located between the major
external surfaces. The second set of partially-reflecting surfaces
19 are at an oblique angle to the major external surfaces 24 so
that a part of image illumination propagating within the LOE by
internal reflection at the major external surfaces from the first
region into the second region is coupled out of the LOE from a
coupling-out region 28 towards the eye-motion box 26. The first set
of partially-reflecting surfaces 17 are oriented so that a part of
image illumination propagating within the LOE by internal
reflection at the major external surfaces from the coupling-in
region is deflected towards the second region.
[0076] According to the teachings of the '542 publication, certain
parts of the first region 16 of the LOE outside the envelope of
useful facets are implemented as an optical continuum (i.e.,
without partially reflecting internal surfaces), thereby reducing
unwanted "ghost" reflections. Within the convex polygonal envelope,
however, the facets are implemented as filling the entire width of
the convex polygon, as illustrated in the drawing. As a result, the
part of the field of view reflected from the facets located on the
side distal from the coupling-in region pass through a long series
of partially-reflecting facets before reaching the facets which
deliver that part of the field of view to the eye-motion box.
[0077] According to one aspect of the present invention, the
regions of facets required to deliver a given field of view to the
eye-motion box is further refined to generate a concave polygon
defining the required facet locations, thereby removing parts of
the intermediate facets which would otherwise unnecessarily
attenuate the image illumination directed to provide the part of
the field reflected by facets furthest from the coupling-in
region.
[0078] Thus, as illustrated in FIG. 3D, the first set of
partially-reflecting surfaces, here labeled 206L, includes a first
partially-reflecting surface 17A proximal to the coupling-in region
240 so as to contribute to a first part of a field of view (FOV) of
the user as viewed at the eye-motion box, a third
partially-reflecting surface 17C distal to the coupling-in region
so as to contribute to a third part of the FOV of the user as
viewed at the eye-motion box, and a second partially-reflecting
surface 17B lying in a medial plane 22 between the first and the
third partially-reflecting surfaces so as to contribute to a second
part of the FOV of the user as viewed at the eye-motion box. In the
example illustrated in FIG. 3D, facet 17A contributes to the right
side of the FOV, facet 17C contributes to the left side of the FOV,
and facet 17B contributes to the central region of the FOV. It is a
particular feature of this aspect of the present invention that the
second partially-reflecting surface 17B is deployed in a subregion
of the medial plane 22 such that image illumination propagating
from the coupling-in region to the third partially-reflecting
surface (arrow 23) and contributing to the third part of the field
of view of the user as viewed at the eye-motion box passes through
the medial plane 22 without passing through the second
partially-reflecting surface 17B.
[0079] In this context, it should be noted that the terms
"proximal", "distal" and "medial" are used herein to denote
relative position with respect to a point or region of interest, in
this case the coupling-in region 240, and refer to facets which are
relatively closer (proximal) to, or relatively further (distal)
from, the coupling-in region, or which are "towards the middle"
(medial), without necessarily denoting the closest, furthest or
central facet according to any specific geometrical definition.
[0080] A conceptual explanation will now be provided in order to
facilitate a better understanding of the geometrical optics
considerations which lead to the preferred design parameters for a
given implementation of this aspect of the present invention. It
should be noted that this explanation is given for informational
purposes only, but that the utility of the invention as claimed is
not dependent on the accuracy of any aspect of this explanation,
and that effective and advantageous implementations of the claimed
invention may alternatively be implemented by empirical
methods.
[0081] FIG. 3A shows front view of few selected beams of the
projected image having parameters corresponding to the exemplary
FOV mentioned above. Solid lines represent beam of an image
injected into the waveguide laterally and dashed lines represent
beams after lateral aperture expansion and reflection as they
propagate vertically. It should be noted throughout this document
that any example describing lateral expansion followed by vertical
expansion can be changed to vertical expansion followed by lateral
without inherent change in structure. This can be exemplified
simply by rotating the above figures by 90 degrees.
[0082] All beams are transmitted from entrance pupil of the
coupling-in region 240. The beams propagate within the waveguide
until being reflected by set of parallel embedded reflectors 206L
(facets). The facets in this diagram are assumed to be
perpendicular to the external faces of the waveguide. Therefore,
every line (solid followed by dashed) represents a different
lateral section of the projected image field onto the observer's
eye. The vertical field of every section is illuminated by
plurality of overlapping beams (as viewed from front) propagating
at different angles inclination (into the page) that are reflected
by TIR (such internal reflection being illustrated in the side view
of FIG. 1A).
