U.S. patent application number 17/663322 was filed with the patent office on 2022-09-08 for evacuated periotic structures and methods of manufacturing.
This patent application is currently assigned to DigiLens Inc.. The applicant listed for this patent is DigiLens Inc.. Invention is credited to Shibu Abraham, Michiel Koen Callens, Alastair John Grant, Baeddan George Hill, Tsung-Jui Ho, Hyesog Lee, Milan Momcilo Popovich, Jonathan David Waldern.
Application Number | 20220283378 17/663322 |
Document ID | / |
Family ID | 1000006333806 |
Filed Date | 2022-09-08 |
United States Patent
Application |
20220283378 |
Kind Code |
A1 |
Waldern; Jonathan David ; et
al. |
September 8, 2022 |
Evacuated Periotic Structures and Methods of Manufacturing
Abstract
Improvements to gratings for use in waveguides and methods of
producing them are described herein. Deep surface relief gratings
(SRGs) may offer many advantages over conventional SRGs, an
important one being a higher S-diffraction efficiency. In one
embodiment, deep SRGs can be implemented as polymer surface relief
gratings or evacuated periodic structures (EPSs). EPSs can be
formed by first recording a holographic polymer dispersed liquid
crystal (HPDLC) periodic structure. Removing the liquid crystal
from the cured periodic structure provides a polymer surface relief
grating. Polymer surface relief gratings have many applications
including for use in waveguide-based displays.
Inventors: |
Waldern; Jonathan David;
(Los Altos Hills, CA) ; Grant; Alastair John; (San
Jose, CA) ; Popovich; Milan Momcilo; (Leicester,
GB) ; Abraham; Shibu; (Sunnyvale, CA) ; Hill;
Baeddan George; (Sunnyvale, CA) ; Ho; Tsung-Jui;
(Sunnyvale, CA) ; Callens; Michiel Koen;
(Sunnyvale, CA) ; Lee; Hyesog; (Sunnyvale,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DigiLens Inc. |
Sunnyvale |
CA |
US |
|
|
Assignee: |
DigiLens Inc.
Sunnyvale
CA
|
Family ID: |
1000006333806 |
Appl. No.: |
17/663322 |
Filed: |
May 13, 2022 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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17653818 |
Mar 7, 2022 |
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17663322 |
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63223311 |
Jul 19, 2021 |
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63174401 |
Apr 13, 2021 |
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63157467 |
Mar 5, 2021 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G03H 1/0248 20130101;
G03H 2270/14 20130101; G03H 2260/33 20130101; G03H 2260/12
20130101; G03H 2270/11 20130101; G03H 2001/0264 20130101; G02B 5/32
20130101; G02B 6/34 20130101; G03H 2223/16 20130101; G02B 5/1857
20130101; G03H 1/0408 20130101; H01L 51/5293 20130101 |
International
Class: |
G02B 6/34 20060101
G02B006/34; G03H 1/04 20060101 G03H001/04; G02B 5/18 20060101
G02B005/18; G02B 5/32 20060101 G02B005/32; G03H 1/02 20060101
G03H001/02; H01L 51/52 20060101 H01L051/52 |
Claims
1. A waveguide device comprising: a waveguide supporting a polymer
grating structure for diffracting light propagating in total
internal reflection in said waveguide, wherein the polymer grating
structure comprises: a polymer regions; air gaps between adjacent
portions of the polymer regions; an optical layer disposed between
the polymer regions and the waveguide; and a coating disposed on
the tops of the polymer regions and the tops of the optical
layer.
2. The waveguide device of claim 1, wherein the coating comprises
an atomic layer deposition (ALD) deposited metallic layer or
dielectric layer to enhance evanescent coupling between the
waveguide and the polymer grating structure.
3. The waveguide device of claim 1, wherein the coating comprises
an atomic layer deposition (ALD) deposited metallic layer or
dielectric layer to enhance the effective refractive index of the
polymer grating structure.
4. The waveguide device of claim 1, wherein the coating comprises
an atomic layer deposition (ALD) deposited metallic layer or
dielectric layer to enhance adhesion and/or perform as a bias
layer.
5. The waveguide device of claim 1, wherein the coating comprises
an atomic layer deposition (ALD) conformally deposited metallic
layer or dielectric layer disposed over the entirety of the polymer
regions and the exposed tops of the optical layer.
6. The waveguide device of claim 1, wherein the coating comprises
an atomic layer deposition (ALD) deposited metallic layer or
dielectric layer disposed over one or more facets of the polymer
regions including one or more of the upper, lower, or sidewall
facets of the polymer regions.
7. The waveguide device of claim 1, wherein a passivation coating
is applied to the surfaces of the polymer grating structure.
8. The waveguide device of claim 1, wherein the polymer regions
include a slant angle with respect to the waveguide.
9. The waveguide device of claim 1, wherein the polymer grating
structure further comprises an isotropic material between adjacent
portions of the polymer network, wherein the isotropic material has
a refractive index higher or lower than the refractive index of the
polymer network.
10. The waveguide device of claim 9, wherein the isotropic material
occupies a space at a bottom portion of the space between adjacent
portions of the polymer network and the air occupies the space from
above the top surface of the isotropic material to the modulation
depth.
11. The waveguide device of claim 9, wherein the isotropic material
comprises a birefringent crystal material.
12. The waveguide device of claim 11, wherein the birefringent
crystal material comprises a liquid crystal material.
13. The waveguide device of claim 11, wherein the refractive index
difference between the polymer network and the birefringent crystal
material is 0.05 to 0.2.
14. The waveguide device of claim 1, wherein the polymer grating
structure has a modulation depth greater than a wavelength of
visible light.
15. The waveguide device of claim 1, wherein the polymer grating
structure comprises a modulation depth and a grating pitch and
wherein the modulation depth is greater than the grating pitch.
16. The waveguide device of claim 1, wherein the waveguide
comprises two substrates and the polymer grating structure is
either sandwiched between the two substrates or positioned on an
external surface of either substrate.
17. The waveguide device of claim 1, wherein the Bragg fringe
spacing of the polymer network is 0.35 .mu.m to 0.8 .mu.m and the
grating depth of the polymer network is 1 .mu.m to 3 .mu.m.
18. The waveguide device of claim 1, wherein the ratio of grating
depth of the polymer network to the Bragg fringe spacing is 1:1 to
5:1.
19. The waveguide device of claim 1, further comprising a picture
generating unit, and wherein the polymer grating structure
comprises a waveguide diffraction grating.
20. The waveguide device of claim 19, wherein the waveguide
diffraction grating is configured as a multiplexing grating.
21. The waveguide device of claim 20, wherein the waveguide
diffraction grating is configured to accept light from the picture
generating unit which includes multiple images.
22. The waveguide device of claim 21, wherein the waveguide
diffraction grating is configured to outcouple light from the
waveguide.
23. The waveguide device of claim 19, wherein the waveguide
diffraction grating is configured as a beam expander.
24. The waveguide device of claim 19, wherein the waveguide
diffraction grating is configured to incouple light including image
data generated from the picture generating unit.
25. The waveguide device of claim 24, wherein the waveguide
diffraction grating is further configured to incouple S-polarized
light with a high degree of efficiency.
26. The waveguide device of claim 25, wherein the diffraction
grating is further configured to incouple S-polarized light at an
efficiency of 70% to 95% at a Bragg angle.
27. The waveguide device of claim 25, wherein the diffraction
grating is further configured to incouple P-polarized light at an
efficiency of 25% to 50% at a Bragg angle.
28. The waveguide device of claim 1, wherein the refractive index
difference between the polymer network and the air gaps is 0.25 to
0.4.
29. The waveguide device of claim 1, wherein the polymer grating
structure comprises a two-dimensional lattice structure or a
three-dimensional lattice structure.
30. The waveguide device of claim 1, further comprising another
grating structure, wherein the polymer grating structure comprises
an incoupling grating and the other grating structure comprises a
beam expander or an outcoupling grating.
Description
CROSS-REFERENCED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 17/653,818, filed Mar. 7, 2022, which claims
priority to U.S. Provisional Application 63/157,467 filed on Mar.
5, 2021, U.S. Provisional Application 63/174,401 filed on Apr. 13,
2021, and U.S. Provisional Application 63/223,311 filed on Jul. 19,
2021, the disclosures of which are incorporated by reference in
their entirety.
FIELD OF THE DISCLOSURE
[0002] The present invention generally relates to waveguides and
methods for fabricating waveguides and more specifically to
waveguide displays containing gratings formed in a multi-component
mixture from which one material component is removed and methods
for fabricating said gratings.
BACKGROUND
[0003] Waveguides can be referred to as structures with the
capability of confining and guiding waves (i.e., restricting the
spatial region in which waves can propagate). One subclass includes
optical waveguides, which are structures that can guide
electromagnetic waves, typically those in the visible spectrum.
Waveguide structures can be designed to control the propagation
path of waves using a number of different mechanisms. For example,
planar waveguides can be designed to utilize diffraction gratings
to diffract and couple incident light into the waveguide structure
such that the in-coupled light can proceed to travel within the
planar structure via total internal reflection (TIR).
[0004] Fabrication of waveguides can include the use of material
systems that allow for the recording of holographic optical
elements within or on the surface of the waveguides. One class of
such material includes polymer dispersed liquid crystal (PDLC)
mixtures, which are mixtures containing photopolymerizable monomers
and liquid crystals. A further subclass of such mixtures includes
holographic polymer dispersed liquid crystal (HPDLC) mixtures.
Holographic optical elements, such as volume phase gratings, can be
recorded in such a liquid mixture by illuminating the material with
two mutually coherent laser beams. During the recording process,
the monomers polymerize, and the mixture undergoes a
photopolymerization-induced phase separation, creating regions
densely populated by liquid crystal (LC) micro-droplets,
interspersed with regions of clear polymer. The alternating liquid
crystal-rich and liquid crystal-depleted regions form the fringe
planes of the grating.
[0005] Waveguide optics, such as those described above, can be
considered for a range of display and sensor applications. In many
applications, waveguides containing one or more grating layers
encoding multiple optical functions can be realized using various
waveguide architectures and material systems, enabling new
innovations in near-eye displays for Augmented Reality (AR) and
Virtual Reality (VR), compact Heads Up Displays (HUDs) for aviation
and road transport, and sensors for biometric and laser radar
(LIDAR) applications. As many of these applications are directed at
consumer products, there is a growing requirement for efficient low
cost means for manufacturing holographic waveguides in large
volumes.
SUMMARY OF THE DISCLOSURE
[0006] Many embodiments are directed to polymer grating structures,
their design, methods of manufacture, and materials.
[0007] Various embodiments are directed to a method for fabricating
a periodic structure, the method including: providing a holographic
mixture on a base substrate; sandwiching the holographic mixture
between the base substrate and a cover substrate, where the
holographic mixture forms a holographic mixture layer on the base
substrate; applying holographic recording beams to the holographic
mixture layer to form a holographic polymer dispersed liquid
crystal periodic structure comprising alternating polymer rich
regions and liquid crystal rich regions; and removing the cover
substrate from the holographic polymer dispersed liquid crystal
periodic structure, wherein the cover substrate has different
properties than the base substrate to allow for the cover substrate
to adhere to the unexposed holographic mixture layer while capable
of being removed from the formed holographic polymer dispersed
liquid crystal periodic structure after exposure.
[0008] Further, various embodiments are directed to a method for
fabricating periodic structures, the method including: providing a
first holographic mixture on a first base substrate; sandwiching
the first holographic mixture between the first base substrate and
a cover substrate, where the first holographic mixture forms a
first holographic mixture layer on the first base substrate;
applying holographic recording beams to the first holographic
mixture layer to form a first holographic polymer dispersed liquid
crystal periodic structure comprising alternating polymer rich
regions and liquid crystal rich regions; removing the cover
substrate from the holographic polymer dispersed liquid crystal
periodic structure; providing a second holographic mixture on a
second base substrate; sandwiching the second holographic mixture
between the second base substrate and the cover substrate, wherein
the second holographic mixture forms a second holographic mixture
layer on the second base substrate; and applying holographic
recording beams to the second holographic mixture layer to form a
second holographic polymer dispersed liquid crystal periodic
structure comprising alternating polymer rich regions and liquid
crystal rich regions.
[0009] Further, various embodiments are directed to a device for
fabricating a deep surface relief grating (SRG) including: a
holographic mixture sandwiched between a base substrate and a cover
substrate, where the holographic mixture is configured to form a
holographic polymer dispersed liquid crystal grating comprising
alternating polymer rich regions and liquid crystal rich regions
when exposed to holographic recording beams, and where the base
substrate and the cover substrate have different properties to
allow the cover substrate to adhere to the unexposed holographic
mixture layer while capable of being removed from the formed
holographic polymer dispersed liquid crystal grating after
exposure.
[0010] Further, various embodiments are directed to a waveguide
device including: a waveguide supporting a polymer grating
structure for diffracting light propagating in total internal
reflection in said waveguide, where the polymer grating structure
includes: a polymer regions; air gaps between adjacent portions of
the polymer regions; and a coating disposed on the tops of the
polymer regions and the tops of the waveguide.
[0011] Further, various embodiments are directed to a waveguide
device including: a waveguide supporting a polymer grating
structure for diffracting light propagating in total internal
reflection in said waveguide, where the polymer grating structure
includes: a polymer regions; air gaps between adjacent portions of
the polymer regions; an optical layer disposed between the polymer
regions and the waveguide; and a coating disposed on the tops of
the polymer regions and the tops of the optical layer.
[0012] Further, various embodiments are directed to a waveguide
device including: a waveguide supporting a polymer grating
structure for diffracting light propagating in total internal
reflection in said waveguide, where the polymer grating structure
includes: a polymer regions; air gaps between adjacent portions of
the polymer regions; and an optical layer disposed between the
polymer regions and the waveguide.
[0013] Further, various embodiments are directed to a waveguide
device including: a waveguide supporting a polymer grating
structure for diffracting light propagating in total internal
reflection in said waveguide, where the polymer grating structure
includes: a polymer regions; and air gaps between adjacent portions
of the polymer regions, where the polymer regions and air gaps
directly contact the waveguide.
[0014] Further, various embodiments are directed to a method for
fabricating a grating, the method including: providing a mixture of
monomer and a nonreactive material; providing a substrate; coating
a layer of the mixture on a surface of the substrate; applying
holographic recording beams to the layer to form a holographic
polymer dispersed grating including alternating polymer rich
regions and nonreactive material rich regions; removing at least a
portion of the nonreactive material in the nonreactive material
rich regions to form a polymer surface relief grating including
alternating polymer regions and air regions; and applying a coating
to the top surfaces of the polymer regions and the top surfaces of
the substrate in the air regions.
[0015] Further, various embodiments are directed to a method for
fabricating a grating, the method including: providing a mixture of
monomer and a nonreactive material; providing a substrate; coating
a layer of the mixture on a surface of the substrate; applying
holographic recording beams to the layer to form a holographic
polymer dispersed grating including alternating polymer rich
regions and nonreactive material rich regions; removing at least a
portion of the nonreactive material in the nonreactive material
rich regions to form a polymer surface relief grating including
alternating polymer regions and air regions, wherein an optical
layer is disposed between the polymer regions and the substrate;
and applying a coating to the top surfaces of the polymer regions
and the top surfaces of the optical layer in the air regions.
[0016] Further, various embodiments are directed to a method for
fabricating a grating, the method including: providing a mixture of
monomer and a nonreactive material; providing a substrate; coating
a layer of the mixture on a surface of the substrate; applying
holographic recording beams to the layer to form a holographic
polymer dispersed grating including alternating polymer rich
regions and nonreactive material rich regions; removing at least a
portion of the nonreactive material in the nonreactive material
rich regions to form a polymer surface relief grating including
alternating polymer regions and air regions; and performing a
plasma ashing process to remove at least a portion of polymer from
the polymer regions.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The description will be more fully understood with reference
to the following figures and data graphs, which are presented as
exemplary embodiments of the invention and should not be construed
as a complete recitation of the scope of the invention.
[0018] FIG. 1A conceptually illustrates a step of a method for
fabricating a surface relief grating in which a mixture of monomer
and liquid crystal deposited on a transparent substrate is exposed
to holographic exposure beams in accordance with an embodiment of
the invention.
[0019] FIG. 1B conceptually illustrates a step of a method for
fabricating a surface relief grating from an HPDLC grating formed
on a transparent substrate in accordance with an embodiment of the
invention.
[0020] FIG. 1C conceptually illustrates a step of a method for
fabricating a surface relief grating in which liquid crystal is
removed from an HPDLC grating to form a polymer surface relief
grating in accordance with an embodiment of the invention.
[0021] FIG. 1D conceptually illustrates a step of a method for
covering a surface relief grating with a protective layer in
accordance with an embodiment of the invention.
[0022] FIG. 2 is a flow chart conceptually illustrating a method
for forming a polymer surface relief grating from an HPDLC grating
formed on a transparent substrate in accordance with an embodiment
of the invention.
[0023] FIG. 3A is an example implementation of a polymer surface
relief grating or evacuated periodic structure.
[0024] FIG. 3B illustrates a cross sectional schematic view of a
polymer-air periodic structure 3000a in accordance with an
embodiment of the invention.
[0025] FIG. 3C is a graph illustrating the effect of optical layer
thickness on the diffraction efficiency versus incident angle.
[0026] FIG. 4A conceptually illustrates a step of a method for
fabricating a surface relief grating in which a mixture of monomer
and liquid crystal deposited on a transparent substrate is exposed
to holographic exposure beams in accordance with an embodiment of
the invention.
[0027] FIG. 4B conceptually illustrates a step of a method for
fabricating a surface relief grating from an HPDLC periodic
structure formed on a transparent substrate in accordance with an
embodiment of the invention.
[0028] FIG. 4C conceptually illustrates a step of a method for
fabricating a surface relief grating in which liquid crystal is
removed from an HPDLC periodic structure to form a polymer surface
relief grating in accordance with an embodiment of the
invention.
[0029] FIG. 4D conceptually illustrates a step of a method for
fabricating a surface relief grating in which the surface relief
grating is partially refilled with liquid crystal to form a hybrid
surface relief-periodic structure in accordance with an embodiment
of the invention.
[0030] FIG. 4E conceptually illustrates a step of a method for
fabricating a surface relief grating in which a hybrid surface
relief-periodic structure is covered with a protective layer in
accordance with an embodiment of the invention.
[0031] FIG. 5 is a flow chart conceptually illustrating a method
for forming a hybrid surface relief-periodic structure in
accordance with an embodiment of the invention.
[0032] FIG. 6 is a graph showing calculated P-polarized and
S-polarized diffraction efficiency versus incidence angle for a
1-micrometer thickness deep surface relief grating in accordance
with an embodiment of the invention.
[0033] FIG. 7 is a graph showing calculated P-polarized and
S-polarized diffraction efficiency versus incidence angle for a
2-micrometer thickness deep surface relief grating in accordance
with an embodiment of the invention.
[0034] FIG. 8 is a graph showing calculated P-polarized and
S-polarized diffraction efficiency versus incidence angle for a
3-micrometer thickness deep surface relief grating in accordance
with an embodiment of the invention.
[0035] FIGS. 9A and 9B illustrate scanning electron microscope
images of multiple embodiments including different thiol
concentrations.
[0036] FIGS. 10A and 10B are images comparing an HPDLC periodic
structure and a polymer surface relief grating or evacuated
periodic structure.
[0037] FIGS. 11A and 11B are two plots comparing an HPDLC periodic
structure and a polymer surface relief grating or evacuated
periodic structure.
[0038] FIGS. 12A and 12B are two plots of S-diffraction efficiency
and P-diffraction efficiency of two example polymer surface relief
gratings with different depths.
[0039] FIGS. 13A and 13B are two different plots of S-diffraction
efficiency and P-diffraction efficiency of various example polymer
surface relief gratings produced with different initial liquid
crystal concentrations.