[0083] For the purpose of simplifying the geometrical analysis,
assume first that only the eyeball center 208 needs to be
illuminated with the entire lateral field. This can theoretically
be achieved by having infinitely small lateral facts 206L placed
infinitely close to each other along the trajectory represented as
244A in FIG. 3B. However, the requirement to accommodate lateral
shifting of the eyeball center (for example due to variation of
interpupillary distance between users) dictates a shift of curve
244A. FIG. 3C shows schematically the curve for three lateral
positions of the eyeball 208 as 244A, 244B and 244C. To cover the
required width of the eye-motion box, widening of the facets is
required.
[0084] Other requirements include:
[0085] There is a finite minimum distance between the facets (i.e.,
they cannot be infinitely close); The aperture size cannot be too
small; The facets must project continuous reflections towards the
vertical expansion facets 206V.
[0086] FIG. 3D shows the finite size facets 206L appropriate for
the above conditions. The length of the facets can vary according
to the facet spacing and other optical parameters such as
refractive index, the size of the projected field and the location
of image injection 240.
[0087] In the case where the lateral expanding facets 206L are at
an oblique angle to the major external surfaces of the LOE, the
image is injected into the waveguide rotated relative to the axes
of the waveguide, and the reflection from facets 206L rotates the
image to the required orientation. Consequently, the curve for
projecting onto the center of eyeball 208 will look like FIG. 3C,
and when additionally considering the spread required for the
lateral eye-motion box, it will look like FIG. 3E, that shows
further multiplication of curves 244A, 244B and 244C. This
therefore requires somewhat wider facets than a corresponding
implementation with orthogonal facets for the first expansion.
[0088] Certain advantages of this aspect of the present invention
can be better appreciated with reference to FIG. 3F. The area of
the lateral expanding facets is described at SL while the area of
the `depression` above it is SD and the vertical expanding facets
area is SV. Due to the concave polygon form of SL, the light
propagating laterally from the entrance 240, propagates mostly in
transparent area SD before being reflected downward in SL. The
propagation in a transparent area reduces the loss of image
illumination by reflection to undesired directions, thereby
improving waveguide efficiency. Furthermore, there are no undesired
reflections of the scenery by facets from SD, thereby substantially
reducing glints and ghost images from the waveguide.
[0089] One possible method for producing the lateral expansion
section SL with `depression` SD is shown in FIGS. 3G and 3H. The
sections including SD and SL are subdivided into blocks as
indicated by heavy outlines in the region designate 300 in FIG. 3G.
FIG. 3H illustrates how this structure can be assembled from a
transparent prism 302 having appropriate face angles together with
three plates having appropriate facet angles (shown as lines along
the plates) that fit together against the corresponding surfaces of
prism 302 and against each other to form the assembled structure as
illustrated. This structure is combined with additional clear
prisms and the vertical-expansion portion of the LOE to generate
the overall structure.
[0090] Optionally, the combined prism and plates can be sliced, or
can first be attached to another stack to be sliced together to
generate the waveguide with all its sections.
[0091] The size of the waveguide as described above is shown in
FIG. 4A, resulting in an image field angular size as shown in FIG.
4B. It is noted that the most laterally-spread beams 250 illuminate
only the lower corners of the image, thereby requiring a large
waveguide area while contributing only to a small part of the
image. In certain applications, it may be acceptable, or even
advantageous, to provide a non-rectangular FOV, and in particular,
a trapezoid image field, as illustrated in FIG. 4D. In this case,
there is shown an image which has the same total area as FIG. 4B
(which is shown with dashed lines in FIG. 4D for comparison), but
distributed as a trapezoid, with a wider field at the top than at
the bottom. The LOE to generate this FOV is illustrated in FIG. 4C,
with corresponding dimensions. In this case, lateral edge light
beams 252 illuminate vertically all the field (with corresponding
different angles into the paper), therefore making much more
efficient use of the LOE size. Consequently, the size of the
waveguide of FIG. 4C is substantially smaller than that of FIG. 4A,
as illustrated by the exemplary dimensions for the same overall FOV
area. The subsequent description with illustrate further aspects of
the invention in the non-limiting exemplary context of the
configuration of FIG. 4A, but it should be appreciated that
configurations such as that of FIG. 4C may be implemented using the
same principles.