[0040] FIGS. 14A and 14B are two different plots of S-diffraction
efficiency and P-diffraction efficiency of various example polymer
surface relief gratings produced with different initial liquid
crystal concentrations.
[0041] FIG. 15 is a graph of diffraction efficiency versus grating
layer thickness showing the dependence of evanescent coupling on
the grating layer thickness.
[0042] FIGS. 16A-16G illustrate various stages of manufacture of a
surface relief grating implementing a cover substrate in accordance
with an embodiment of the invention.
[0043] FIG. 17 illustrates an example reaction forming a
holographic mixture layer in accordance with an embodiment of the
invention.
[0044] FIG. 18 illustrates a reaction between reagents and a base
substrate in accordance with an embodiment of the invention.
[0045] FIG. 19 illustrates a reaction between release material and
a cover substrate in accordance with an embodiment of the
invention.
[0046] FIGS. 20A and 20B illustrate various grating in accordance
with an embodiment of the invention.
[0047] FIG. 20C illustrates a grating in accordance with an
embodiment of the invention.
[0048] FIGS. 21A-21C conceptually illustrate three embodiments of
waveguides in which evanescent coupling into a grating can
occur.
[0049] FIGS. 22A-22D illustrate various stages of manufacturing an
inverse grating in accordance with an embodiment of the
invention.
[0050] FIG. 23A illustrates a schematic representation of a grating
in accordance with an embodiment of the invention.
[0051] FIG. 23B illustrates a schematic representation of a grating
in accordance with an embodiment of the invention.
[0052] FIG. 23C illustrates a schematic representation of a grating
in accordance with an embodiment of the invention.
[0053] FIG. 24 illustrates an example process flow for fabricating
SRGs in accordance with an embodiment of the invention.
[0054] FIGS. 25A and 25B illustrate the principles of a dual
interaction grating for implementation in a waveguide.
[0055] FIG. 26 conceptually illustrates a cross section of a
grating in accordance with an embodiment of the invention.
[0056] FIG. 27 is a conceptual representation of beam propagation
with the grating of FIG. 26.
[0057] FIG. 28 illustrates an example of a partially backfilled
grating in accordance with an embodiment of the invention.
[0058] FIG. 29 schematically illustrates a ray-grating interaction
geometry of a TIR surface grating.
[0059] FIG. 30 conceptually illustrates a waveguide display in
accordance with an embodiment of the invention.
[0060] FIG. 31 conceptually illustrates a waveguide display having
two air-spaced waveguide layers in accordance with an embodiment of
the invention.
[0061] FIG. 32 conceptually illustrates typical ray paths for a
waveguide display in accordance with an embodiment of the
invention.
[0062] FIG. 33 conceptually illustrates a waveguide display in
which the waveguide supports a curved optical surface in accordance
with an embodiment of the invention.
[0063] FIG. 34 conceptually illustrates a waveguide display in
which the waveguide supports upper and lower curved optical
surfaces in accordance with an embodiment of the invention.
[0064] FIG. 35 conceptually illustrates a waveguide display in
which the waveguide supports a curved optical surface and an input
image is provided using a pixel array predistorted to compensate
for aberrations introduced by the curved optical surface in
accordance with an embodiment of the invention.
[0065] FIG. 36 conceptually illustrates a waveguide display in
which the waveguide supports a curved optical surface and an input
image is provided using a pixel array supported by a curved
substrate and predistorted to compensate for aberrations introduced
by the curved optical surface in accordance with an embodiment of
the invention.
[0066] FIG. 37 is a flow chart conceptually illustrating a method
for projecting image light for view using a waveguide containing
S-diffracting and P-diffracting gratings in accordance with an
embodiment of the invention.
[0067] FIG. 38 is a flow chart conceptually illustrating a method
for projecting image light for view using a waveguide supporting an
optical prescription surface and containing S-diffracting and
P-diffracting gratings in accordance with an embodiment of the
invention.
[0068] FIG. 39A conceptually illustrates a portion of a pixel
pattern having rectangular elements of differing size and aspect
ratio for use in an emissive display panel in accordance with an
embodiment of the invention.
[0069] FIG. 39B conceptually illustrates a portion of a pixel
pattern having Penrose tiles for use in an emissive display panel
in accordance with an embodiment of the invention.
[0070] FIG. 39C conceptually illustrates a portion of a pixel
pattern having hexagonal elements for use in an emissive display
panel in accordance with an embodiment of the invention.
[0071] FIG. 39D conceptually illustrates a portion of a pixel
pattern having square elements for use in an emissive display panel
in accordance with an embodiment of the invention.
[0072] FIG. 39E conceptually illustrates a portion of a pixel
pattern having diamond-shaped elements for use in an emissive
display panel in accordance with an embodiment of the
invention.
[0073] FIG. 39F conceptually illustrates a portion of a pixel
pattern having isosceles triangular elements for use in an emissive
display panel in accordance with an embodiment of the
invention.
[0074] FIG. 39G conceptually illustrates a portion of a pixel
pattern having hexagonal elements with horizontally biased aspect
ratios for use in an emissive display panel in accordance with an
embodiment of the invention.
[0075] FIG. 39H conceptually illustrates a portion of a pixel
pattern having rectangular elements with horizontally biased aspect
ratios for use in an emissive display panel in accordance with an
embodiment of the invention.
[0076] FIG. 39I conceptually illustrates a portion of a pixel
pattern having diamond shaped elements with horizontally biased
aspect ratios for use in an emissive display panel in accordance
with an embodiment of the invention.
[0077] FIG. 39J conceptually illustrates a portion of a pixel
pattern having triangles with horizontally biased aspect ratios for
use in an emissive display panel in accordance with an embodiment
of the invention.
[0078] FIG. 40 conceptually illustrates a portion of a pixel
pattern having diamond shaped elements in which different pixels
can have different emission characteristics in accordance with an
embodiment of the invention.
DETAILED DESCRIPTION
[0079] There is a growing interest in the use of various periodic
structure (e.g. gratings) on waveguides in order to provide a
variety of functions. These periodic structure may include angle
multiplexed gratings, color multiplexed gratings, fold gratings,
dual interaction gratings, rolled K-vector gratings, crossed fold
gratings, tessellated gratings, chirped gratings, gratings with
spatially varying refractive index modulation, gratings having
spatially varying grating thickness, gratings having spatially
varying average refractive index, gratings with spatially varying
refractive index modulation tensors, and gratings having spatially
varying average refractive index tensors. In specific examples,
gratings for diffraction of various polarizations of light (e.g.
S-polarized light and P-polarized light) may be beneficial. It
would be specifically advantageous to have a grating which
diffracts either S-polarized light or P-polarized light. Specific
applications for this technology include waveguide-based displays
such as augmented reality displays and virtual reality displays.
One example is input gratings which may be used to input one or
both of S-polarized light or P-polarized light into the waveguide.
However, in many cases, it would be advantageous to have a grating
which diffracts either S-polarized light and P-polarized light. For
example, waveguide displays using unpolarized light sources such as
OLED light sources produce both S-polarized and P-polarized light
and thus it would be advantageous to have gratings which can
diffract both S-polarized and P-polarized light.
[0080] One specific class of gratings includes surface relief
gratings (SRGs) which may be used to diffract either P-polarized
light or S-polarized light. Another class of gratings are surface
relief gratings (SRGs) which are normally P-polarization selective,
leading to a 50% efficiency loss with unpolarized light sources
such as organic light emitting diodes (OLEDs) and light emitting
diodes (LEDs). Combining a mixture of S-polarization diffracting
and P-polarization diffracting gratings may provide a theoretical
2.times. improvement over waveguides using P-diffracting gratings
only. Thus, it would be advantageous to have a high efficiency
S-polarization diffraction grating. In many embodiments, an
S-polarization diffracting grating can be provided by a periodic
structure formed in a holographic photopolymer. One periodic
structure includes a grating such as a Bragg grating. In some
embodiments, an S-polarization diffracting grating can be provided
by a periodic structure formed in a holographic polymer dispersed
liquid crystal (HPDLC) with birefringence altered using an
alignment layer or other processes for realigning the liquid
crystal (LC) directors. In several embodiments, an S-polarization
diffracting periodic structure can be formed using liquid crystals,
monomers, and other additives that naturally organize into
S-diffracting periodic structures under phase separation. In some
embodiments, these HPDLC periodic structures may form deep SRGs
which have superior S-polarization diffraction efficiency.
[0081] One class of deep SRGs are polymer-air SRGs or evacuated
periodic structure (EPSs) which may exhibit high S-diffraction
efficiency (up to 99%) and low P-diffraction efficiency and may be
implemented as input gratings for waveguides. The EPSs may be
evacuated Bragg gratings (EBGs). Such periodic structures can be
formed by removing the liquid crystal from HPDLC periodic
structures formed from holographic phase separation of a liquid
crystal and monomer mixture. Deep SRGs formed by such a process
typically have a thickness in the range 1-3 micrometers with a
fringe spacing 0.35 to 0.80 micrometers. In some embodiments, the
ratio of grating depth to fringe spacing may be 1:1 to 5:1. As can
readily be appreciated, such gratings can be formed with different
dimensions depending on the specific requirements of the given
application. Examples of how the thickness of SRGs may yield
different resultant diffraction efficiencies are described in
connection with FIGS. 6-8.
[0082] In many embodiments, the condition for a deep SRGs is
characterized by a high grating depth to fringe spacing ratio. In
some embodiments, the condition for the formation of a deep SRGs is
that the grating depth is approximately twice the grating period.
Modelling such deep SRGs using the Kogelnik theory can give
reasonably accurate estimates of diffraction efficiency, avoiding
the need for more advanced modelling, which typically entails the
numerical solution of Maxwell's equations. The grating depths that
can be achieved using liquid crystal removal from HPDLC periodic
structures greatly surpass those possible using conventional
nanoimprint lithographic methods, which cannot achieve the
conditions for deep SRGs (typically providing only 250-300 nm depth
for grating periods 350-460 nm). (Pekka Ayras, Pasi Saarikko,
Tapani Levola, "Exit pupil expander with a large field of view
based on diffractive optics", Journal of the SID 17/8, (2009), pp
659-664). It should be emphasized here that, although the
S-polarization diffracting deep SRGs are emphasized within the
present application, deep SRGs can, as will be discussed below,
provide a range of polarization response characteristics depending
on the thickness of the grating prescription and, in particular,
the grating depth. As such, deep SRGs can be implemented in a
variety of different applications.
[0083] The literature supports equivalence of deep SRGs and
periodic structures. One reference (Kiyoshi Yokomori, "Dielectric
surface-relief gratings with high diffraction efficiency" Applied
Optics; Vol. 23; Issue 14; (1984); pp. 2303-2310), discloses the
investigation of the diffraction properties of dielectric
surface-relief gratings by solving Maxwell's equations numerically.
The diffraction efficiency of a grating with a groove depth about
twice as deep as the grating period was found to be comparable with
the efficiency of a volume phase grating. The modelling by Yokomori
predicted that dielectric surface-relief gratings
interferometrically recorded in photoresist can possess a high
diffraction efficiency of up to 94% (throughput efficiency 85%).
The equivalence of deep SRGs and periodic structures is also
discussed in another article by Golub (M. A. Golub, A. A. Friesem,
L. Eisen "Bragg properties of efficient surface relief gratings in
the resonance domain", Optics Communications; 235; (2004); pp
261-267). A further article by Gerritsen discusses the formation of
Bragg-like SRGs in photoresist (Gerritsen H J, Thornton D K, Bolton
S R; "Application of Kogelnik's two-wave theory to deep, slanted,
highly efficient, relief transmission gratings" Applied Optics;
Vol. 30; Issue 7; (1991); pp 807-814).
[0084] Many embodiments of this disclosure provide for methods of
making SRGs such as deep SRGs that can offer very significant
advantages over nanoimprint lithographic process particularly for
slanted gratings. Periodic structures of any complexity can be made
using interference or master and contact copy replication. In some
embodiments, after removing the LC, the SRGs can be back filled
with a material with different properties to the LC. This allows a
periodic structure with modulation properties that are not limited
by the grating chemistry needed for grating formation.
[0085] In some embodiments the backfill material may not be a LC
material. In some embodiments, the backfill material may have a
higher index of refraction than air which may increase the angular
bandwidth of a waveguide. In several embodiments, the deep SRGs can
be partially backfilled with LC to provide a hybrid SRG/periodic
structure. Alternatively, in some embodiments, the refill step can
be avoided by removing just a portion of the LC from the LC rich
regions of the HPDLC to provide a hybrid SRG/periodic structure.
The refill approach has the advantage that a different LC can be
used to form the hybrid periodic structures. The materials can be
deposited using an inkjet deposition process.
[0086] In some embodiments, the methods described herein may be
used to create photonic crystals. Photonic crystals may be
implemented to create a wide variety of diffracting structures
including periodic structures such as Bragg gratings. Periodic
structures may be used as diffraction gratings to provide
functionality including but not limited to input gratings, output
gratings, beam expansion gratings, diffract more than one primary
color. A photonic crystal can be a three-dimensional lattice
structure that can have diffractive capabilities not achievable
with a basic periodic structures. Photonic crystals can include
many structures including all 2-D and 3-D Bravais lattices.
Recording of such structures may benefit from more than two
recording beams.
[0087] In some embodiments, waveguides incorporating photonic
crystals can be arranged in stacks of waveguides, each having a
grating prescription for diffracting a unique spectral bandwidth.
In many embodiments, a photonic crystal formed by liquid crystal
extraction provide a deep SRG. In many embodiments, a deep SRG
formed using a liquid crystal extraction process can typically have
a thickness in the range 1-3 micron with a fringe spacing 0.35
micron to 0.80 micron. The fringe spacing may be a Bragg fringe
spacing. In many embodiments, the condition for a deep SRG is
characterized by a high grating depth to fringe spacing ratio. In
some embodiments the condition for the formation of a deep SRG is
that the grating depth can be approximately twice the grating
period. It should be emphasized here that, although S-polarization
diffracting deep SRGs are described in the present application,
deep SRGs can, as will be discussed below, provide a range of
polarization response characteristics depending on the thickness of
the grating prescription and, in particular, the grating depth.
Deep SRGs can also be used in conjunction with conventional Bragg
gratings to enhance the color, uniformity and other properties of
waveguide displays.
[0088] Deep SRGs have been fabricated in glassy monomeric
azobenzene materials using laser holographic exposure (O. Sakhno,
L. M. Goldenberg, M. Wegener, J. Stumpe, "Deep surface relief
grating in azobenzene-containing materials using a low intensity
532 nm laser", Optical Materials: X, 1, (2019), 100006, pp 3-7. The
Sakhno reference also discloses how SRGs can be recorded in a
holographic photopolymer using two linearly orthogonally polarized
laser beams.
[0089] The disclosure provides a method for making a surface relief
grating that can offer very significant advantages over nanoimprint
lithographic process particularly for slanted gratings. Periodic
structures of any complexity can be made using interference or
master and contact copy replication. In some embodiments after
removing the LC the SRG can be back filled with a material with
different properties to the LC. This allows a periodic structure
with modulation properties that are not limited by the grating
chemistry needed for grating formation. In some embodiments the
SRGs can be partially backfilled with LC to provide a hybrid
SRG/periodic structure. Alternatively, in some embodiments, the
refill step can be avoided by removing just a portion of the LC
from the LC rich regions of the HPDLC to provide a hybrid
SRG/periodic structure. The refill approach has the advantage that
a different LC can be used to form the hybrid grating. The
materials can be deposited using an inkjet process. In some
embodiments, the refill material may have a higher index of
refraction than air which may increase diffraction efficiency of
the periodic structure.
[0090] While this disclosure has been made in the context of
fabricating deep SRGs, it is appreciated that many other grating
structures may be produced using the techniques described herein.
For example, any type of SRG including SRGs in which the grating
depth is smaller than the grating frequency (e.g. Raman-Nath
gratings) may be fabricated as well.
[0091] FIGS. 1A-1D illustrate a processing apparatus that can be
used in a method for fabricating deep SRGs or EPSs in accordance
with an embodiment. FIG. 1A conceptually illustrates an apparatus
190A that can be used in a step of a method for fabricating a
surface relief grating in which a mixture 191 of monomer and liquid
crystal deposited on a transparent substrate 192 is exposed to
holographic exposure beams 193,194, in accordance with an
embodiment of the invention. The holographic exposure beams 193,194
may be deep UV beams. In some examples, the mixture 191 may also
include at least one of a photoinitiator, a coinitiator, a
multifunctional thiol, adhesion promoter, surfactant, and/or
additional additives.
[0092] The mixture 191 may include nanoparticles. The mixture 191
may include photoacids. The mixture 191 may be a monomer diluted
with a non-reactive polymer. The mixture 191 may include more than
one monomer. In some embodiments, the monomer may be
isocyanate-acrylate based or thiolene based. In some embodiments,
the liquid crystal may be a full liquid crystal mixture or a liquid
crystal single. A liquid crystal single may only include a portion
of a full liquid crystal mixture. Various examples, liquid crystal
singles may include one or all of cyanobiphenyls, alkyl, alkoxy,
cyanobiphenyls, and/or terphenyls. The liquid crystal mixture may
be a cholesteric liquid crystal. The liquid crystal mixture may
include chiral dopants which may control the grating period. The
liquid crystal mixture may include photo-responsive and/or halogen
bonded liquid crystals. In some embodiments, liquid crystal may be
replaced with another substance that phase separates with the
monomer during exposure to create polymer rich regions and
substance rich regions. Advantageously, the substance and liquid
crystal singles may be a cost-effective substitute to full liquid
crystal mixtures which are removed at a later step as described
below.
[0093] In some embodiments, the liquid crystal in the mixture 191
may have a different between an extraordinary refractive index and
an ordinary refractive index of less than 0.01. In some
embodiments, the liquid crystal in the mixture 191 may have a
different between an extraordinary refractive index and an ordinary
refractive index of less than 0.025. In some embodiments, the
liquid crystal in the mixture 191 may have a different between an
extraordinary refractive index and an ordinary refractive index of
less than 0.05.
[0094] FIG. 1B conceptually illustrates an apparatus 190B that can
be used in a step of a method for fabricating a surface relief
grating from an HPDLC Bragg grating 195 formed on a transparent
substrate using the holographic exposure beams, in accordance with
an embodiment of the invention. The holographic exposure beams may
transform the monomer into a polymer in some areas. The holographic
exposure beams may include intersecting recording beams and include
alternating bright and dark illumination regions. A
polymerization-driven diffusion process may cause the diffusion of
monomers and LC in opposite directions, with the monomers
undergoing gelation to form polymer-rich regions (in the bright
regions) and the liquid crystal becoming trapped in a polymer
matrix to form liquid crystal rich regions (in the dark
regions).
[0095] FIG. 1C conceptually illustrates an apparatus 190C that can
be used in a step of a method for fabricating a deep polymer
surface relief grating 196 or EPS in which liquid crystal is
removed from an HPDLC periodic structure of FIG. 1B to form a
polymer surface relief grating in accordance with an embodiment of
the invention. Advantageously, a polymer surface relief grating 196
may include a large depth with a comparatively small grating period
in order to form a deep SRG. The liquid crystal may be removed by
washing with a solvent such as isopropyl alcohol (IPA). The solvent
may be strong enough to wash away the liquid crystal but weak
enough to maintain the polymer. In some embodiments, the solvent
may be chilled below room temperature before washing the grating.
FIG. 1D conceptually illustrates an apparatus 190D that can be used
in a step of a method for fabricating a polymer surface relief
grating in which the polymer surface relief grating is covered with
a protective layer 197 in accordance with an embodiment of the
invention.
[0096] FIG. 2 conceptually illustrates a method for forming deep
SRGs from a HPDLC periodic structure formed on a transparent
substrate in accordance with an embodiment of the invention. As
shown, a method 200 of forming deep SRGs or EPSs is provided.