[0092] Injecting a shallow image into a waveguide requires a
relatively large coupling prism 202. FIG. 5A shows the waveguide
with lateral entrance pupil 203L and coupling prism 202M to scale.
The image projector 200 is illustrated schematically. FIG. 5B is an
isometric view of the coupling prism 202M with vertical aperture
203T and lateral aperture 203L, both located at same plane so as to
define a rectangular aperture. FIG. 5C illustrates a side view of
coupling prism 202M which, for a 1.7 mm thick waveguide, requires a
14 mm-long coupling prism designed to couple light from all field
angles into the waveguide. Part of the beams 262 are reflected from
the bottom of the prism before entering through pupil 203V into
waveguide 204. The height of prism 202M above the waveguide is 6.4
mm, which is acceptable in many applications. However, the size of
projector 200 that is need to inject the image through prism 202M
also takes space and volume and, in many applications, will not be
acceptable.
[0093] The prism 202M (and others described herein) preferably has
a lower face that is parallel to the waveguide faces for consistent
reflection, while the upper and side faces do not need specific
optical properties, so their shapes can be other than the ones
shown in these figures.
[0094] FIG. 5D illustrates an alternative architecture where a
coupling prism 202L is located above the waveguide, and where the
entrance pupil is the prism face 264. In this case, the prism and
the required projector are larger than in FIGS. 5A-5C, making this
configuration non-optimal.
[0095] One option for reducing the overall dimensions of the
coupling arrangement and image projector is illustrated in FIGS. 6A
and 6B, which illustrate integration of the image projector with
the coupling prism. A scanning laser image projector is illustrated
here by way of a non-limiting example, but the same principles can
be implemented using an image projector based on another type of
image generator, such as employing an LCOS (liquid crystal on
silicon) spatial light modulator, or a micro-LED image
generator.
[0096] FIG. 6A shows a coupling prism 202P attached to waveguide
204. FIG. 6B shows a side view of the integrated (embedded) image
projector. Laser 270 directs a polarized beam onto scanning mirrors
272 that scan intermediate image plane across a micro-lens array
(MLA) or diffuser 274. The scanned light passes through the
diffuser and is reflected from polarizing-beam-splitter 276 onto
collimating reflecting lens 278 (combined with a quarter-wave
plate). The reflected light passes through PBS 276 into coupling
prism 202P. This coupling prism thus serves also as part of the PBS
276. Part of the light passes directly into the waveguide and part
is reflected by the lower face 279 before entering the waveguide,
thereby filling the aperture of the waveguide with both the image
and its conjugate.
[0097] Parenthetically, wherever a PBS arrangement is illustrated
herein as sequentially reflecting and then transmitting light, or
the reverse, it will be understood that a half-wave plate (for
single transmission) or a quarter-wave plate (for double
transmission) is appropriately placed to achieve rotation of the
polarization as required for the functionality described. The
polarization-rotating elements will not be mentioned in each
case.
[0098] Alternative architectures for combining the image projector
with the coupling prism are shown in FIGS. 7A-7D. FIG. 7A shows
light from image generator (not shown, but as before, may be a
scanned laser, LCOS or other) being collimated by a refractive lens
280 (beams in diagram from different fields points therefore not
parallel), entering prism section 282 and being reflected by mirror
284 into prism section 202Q and into waveguide 204. In this
configuration, prism sections 282 and 202Q can be combined to a
single prism, as illustrated in FIG. 7B. Furthermore, there is no
need for the light to be polarized in this case.
[0099] The structure of FIG. 7B employs an equivalent reflector
architecture to FIG. 7A, but with smaller prism. Here the prism
length is of the order of 14 mm, similar to prism 202M in FIG. 5C
for similar output parameters. However, the height will be only 3.2
mm, which is half that of 202M. As in all of the prisms described
herein, the upper (non-reflecting) face of the prism 283 is
preferably absorbing. It is drawn here according to the upper beam
260 (defined in FIG. 5C), but since the upper surface is not
optically significant, it can be higher and/or have other
shapes.
[0100] This prism can also be provided with a coupling
configuration including a lower refractive index part at its lower
face equivalent to elements 286 or 228 described below with
reference to FIGS. 7C and 7D. The interface can be used to attached
to a PBS as an image projector.
[0101] FIG. 7C shows injection of diverging polarized light
corresponding to an image (originated from a MLA, scanning laser,
LCOS or other image generator) passing through interface 286 into
PBS section 290 and reflected by PBS 292 onto reflecting
collimating lens 294. The reflected collimated light passes through
PBS 292 into coupling prism 202Q and into the waveguide 204. In
this architecture some of the light is reflected by the lower
section of prisms 290 and 202Q, therefore these surfaces need to
have good image quality and to be continuous. The interface 286 can
be air, but also a low refractive index medium (relative to prism
290), so that TIR will occur for light reflected from 294.
[0102] FIG. 7D shows an arrangement similar to FIG. 7C, but with
external optics (e.g., a refractive lens 296) that collimates the
light and a flat reflector 298.
[0103] Turning now to FIGS. 8A and 8B, these illustrate an
alternative configuration according to a further aspect of the
present invention in which a coupling prism is integrated with part
of the waveguide instead of as an extension shown in FIG. 5A. FIG.
8A shows coupling prism 202Y (dotted area) on top of waveguide 204.
Image generator 200 is therefore located closer to the waveguide
and has a smaller size. All of the light rays propagating in the
waveguide continue to emerge from point 240, therefore the lateral
aperture 203L2 is located at same place as the previous
embodiments. However, the vertical aperture 203V is here located at
the end of the prism, where the thickened portion of the prism
meets with the major external surface which defines the main
portion of the LOE. FIG. 8B shows the shape of the coupling prism
in an isometric view. The two apertures 203L2 and 203V2 have same
width as previously described but because of the separation of
location the prism becomes vertically elongated at 203L2.
[0104] It is apparent from FIG. 8A that some of the facets (here
represented as 206A and 206B) are located within the prism. A
number of possible implementations of these facets in prism 202Y
are illustrated in FIGS. 9A-9F. For clarity of presentation, the
facets lying within the main part of the LOE have been omitted
here.
[0105] FIG. 9A shows prism 202Y attached to the edge of the
waveguide, and FIG. 9B shows in isometry the placement of the
facets in the prism. However, since there is no need for the facets
to reflect light across the entire width of the prism (as can be
seen in FIG. 8A, which illustrates that the required width of
facets 206A and 206B is limited), FIG. 9C shows the reflecting
parts (shaded area) to be only a part of the corresponding plane
within the prism.
[0106] FIG. 9D shows an alternative configuration where prism 202Y
is formed by attaching a correspondingly-shaped block on top of
waveguide 204 (facets in 204 are not shown). In FIG. 9E, the same
structure is illustrated with facets across the entire
cross-section of 202Y above the LOE thickness, while in FIG. 9F,
the reflective area is implemented only as the shaded region,
corresponding to only the optimal required area.
[0107] In certain cases, it is possible to combine the
earlier-mentioned integrated image projector (FIGS. 6A-7D) together
with the LOE-integrated coupling prism of FIGS. 8A-9F. Certain
geometrical considerations in such an implementation are
illustrated with reference to FIGS. 10A-10D.
[0108] FIG. 10A shows a side view of an angular distribution
equivalent to FIG. 2C, but with markings of two field points
associated with facets 206A (circle) and 206B (square). Same field
points are shown in FIG. 10B.
[0109] FIG. 10C shows a side view of the waveguide-overlapping
coupling prism where the shaded area represents a preferred
location for the facets associated with 206A and FIG. 10D shows the
preferred location for the facets for 206B. The PBS 292 is shown
here for reference. It is apparent that the preferred location for
the facets in the overlapping coupling prism should be above the
PBS plane. Implementation of facets at before the PBS plane would
cause distortion to the transmitted image.
[0110] FIGS. 11A-11D are side views illustrating implementations of
facets to coupling prisms incorporating projector optics. FIGS.
11A, 11B and 11C show integration of facet section 202T (marked as
a shaded area) into configurations which are otherwise similar to
those of FIGS. 7A, 7C and 7D, respectively. The 3D representation
remains as was described with reference to 10A-10D.
[0111] FIG. 11D parallels FIG. 6B, and illustrates that, where the
PBS orientation is opposite, the facet section 202T2 is best
implemented only partially after the PBS plane. The coupling prism
will therefore extend slightly further outside lateral aperture
plane 203L2 (illustrated in FIGS. 8A-8B).