Referring to the flow diagram, the method 200 includes providing
(201) a mixture of at least one monomer and at least one liquid
crystal. The at least one monomer may include an
isocyanate-acrylate monomer or thiolene. For example, the mixture
may include a liquid crystal and a thiolene based photopolymer. In
some embodiments, the mixture may include a liquid crystal and an
acrylate-based photopolymer. In some embodiments, the at least one
liquid crystal may be a full liquid crystal mixture or may be a
liquid crystal single which may include only a portion of the
liquid crystal mixture such as a single component of the liquid
crystal mixture. In some embodiments, the at least one liquid
crystal may be substituted for a solution which phase separates
with the monomer during exposure. The criteria for such a solution
may include ability to phase separate with the monomer during
exposure, ease of removal after curing and during washing, and ease
of handing. Example substitute solutions include solvents,
non-reactive monomers, inorganics, and nanoparticles.
[0097] Providing the mixture of the monomer and the liquid crystal
may also include mixing one or more of the following with the at
least one monomer and the liquid crystal: initiators such as
photoinitiators or coinitiators, multifunctional thiol, dye,
adhesion promoters, surfactants, and/or additional additives such
as other cross linking agents. This mixture may be allowed to rest
in order to allow the coinitiator to catalyze a reaction between
the monomer and the thiol. The rest period may occur in a dark
space or a space with red light (e.g. infrared light) at a cold
temperature (e.g. 20.degree. C.) for a period of approximately 8
hours. After resting, additional monomers may be mixed into the
monomer. This mixture may be then strained or filtered through a
filter with a small pore size (e.g. 0.45 .mu.m pore size). After
straining, this mixture may be stored at room temperature in a dark
space or a space with red light before coating.
[0098] Next, a transparent substrate can be provided (202). In
certain embodiments, the transparent substrate may be a glass
substrate or a plastic substrate. In some embodiments, the
transparent substrate may be a flexible substrate to facilitate
roll to roll processing. In some embodiments, the EPS may be
manufactured on a flexible substrate through a roll to roll process
and then peeled off and adhered to a rigid substrate. In some
embodiments, the EPS may be manufactured on a flexible substrate
and a second flexible release layer may be peeled off and discarded
which would leave the EPS on a flexible layer. The flexible layer
may be then bonded to another rigid substrate.
[0099] A layer of the mixture can be deposited or coated (203) onto
a surface of the substrate. The layer of mixture may be deposited
using inkjet printing. In some embodiments, the mixture is
sandwiched between the transparent substrate and another substrate
using glass spacers to maintain internal dimensions. A non-stick
coating may be applied to the other substrate before the mixture is
sandwiched. The non-stick coating may include a fluoropolymer such
as OPTOOL UD509 (produced by Daikin Chemicals), Dow Corning 2634,
Fluoropel (produced by Cytonix), and EC200 (produced by PPG
Industries, Inc). Holographic recording beams can be applied (204)
to the mixture layer. holographic recording beams may be a two-beam
interference pattern which may cause phase separation of the LC and
the polymer. In response to the holographic recording beam, the
liquid monomer changes to a solid polymer whereas the neutral,
non-reactive substance (e.g. LC) diffuses during holographic
exposure in response to a change in chemical potential driven by
polymerization. While LC may be one implementation of the neutral,
non-reactive substance, other substances may also be used. The
substance and the monomer may form a miscible mixture prior to the
holographic exposure and become immiscible upon holographic
exposure.
[0100] After applying the holographic recording beams, the mixture
may be cured. The curing process may include leaving the mixture
under low-intensity white light for a period of time until the
mixture fully cures. The low intensity white light may also cause a
photo-bleach dye process to occur. Thus, a HPDLC periodic structure
having alternating polymer rich and liquid crystal rich regions can
be formed (205). In some embodiments, the curing process may occur
in two hours or less. After curing, one of the substrates may be
removed exposing the HPDLC periodic structure. Advantageously, the
non-stick coating may allow the other substrate to be removed while
the HPDLC periodic structure remaining.
[0101] HPDLC periodic structure may include alternating sections of
liquid crystal rich regions and polymer regions. The liquid crystal
in the liquid crystal rich regions can be removed (206) to form
polymer surface relief gratings or EPSs which may be used as deep
SRGs. The liquid crystal may be removed by gently immersing the
grating into a solvent such as IPA. The IPA may be chilled and may
be kept at a temperature lower than room temperature while the
grating is immersed in the IPA. The periodic structure may be then
removed from the solvent and dried. In some embodiments, the
periodic structure is dried using a high flow air source such as
compressed air. After the LC is removed from the periodic
structure, a polymer-air surface relief grating is formed.
[0102] As shown in FIGS. 1A-1D, the formed surface relief grating
can further be covered with a protective layer. In some instances,
the protective layer may be a moisture and oxygen barrier with
scratch resistance capabilities. In some instances, the protective
layer may be a coating that does not fill in air gap regions where
LC that was removed once existed. The coating may be deposited
using a low temperature process. In some implementations, the
protective layer may have anti-reflective (AR) properties. The
coating may be a silicate or silicon nitride. The coating process
may be performed by a plasma assisted chemical vapor deposition
(CVD) process such as a nanocoating process. The coating may be a
parylene coating. The protective layer may be a glass layer. A
vacuum or inert gas may fill the gaps where LC that was removed
once existed before the protective layer is applied. In some
embodiments, the coating process may be integrated with the LC
removal process (206). For example, a coating material may be mixed
with the solvent which is used to wash the LC from the periodic
structure.
[0103] FIG. 3A illustrates a cross sectional schematic view of an
exemplary embodiment of a polymer-air periodic structure 3000
implemented on a waveguide 3002. The polymer-air surface relief
grating 3000 includes periodic polymer sections 3004a. Adjacent
polymer sections 3004a sandwich air sections 3004b. The air
sections 3004b are sandwiched by polymer sections 3004a. The air
sections 3004b and polymer sections 3004a have different indexes of
refraction. Advantageously, the polymer-air surface relief Bragg
grating 3000 may be formed with a high grating depth 3006a to Bragg
fringe spacing 3006b ratio which may create a deep SRG. As
illustrated, the polymer sections 3004a and the air sections 3004b
extend all the way to the waveguide 3002 to directly contact the
waveguide 3002. As illustrated, there may be no bias layer between
the polymer sections 3004a and the air sections 3004b and the
waveguide 3002. As discussed previously, deep SRGs may exhibit many
beneficial qualities such as high S-diffraction efficiency which
may not be present within the typical SRGs.
[0104] In one example, a polymer-air surface relief Bragg grating
3000 may have a Bragg fringe spacing 3006b of 0.35 .mu.m to 0.8
.mu.m and a grating depth of 1 .mu.m to 3 .mu.m. in some
embodiments, a grating depth of 1 .mu.m to 3 .mu.m may be too thick
for most EPS (with ashing and ALD) for fold and output gratings for
waveguide applications, where leaky structures are needed. Values
in the ranges of 0.1 .mu.m to 0.5 .mu.m might be more suitable for
leaky structures, particularly when modulation is increased with
ashing and ALD. For example, Input structures may include a depth
in the range of 0.4 .mu.m up to 1 .mu.m. Structures with a depth
from 1 .mu.m to 3 .mu.m may be advantageous for display cases, and
structures even taller may be advantageous for non-display
applications. Structures with half period (e.g. a critical
dimension) to height ratio of 7:1 or even 8:1 have been
demonstrated with advantageous effects.
[0105] In some embodiments, the polymer sections 3004a may include
at least some residual liquid crystal when the liquid crystal is
not completely removed during step 206 described in connection with
FIG. 2. In some embodiments, the presence of residual LC within the
polymer rich regions may increase refractive index modulation of
the final polymer SRG. In some embodiments, the air sections 3004b
may include some residual liquid crystal if the liquid crystal is
not completely removed during step 206 from these air sections
3004b. In some embodiments, by leaving some residual liquid crystal
within the air sections 3004b, a hybrid grating as described in
connection with FIGS. 4-5 may be created.
[0106] In some embodiments, an optical layer 3008 may also exist
between the polymer sections 3004a and the air sections 3004b and
the waveguide 3002. The optical layer 3008 may be a bias layer
between the polymer sections 3004a and the air sections 3004b and
the waveguide 3002. FIG. 3B illustrates a cross sectional schematic
view of a polymer-air periodic structure 3000a in accordance with
an embodiment of the invention. The polymer-air periodic structure
3000a includes many identically numbered components with the
polymer-air periodic structure 3000 of FIG. 3A. The description of
these components is applicable with the polymer-air periodic
structure 3000a described in connection with FIG. 3B and this
description will not be repeated in detail. As illustrated, an
optical layer 3008 is positioned between the polymer sections 3004a
and the air sections 3004b and the waveguide 3002. The waveguide
may include a substrate 3002 and an optical layer 3008 (e.g. the
bias layer) sandwiched by the substrate 3002 and the polymer
periodic structure and wherein the polymer periodic structure
extends all the way to the optical layer to directly contact the
optical layer. The polymer periodic structure includes the polymer
sections 3004a and the air sections 3004b.
[0107] In some examples, an optical layer 3008 may be formed when
gratings are formed using Nano Imprint Lithography (NIL). The
grating pattern may be imprinted in a resin leaving a thin layer
underneath the period structure which is a few microns thick. This
optical layer 3008, which may be a few microns in thickness, may
reside between the waveguide (e.g. glass) substrate and the period
grating layer and may not be removed without damaging the NIL
grating structure. When the bias refractive index is lower than
that of the waveguide substrate the bias layer may confine light
for some field angles (furthest from TIR in the waveguide) to the
high index substrate which may be analogous to cladding on an
optical fiber core. This may cause the field supported in the
waveguide to be clipped and hence not supported by the waveguide.
Elimination of the bias layer can offer grating coupling from a
high index substrate with a grating structure of lower index than
the substrate which may not be possible with the bias layer
present.
[0108] In formation of EPSs, since the phase separation process
leading to grating formation may take place through the entire
holographic recording material layer, gratings may be formed
throughout the volume of the cell gap resulting in no optical layer
3008. The elimination of the optical layer 3008 can allow wider
fields of view to be realized when using high index waveguide
substrates. Wide field of view angular content may be propagated
with lower refractive index grating structures. EPSs may deliver
similar optical performance characteristics to nanoimprinted SRGs
by offering taller structures albeit at lower peak refractive
index. This may open up the possibility of low-cost fabrication of
diffractive structures for high efficiency waveguides.
[0109] Although the elimination of the optical layer 3008 from a
waveguide grating device can offer the field of view benefits as
discussed above, in some embodiments, an optical layer 3008 may be
present in EPSs. The present disclosure allows for waveguide
grating devices with or without the optical layer 3008.
[0110] In some embodiments, having the optical layer 3008 can be an
advantage as the evanescent coupling between the waveguide and the
grating is a function of the indices of the gratings structure
(e.g. the grating depth the angles of the faces making up the
structure and the grating depth), the waveguide core, and the
optical layer 3008 (if present). In some embodiments, the optical
layer 3008 may be used as a tuning parameter for optimizing the
overall waveguide design for better efficiency and bandwidth.
Unlike nanograting SRGs, a bias layer used with an EPS may not be
of the same index as the grating structure.
[0111] FIG. 3C is a graph illustrating the effect of optical layer
3008 thickness on the diffraction efficiency versus incident angle.
The dotted line 3052 represents an incident angle of +6 degrees.
Evanescent coupling may begin (towards negative angles) at an angle
of approximately +6 degrees. The various plots represent different
thicknesses of optical layer 3008. The plots show that the optical
layer 3008 thickness can be used to increase the diffractive
coupling (e.g. for an optical layer thickness of 300 nm) over the
approximate angular range from +6 degrees to +16 degrees. There may
be lower coupling over the approximate angular range from 0 degrees
to +6 degrees. The S-shaped characteristic can be altered by
replacing the 300 nm optical layer with a thicker or thinner bias
layer as shown in FIG. 3C. In some embodiments, the thickness of
the optical layer may be 2 .mu.m to 3 .mu.m, 1 .mu.m to 2 .mu.m, or
0.5 .mu.m to 1 .mu.m.
[0112] In some embodiments, the EPS may be fabricated as part of a
stacked grating structure. Examples of stacked grating structures
are discussed in International Pub. No. WO 2022015878, entitled
"Nanoparticle-based holographic photopolymer materials and related
applications" and filed Jul. 14, 2021, which is hereby incorporated
by reference in its entirety for all purposes. In some embodiments,
the EPS may include a multilayer structure including a release
layer. Release layers may be used in a grating stacking process
that may reduce the number of glass layers. The release layer may
be applied at each exposure step to allow the deposition of a new
layer of recording material. Similar processes may also allow
angular bandwidth to be increased by stacking multiple gratings
with different slant angles.
[0113] As discussed above, in many the embodiments, the invention
also provides a method for fabricating a hybrid surface
relief/periodic structure. FIG. 4A conceptually illustrates an
apparatus 210A that can be used in a step of a method for
fabricating hybrid surface relief gratings (hybrid SRGs) in which a
mixture 211 of monomer and liquid crystal deposited on a
transparent substrate 212 is exposed to holographic exposure beams
213,214, in accordance with an embodiment of the invention. FIG. 4B
conceptually illustrates an apparatus 210B that can be used in a
step of a method for fabricating hybrid SRGs from an HPDLC periodic
structure 215 formed on the transparent substrate using the
holographic exposure beams in accordance with an embodiment of the
invention. FIG. 4C conceptually illustrates an apparatus 210C that
can be used in a step of a method for fabricating a surface relief
grating in which liquid crystal is removed from an HPDLC periodic
structure 215 to form polymer-air SRGs 216 in accordance with an
embodiment of the invention. These polymer-air SRGs 216 or EPSs may
be deep SRGs. It is appreciated that the steps illustrated in and
described in connection with FIGS. 4A-4C roughly correspond to the
steps illustrated in and described in connection with FIGS. 2A-2C
in the process to create a polymer-air SRG and thus the previous
description will be applicable to FIGS. 4A-4C.
[0114] In addition, FIG. 4D conceptually illustrates an additional
step which may be performed to create a hybrid grating. The
apparatus 210D can be used in a step of a method for fabricating a
surface relief grating in which a surface relief grating is at
least partially refilled with liquid crystal to form a hybrid SRGs
217, in accordance with an embodiment of the invention. The
refilled liquid crystal may be of different consistency to the
previously removed liquid crystal that was previously removed in
FIG. 4C. Further, it is appreciated that the liquid crystal removed
in FIG. 3C may only be partially removed in an alternative method
to forming hybrid SRGs 217. In addition, FIG. 4E conceptually
illustrates an apparatus 210E can be used in a step of a method for
fabricating a surface relief grating in which hybrid SRGs 217
formed in the step illustrated in FIG. 4D is covered with a
protective layer 218, in accordance with an embodiment of the
invention. In the hybrid EPSs, the air sections 3004b of FIGS. 3A
and 3B may be replaced with a backfill material as discussed
above.
[0115] FIG. 5 is a flowchart showing an exemplary method for
forming a hybrid surface relief-periodic structure from a HPDLC
periodic structure formed on a transparent substrate in accordance
with an embodiment of the invention. As shown, the method 220 of
forming hybrid surface relief-periodic structure is provided.
Referring to the flow diagram, method 220 includes providing (221)
a mixture of at least one monomer and at least one liquid crystal.
The at least one monomer may include an isocyanate-acrylate
monomer. Providing the mixture of the monomer and the liquid
crystal may also include mixing one or more of the following with
the at least one monomer and the liquid crystal: photoinitiator,
coinitiator, multifunctional thiol, and/or additional additives.
This mixture may be allowed to rest in order to allow the
coinitiator to catalyze a reaction between the monomer and the
thiol. The rest period may occur in a dark space or a space with
red light (e.g. infrared light) at a cold temperature (e.g.
20.degree. C.) for a period of approximately 8 hours. After
resting, additional monomers may be mixed into the monomer. This
mixture may be then strained or filtered through a filter with a
small pore size (e.g. 0.45 .mu.m pore size). After straining this
mixture may be stored at room temperature in a dark space or a
space with red light before coating.
[0116] Next, a transparent substrate can be provided (222). In
certain embodiments, the transparent substrate may be a glass
substrate or a plastic substrate. A non-stick coating may be
applied to the transparent substrate before the mixture is coated
on the substrate. The non-stick coating may be a release layer
which allows the transparent substrate to easily release from the
exposed periodic structure. Various examples of release layers are
discussed below. A layer of the mixture can be deposited (223) onto
a surface of the substrate. In some embodiments, the mixture is
sandwiched between the transparent substrate and another substrate
using glass spacers to maintain internal dimensions. Holographic
recording beams can be applied (224) to the mixture layer. The
holographic recording beams may be a two-beam interference pattern
which may cause phase separation of the LC and the polymer. After
applying the holographic recording beams, the mixture may be cured.
The curing process may include leaving the mixture under
low-intensity white light for a period of time under the mixture
fully cures. The low intensity white light may also cause a
photo-bleach dye process to occur. Thus, an HPDLC periodic
structure having alternating polymer rich and liquid crystal rich
regions can be formed (225). In some embodiments, the curing
process may occur in 2 hours or less. After curing, one of the
substrates may be removed exposing the HPDLC periodic structure.
The release layer may aid in allowing the one of the substrates to
not stick to the exposed periodic structure.
[0117] HPDLC grating may include alternating sections of liquid
crystal rich regions and polymer regions. The liquid crystal in the
liquid crystal rich regions can be removed (226) to form polymer
surface relief gratings or EPSs which is a form of deep SRGs. The
liquid crystal may be removed by gently immersing the exposed
periodic structure into a solvent such as isopropyl alcohol (IPA).
The IPA may be kept at a lower temperature while the periodic
structure is immersed in the IPA. The periodic structure is them
removed from the solvent and dried. In some embodiments, the
periodic structure is dried using a high flow air source such as
compressed air. After the LC is removed from the grating, a
polymer-air surface relief periodic structure is formed. The
resulting periodic structure may be the periodic structure
described in connection with FIGS. 3A and 3B. There may or may not
be a bias layer present as illustrated in FIG. 3A or 3B. The steps
221-226 of FIG. 5 roughly correspond to the steps described in
connection with FIG. 2 in creating a polymer-air SRG and thus these
descriptions are applicable to FIG. 5.
[0118] Further, method 220 includes at least partially refilling
(227) cleared liquid crystal rich regions with liquid crystal to
form hybrid SRGs. The refilled liquid crystal may be of different
consistency to the previously removed liquid crystal that was
previously removed in step 226. Further, it is appreciated that the
liquid crystal removed in step 226 may only be partially removed in
an alternative method to forming hybrid SRGs. Advantageously,
hybrid SRGs may provide the ability to tailor specific beneficial
characteristics of the SRGs. One particular characteristic that may
be improved by the inclusion of at least some liquid crystal within
the SRGs is a decrease in haze properties. In some embodiments, the
cleared liquid crystal rich regions may be backfilled with a
different refractive material than liquid crystal. The backfill
material may have a different refractive index than the remaining
polymer rich regions.
[0119] As shown in FIG. 4E, the formed surface relief grating can
further be covered with a protective layer. In some instances, the
protective layer may be a moisture and oxygen barrier with scratch
resistance capabilities. In some instances, the protective layer
may be a coating that does not fill in air gap regions where LC
that was removed once existed. The coating may be deposited using a
low temperature process. In some implementations, the protective
layer may have anti-reflective (AR) properties. The coating may be
a silicate or silicon nitride. The coating process may be performed
by a plasma assisted chemical vapor deposition (CVD) process such
as a plasma-treat nanocoating process. The coating may be a
parylene coating. The protective layer may be a glass layer. A
vacuum or inert gas may fill the gaps where LC that was removed
once existed before the protective layer is implemented. In some
embodiments, the coating process may be integrated with the LC
removal process (226). For example, a coating material may be mixed
with the solvent which is used to wash the LC from the grating. In
some implementations, the coating material may be a material with a
lower or higher refractive index than the polymer and fill the
spaces between adjacent polymer portions. The refractive index
difference between the polymer and the coating material may allow
the polymer SRGs to continue to diffract.
[0120] Although FIGS. 1-5 illustrate specific methods and apparatus
for forming deep SRGs and hybrid surface relief/Bragg gratings,
various manufacturing methods implementing different steps or
modifications of such steps can be utilized. As can readily be
appreciated, the specific process utilized can depend on the
specific requirements of the given application. For example, many
embodiments utilize another periodic structure as a protective
layer.
[0121] Hybrid SRG/periodic structure with shallow SRG structures
may lead to low SRG diffraction efficiencies. The methods disclosed
in the present disclosure allows for more effective SRG structures
to be formed by optimizing the depth of the liquid crystal in the
liquid crystal rich regions such that the SRGs has a high depth to
grating pitch ratio while allowing the periodic structure to be
sufficiently thick for efficient diffraction. In many embodiments,
the periodic structure component of the hybrid grating can have a
thickness in the range 1-3 micrometer. In some embodiments, the SRG
component of the hybrid grating can have a thickness in the range
0.25-3 micrometer. The initial HPDLC periodic structure would have
a thickness equal to the sum of the final SRG and periodic
structure components. As can readily be appreciated, the thickness
ratio of the two periodic structure components can depend on the
waveguide application. In some embodiments, the combination of an
SRG with a periodic structure may be used to fine-tune angular
bandwidth of the periodic structure. In some cases, the SRG can
increase the angular bandwidth of the periodic structure.
[0122] In many embodiments, in the hybrid SRGs illustrated in FIGS.
4A-4E, the refill depth of the liquid crystal regions of the
periodic structure can be varied across the periodic structure to
provide spatially varying relative SRG/periodic structure
strengths. In some embodiments, during the liquid crystal removal
and refill as defined in steps 206, 226, and 227, the liquid
crystal in the liquid crystal rich grating regions can be totally
or partially removed. In several embodiments, the liquid crystal
used to refill or partially refill the liquid crystal-cleared
regions can have a different chemical composition to the liquid
crystal used to form the initial HPDLC periodic structure. In
various embodiments, a first liquid crystal with phase separation
properties compatible with the monomer can be specified to provide
a HPDLC grating with optimal modulation and grating definitions
while a second refill liquid crystal can be specified to provide
desired index modulation properties in the final hybrid grating. In
a number of embodiments, the polymer portion of the hybrid grating
can be switchable with electrodes applied to surfaces of the
substrate and the cover layer. In many embodiments, the refill
liquid crystals can contain additives which may include but are not
limited to the features of improving switching voltage, switching
time, polarization, transparency, and other parameters. A hybrid
grating formed using a refill process would have the further
advantages that the LC would form a continuum (rather than an
assembly of LC droplets), thereby reducing haze. In some
embodiments the backfill material may be a material with a
different refractive index than the polymer regions. The backfill
material may not be a liquid crystal material.
[0123] While deep SRGs, EPSs, and/or hybrid SRGs may be described
in the context of S-diffracting gratings and P-diffracting
gratings, these periodic structures have applicability in many
other periodic structure types. These include but are not limited
to angle multiplexed gratings, color multiplexed gratings, fold
gratings, dual interaction gratings, rolled K-vector gratings,
crossed fold gratings, tessellated gratings, chirped gratings,
gratings with spatially varying refractive index modulation,
gratings having spatially varying grating thickness, gratings
having spatially varying average refractive index, gratings with
spatially varying refractive index modulation tensors, and gratings
having spatially varying average refractive index tensors. Further,
deep SRGs, EPSs, and/or hybrid SRGs may be switchable or
non-switchable periodic structures depending on their specific
implementation. Deep SRGs, EPSs, and/or hybrid SRGs may be
fabricated on a plastic substrate or a glass substrate. These
periodic structures may also be fabricated on one substrate and
transferred to another substrate.
[0124] In some embodiments, EPSs may be either unslanted or
slanted, or spatially varying slanted structures (e.g., rolled
K-vector type with very large height to period aspect ratio,
typically in the range of 2 to 12). Slanted EPSs will be
illustrated in various examples below. An EPS may include a height
of 2.0 .mu.m with a 0.400 .mu.m period (e.g. aspect ratio=5). The
combination of controlled, repeatable, slant angles and tall aspect
ratios may provide EPS structures Bragg properties which enable
high efficiency waveguide designs. Moreover, EPSs can be fabricated
with or without bias layers. EPSs may be made using a phase
separation process that can be implemented using ink jet printing
processes and offers significant economic advantages in mass
production over the complex wafer etching and nano imprint
lithographic process used to produce some SRG display
waveguides.
[0125] In some embodiments, EPSs may be configured as at least one
of multiplexed grating, a slanted grating, a photonic crystal,
mixed modulation grating, a hybrid polymer grating structure, a
sinusoidal grating (e.g. formed by plasma ashing of isotropic
photopolymer gratings), a metasurface, or a grating structure
combining a slanted volume grating overlaid by a surface relief
grating. Slanted volume grating overlaid by a surface relief
grating may include a grating structure which is substantially a
volume grating with the grating thickness of the low index regions
having a slight smaller grating thickness than the high index
regions. The variation of the grating thickness may be tens of
nanometers while the average volume grating thickness may be from
1-10 micron depending on the application. The configuration is
equivalent to an SRG layer sitting on top of a volume grating
layer. In some embodiments, the SRG and volume grating may combine
the benefit of the wider angular bandwidth of the SRG and the
higher efficiency of the volume grating. This is more likely to be
the case when the volume grating is thinner. The surface relief
structure can arise naturally as a result of non-linearity in the
diffusion process at the extremities of the grating. The effect may
be controlled using plasma ashing or some other type of etching
processed applied to the grating. A combined SRG and volume grating
can also be formed by fabricating an EPS and then partially
backfilling it with another material. Such a configuration is
discussed as a hybrid grating throughout the current
disclosure.
[0126] In some embodiments, the EPS is formed using different
diffusion regimes having different diffusion constants in at least
two different directions. In complex grating structures such as
photonic crystals the spacing of the diffracting nodes may lead to
nonuniformities in the modulation of the finished grating. Material
components with different diffusion time constants may allow more
efficient grating formation along different directions. In some
embodiments, the EPS is formed to provide a photonic structure
incorporating a slanted grating structure and a photonic crystal
structure including diffracting nodes. Grating configurations
including regions in which the grating includes slanted (or
unslanted) planar fringes and photonic crystal regions where the
diffracting structures comprising diffracting nodes may include
elongate elements such as cylinders which many may be tilted. The
photonic crystal regions may include a 3D diffracting node
structure. In some embodiments, the EPS is formed to provide a
photonic crystal including slanted diffracting features wherein the
principle nodes of the photonic crystal are formed by multiplexed
gratings wherein plasma ashing is applied along tracks parallel to
principal crystal directions. The photonic crystal may be formed by
multiplexing two or more gratings such that the intersection
regions of the bright fringes form modulation peaks. The regions
around these peaks may be eroded using plasma ashing applied along
the low modulation tracks which are parallel to the principle
crystal directions. The cross-section geometry of the nodes may
depend on the number of gratings and their relative orientations.
For example, crossing two gratings at ninety degrees may result in
square cross section nodes. Tilted photonic crystal nodes may be
formed using slanted gratings. This principle can be extended to
three dimensional photonic crystals.
[0127] In some embodiments, the polymer grating structure may be
formed to provide photonic crystal formed by three-beam-recorded
Bravais lattices and other structures, the process including plasma
ashing. All five two dimensional Bravais lattices (e.g. square,
triangular, rhombic) may be recoded using a three-beam exposure
system. The techniques for fabricating two dimensional photonic
crystals may also be applied to more complex three-dimensional
structures, including 3D Bravais lattices and other structures. All
fourteen of the Bravais lattice can be recorded using three beams
or even two beams using more multiple exposure techniques.
Dual-beam multiple exposure schemes may be used with the recording
medium undergoing a single axis rotation between each exposure.
Discussion of Various Implementations of Deep SRGs or EPSs
[0128] In many embodiments, deep SRGs can provide a means for
controlling polarization in a waveguide. SBGs are normally
P-polarization selective, leading to a 50% efficiency loss with
unpolarized light sources such as OLEDs and LEDs. Hence, combining
S-polarization diffracting and P-polarization diffracting periodic
structures can provide a theoretical 2.times. improvement over
waveguides using P-diffracting periodic structures only. In some
embodiments, an S-polarization diffracting periodic structures can
be provided by a periodic structure formed in a conventional
holographic photopolymer. In some embodiments an S-polarization
diffracting periodic structures can be provided by a periodic
structure formed in a HPDLC with birefringence altered using an
alignment layer or other process for realigning the liquid crystal
directors. In some embodiments, an S-polarization diffracting
periodic structure can be formed using liquid crystals, monomers
and other additives that naturally organize into S-diffracting
periodic structures under phase separation. In many embodiments, an
S-polarization diffracting periodic structures can be provided by
SRGs. Using the processes described above, a deep SRG exhibiting
high S-diffraction efficiency (up to 99%) and low P-diffraction
efficiency can be formed by removing the liquid crystal from SBGs
formed from holographic phase separation of a liquid crystal and
monomer mixture.
[0129] Deep SRGs can also provide other polarization response
characteristics. Several prior art theoretical studies such as an
article by Moharam (Moharam M. G. et al. "Diffraction
characteristics of photoresist surface-relief gratings", Applied
Optics, Vol. 23, page 3214, Sep. 15, 1984) point to deep surface
relief gratings having both S and P sensitivity with S being
dominant. In some embodiments, deep SRGs demonstrate the capability
of providing an S-polarization response. However, deep SRGs may
also provide other polarization response characteristics. In many
embodiments, deep surface relief gratings having both S and P
sensitivity with S being dominant are implemented. In some
embodiments, the thickness of the SRG can be adjusted to provide a
variety of S and P diffraction characteristics. In several
embodiments, diffraction efficiency can be high for P across a
spectral bandwidth and angular bandwidth and low for S across the
same spectral bandwidth and angular bandwidth. In number of
embodiments, diffraction efficiency can be high for S across the
spectral bandwidth and angular bandwidth and low for P across the
same spectral bandwidth and angular bandwidth. In some embodiments,
high efficiency for both S and P polarized light can be provided. A
theoretical analysis of an SRG of refractive index 1.6 immersed in
air (hence providing an average grating index of 1.3) of period
0.48 micron, with a 0 degrees incidence angle and 45 degree
diffracted angle for a wavelength of 0.532 micron is shown in FIGS.
5-7. FIG. 5 is a graph showing calculated P-polarized and
S-polarized diffraction efficiency versus incidence angle for a
1-micrometer thickness deep surface relief grating, demonstrating
that in this case high S and P response can be achieved. FIG. 6 is
a graph showing calculated P-polarized and S-polarized diffraction
efficiency versus incidence angle for a 2-micrometer thickness deep
surface relief grating, demonstrating that in this case the
S-polarization response is dominant over most of the angular range
of the grating. FIG. 7 is a graph showing calculated P-polarized
and S-polarized diffraction efficiency versus incidence angle for a
3-micrometer thickness, demonstrating that in this case the
P-polarization response is dominant over a substantial portion of
the angular range of the grating.
[0130] In many embodiments, a photonic crystal can be a reflection
periodic structure or deep SRG formed by a LC extraction process. A
reflection deep SRG made using phase separation followed by LC
subtraction can enable wide angular and spectral bandwidth. In many
embodiments replacing the current input SBG with a reflection
photonic crystal can be used to reduce the optical path from a
picture generation unit (PGU) to a waveguide. In some embodiments,
a PGU pupil and the waveguide can be in contact. In many
embodiments, the reflection deep SRG can be approximately 3 microns
in thickness. The diffracting properties of an LC extracted
periodic structure mainly result from the index gap between the
polymer and air (not from the depth of the periodic structure as in
the case of a typical SRG).
Discussion of Thiol Additives within Initial Mixture
[0131] FIGS. 9A and 9B illustrate comparative scattering electron
microscopy (SEM) images of example mixtures used to fabricate
polymer-air SRGs. As discussed previously, the monomer within the
initial mixture may be acrylate or thiolene based. It has been
discovered that with some monomers such as acrylate-based monomers,
after holographic exposure, during washing, the solvent not only
removes liquid crystal material but also polymer which is unideal.
It has been discovered that a multifunctional thiol additive may
solve this issue by strengthening the polymer and thus allowing it
to be strong enough to withstand the solvent wash. Without limiting
to any particular theory, thiol additive may improve the mechanical
strength of formulations consisting of low functionality acrylate
monomers which tend to form mechanically weak polymers due to
reduced cross-linking. Acrylate monomer formulations may be
advantageous because they may exhibit high diffraction efficiency
with lower haze. Thus, adding thiol could allow Acrylate monomer
formations to be a viable option in fabrication of polymer
SRGs.
[0132] There may be a trade-off between phase separation, periodic
structure formation, and mechanical strength between different
formulations. Periodic structure formation may benefit from
mixtures that contain low functionality monomers that react slower,
form fewer cross-linkages, and allow greater diffusion of
non-reactive components (e.g. LC) during holographic exposure.
Conversely, mixtures consisting of high functionality monomers may
exhibit better phase separation and polymer mechanical strength due
to greater cross-linking, but may react so rapidly that the
non-reactive components do not have sufficient time to diffuse and
thus may exhibit lower diffraction efficiency as a result.
[0133] Without limitation to any particular theory, the thiol
additives may get around these limitations by reacting with
acrylates or isocyanate-acrylates to form a loose scaffolding prior
to holographic exposure. This scaffolding may improve the
mechanical strength and uniformity of the cured polymer. Thus, the
mechanical strength may be tuned through slight adjustments of the
thiol functionality and concentration without significantly raising
the average functionality of the monomer mixture and disrupting
grating formation.
[0134] FIG. 9A illustrates an initial mixture whereas FIG. 9B
illustrate a comparative mixture which includes 1.5 wt % thiol.
However, other weight percentages of thiol additive have been
contemplated. For example, a weight percentage of thiol additive
may be 1% to 4% or 1.5% to 3%. In some embodiments, the
multifunctional thiol may be trimethylolpropane
tris(3-mercaptopropionate). Both FIGS. 9A and 9B include polymer
dense regions 902a/902b and air regions 904a/904b. As illustrated,
the added thiol may produce a denser polymer structure within the
polymer dense regions 902a of FIG. 9B than the polymer dense
regions 902b of FIG. 9A which may increase grating performance. It
has been discovered that the weight percentage of thiol additive
should be balanced in order to provide stability within the polymer
structure to withstand the solvent wash however not to be rigid as
to not allow the liquid crystal to be released during the solvent
wash.
Comparison Between HPDLC Periodic Structure Performance with
Polymer-Air SRG Performance
[0135] FIGS. 10A and 10B illustrates images of comparative examples
of an HPDLC grating and a polymer SRG or EPS. FIG. 10A illustrates
performance for an example HPDLC periodic structure where liquid
crystal has not been removed. The periodic structure of FIG. 10A
includes a 20-30% P-diffraction efficiency while exhibiting a
nominal or almost 0% S-diffraction efficiency. FIG. 10B illustrates
performance of an example polymer-air SRG where the LC has been
removed. The periodic structure of FIG. 10B includes a 18-28%
P-diffraction efficiency while exhibiting a S-diffraction
efficiency of 51-77%. Thus, polymer-air SRGs where LC has been
removed demonstrate a comparatively high S-diffraction efficiency
while maintaining a comparable P-diffraction efficiency. Further,
the grating of FIG. 10B includes a P-diffraction haze of 0.11-0.15%
and a S-diffraction haze of 0.12-0.16%.
[0136] FIGS. 11A and 11B illustrates plots of comparative examples
of an HPDLC periodic structure where liquid crystal has not been
removed and a polymer SRG or EPS where liquid crystal has been
removed. FIG. 11A illustrates the P-diffraction efficiency and
S-diffraction efficiency for an HPDLC periodic structure where
liquid crystal remains. A first line 1102a corresponds to
P-diffraction efficiency and a second line 1104a corresponds to
S-diffraction efficiency. FIG. 11B illustrates the P-diffraction
efficiency and S-diffraction efficiency for a polymer SRG or EPS
where liquid crystal has been removed. A first line 1102b
corresponds to P-diffraction efficiency and a second line 1104b
corresponds to S diffraction efficiency. As illustrated,
S-diffraction efficiency dramatically increases after liquid
crystal has been removed while P-diffraction efficiency remains
relatively similar. In some embodiments, the ratio of S-diffraction
efficiency to P-diffraction efficiency may be adjusted by using
different grating periods, grating slant angles, and grating
thicknesses.
Various Example Deep SRG Depths
[0137] FIGS. 12A and 12B illustrate various comparative examples of
P-diffraction and S-diffraction efficiencies with deep SRGs of
various depths. Each of these plots show diffraction efficiency vs.
angle. In FIG. 12A, the deep SRG has a depth of approximately 1.1
.mu.m. The first line 1102a represents S-diffraction efficiency and
the second line 1104a represents P-diffraction efficiency. As
illustrated the peak S-diffraction efficiency is approximately 58%
and the peak P-diffraction efficiency is 23%. It is noted that the
haze for S-diffraction is 0.12% and haze for P-diffraction is 0.11%
for this example. Such high diffraction efficiency with low haze
may make deep SRGs with a depth of approximately 1.1 .mu.m
particularly suitable for multiplexed gratings.
[0138] In FIG. 12B, the deep SRG has a depth of approximately 1.8
.mu.m. The first line 1102b represents S-diffraction efficiency and
the second line 1104b represents P-diffraction efficiency. As
illustrated the peak S-diffraction efficiency is approximately 92%
and the peak P-diffraction efficiency is 63%. It is noted that the
haze for S-diffraction is 0.34% and haze for P-diffraction is 0.40%
for this example. Thus, both S-diffraction and P-diffraction
efficiency increase dramatically with an increased grating depth.
It is noted that haze appears to increase with the increased
grating depth.
[0139] In some embodiments, an EPS may be spatially variable depth
for a single EPS grating. In some embodiments, different EPSs on
the same substrate may have different depths from each other not
forgoing the modulation variation mentioned above on one or more of
a multiplicity of EPS gratings on a single substrate. In some
embodiments, one or more EPSs may be positioned on each side of a
same substrate. In some embodiments, a mixture of planar and
multiplexed EPSs may be positioned on a same waveguide.
[0140] In some embodiments, multiple EPSs may be positioned on a
substrate including spacially varied duty cycle, grating shape,
slant, and/or ALD coating properties. The different ALD coating
properties may spatially affect modulation.
Various Example Initial LC Concentrations in Mixture
[0141] FIGS. 13A and 13B illustrate the results of a comparative
study of various EPSs with various initial LC concentrations in the
initial mixture. FIG. 13A illustrates S-diffraction efficiency vs.
angle. FIG. 13B illustrates P-diffraction efficiency vs. angle. In
FIG. 13A, a first line 1202a corresponds to 20% initial LC content,
a second line 1204a corresponds to 30% initial LC content, and a
third line 1206a corresponds to 40% initial LC content. In FIG.
13B, a first line 1202b corresponds to 20% initial LC content, a
second line 1204b corresponds to 30% initial LC content, and a
third line 1206b corresponds to 40% initial LC content. Table 1
illustrates a summary of various results of the comparative
study.