[0112] Parenthetically, the deployment of facets 202T2 as
illustrated in FIG. 11D will also be suitable for configurations
employing the waveguide architecture of FIGS. 4C and 4D.
[0113] Turning now to FIGS. 12A-12D, as an alternative to the
production process illustrated above with reference to FIGS. 3G-3H,
the facet patterns of FIG. 3D or 3F can be produced based on
stacking and slicing selectively-coated plates. In this case, the
plates are coated in a predefined pattern as shown in FIG. 12A,
which shows a set of plates shown from the front 300F that are
coated in predefined patterns 302F. These patters have width and
position according to required coated facets shown in 112. These
patterns are preferably produced by masking the uncoated part of
the waveguide while coating. It is also possible to coat only the
other part of the face of the plates in 304F by coating a
non-reflective coating in order to maintain flat surface or to
preserve the phase of transmitted light through 304 to be
equivalent to phase of transmitted light through 302.
[0114] FIG. 12B illustrates a stack formed by bonding together the
partially coated plates, where the dashed line shows the slicing
planes across the stack. FIG. 12C shows one slice having side view
of the plates 300S and the reflective patterns 302S. Another slice
is done as shown by the dashed lines in FIG. 12C to generate the
final upper section of FIG. 12D, corresponding to the upper part of
the LOE of FIG. 3D.
[0115] It should be noted that the order of the slicing may be
changed. It will also be appreciated that the illustrations of
FIGS. 12A-12D are highly schematic, and that a larger number of
plates are typically used.
[0116] Reducing the refractive index of the coupling prism 202M can
also be used for reducing prism size and thereby making the system
more compact. FIG. 13 illustrates an extreme case of this concept
where 202M is replaced with air-gap and mirror 310 that is in-plane
with lower waveguide plane 312. The light from projecting optics
308 is directed onto perpendicular entrance 306 to waveguide 204
and onto mirror plane 310. Because of the lower refractive index of
the air-gap, angles of the beams change and consequently the length
of the mirror is shorter than length of prism 202M. The angle of
the lower beam 262 is now 11.5 degrees instead of 7 before.
Consequently, the mirror length is now 8.5 mm instead of 14 mm in
FIG. 5C. As the beam enter the waveguide its angular distribution
is as in FIG. 5C. The mirror can overlap the waveguide for
mechanical attachment.
[0117] A conceptually-similar approach of employing low refractive
index material can be implemented using a low refractive index
glass prism. When using a low refractive index glass prism, it is
possible to compensate some of the dispersion generated by the
angle in incidence of the light entering face 306.
[0118] In the embodiments detailed thus far, the facets employed
206L employed for the first set of facets have been orthogonal to
the major external surfaces of the LOE, as detailed in FIGS. 2A-2C.
In an alternative set of embodiments illustrated with reference to
FIGS. 14A-14C, the first set of facets is implemented using
obliquely angle facets 336. FIG. 14A shows an isometric angular
representation of such system used to transmit shallow angle
images, while FIG. 14B shows a corresponding partial side view of
the angular representation. This non-limiting example employs a
trapezoidal FOV, equivalent to the image for minimal size shown in
FIGS. 4C and 4D, although this structure could clearly also be used
for a rectangular FOV.
[0119] In this architecture the initial laterally propagating image
334A1 is coupled with 334A2 by TIR reflections. Only 334A2 is
redirected towards the second region of the LOE 334B1 by tilted
facets 336, which are at an oblique angle relative to waveguide
faces. Facets 336 are preferably coated with multilayer dielectric
coatings, as is known in the art, to provide the desired degree of
partial reflectivity for the range of incident angles corresponding
to image 334A2 (as in all of the above embodiments), while being
primarily transparent to the range of incident angles corresponding
to image 334A1, so as to minimize energy losses and formation of
undesired reflections. The image 334B1 is coupled to 334B1 by TIR
as it propagates at shallow angle along the second region of the
waveguide. Image 334B2 is then coupled out to 334C by facets 338
(shown only in FIG. 14A), in a manner equivalent to facets 226 of
FIGS. 2A-2C.
[0120] FIG. 14C illustrates the waveguide footprint that is
equivalent to FIG. 4C, where shaded region 340 is the optimal area
for the first set of facets 336, and area 342 is the optimal area
for output coupling facets 338.