TABLE-US-00001 TABLE 1 Initial LC Maximum Maximum Content
S-Diffraction P-Diffraction S-Diffraction P-Diffraction in Mixture
Efficiency Efficiency Haze Haze 20% .sup. 10% 5% 0.10% 0.12% 30%
.gtoreq.40% 18% 0.14% 0.13% 40% .gtoreq.55% 23% 0.12% 0.11%
[0142] As is illustrated in FIGS. 13A and 13B and noted in Table 1,
the maximum S-diffraction and maximum P-diffraction appear to both
increase with higher initial LC content while the S-diffraction
haze and P-diffraction haze stay approximately constant.
[0143] FIGS. 14A and 14B illustrate additional example
S-diffraction and P-diffraction efficiencies for various initial LC
concentrations. FIG. 14A illustrates S-diffraction efficiency for
various example EPSs including various initial LC contents. FIG.
14B illustrate P-diffraction efficiency for various example EPSs
including various LC contents. For both FIGS. 14A and 14B,
sequentially from top to bottom the lines represent: 32% LC
content, 30% LC content, 28% LC content, 26% LC content, 24% LC
content, 22% LC content, and 20% LC content. As illustrated, the
S-diffraction and P-diffraction efficiencies are directly related
to the amount of LC content (e.g. higher LC content yields higher
S-diffraction and P-diffraction efficiencies).
[0144] Without being limited to any particular theory, the initial
LC content relates to the amount of phase separation between the LC
and the monomer that occurs during the holographic exposure process
and polymerization process. Thus, a higher LC content will increase
the amount of LC rich regions which are removed to make more air
regions after washing. The increased air regions make greater
refractive index differences (An) between the air regions (formerly
liquid crystal rich regions) and the polymer rich regions which
increases both S-diffraction and P-diffraction efficiencies. In
some embodiments, the average refractive index of the polymer SRGs
may be adjusted by adjusting the initial neutral substance (e.g.
LC) content, thereby either increasing or decreasing the volume of
polymer after removal of the neutral substance. Further, increasing
the initial neutral substance content may impact the mechanical
strength. Thus, an increase or decrease in mechanical strengthener
such as thiol additive may be used to balance out the increase or
decrease in mechanical strength.
Various Example Grating Thicknesses
[0145] FIG. 15 is a graph of diffraction efficiency versus grating
layer thickness showing the dependence of evanescent coupling on
the grating layer thickness. The duty cycle refers to the ratio of
the width of a polymer fringe to the width of the air gap between
neighboring polymer fringes. In other words, a 90% duty cycle means
90% of the grating is polymer and 10% is air.
[0146] Note that increased grating thickness may lead to increased
coupling when fringe and substrate refractive indices are matched.
For poor refractive index match to substrate (e.g. 1.6 refractive
index fringes on 1.8 refractive index substrate) there may be only
evanescent coupling, so increasing fringe depth may not affect
coupling significantly. The plots in FIG. 15 show that a grating
structure of refractive index 1.6 with a 90% duty cycle gives an
average refractive index of 1.54. Increasing the grating index to
1.65 at the same duty cycle results in an average refractive index
of 1.59. No diffraction efficiency exists in either case. Increase
the grating refractive index may result in a diffraction
efficiency. For example, for a grating structure of index 1.7 and
1.8 with a 90% duty cycle with resulting average refractive indices
of 1.63 and 1.72 respectively both provide diffractive efficiency.
In some embodiments, there may be grating structures on a 1.8 index
substrate with input light incident at 0 degrees to the grating
normal.
Embodiments Manufactured Using Various Substrate Configurations
[0147] In various embodiments, a pair of substrates may sandwich an
unexposed holographic mixture. The pair of substrates may include a
base substrate and a cover substrate. Advantageously, the cover
substrate may have different properties than the base substrate to
allow for the cover substrate to adhere to the unexposed
holographic mixture layer while capable of being removed from the
formed holographic polymer dispersed liquid crystal periodic
structure after exposure. The formed holographic polymer dispersed
liquid crystal grating may remain on the base substrate after the
cover substrate is removed.
[0148] FIGS. 16A-16G illustrate an example process flow for
fabricating deep SRGs in accordance with an embodiment of the
invention. This process flow is similar to the process flows
described in connection with FIGS. 1A-1D and FIGS. 4A-4E and
includes many of the same references numbers the description of
which is applicable to the description of FIGS. 15A-15G. Further,
FIGS. 15A-15G also includes a cover substrate 1502, the function of
which will be described in detail below.
[0149] In FIG. 16A, a pair of substrate 212,1502 sandwiches an
unexposed holographic mixture layer 211. The pair of substrate
212,1502 may include a base substrate 212 and a cover substrate
1502. The cover substrate 1502 may have different properties than
the base substrate 212 to allow for the cover substrate to adhere
to the unexposed holographic mixture layer 211 while capable of
being removed from the formed holographic polymer dispersed liquid
crystal grating after exposure.
[0150] In FIG. 16B, the holographic mixture layer 211 is exposed by
a pair of holographic recording beams 213,214. As illustrated in
FIG. 16C, the holographic recording beams 213,214 expose the
holographic mixture layer 211 to form a holographic polymer
dispersed liquid crystal grating 215. The holographic polymer
dispersed liquid crystal grating 215 may include alternating
polymer rich regions and liquid crystal rich regions. In FIG. 16D,
the cover substrate 1502 may be removed exposing the holographic
polymer dispersed liquid crystal grating 215.
[0151] Advantageously, the cover substrate 1502 may have different
properties than the base substrate 212 such as different materials
or different surface properties. For example, the base substrate
212 may be made out of plastic whereas the cover substrate 1502 may
be made out of glass. The cover substrate 1502 may be removed
allowing the holographic polymer dispersed liquid crystal grating
215 to remain on the base substrate without damaging the
holographic polymer dispersed liquid crystal grating 215 during
removal.
[0152] In some embodiments, the base substrate 212 may be treated
on the surface contacting the holographic mixture layer 211 with an
adhesion promotion layer such as reagents.
[0153] As illustrated in FIG. 16E, the liquid crystal may be
removed or evacuated from the liquid crystal rich regions between
the polymer rich regions leaving air regions. The polymer rich
regions and the air regions form polymer-air SRGs 216. In FIG. 16F,
a material of different refractive index from the polymer rich
regions may be refilled into the air regions to form hybrid SRGs
217. In some embodiments, the material may be a liquid crystal
material. The liquid crystal material may be different from the
liquid crystal material removed or evacuated from the liquid
crystal rich regions. In some embodiments, a portions of the liquid
crystal in the liquid crystal rich regions may be left between the
polymer rich regions to form the hybrid SRGs 217.
[0154] In FIG. 16G, a protective substrate 218 may be positioned
such that the hybrid SRGs 217 are between the protective substrate
218 and the base substrate 212. The protective substrate 218 may be
used to protect the hybrid SRGs 217. The protective substrate 218
may be omitted in some instances. The protective substrate 218 and
the cover substrate 1502 may have different properties where the
protective substrate 218 may add more protection when the grating
is implemented into a usable device than the cover substrate
1502.
[0155] In some embodiments, the polymer-air SRGs 216 may be
manufactured as described in connection with FIGS. 1A-1D. In these
embodiments, the protective substrate 218 may be used to protect
the polymer-air SRGs 216.
[0156] In some embodiments the base substrate 212 may be a glass,
quartz, or silica substrate including a glass surface. In some
embodiments, the base substrate 212 may be a plastic substrate and
may be coated with a silicon oxide coating (e.g. SiO.sub.2) which
may act similar to a glass surface. The silicon oxide coating or
the glass surface may include hydroxyl groups on the top surface.
The adhesion promotion material may be coated on top of the silicon
oxide coating. The hydroxyl groups may be beneficial in allowing
the adhesion promotion material to adhere to the base substrate
212.
[0157] In some embodiments, the base substrate 212 may include a
glass surface including hydroxyl groups and may be reacted with
reagents such that the reagents react with the hydroxyl groups.
FIG. 17 illustrates an example reaction where the base substrate
212 is exposed to reagents 1604 in accordance with an embodiment of
the invention. The base substrate 212 may include hydroxyl groups
1608 on the surface. The base substrate 212 is exposed to reagents
1604 and a holographic mixture material 1602 including polymer. The
reagents 1604 may be a silane coupling agent. In some embodiments,
the reagents 1604 include (R'O).sub.3--Si--R where R'O-- is an
alkoxy group and --R is an organofunctional group. The alkoxy
groups may condense with the hydroxyl groups 1608 available on the
surface resulting in surfaces decorated with organofunctional --R
groups, which may promote formation of covalent bonding of the
coupling agent with polymeric networks within the holographic
polymer dispersed liquid crystal grating 215. The reagents 1604 may
adhere to the hydroxyl groups 1608 and to the holographic mixture
material 1602 creating improved adhesion when compared to the
adhesion of the holographic mixture material 1602 without the
reagents 1604. The holographic mixture material 1602 may form a
holographic mixture layer 1610 on the surface of the base substrate
212.
[0158] FIG. 18 illustrates an example reaction where reagents 1704
are exposed to the base substrate 212. The reagents 1704 may
include a silane coupling agent as illustrated and may couple to
hydroxyl groups on the surface of a glass surface of the base
substrate 212.
[0159] In some embodiments the cover substrate 1502 may be a glass,
quartz, or silica substrate including a glass surface. In some
embodiments, the cover substrate 1502 may be a plastic substrate
and may be coated with a silicon oxide coating (e.g. SiO.sub.2)
which may act similar to a glass surface. A release layer may be
coated on top of the glass surface. In some embodiments, similar to
the base substrate 212 discussed above, the cover substrate 1502
may include a glass surface including hydroxyl groups and may be
reacted with reactants such that the reactants bond with the
hydroxyl groups to form the release layer.
[0160] FIG. 19 illustrates an example process for forming the
release layer. The cover substrate 1502 may be exposed to a release
material 1804. The release material 1804 may include a silane based
fluoropolymer or fluoro monomer reactant as illustrated. The
release material 1804 may include a fluoropolymer such as OPTOOL
UD509 (produced by Daikin Chemicals), Dow Corning 2634, Fluoropel
(produced by Cytonix), and EC200 (produced by PPG Industries, Inc)
or a fluoro monomer. In some embodiments, the release material 1804
may include a polysiloxane coating. A polysiloxane coating may
adhere better to materials such as plastic that do not have
hydroxyl groups on the surface. A polysiloxane coating may be more
robust and processable, and may be more environmentally-friendly to
produce than a fluoropolymer. The release material 1804 may be
applied through vapor deposition, spin coating, or spraying. In
some embodiments, the cover substrate 1502 may be reusable and thus
after removal after holographic exposure, the cover substrate 1502
may be placed on another holographic mixture layer which may be
exposed with holographic beams.
[0161] In some embodiments, the cover substrate 1502 and/or the
base substrate 212 may be a substrate that does not include
SiO.sub.2 as discussed above. In these instances, a very thin layer
of SiO.sub.2 may be applied to the surface to facilitate
bonding/adhesion of the applied reagent hence enabling silane
chemistry. When the cover substrate 1502 and/or the base substrate
212 is a substrate that does not include SiO.sub.2 any surface
modification followed by bonding can provide adhesion. Surface
modification may include treating with reagents to introduce
reactive functional groups including but not limited to hydroxyl
groups. In some embodiments, the cover substrate 1502 and/or the
base substrate 212 may not be a glass substrate but may still
include hydroxyl groups on the surface. For example, the cover
substrate 1502 and/or the base substrate 212 may be sapphire or
silicate which may include hydroxyl groups on the surface. In this
case, the hydroxyl groups may help facilitate adhesion of the
reagent and thus the thin layer of SiO.sub.2 would not be present.
Examples of silicate substrates are manufactured by: Corning Inc.
of Corning, N.Y., Schott A G of Mainz, Germany, Ohara Inc. of
Chuo-ku, Sagamihara, Kanagawa, Japan, Hoya Inc. of Japan, AGC Inc.
of Marunouchi, Chiyoda-ku, Tokyo, Japan, and CDGM Glass of Central
Islip, N.Y.
[0162] In some embodiments, the cover substrate 1502 and/or the
base substrate 212 may include Cleartran which is a form of
chemical vapor deposited (CVD) zinc sulfide. A thin layer of
SiO.sub.2 may be applied to the Cleartran substrate to facilitate
bonding/adhesion of the applied reagent. In some embodiments, the
cover substrate 1502 and/or the base substrate 212 may be a
transparent ceramic such as aluminum oxynitride or magnesium
aluminate. A thin layer of SiO.sub.2 may be applied to the
transparent ceramic substrate to facilitate bonding/adhesion of the
applied reagent. In some embodiments, the cover substrate 1502
and/or the base substrate 212 may include plastic such as PMMA,
acrylic, polystyrene, polycarbonate, cyclic olefin copolymer, cyclo
olefin polymer, polyester. A thin layer of SiO.sub.2 may be applied
to the plastic substrate to facilitate bonding/adhesion of the
applied reagent.
Application of Ashing and/or Atomic Layer Deposition Processes in
EPS Fabrication
[0163] In some embodiments, a further post treatment of the EPSs
might be used to remove more of the weak polymer network regions.
The post treatment may include using a plasma ashing, to reduce or
eliminate this vestigial polymer network. The plasma ashing may be
similar to the plasma ashing in semiconductor manufacturing for
removing the photoresist from an etched wafer. Exemplary equipment
and processes are supplied by Plasma Etch, Inc. incorporated in CA,
USA. In plasma ashing, a monatomic (single atom) substance known as
a reactive species may be generated from a plasma source and may be
introduced into a vacuum chamber where it is used to oxidize or
plasma ash the material to be removed. The reactive species may
include oxygen or fluorine during the plasma ashing.
Advantageously, for processing slanted gratings, the plasma beam
can be directional. In some embodiments, the plasma ashing may be
inductively coupled plasma ashing which is a process that allows
independent control of chemical and physical contributions to the
ashing process by forming reactive species and ions. A RF bias on a
substrate electrode may be used to control the acceleration of the
ions to match the requirements of different surface structures.
Electrons and ions in a plasma have different mobilities resulting
in a direct current (DC) bias. Electrons, with their low mass, may
respond quickly to RF fields, resulting in a fast electron flow to
surfaces which in turn imparts a net negative dc bias to the
(wafer) surface in contact with the plasma. The voltage difference
between the plasma and the wafer surface accelerates positive ions
to the surface. The negative DC bias may be used to fine tune many
features of the ashing process, such as ashing rate, anisotropy,
angular/spatial selectivity and others. In some embodiments, a
surface treatment of chemical additives may be applied to the EPS
before plasma ashing which may enhance DC bias application. In some
embodiments, the EPS may be placed in the presence of a gas such as
a noble gas during plasma ashing. The noble gas may be argon. In
some embodiments, the plasma ashing may be used to adjust at least
one of fringe shape and spatial variation of the polymer grating
structure. In some embodiments, the plasma ashing beam intensity
may be variable to provide spatially varying modulation depths.
Angular variation of the intensity of the plasma ashing beam may be
used for fringe shaping. In some embodiments, the plasma ashing may
be applied along more than one intersecting direction for forming a
photonic crystal. In some embodiments, a high functionality
acrylate around the edge of the diffracting features may change the
density of a diffracting feature of the EPS with the plasma ashing
rate being controlled at a spatial resolution comparable to the EPS
spatial frequency. The morphology of the EPS may be modified to
improve grating performance and increase the efficiency of
processes such as ashing, improve the grating definition, change
the surface structure to reduce haze adding materials for
increasing the chemical affinity with gases present during the
plasma ashing process, and/or change the effective refractive index
of the grating. In some embodiments, the modulation depth of the
EPS may be determined by the plasma ashing time since the greater
the plasma ashing time the more material is removed.
[0164] In some embodiments, oxygen and/or fluorine may be used as
reactive species in the plasma ashing process. In some embodiments,
hydrogen plasmas may be used in the plasma washing process. In some
embodiments, ashing rates in oxygen plasma may be controlled by
additives in the HPDLC mixture such as nitrogen. In some
embodiments, a plasma ashing process for ashing organic material
may use a gas mixture of oxygen and NH.sub.3. An oxygen based
process may suffer from substrate surface oxidation. In some
embodiments, the plasma ashing process may include oxygen free
plasmas which may include mixtures of nitrogen and hydrogen to
overcome surface oxidation. Such plasma mixtures may further
comprise fluorine.
[0165] In some embodiments, post coating the EPSs with a very thin
atomic layer of high index material can enhance the diffractive
properties (e.g. the refractive index modulation) of the grating.
The coating may be a metallic layer or a dielectric layer. One such
process, Atomic Layer Deposition (ALD), involves coating the
gratings with TiO.sub.2 or ZnO.sub.2 or similar. The coating may
provide a grating structure that is more robust against temperature
variations and various other environmental conditions. The ALD
process can also provide a large effective index even when the
grating structures are made of lower index materials. This
technique may be similarly applied to the fabrication of
nanoimprinted SRGs where a few nanometer thick ALD can protect the
resin into which the SRG is stamped and can also improve the
effective refractive index modulation. The use of Atomic Layer
Deposition (ALD) on top of an EPS may yield further performance
improvement. In many embodiments, the duty cycle of the EPS might
not be optimal for weak polymer networks. In some embodiments, the
duty cycle of the EPS may be 30% polymer.
[0166] Various EPS manufacturing processes are described above in
FIGS. 1A-1D. FIGS. 3A and 3B illustrate various EPSs after
manufacturing. FIGS. 20A and 20B illustrate various grating in
accordance with an embodiment of the invention. The grating
includes many identically numbered elements to those of FIGS. 3A
and 3B. The description of these elements of FIGS. 3A and 3B are
applicable to the gratings of FIGS. 19A and 19B and will not be
repeated in detail. The gratings may be EPSs which are manufactured
using processes described in connection with FIGS. 1A-1D and FIG.
2. The gratings may also be hybrid gratings which are manufactured
using processes described in connection with FIGS. 4A-4E and 5. As
illustrated in FIGS. 19A and 19B, the grating may include a coating
1902. The coating 1902 may be present on the horizontal surfaces
such as the top of the polymer regions 3004a and the substrate
3002. As illustrated, FIG. 19B includes an optical layer 3008 which
is in direction contact with the substrate 3002 such that the
optical layer 3008 is positioned between the polymer regions 3004a
and the substrate 3002. The coating 1902 may be positioned on the
optical layer 3008. The coating 1902 may be deposited using a
process such as ALD. The coating 1902 may not have step coverage
and thus only be deposited on the horizontal surfaces such as the
top of the polymer regions 3004a and the substrate 3002 or optical
layer 3008. In some embodiments, the coating 1902 may be deposited
using a process that includes step coverage such that the coating
1902 is present on the sidewalls of the polymer regions 3004a. In
some embodiments, the coating 1902 may be TiO.sub.2 or ZnO.sub.2.
The coating 1902 may be multilayered to include multiple different
layered materials. In some embodiments, an additional passivation
coating may be applied to the surfaces of the polymer grating
structure over the coating 1902. The additional passivation coating
may provide environmental protection (e.g. protection from moisture
and/or contamination).
[0167] In some embodiments, the coating 1902 may be present on the
substrate 3002 or optical layer 3008 and not the top of the polymer
regions 3004a. FIG. 20C illustrates a grating in accordance with an
embodiment of the invention. The grating includes many identically
numbered elements to those of FIGS. 3A and 3B. The description of
these elements of FIGS. 3A and 3B are applicable to the gratings of
FIG. 20C and will not be repeated in detail. As illustrated, the
grating of FIG. 20C includes a coating 1902 similar to FIGS. 20A
and 19B. However, the coating 1902 is only present on the substrate
3002 and not the tops of the polymer regions 3004a as is the case
in FIGS. 20A and 20B. In embodiments with an optical layer 3008,
the coating 1902 may only be present on the optical layer 3008 and
not on the tops of the polymer regions 3004a. In some embodiments,
the coating 1902 may be removed off the tops of the polymer regions
3004a or the coating 1902 may be selectively deposited on the
substrate 3002. The coating 1902 may function as a bias layer
similar to the optical layer 3008.
Embodiments Including Slanted EPSs
[0168] In some embodiments, the gratings include slanted EPSs
making up slanted gratings. Slanted gratings can be configured as
binary gratings, blazed gratings, and/or multilevel gratings and
other structures. Slanted gratings may couple monochromatic angular
light into waveguides with high diffraction efficiency. They also
allow angular content to be managed more efficiency once the light
is inside the waveguide. When configured with stepwise or
continuously spatially varying K-vectors the angular bandwidth that
can be coupled into a waveguide may be increased.
Embodiments Including Eyeglow Suppression
[0169] In waveguide-based displays light may be diffracted toward
the user and also away from the user. Eye glow may include unwanted
light emerging from the front face of a display waveguide (e.g. the
waveguide face furthest from the eye) and originating at a
reflective surface of the eye, a waveguide reflective surface and a
surface of grating (due to leakage, stray light diffractions,
scatter, and other effects). The light that is diffracted away is
commonly called "eye-glow" and poses a liability for security,
privacy, and social acceptability. "Eye glow" may refer to the
phenomenon in which a user's eyes appear to glow or shine through
an eye display caused by leakage of light from the display, which
creates an aesthetic that can be unsettling to some people. In
addition to concerns regarding social acceptability in a fashion
sense, eye glow can present a different issue where, when there is
sufficient clarity to the eye glow, a viewer looking at the user
may be able to see the projected image intended for only the user.
As such, eye glow can pose a serious security concern for many
users. A discussion of various eyeglow suppression systems is
discussed in detail in WO 2021/242898, entitled "Eye Glow
Suppression in Waveguide Based Displays" and filed May 26, 2021,
which is hereby incorporated by reference in its entirety for all
purposes.
[0170] FIGS. 21A-21C conceptually illustrate three embodiments of
waveguides in which evanescent coupling into a grating can occur.
In these embodiments, a grating layer 2004 is positioned on a
substrate 2002. In FIG. 21A, two identical substrates 2002, 2006
sandwich the grating layer 2004. In FIG. 21B, a thin substrate
2006a and a thick substrate 2006 sandwich the grating layer 2004.
In FIG. 21C, a thick substrate 2002 supports the grating layer 2004
without the presence of a top substrate. The top substrate 2006,
2006a may be a cover substrate or coating. In other embodiments, a
thin protective coating can be applied to the grating layer 2004.
The upper surface of each the waveguide embodiments faces the
user's eye. The grating layer 2004 may eject light 2010 from the
waveguide towards the user's eye. Unwanted eyeglow light 2008 may
also be ejected towards the environment as illustrated in the cases
of FIGS. 21A and 21B.
[0171] Eyeglow and/or light leakage can be reduced from the
opposing outer surface by eliminating the top substrate as
illustrated in FIG. 21C. The elimination of an upper substrate may
result in less eyeglow/light leakage than the other two
embodiments. Note that, in each embodiment illustrated, all rays
shown undergoing TIR are at TIR angles that may be evanescently
coupled to the grating layer 2004. Zero order light rays are
indicated by dashed lines. In some embodiments, the evanescent
grating coupling may result in eyeside output light substantially
normal to the waveguide, as shown.
[0172] Where the grating average refractive index is lower than the
substrates, then for high angles (far from TIR) where only
evanescent coupling can occur, zero order TIR light cannot pass
through the grating layer 2004 to TIR off both air interfaces.
Light propagating in TIR can therefore get trapped on one side of
the grating or the other. Grating depth in the thickness of the
waveguide may affect the amount of light that is coupled to the
desired eyeside, and the undesired non-eye side where light is lost
as eyeglow/light leakage. In some embodiments, evanescent coupling
may result in at least a portion of the coupled light being
converted to guided modes within at least one the grating and the
eye side waveguide substrate 2006, 2006a. The evanescent coupling
behaviors may be a function of the TIR angle, grating thickness,
modulation, average index and the index and thickness of the
eyeside substrate 2006, 2006a.
[0173] In some embodiments, a slanted EPS may also provide eyeglow
suppression. One advantage to the use of EPSs in the context of
eyeglow suppression and other stray light control applications such
as glint suppression, is that a variety of grating types can be
implemented on a waveguide substrate to provide different types of
beam angular selectivity for dealing with the stray light present
in various regions of the waveguide. In some regions of a waveguide
where wide angle capability is desired, an EPS may be configured as
a Raman-Nath grating, which may have a modulation depth less than
the grating pitch across at least a portion of the polymer grating
structure. In other regions where high diffraction efficiency for
certain beam angles is required, an EPS may operate in the Bragg
regime.
Embodiments Including Inverse Gratings
[0174] In some embodiments, the gratings disclosed in connection
with FIGS. 20A and 20B may be used to create inverse gratings.
These inverse gratings may be thin film gratings. FIGS. 22A-22D
illustrate various stages of manufacturing an inverse grating in
accordance with an embodiment of the invention. The various stages
of manufacturing includes many identically numbered elements to
those of FIGS. 3A, 3B, 20A, and 20B. The description of these
elements of FIGS. 3A, 3B, 20A, and 20B are applicable to the
gratings of FIG. 20C and will not be repeated in detail. FIG. 22A
corresponds to the structure created in FIG. 1B which includes
polymer regions 3004a separated by phase separated material 2102.
The phase separation grating may be formed from a mixture of
monomer and a second component deposited onto the substrate 3002
using the recording process described above. The second component
can include a liquid crystal or a suspension of nanoparticles.
Other materials capable of phase separation can be used. After
exposure, a grating may be created including alternating fringes
rich in polymer and fringes rich in the second component.
[0175] In FIG. 22B, the phase separated material 2102 is removed to
create air gap regions 3004b to create an EPS. The EPS structure
created in FIG. 22B corresponds to the EPS structure in FIG. 3A. In
this step, the second component can be removed to form a polymer
surface relief grating including polymer regions separated by air
spaces.
[0176] In FIG. 22C, a coating 1902 is applied to the surfaces of
the substrate 3002 and the tops of the polymer regions 3004a. In
some embodiments, the coating 1902 may be applied through an ALD
process. The structure created in FIG. 22C corresponds to the
structure in FIG. 19A. In some embodiments, the air regions 3004b
can be at least partially backfilled with a material of refractive
index differing from that of the polymer regions 3004a. The
backfilling can be performed by applying an ALD coating similar to
the one described above. In some embodiments, the ALD coating may
be higher thickness than the thin coatings described in connection
with FIGS. 20A-20C. Other methods of backfilling the grating may be
used depending on the type of material and the thickness of
backfilled layer. The backfill material can have an index higher or
lower than that of the polymer regions 3004a, according to the
intended grating application. At the end of this step, the polymer
surface relief grating may be partially filled with the backfill
material as shown in FIG. 22C. As illustrated, some of the backfill
material may adhere to the top faces of the polymer regions 3004a.
Some of the backfill material may also adhere to the upper portions
of the polymer regions 3004a.
[0177] In FIG. 22D, the polymer regions 3004a are removed. The
coating 1902 on the tops of the polymer regions 3004a is removed as
well. The remaining coating 1902 disposed on the substrate 3002 may
be used as an inverse grating. The remaining coating 1902
alternates with air regions 2104. In this step, the polymer regions
3004a and unwanted coating 1902 can be removed using an etching
process such as a plasma ashing process to reveal a slanted Bragg
surface relief grating composed of the coating 1902 supported by
the substrate 3002. In some embodiments, the polymer regions 3004a
may be removed through a plasma ashing technique. The inverse
grating may be a thin film Bragg surface relief grating.
Embodiments for Fabricating a Surface Relief Grating with Improved
Grating Definition
[0178] One strategy for reducing haze is to reduce the surface
roughness of SRGs. In many embodiments, a composite grating with
improved surface definition, e.g. low surface roughness. FIG. 23A
illustrates a schematic representation of a grating in accordance
with an embodiment of the invention. In a first step, the grating
may be formed using phase separation of a starting mixture
including a material A and a material B using the procedures
discussed earlier. Material A may be a polymer. After curing of the
grating, component B may be extracted to leave a grating including
high index regions containing voids 2301 embedded in polymer 2302
and low index regions containing a weak polymer structure and other
residues resulting from incomplete phase separation. The polymer
structure and other residues may be further removed using a process
such as plasma ashing to leave air regions 2303.
[0179] FIG. 23B illustrates a schematic representation of a grating
in accordance with an embodiment of the invention. The grating may
be manufactured with a process starting with the process described
in connection of FIG. 23A. In a next step, the grating is immersed
in a material C which fills the voids 2304 and air regions 2305.
The material C may be cured using a process such as UV
exposure.
[0180] FIG. 23C illustrates a schematic representation of a grating
in accordance with an embodiment of the invention. The grating may
be manufactured with a process starting with the process described
in connection of FIG. 23B. In a next step, material C may be
removed from the gap regions by a process such as plasma ashing to
leave composite polymer and material C regions 2306 separated by
air gaps 2307. The plasma ashing step may be separate from the
plasma ashing step described in connection with FIG. 30A. After
plasma ashing, the composite material may have a smoother surface
the polymer 2302 described in connection with FIG. 23A. Material A
and material C may provide a refractive index contrast that is low
enough to minimise scattering while providing a desired refractive
index modulation.
[0181] In many embodiments bulk scatter may be strongly influenced
by the refractive index contrast within the high index region while
surface scattering may be dependent on the surface texture. In many
embodiments, by filling surface voids as in the process discussed
in FIGS. 23A-23C in combination with ashing may result in a
smoother surface structure. In many embodiments, the above process
may be used to eliminate the bulk scatter contributions that may
arise from voids within the polymer regions 2304.
[0182] FIG. 24 illustrates an example process flow for fabricating
SRGs in accordance with an embodiment of the invention. In a first
step, a grating structure may be formed 2410 using a phase
separation process utilizing a starting mixture including a
material A and a material B. After phase separation, there may be a
material A rich region and a material B rich region. In a second
step which includes a first ashing step, material B may be
extracted (2411) to leave a grating structure including high index
regions containing voids embedded in polymer and index regions
containing a residual polymer matrix. The material B rich regions
may become an air regions after the first ashing step. In a third
step, the grating structure may be immersed (2412) in a material C
to fill the voids in the polymer rich regions and air regions. In a
fourth step, the material C may be extracted (2413), using a second
ashing step, to remove material C from the previous air regions to
leave a composite polymer and material C region separated by air
gaps. As described previously, this may result in a lower surface
roughness in the fabricated SRGs. In some embodiments, the SRGs may
be deep SRGs as discussed previously.
Surface Relief Gratings Configured as Dual Interaction Gratings
[0183] In conventional Bragg gratings, dual interaction can be
understood using basic ray optics by considering upwards and
downward TIR ray interactions with a fold grating. The upward and
downwards rays occurring when guided light is reflected at the
lower and upper waveguide TIR surfaces. The two ray paths give rise
to two shifted diffraction efficiency vs angle characteristics
which combine to extend the angular bandwidth. Examples of an
optical waveguide including at least two TIR surfaces and
containing a grating of a first prescription configured such that
an input TIR light with a first angular range along a first
propagation direction undergoes at least two diffractions within
said grating and undergoes a change in propagation direction from
said first propagation direction to a second propagation direction,
wherein each ray from said first angular range and its
corresponding diffracted rays lie on a diffraction cone of said
grating, wherein each diffraction provides a unique TIR angular
range along said second propagation direction are disclosed in U.S.
Pat. No. 9,632,226, entitled "Waveguide Grating Device" and filed
Feb. 12, 2015, which is incorporated herein by reference in its
entirety for all purposes.
[0184] FIGS. 25A and 25B illustrate the principles of a dual
interaction grating for implementation in a waveguide. The
waveguide 30 includes grating fringes 31 slanted with respect to
the waveguide TIR faces and aligned at a clocking angle within the
waveguide plane. In many embodiments clocking angle may be 45
degrees to provide a 90 degree beam deflection. In FIG. 25A, a
first TIR path lies in the input propagation plane 2020 and, after
diffraction in the output propagation plane 2021. The grating has a
k-vector 2022 also labelled by the symbol k. The tilt angle 2023 of
the grating fringes relative to the waveguide surface normal 2024
is also indicated. TIR light 2025 in the propagation plane 2001
having a TIR angle 2026 relative to the waveguide plane normal 2027
strikes the grating fringe as an upward-going ray 2028 which is
diffracted into the TIR direction 2029 lying inside the propagation
plane 2021. In FIG. 25B, a second TIR path in the input propagation
plane 2001 indicated by 2030 has a TIR angle 2031 relative to the
waveguide plane normal 2027 strikes the grating fringe as a
downward-going ray 2033 which is diffracted into the TIR direction
2034 lying inside the output propagation plane 2021. Since the
upward-going and downward-going TIR rays are asymmetric in this
case there may be two peaks in the output diffraction efficiency
versus angle characteristics.
[0185] FIG. 26 conceptually illustrates a cross section of a
grating in accordance with an embodiment of the invention. The
grating may be a SRG 2100 including slanted fringes 2101 separated
by air volumes 2103. In many embodiments, the gratings may be
clocked or slanted within the waveguide plane. FIG. 27 is a
conceptual representation of beam propagation with the grating of
FIG. 26. The grating is represented as a configuration 2110 which
for conceptual purposes may be divided up into a deep grating
portion 2111 including alternating high index fringes 2113 and low
index fringes 2114, which operates in the Bragg regime, overlaid by
a thin grating portion 2112 including alternating high index
regions 2115 and low index regions 2116 which operates in the
Raman-Nath regime. In many embodiments, the high index regions 2115
are polymer and the low index regions 2116 are air. The grating
configuration 2110 supports TIR beam propagation include ray paths
such as 2117. To simplify the explanation of the embodiment the
guided ray reflection as represented by the rays 2118,2119, is
represented as taking place at the interface of the volume grating
portion 2111 and the thin grating portion 2112. A reasonable
approximation of the TIR at the thin grating portion 2112 may be
considered separated from the coupled wave propagation through the
volume grating portion 2112.
[0186] In some embodiments, the thick grating portion 2112 may be
partially backfilled with a different refractive index material up
to the level of the thin grating portion 2112 and thick grating
portion 2111 interface. FIG. 28 illustrates an example of a
partially backfilled grating 2121 in accordance with an embodiment
of the invention. This partially backfilled grating 2121 may be
considered a hybrid surface relief grating/volume Bragg grating.
The backfilled grating 2121 is the grating described in connection
with FIG. 27 that has been backfilled with a different refractive
index material. The backfilled grating 2121 may be considered a
volume grating. In many embodiments, the unfilled regions that
remain after partial backfilling of the air regions may provide a
polymer Raman-Nath surface relief grating 2802 including
alternating polymer regions and air regions overlaying a Bragg
grating 2804 comprising alternating polymer regions and backfilled
material regions. In a waveguide implementation the upward and
downward TIR propagation directions may be produced by TIR at the
waveguide to air interfaces.
[0187] The dual interaction illustrated in FIGS. 25A-25B may
include upward and downward propagating TIR rays. In an SRG, one of
the TIR propagation directions results from the reflective
diffraction at the SRG taking place at an angle equal to the TIR
angle. The SRG may allow diffraction TIR to take place with high
efficiency subject to some constraints on the ranges of incidence
angles, K-vector directions, grating clock angles, grating period,
and/or grating thickness. In some embodiments, the SRG may be a
fold grating. Hence a first TIR propagation direction 2119 produced
by the surface grating and an opposing TIR propagation direction
2120 produced by reflection from the opposite face of the grating
substrate may interact within the volume grating portion shown in
FIG. 28. In many embodiments, this ray-grating interaction may
result in a dual interaction according to the embodiments and
teachings of U.S. Pat. No. 9,632,226 which is hereby incorporated
by reference in its entirety for all purposes. The grating
diffraction efficiency may be dependent on the at least one of the
guide beam angular bandwidth, grating vector, grating thickness,
and/or grating fringe spacing. In some embodiments, the thick
grating portion 2111 may be eliminated to provide only the thin
surface relief grating portion 2112 supported by a transparent
substrate.
[0188] Hybrid surface relief grating/volume Bragg grating
structures may offer several advantages including wider cumulative
angular response which, in many embodiments, may allow thicker
gratings to be used for improving DE without compromising angular
bandwidth. Coating the hybrid gratings with an ALD coating to
increase the effective index may further enhance the angular
bandwidth. In many embodiments, the hybrid surface relief
grating/volume Bragg grating structures may improve the diffraction
efficiency for P-polarized light. In some embodiments, a hybrid
surface relief grating/volume Bragg grating structures formed by
phase separating a mixture of an inorganic component and a monomer
may include fully inorganic SRG after complete removal of the final
polymer component from the cured grating. In many embodiments the
inorganic component may be nanoparticles. In many embodiments, a
hybrid surface relief grating/volume Bragg grating structures may
be used in at least one of a fold grating and/or an output grating
to reduce haze and to reduce coupling losses in a fold grating.
Reducing haze may increase contrast. Reducing coupling losses in
the fold grating may be equivalent to increasing diffraction
efficiency in the fold grating. In many embodiments, a polymer/air
SRG may be used as an input grating with high diffraction
efficiency.
[0189] As illustrated previously, hybrid surface relief
grating/volume Bragg grating structures may be formed by partial
back filling of a grating structure to form a structure comprising
a volume Bragg grating with an overlaid surface relief grating.
Hybrid surface relief grating/volume Bragg grating structures may
show improved angular response after an additional plasma ashing or
reactive ion etch.
[0190] In many embodiments, hybrid surface relief grating/volume
Bragg grating structures may be formed during holographic phase
separation and curing. In many embodiments, the grating may be
formed in a cell in which the grating material is sandwiched by a
base substrate and a release layer. The surface structure may be
revealed when the release layer is removed. Without limitation to
any particular theory, the surface grating may be formed because of
polymerization induced shrinkage during to mass migration and phase
separation. The relative depths of high and low index regions can
be adjusted by utilizing an additional plasma ashing step. An ALD
deposited layer can be added to the grating surface to increase
effective index. In many embodiments, the grating thickness may be
1.1 microns with a grating period of 375 nm and a 22-degree slant
angle (relative to the cell optical surface normal). The finished
gratings may be isotropic or anisotropic depending on the system
components in the initial mixture.
[0191] FIG. 29 schematically illustrates a ray-grating interaction
geometry 2130 of a TIR surface grating. Such configurations are
commonly referred to as conical diffraction configurations. For a
TIR grating recorded on a transparent substrate of refractive index
n.sub.S immersed in a low index medium of index n.sub.0 (which in
many embodiments will be air) but can be any medium satisfying the
relation n.sub.S>n.sub.0, only reflected diffracted orders exist
for rays that satisfy the relation
n.sub.S/n.sub.0.ltoreq.|sin(u.sub.inc)|.ltoreq.1. Referring to the
xyz Cartesian reference frame in FIG. 28, the equations relating
incident and diffracted ray angles to the grating vectors may be
expressed as follows:
x direction: -k n.sub.S sin(u.sub.inc)+K.sub.S cos(.phi..sub.s)=-k
n.sub.S sin(u.sub.diff)cos(.phi..sub.diff);
y direction: K.sub.S sin(.phi..sub.s)=k n.sub.S
sin(u.sub.diff)sin(.phi..sub.diff); and
z direction: k n.sub.S cos(u.sub.inc)=k n.sub.S
cos(u.sub.diff)+K.sub.S/tan(.phi..sub.s).
where u.sub.inc is the polar angle of the incident ray vector
r.sub.inc, .phi..sub.s is the azimuth angle of the incident ray,
u.sub.diff is the polar angle of the diffracted ray vector
r.sub.diff, .phi..sub.s is the azimuth angle of the grating vector,
and us is the polar angle of the grating vector K.