[0121] The various coupling-in prism arrangements described above
are configured to couple-in to the LOE both an image and its
conjugate to "fill" the waveguide with the image. An alternative
approach particularly attractive for shallow-angle image injection
into the waveguide is direct injection of image into the waveguide,
as illustrated in FIG. 15. In order to fill waveguide 370 with the
injected image and its conjugate, waveguide 370 has a coupling
region 372 that has a partial reflector 374 along a center plane of
the waveguide. The partial reflector 374 is most preferably
implemented as an 50% reflector, preferably insensitive to angle
and achromatic, such as a partially-silvered surface.
[0122] In FIG. 15, three beams are shown associated with the lowest
point in the field, and are therefore the shallowest beams of the
image illumination. The lower beam (solid arrow) passes through
collimating optics 376 and a coupling prism 378 and enters the
waveguide. After one reflection, it experiences partial reflection
by 374 and is split into two beams. The central beam (dashed line)
is split at the entrance and the top beam (dash-dot line) is split
half way along combiner 372. It is apparent that after the beams
are split (thereby splitting the image illumination between the
image and its conjugate), the waveguide is illuminated uniformly.
Therefore, uniform image is expected after light is coupled
out.
[0123] If the partial reflector 374 has 50% reflectivity and 50%
transmittance then for length equivalent to that of FIG. 5C (14 mm
in our example), the waveguide will be illuminated uniformly. In
this configuration the aperture of the illuminating optics 376 is
very small since the optics is almost adjacent to the entrance of
the waveguide, resulting in a small thickness of the optical
assembly.
[0124] Turning now to FIGS. 16A-16C, this illustrates an
alternative scheme for coupling-out of the image in the second
region of the LOE toward the eye-motion box for viewing by the eye
of the user. The angular representation of FIG. 16A is similar to
FIG. 2C, but in this case, the output coupling facets 390 have a
steep angle. As a result, image 220B1 is coupled out to 220C
(instead of 220B1 as in FIG. 2C). In this configuration, the images
220B can be taller and are not limited by the angle of the facets
390.
[0125] FIG. 16B shows schematically how such a configuration looks
in real space. As the beam propagates downward (in this drawing),
it is partially reflected by the facets downward out of the
waveguide. In such a configuration it is preferable to have the
facets closely spaced in order to ensure a uniform image.
[0126] FIG. 16C shows schematically the preferred reflectivity of
facets for such configuration. Here, low reflectivity is desired at
the low incidence angles (close to perpendicular) and higher
reflectivity (for output coupling) at higher angles. Here too, such
properties are readily achieved using appropriately designed
multilayer dielectric coatings, as is well-known in the art.
[0127] Turning now to FIGS. 17A-17F, various of the preferred
embodiments described herein require partial selective application
of reflective coatings on only part of a plate which is then
assembled into a stack from which part or all of the LOE is then
sliced. Partial coating of facets as illustrated in FIG. 17A could
potentially introduce scattering effects at the edges of the
coating, due to the physical discontinuity in coating as
illustrated in schematic cross section in FIG. 17B. Additionally,
this mechanical discontinuity may cause mechanical stress on the
plates when stacked (as in FIG. 12B). FIGS. 17C-17F illustrate a
preferred production method according to an aspect of the present
invention for overcoming these limitations.
[0128] FIG. 17C illustrates the principles of coating
characteristics when a mask 394 is placed close to plate surface
300F but slightly spaced from the surface. When implementing
coating (thick arrow), it will coat the plate where there is no
mask but close to the mask a gradual decree in coating thickness
will be generated around the edge of the mask 396. FIG. 17D
illustrates schematically how this characteristic can be used to
generate a gradual decrease ("tail-off") of the coating pattern
302F at the periphery of the desired region.
[0129] For thin coating thickness, this configuration of gradual
thinning of the coating may be sufficient. For thicker coatings, it
may be advantageous to use a second mask over the region 302F (FIG.
17E) and to apply a complimentary transparent coating 98 beside the
reflecting area 302F, as illustrated in FIG. 17F. It is noted that
the mask of FIG. 17E is typically not the exact inverse of the mask
of FIG. 17D, since it is preferably increased around the boundary
by an amount corresponding to the tailing-off region (which can be
determined empirically).
[0130] It will be appreciated that the above descriptions are
intended only to serve as examples, and that many other embodiments
are possible within the scope of the present invention as defined
in the appended claims.
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