[0192] The wavenumber k of the incident light may be provided by
k=2.pi./.lamda., where .lamda. is the wavelength of the guided
light. The modulus of the surface component of the grating vector
is given by K.sub.S=k=2.pi./ .sub.S where .sub.S is the surface
grating pitch. Solutions to the above equations may be obtain by
setting the incidence angle equal to the diffracted angle.
[0193] In many embodiments, the dual interaction grating is
implemented in a polymer grating structure comprising alternating
polymer rich and air regions. In many embodiments, the grating
depth of the polymer grating structure is less than the Bragg
fringe spacing. In many embodiments, the grating depth of the
polymer grating structure is greater than the Bragg fringe spacing.
In many embodiments, the total internal reflection from the polymer
grating structure occurs when the first order diffraction from the
polymer grating structures has a diffraction angle equal to the TIR
angle of the waveguide. In many embodiments, the polymer grating
structure provides no transmitted diffraction orders. In many
embodiments, the polymer grating structure is a photonic crystal.
In many embodiments, the polymer grating structure is configured as
a Raman Nath grating having a first grating period overlaying a
Bragg grating having the same grating period with the minima of the
Raman Nath grating overlaying the minima of the Bragg grating. In
many embodiments, the polymer grating structure is a slanted
grating. In many embodiments, the air regions of polymer grating
structure may be at least partially backfilled with a material
having a refractive index different than that of the polymer rich
regions.
Embodiments Including OLED Arrays as Image Generators
[0194] There is growing interest in the use of Organic Light
Emitting Diode (OLED) arrays as image generators in waveguide
displays. OLEDs have many advantages in waveguide display
applications. As an emissive technology, OLEDs require no light
source. OLEDs can be printed cost--effectively over large areas.
Non-rectangular pixel array patterns can be printed onto curved or
flexible substrates. As will be discussed below, the ability to
pre-distort a pixel array and create a curved focal plane adds a
new design dimension that can enable compensation for guided beam
wavefront distortions caused by curved waveguides and prescription
lenses supported by a waveguide. OLEDs with resolutions of
4K.times.4K pixels are currently available with good prospects of
higher resolution in the near term, offering a faster route to high
resolution, wide FOV AR displays than can be provided by
technologies such as Liquid Crystal on Silicon (LCoS) and Micro
Electro Mechanical Systems (MEMS) devices such as digital light
processing (DLP) devices. Another significant advantage over LCoS
is that OLEDs can switch in microseconds (compared with
milliseconds for LC devices).
[0195] OLEDs have certain disadvantages. In their basic form, OLEDs
are Lambertian emitters, which makes efficient light collection
much more challenging than with LCoS and DLP micro displays. The
red, green, and blue spectral bandwidths of OLEDs are broader than
those of Light Emitting Diodes (LEDs), presenting further light
management problems in holographic waveguides. The most significant
disadvantage of OLEDs is that in waveguides using HPDLC periodic
structures such as switchable periodic structures, which tend to be
P-polarization selective, half of the available light from the OLED
is wasted. As such, many embodiments of the invention are directed
towards waveguide displays for use with emissive unpolarized image
sources that can provide high light efficiency for unpolarized
light and towards related methods of manufacturing such waveguide
displays.
[0196] For the purposes of describing embodiments, some well-known
features of optical technology known to those skilled in the art of
optical design and visual displays have been omitted or simplified
in order to not obscure the basic principles of the invention.
Unless otherwise stated, the term "on-axis" in relation to a ray or
a beam direction refers to propagation parallel to an axis normal
to the surfaces of the optical components described in relation to
the invention. In the following description the terms light, ray,
beam, and direction may be used interchangeably and in association
with each other to indicate the direction of propagation of
electromagnetic radiation along rectilinear trajectories. The term
light and illumination may be used in relation to the visible and
infrared bands of the electromagnetic spectrum. Parts of the
following description will be presented using terminology commonly
employed by those skilled in the art of optical design. As used
herein, the term grating may encompass a grating comprised of a set
of gratings in some embodiments. For illustrative purposes, it is
to be understood that the drawings are not drawn to scale unless
stated otherwise.
[0197] Turning now to the drawings, methods and apparatus for
providing waveguide displays using emissive input image panels in
accordance with various embodiments of the invention are
illustrated. FIG. 30 conceptually illustrates a waveguide display
in accordance with an embodiment of the invention. As shown, the
apparatus 100 includes a waveguide 101 supporting input 102 and
output 103 gratings with high diffraction efficiency for
P-polarized light in a first wavelength band and input 104 and
output 105 gratings with high diffraction efficiency for
S-polarized light in the first wavelength band.
[0198] The apparatus 100 further includes an OLED microdisplay 106
emitting unpolarized light with an emission spectral bandwidth that
includes the first wavelength band and a collimation lens 107 for
projecting light from the OLED microdisplay 106 into a field of
view. In the illustrative embodiment, the S and P diffracting
gratings 102-105 can be layered with no air gap required. In other
embodiments, the grating layers can be separated by an air gap or a
transparent layer. The S and P diffracting gratings 102-105 may be
the deep SRGs or EPSs described above.
[0199] FIG. 31 conceptually illustrates a waveguide display in
accordance with an embodiment of the invention in which the
P-diffracting and S-diffracting gratings are disposed in separate
air-spaced waveguide layers. As shown, the apparatus 110 comprises
upper 111 and lower 112 waveguide layers (supporting the gratings
102,103 and 104,105, respectively) separated by an air gap 113. The
gratings 102,103 and 104,105 may be the deep SRGs and EPSs
described above.
[0200] FIG. 32 conceptually illustrates typical ray paths in a
waveguide display in accordance with an embodiment of the
invention. In the embodiment 120 illustrated in FIG. 32, a
microdisplay 106 is configured to emit unpolarized light 121 in a
first wavelength band, which is collimated and projected into a
field of view by a collimator lens 107. The S-polarized emission
from the microdisplay 106 can be coupled into a total internal
reflection path in a waveguide 101 by an S-diffracting input
grating 104 and extracted from the waveguide 101 by an
S-diffracting output grating 105. P-polarized light from the
microdisplay 106 can be in-coupled and extracted using
P-diffracting input and output gratings 102,103 in a similar
fashion. Dispersion can be corrected for both S and P light
provided that the input and output gratings spatial frequencies are
matched. The input and output gratings 102,103 may be the deep SRGs
or EPSs described above.
[0201] Although FIGS. 23-25 show specific waveguide display
configurations, various configurations including modifications to
those shown can be implemented, the specific implementation of
which can depend on the specific requirements of the given
application. Furthermore, such displays can be manufactured using a
number of different methods. For example, in many embodiments, the
two grating layers are formed using an inkjet printing process.
[0202] In many embodiments, the waveguide operates in a monochrome
band. In some embodiments, the waveguide operates in the green
band. In several embodiments, waveguide layers operating in
different spectral bands such as red, green, and blue (RGB) can be
stacked to provide a three-layer waveguiding structure. In further
embodiments, the layers are stacked with air gaps between the
waveguide layers. In various embodiments, the waveguide layers
operate in broader bands such as blue-green and green-red to
provide two-waveguide layer solutions. In other embodiments, the
gratings are color multiplexed to reduce the number of grating
layers. Various types of gratings can be implemented. In some
embodiments, at least one grating in each layer is a switchable
periodic structure.
[0203] The invention can be applied using a variety of waveguides
architectures, including those disclosed in the literature. In many
embodiments, the waveguide can incorporate at least one of: angle
multiplexed gratings, color multiplexed gratings, fold gratings,
dual interaction gratings, rolled K-vector gratings, crossed fold
gratings, tessellated gratings, chirped gratings, gratings with
spatially varying refractive index modulation, gratings having
spatially varying grating thickness, gratings having spatially
varying average refractive index, gratings with spatially varying
refractive index modulation tensors, and gratings having spatially
varying average refractive index tensors. In some embodiments, the
waveguide can incorporate at least one of: a half wave plate, a
quarter wave plate, an anti-reflection coating, a beam splitting
layer, an alignment layer, a photochromic back layer for glare
reduction, louvre films for glare reduction In several embodiments,
the waveguide can support gratings providing separate optical paths
for different polarizations. In various embodiments, the waveguide
can support gratings providing separate optical paths for different
spectral bandwidths. In a number of embodiments, gratings for use
in the invention can be HPDLC gratings, switching gratings recorded
in HPDLC (such switchable Bragg Gratings), Bragg gratings recorded
in holographic photopolymer, or surface relief gratings.
[0204] In some embodiments, the EPS may be a dual axis expansion
grating for use in a display waveguide. In Bragg gratings, dual
interaction can be understood using basic ray optics by considering
upwards and downward TIR ray interactions with a fold grating, the
upward and downwards rays occurring when guided light is reflected
at the lower and upper waveguide TIR surfaces. In an EPS, one of
the TIR interfaces is replaced by the grating. Using diffraction
grating theory, it can be shown that a SRG (and a SRG fold in
particular) may allow the diffraction angle into first order to
equal the incidence angle such that TIR can take place subject to
some constraints on the ranges of incidence angles, K-vector
directions, grating clock angles, grating depths and grating
periods. Hence upward and downward TIR paths through the grating
exist for SRGs. Increasing the SRG thickness into the Bragg domain,
dual interaction may occur in an EPS in the same way as in a volume
Bragg grating. Thus, various embodiments of the invention pertain
to a dual interaction EPS.
[0205] In many embodiments, the waveguide display can provide an
image field of view of at least 50.degree. diagonal. In further
embodiments, the waveguide display can provide an image field of
view of at least 70.degree. diagonal. In some embodiments, an OLED
display can have a luminance greater than 4000 nits and a
resolution of 4 k.times.4 k pixels. In several embodiments, the
waveguide can have an optical efficiency greater than 10% such that
a greater than 400 nit image luminance can be provided using an
OLED display of luminance 4000 nits. Waveguide displays
implementing P-diffracting gratings typically have a waveguide
efficiency of 5%-6.2%. Providing S-diffracting gratings as
discussed above can increase the efficiency of the waveguide by a
factor of 2. In various embodiments, an eyebox of greater than 10
mm with an eye relief greater than 25 mm can be provided. In many
embodiments, the waveguide thickness can be between 2.0-5.0 mm.
[0206] FIG. 33 conceptually illustrates a waveguide display in
accordance with an embodiment of the invention in which at least
one portion of at least one of the waveguide optical surfaces is
curved and the effect of the curved surface portion on the guided
beam wavefronts. As shown, the apparatus 130 includes a waveguide
131 supporting the curved surface portion 132. In the illustrative
embodiment, the waveguide 131 supports input 102 and output 103
gratings with high diffraction efficiency for P-polarized light in
a first wavelength band and input 104 and output 105 gratings with
high diffraction efficiency for S-polarized light in the first
wavelength band. The microdisplay 106, which displays a rectangular
array of pixels 133 emits unpolarized light 134 in the first
wavelength band, which is collimated and projected into a field of
view by a collimator lens 107. The P-polarized emission from the
microdisplay 106 can be coupled into a total internal reflection
path into the waveguide by the P-diffracting input grating 102 and
extracted from the waveguide by the P-diffracting output grating
103. The presence of any non-planar surface in a waveguide can
distort the waterfronts of the guided light such that the output
light when viewed from the eyebox exhibits defocus, geometric
distortion, and other aberrations. For example, in FIG. 33, the
light projected by the collimator lens 107 from a single pixel has
planar wavefronts 135, which after propagating through the
waveguide 131 along the TIR path 136 forms non-parallel output rays
137-139 that are normal to the curved output wavefront 139A. On the
other hand, a perfect planar waveguide would instead provide
parallel beam expanded light. FIG. 34 conceptually illustrates a
version 140 of the waveguide in which the waveguide substrate 141
supports two overlapping upper 142 and lower 143 curved
surfaces.
[0207] FIG. 35 conceptually illustrates a waveguide display in
accordance with an embodiment of the invention in which the
aberrations introduced by a curved surface portion can be corrected
by pre-distorting the pixel pattern of the OLED microdisplay. In
the illustrative embodiment, the waveguide apparatus 150 is similar
to the one illustrated in FIG. 25. As shown, the apparatus 150
includes a microdisplay 151 that supports a pre-distorted pixel
pattern 152. Unpolarized first wavelength light 153 emitted by the
microdisplay is focused by the lens 107, which substantially
collimates the beam entering the waveguide while forming wavefronts
154 that are pre-distorted by a small amount. After in-coupling and
propagation 155 through the waveguide 131, the predistorted
wavefronts are focused by the curved surface 132 to form parallel
output rays 156-158, which are normal to the planar output
wavefront 159.
[0208] FIG. 36 conceptually illustrates a waveguide display in
accordance with an embodiment of the invention in which the
aberrations introduced by a curved surface portion can be corrected
by pre-distorting the pixel pattern of an OLED microdisplay formed
on a curved substrate. The curved microdisplay substrates can help
to correct focus errors field curvature, distortion, and other
aberrations in association with the distorted pixel pattern. In the
illustrative embodiment, the waveguide apparatus 160 is similar to
the one illustrated in FIG. 32. As shown, the curved substrate
microdisplay 161 supports the pre-distorted pixel pattern 164.
Unpolarized first wavelength light 163 emitted by the microdisplay
is focused by the lens 107 to form substantially collimated guided
beams with slightly pre-distorted wavefronts 164, which, after
in-coupling and propagation 165 through the waveguide 131, form
parallel output rays 166-168 that are normal to the planar output
wavefront 169.
[0209] Although FIGS. 32-36 show specific configurations of
waveguides having curved surfaces, many other different
configurations and modifications can be implemented. For example,
the techniques and underlying theory illustrated in such
embodiments can also be applied to waveguides supporting eye
prescription optical surfaces. In many embodiments, prescription
waveguide substrates can be custom-manufactured using similar
processes to those used in the manufacture of eye prescription
spectacles, with a standard baseline prescription being fine-tuned
to individual user requirements. In some embodiments, waveguide
gratings can be inkjet printed with a standard baseline
prescription. In several embodiments, the OLED display can be
custom-printed with a pre-distorted pixel pattern formed. In
various embodiments, the OLED display can be printed onto a curved
backplane substrate. In a number of embodiments, additional
refractive or diffractive pre-compensation elements can be
supported by the waveguide. In many embodiments, additional
correction functions can be encoded in at least one of the input
and output gratings. The input and output gratings may be the deep
SRGs or EPSs or the hybrid gratings described above and may be
manufactured in the methods described in connection with FIGS. 1-5.
The input and output gratings may also have thicknesses described
in connection with FIGS. 6-8.
[0210] FIG. 37 is a flow chart conceptually illustrating a method
for projecting image light for view using a waveguide containing
S-diffracting and P-diffracting gratings in accordance with an
embodiment of the invention. As shown, the method 170 of forming an
image is provided. Referring to the flow diagram, method 170
includes providing (171) an OLED array emitting light in a first
wavelength range, a collimation lens, and a waveguide supporting
input and output gratings with high diffraction efficiency for
S-polarized light in a first wavelength band and input and output
gratings with high diffraction efficiency for P-polarized light in
the first wavelength band. In some embodiments, the input and
output gratings may be the deep SRGs, EPSs, or hybrid gratings
discussed previously. Image light emitted by the OLED array can be
collimated (172) using the collimation lens. S-polarized light can
be coupled (173) into a total internal reflection path in the
waveguide using the S-diffracting input grating. P-polarized light
can be coupled (174) into a total internal reflection path in the
waveguide using the P-diffracting input grating. S-polarized light
can be beam expanded and extracted (175) from the waveguide for
viewing. P-polarized light can be beam expanded and extracted (176)
from the waveguide for viewing.
[0211] FIG. 38 is a flow chart conceptually illustrating a method
for projecting image light for view using a waveguide supporting an
optical prescription surface and containing S-diffracting and
P-diffracting gratings in accordance with an embodiment of the
invention. As shown, the method 180 of forming an image is
provided. Referring to the flow diagram, method 180 includes
providing (181) an OLED array with a predistorted pixel pattern
emitting light in a first wavelength range, a collimation lens, and
a waveguide supporting input and output gratings with high
diffraction efficiency for S-polarized light into a first
wavelength band and input and output gratings with high diffraction
efficiency for P-polarized light in the first wavelength band and
further providing (182) a prescription optical surface supported by
the waveguide. In some embodiments, the input and output gratings
may be the deep SRGs, EPSs, or hybrid gratings discussed
previously. Image light emitted by the OLED array can be collimated
(183) using the collimation lens. S-polarized light can be coupled
(184) into a total internal reflection path in the waveguide using
the S-diffracting input grating. P-polarized light can be coupled
(185) into a total internal reflection path in the waveguide using
the P-diffracting input grating. The pre-distorted wavefront can be
reflected (186) at the prescription surface. A planar wavefront can
be formed (187) from the pre-distorted wavefront using the optical
power of the prescription surface. S-polarized light can be beam
expanded and extracted (188) from the waveguide for viewing.
P-polarized light can be beam expanded and extracted (189) from the
waveguide for viewing.
Discussion of Embodiments Including Varied Pixel Geometries
[0212] The various apparatus discussed in this disclosure can be
applied using emissive displays with input pixel arrays of many
different geometries that are limited only by geometrical
constraints and the practical issues in implementing the arrays. In
many embodiments, the pixel array can include pixels that are
aperiodic (non-repeating). In such embodiments, the asymmetry in
the geometry and the distribution of the pixels can be used to
produce uniformity in the output illumination from the waveguide.
The optimal pixel sizes and geometries can be determined using
reverse vector raytracing from the eyebox though the output and
input gratings (and fold gratings, if used) onto the pixel array. A
variety of asymmetric pixel patterns can be used in the invention.
For example, FIG. 39A conceptually illustrates a portion 230 of a
pixel pattern comprising rectangular elements 230A-230F of
differing size and aspect ratios for use in an emissive display
panel in accordance with an embodiment of the invention. In some
embodiments, the pixels array can be based a non-repeating pattern
based on a finite set of polygonal base elements. For example, FIG.
39B conceptually illustrates a portion 240 of a pixel pattern
having Penrose tiles 240A-240J for use in an emissive display panel
in accordance with an embodiment of the invention. The tiles can be
based on the principles disclosed in U.S. Pat. No. 4,133,152 by
Penrose entitled "Set of tiles for covering a surface" which is
hereby incorporated by reference in its entirety. Patterns
occurring in nature, of which honeycombs are well known examples,
can also be used in many embodiments.
[0213] In many embodiments, the pixels can include arrays of
identical regular polygons. For example, FIG. 39C conceptually
illustrates a portion 250 of a pixel pattern having hexagonal
elements in accordance with an embodiment of the invention. FIG.
39D conceptually illustrates a portion 260 of a pixel pattern
having square elements 250A-250C in accordance with an embodiment
of the invention. FIG. 39E conceptually illustrates a portion 270
of a pixel pattern having diamond-shaped elements 270A-270D in
accordance with an embodiment of the invention. FIG. 39F
conceptually illustrates a portion 280 of a pixel pattern having
isosceles triangle elements 280A-280H in accordance with an
embodiment of the invention.
[0214] In many embodiments, the pixels have vertically or
horizontally biased aspect ratios. FIG. 39G conceptually
illustrates a portion 290 of a pixel pattern having hexagonal
elements 290A-290C of horizontally biased aspect ratio. FIG. 39H
conceptually illustrates a portion 300 of a pixel pattern having
rectangular elements 300A-300D of horizontally biased aspect ratio
in accordance with an embodiment of the invention. FIG. 39I
conceptually illustrates a portion 310 of a pixel pattern having
diamond shaped elements 310A-310D of horizontally biased aspect
ratio in accordance with an embodiment of the invention. FIG. 39J
conceptually illustrates a portion 320 of a pixel pattern having
triangular elements 320A-320H of horizontally biased aspect ratio
in accordance with an embodiment of the invention.
[0215] In many embodiments, OLEDs can be fabricated with cavity
shapes and multilayer structures for shaping the spectral emission
characteristics of the OLED. In some embodiments microcavity OLEDs
optimized to provide narrow spectral bandwidths can be used. In
some embodiments, the spectral bandwidth can be less than 40 nm. In
some embodiments, spectral bandwidth of 20 nm or less can be
provided. In some embodiments, OLEDs can be made from materials
that provide electroluminescent emission in a relatively narrow
band centered near selected spectral regions which correspond to
one of the three primary colors. FIG. 40 conceptually illustrates a
pixel pattern in which different pixels may have different emission
characteristics. In some embodiments, pixels may have differing
spectral emission characteristics according to their position in
the pixel array. In some embodiments, pixels may have differing
angular emission characteristics according to their position in the
pixel array. In some embodiments the pixels can have both spectral
and angular emission characteristics that vary spatially across the
pixel array. The pixel pattern can be based on any of the patterns
illustrated in FIGS. 39A-39J. In many embodiments, pixels of
different sizes and geometries can be arranged to provide a spatial
emission variation for controlling uniformity in the final
image.
[0216] In many embodiments, OLEDs can have cavity structures
designed for transforming a given light distribution into a
customized form. This is typically achieved by secondary optical
elements, which can be bulky for wearable display application. Such
designs also suffer from the problem that they limit the final
light source to a single permanent operational mode, which can only
be overcome by employing mechanically adjustable optical elements.
In some embodiments, OLEDs can enable real-time regulation of a
beam shape without relying on secondary optical elements and
without using any mechanical adjustment. In some embodiments, an
OLED can be continuously tuned between forward and off axis
principal emission directions while maintaining high quantum
efficiency in any setting as disclosed in an article by Fries
(Fries F. et al, "Real-time beam shaping without additional optical
elements", Light Science & Applications, 7(1), 18, (2018)).
[0217] An important OLED development, the "microcavity OLED", may
offer potential for more controlled spectral bandwidths and
emission angles in some embodiments. However, microcavity OLEDs are
not yet ready for commercial exploitation. In one embodiment
(corresponding to a 2-micron grating with index modulation 0.1, an
average index 1.65 and an incident angle in the waveguide of 45
degrees) the diffraction efficiency of an SBG is greater than 75%
over the OLED emission spectrum (between 25%-of-peak points).
Narrower bandwidth OLEDs using deeper cavity structures will reduce
bandwidths down 40 nm. and below.
[0218] Advantageously, the invention can use OLEDs optimized for
use in the blue at 460 nm., which provides better blue contrast in
daylight AR display applications than the more commonly used 440 nm
OLED as well as better reliability and lifetime.
[0219] In some embodiments, the emissive display can be an OLED
full color silicon backplane microdisplay similar to one developed
by Kopin Corporation (Westborough, Mass.). The Kopin microdisplay
provides an image diagonal of 0.99 inch and a pixel density of 2490
pixels per inch. The microdisplay uses Kopin's patented Pantile.TM.
magnifying lenses to enable a compact form factor.
[0220] Although the invention has been discussed in terms of
embodiments using OLED microdisplays as an input image source, in
many other embodiments, the invention can be applied with any other
type of emissive microdisplay technology. In some embodiment the
emissive microdisplay can be a micro LED. Micro-LEDs benefit from
reduced power consumption and can operate efficiently at higher
brightness than that of an OLED display. However, microLEDs are
inherently monochrome Phosphors typically used for converting color
in LEDs do not scale well to small size, leading to more
complicated device architectures which are difficult to scale down
to microdisplay applications.
[0221] Although polymer periodic structures have been discussed in
terms of use within OLED array based waveguide displays, polymer
periodic structures have advantageous synergetic applications with
other classes of displays. Examples of these displays include image
generators using a non-emissive display technology such as LCoS and
MEMS based displays. While LCoS based displays typically emit
polarized light which may make the polarization based advantages of
polymer grating structures less applicable, polymer grating
structures may provide an advantageous efficiency and manufacturing
cost savings over conventional imprinted gratings. Further, polymer
grating structures may be applicable in various other non-display
waveguide-based implementations such as waveguide sensors and/or
waveguide illumination devices.
EXAMPLE EMBODIMENTS
[0222] Although many embodiments of the invention have been
described in detail, it should be appreciated that the invention
may be implemented in many other forms without departing from the
spirit or scope of the invention. For example, embodiments such as
enumerated below are contemplated:
[0223] Item 1: A method for fabricating a periodic structure, the
method comprising:
[0224] providing a holographic mixture on a base substrate;
[0225] sandwiching the holographic mixture between the base
substrate and a cover substrate, wherein the holographic mixture
forms a holographic mixture layer on the base substrate;
[0226] applying holographic recording beams to the holographic
mixture layer to form a holographic polymer dispersed liquid
crystal periodic structure comprising alternating polymer rich
regions and liquid crystal rich regions; and
[0227] removing the cover substrate from the holographic polymer
dispersed liquid crystal periodic structure, wherein the cover
substrate has different properties than the base substrate to allow
for the cover substrate to adhere to the unexposed holographic
mixture layer while capable of being removed from the formed
holographic polymer dispersed liquid crystal periodic structure
after exposure.
[0228] Item 2: The method of Item 1, further comprising removing at
least a portion of the liquid crystal in the liquid crystal rich
regions to form a polymer periodic structure.
[0229] Item 3: The method of Item 2, further comprising refilling
the liquid crystal rich regions with a backfill material.
[0230] Item 4: The method of Item 3, wherein the backfill material
has a different refractive index than the refractive index of the
remaining polymer rich regions.
[0231] Item 5: The method of Item 3, wherein the backfill material
comprises a liquid crystal material.
[0232] Item 6: The method of claim 5, wherein the liquid crystal
material is different from the liquid crystal removed from the
liquid crystal rich regions.
[0233] Item 7: The method of Item 2, wherein removing at least a
portion of the liquid crystal comprises removing substantially all
of the liquid crystal in the liquid crystal rich regions.
[0234] Item 8: The method of Item 2, wherein removing at least a
portion of the liquid crystal further comprises leaving at least a
portion of the liquid crystal in the liquid crystal rich
regions.
[0235] Item 9: The method of Item 2, wherein removing at least a
portion of liquid crystal comprises washing the holographic polymer
dispersed liquid crystal grating with a solvent.
[0236] Item 10: The method of any one of the preceding items,
wherein the base substrate comprises plastic.
[0237] Item 11: The method of Item 1, wherein a silicon oxide layer
is deposited on the base substrate.
[0238] Item 12: The method of any one of Items 1-6, wherein the
base substrate comprises glass, quartz, or silica.
[0239] Item 13: The method of any one of items 1-6, wherein the
cover substrate comprises plastic.
[0240] Item 14: The method of Item 10, wherein a silicon oxide
layer is deposited on the cover substrate.
[0241] Item 15: The method of any one of items 1-6, wherein the
cover substrate comprises glass, quartz, or silica.
[0242] Item 16: The method of any one of the preceding Items,
wherein an adhesion promotion layer is coated on top of the base
substrate which promotes adhesion between the base substrate and
the holographic polymer dispersed liquid crystal periodic
structure.
[0243] Item 17: The method of Item 16, wherein the base substrate
comprises a glass surface including hydroxyl groups and wherein a
silane-based reagent bonds with the hydroxyl group and the adhesion
promotion layer.
[0244] Item 18: The method of any one of the preceding items,
wherein a release layer is coated on top of the cover substrate
which allows the cover substrate to easily release from the
holographic polymer dispersed liquid crystal periodic
structure.
[0245] Item 19: The method of Item 18, wherein the cover substrate
comprises a glass surface including hydroxyl groups and wherein the
release layer is a silane based fluoro reactant which bonds with
the hydroxyl groups.
[0246] Item 20: The method of any one of the preceding items,
further comprising applying a protective substrate to the
holographic polymer dispersed liquid crystal periodic structure,
wherein the holographic polymer dispersed liquid crystal periodic
structure is positioned between the protective substrate and the
base substrate.
[0247] Item 21: A method for fabricating periodic structures, the
method comprising:
[0248] providing a first holographic mixture on a first base
substrate;
[0249] sandwiching the first holographic mixture between the first
base substrate and a cover substrate, wherein the first holographic
mixture forms a first holographic mixture layer on the first base
substrate;
[0250] applying holographic recording beams to the first
holographic mixture layer to form a first holographic polymer
dispersed liquid crystal periodic structure comprising alternating
polymer rich regions and liquid crystal rich regions;
[0251] removing the cover substrate from the holographic polymer
dispersed liquid crystal periodic structure;
[0252] providing a second holographic mixture on a second base
substrate;
[0253] sandwiching the second holographic mixture between the
second base substrate and the cover substrate, wherein the second
holographic mixture forms a second holographic mixture layer on the
second base substrate; and
[0254] applying holographic recording beams to the second
holographic mixture layer to form a second holographic polymer
dispersed liquid crystal periodic structure comprising alternating
polymer rich regions and liquid crystal rich regions.
[0255] Item 22: The method of Item 21, wherein the cover substrate
has different properties than the first base substrate and second
base substrate to allow for the cover substrate to adhere to the
first and second unexposed holographic mixture layer while capable
of being removed from the formed first and second holographic
polymer dispersed liquid crystal periodic structure after
exposure.
[0256] Item 23: The method of any one of Items 21 or 22, further
comprising removing the cover substrate from the second holographic
polymer dispersed liquid crystal periodic structure.
[0257] Item 24: The method of any one of Items 21-23, further
comprising removing at least a portion of the liquid crystal in the
liquid crystal rich regions of the first or second holographic
polymer dispersed liquid crystal periodic structure to form a
polymer surface relief grating.
[0258] Item 25: The method of Item 24, further comprising refilling
the liquid crystal rich regions of the first or second holographic
polymer dispersed liquid crystal periodic structure with a backfill
material.
[0259] Item 26: The method of Item 25, wherein the backfill
material has a different refractive index than the refractive index
of the remaining polymer rich regions.
[0260] Item 27: The method of Item 25, wherein the backfill
material comprises a liquid crystal material.
[0261] Item 28: The method of Item 27, wherein the liquid crystal
material is different from the liquid crystal removed from the
liquid crystal rich regions.
[0262] Item 29: The method of Item 24, wherein removing at least a
portion of the liquid crystal comprises removing substantially all
of the liquid crystal in the liquid crystal rich regions.
[0263] Item 30: The method of Item 24, wherein removing at least a
portion of the liquid crystal further comprises leaving at least a
portion of the liquid crystal in the liquid crystal rich
regions.
[0264] Item 31: The method of Item 24, wherein removing at least a
portion of liquid crystal comprises washing the holographic polymer
dispersed liquid crystal grating with a solvent.
[0265] Item 32: The method of any one of Items 21-31, wherein the
first base substrate and/or second base substrate comprises
plastic.
[0266] Item 33: The method of Items 21-32, wherein a silicon oxide
layer is deposited on the first base substrate and/or second base
substrate.
[0267] Item 34: The method of any one of Items 21-31, wherein the
first base substrate and/or second base substrate comprises glass,
quartz, or silica.
[0268] Item 35: The method of any one of Items 21-31, wherein the
cover substrate comprises plastic.
[0269] Item 36: The method of Item 35, wherein a silicon oxide
layer is deposited on the cover substrate.
[0270] Item 37: The method of any one of Items 21-31, wherein the
cover substrate comprises glass, quartz, or silica.
[0271] Item 38: The method of any one of Items 21-31, wherein an
adhesion promotion layer is coated on top of the first base
substrate which promotes adhesion between the first base substrate
and the first holographic polymer dispersed liquid crystal
grating.
[0272] Item 39: The method of Item 38, wherein the first base
substrate comprises a glass surface including hydroxyl groups and
wherein a silane-based reagent bonds with the hydroxyl group and
the adhesion promotion layer.
[0273] Item 40: The method of Items 21-39, wherein a release layer
is coated on top of the cover substrate which allows the cover
substrate to easily release from the holographic polymer dispersed
liquid crystal grating.
[0274] Item 41: The method of Item 40, wherein the cover substrate
comprises a glass surface including hydroxyl groups and wherein the
release layer is a silane based fluoro reactant which bonds with
the hydroxyl groups.
[0275] Item 42: A device for fabricating a deep surface relief
grating (SRG) comprising:
[0276] a holographic mixture sandwiched between a base substrate
and a cover substrate,
[0277] wherein the holographic mixture is configured to form a
holographic polymer dispersed liquid crystal grating comprising
alternating polymer rich regions and liquid crystal rich regions
when exposed to holographic recording beams, and
[0278] wherein the base substrate and the cover substrate have
different properties to allow the cover substrate to adhere to the
unexposed holographic mixture layer while capable of being removed
from the formed holographic polymer dispersed liquid crystal
grating after exposure.
[0279] Item 43: The device of Item 42, wherein the base substrate
comprises plastic.
[0280] Item 44: The device of Item 43, wherein a silicon oxide
layer is disposed on the base substrate.
[0281] Item 45: The device of Item 42, wherein the base substrate
comprises glass, quartz, or silica.
[0282] Item 46: The device of Item 45, wherein the cover substrate
comprises plastic.
[0283] Item 47: The device of Item 46, wherein a silicon oxide
layer is disposed on the cover substrate.
[0284] Item 48: The device of Item 42, wherein the cover substrate
comprises glass, quartz, or silica.
[0285] Item 49: The device of any one of Items 42-48, wherein an
adhesion promotion layer is coated on top of the first base
substrate which promotes adhesion between the first base substrate
and the first holographic polymer dispersed liquid crystal
grating.
[0286] Item 50: The device of Item 49, wherein the first base
substrate comprises a glass surface including hydroxyl groups and
wherein a silane-based reagent bonds with the hydroxyl group and
the adhesion promotion layer.
[0287] Item 51: The device of any one of Items 42-50, wherein a
release layer is coated on top of the cover substrate which allows
the cover substrate to easily release from the holographic polymer
dispersed liquid crystal grating.
[0288] Item 52: The device of Item 51, wherein the cover substrate
comprises a glass surface including hydroxyl groups and wherein the
release layer is a silane based fluoro reactant which bonds with
the hydroxyl groups.
[0289] Item 53: A waveguide device comprising:
[0290] a waveguide supporting a polymer grating structure for
diffracting light propagating in total internal reflection in said
waveguide,
[0291] wherein the polymer grating structure comprises: [0292] a
polymer regions; [0293] air gaps between adjacent portions of the
polymer regions; and [0294] a coating disposed on the tops of the
polymer regions and the tops of the waveguide.
[0295] Item 54: The waveguide device of Item 53, wherein the
coating comprises an atomic layer deposition (ALD) deposited
metallic layer or dielectric layer to enhance evanescent coupling
between the waveguide and the polymer grating structure.
[0296] Item 55: The waveguide device of Item 53, wherein the
coating comprises an atomic layer deposition (ALD) deposited
metallic layer or dielectric layer to enhance the effective
refractive index of the polymer grating structure.
[0297] Item 56: The waveguide device of Item 53, wherein the
coating comprises an atomic layer deposition (ALD) deposited
metallic layer or dielectric layer to enhance adhesion and/or
perform as a bias layer.
[0298] Item 57: The waveguide device of Item 53, wherein the
coating comprises an atomic layer deposition (ALD) conformally
deposited metallic layer or dielectric layer disposed over the
entirety of the polymer regions and the tops of the waveguide.
[0299] Item 58: The waveguide device of Item 53, wherein the
coating comprises an atomic layer deposition (ALD) deposited
metallic layer or dielectric layer disposed over one or more facets
of the polymer regions including one or more of the upper, lower,
or sidewall facets of the polymer regions.
[0300] Item 59: The waveguide device of Item 53, wherein a
passivation coating is applied to the surfaces of the polymer
grating structure and/or the coating.
[0301] Item 60: The waveguide device of Item 53, wherein the
polymer regions include a slant angle with respect to the
waveguide.
[0302] Item 61: The waveguide device of Item 53, wherein the
polymer grating structure further comprises an isotropic material
between adjacent portions of the polymer network, wherein the
isotropic material has a refractive index higher or lower than the
refractive index of the polymer network.
[0303] Item 62: The waveguide device of Item 61, wherein the
isotropic material occupies a space at a bottom portion of the
space between adjacent portions of the polymer network and the air
occupies the space from above the top surface of the isotropic
material to the modulation depth.
[0304] Item 63: The waveguide device of Item 61, wherein the
isotropic material comprises a birefringent crystal material.
[0305] Item 64: The waveguide device of Item 63, wherein the
birefringent crystal material comprises a liquid crystal
material.
[0306] Item 65: The waveguide device of Item 53, wherein the
polymer grating structure has a modulation depth greater than a
wavelength of visible light.
[0307] Item 66: The waveguide device of Item 53, wherein the
polymer grating structure comprises a modulation depth and a
grating pitch and wherein the modulation depth is greater than the
grating pitch.
[0308] Item 67: The waveguide device of Item 53, wherein the
waveguide comprises two substrates and the polymer grating
structure is either sandwiched between the two substrates or
positioned on an external surface of either substrate.
[0309] Item 68: The waveguide device of Item 53, wherein the Bragg
fringe spacing of the polymer network is 0.35 .mu.m to 0.8 .mu.m
and the grating depth of the polymer network is 1 .mu.m to 3
.mu.m.
[0310] Item 69: The waveguide device of Item 53, wherein the ratio
of grating depth of the polymer network to the Bragg fringe spacing
is 1:1 to 5:1.
[0311] Item 70: The waveguide device of Item 53, further comprising
a picture generating unit, and wherein the polymer grating
structure comprises a waveguide diffraction grating.
[0312] Item 71: The waveguide device of Item 70, wherein the
waveguide diffraction grating is configured as a multiplexing
grating.
[0313] Item 72: The waveguide device of Item 71, wherein the
waveguide diffraction grating is configured to accept light from
the picture generating unit which includes multiple images.
[0314] Item 73: The waveguide device of Item 70, wherein the
waveguide diffraction grating is configured to outcouple light from
the waveguide.
[0315] Item 74: The waveguide device of Item 70, wherein the
waveguide diffraction grating is configured as a beam expander.
[0316] Item 75: The waveguide device of Item 70, wherein the
waveguide diffraction grating is configured to incouple light
including image data generated from the picture generating
unit.
[0317] Item 76: The waveguide device of Item 75, wherein the
waveguide diffraction grating is further configured to incouple
S-polarized light with a high degree of efficiency.
[0318] Item 77: The waveguide device of Item 76, wherein the
diffraction grating is further configured to incouple S-polarized
light at an efficiency of 70% to 95% at a Bragg angle.
[0319] Item 78. The waveguide device of Item 76, wherein the
diffraction grating is further configured to incouple P-polarized
light at an efficiency of 25% to 50% at a Bragg angle.
[0320] Item 79: The waveguide device of Item 53, wherein the
refractive index difference between the polymer network and the air
gaps is 0.25 to 0.4.
[0321] Item 80: The waveguide device of Item 63, wherein the
refractive index difference between the polymer network and the
birefringent crystal material is 0.05 to 0.2.
[0322] Item 81: The waveguide device of Item 53, wherein the
polymer grating structure comprises a two-dimensional lattice
structure or a three-dimensional lattice structure.
[0323] Item 82: The waveguide device of Item 53, further comprising
another grating structure.
[0324] Item 83: The waveguide device of Item 82, wherein the
polymer grating structure comprises an incoupling grating and the
other grating structure comprises a beam expander or an outcoupling
grating.
[0325] Item 84: A waveguide device comprising:
[0326] a waveguide supporting a polymer grating structure for
diffracting light propagating in total internal reflection in said
waveguide,
[0327] wherein the polymer grating structure comprises: [0328] a
polymer regions; [0329] air gaps between adjacent portions of the
polymer regions; [0330] an optical layer disposed between the
polymer regions and the waveguide; and [0331] a coating disposed on
the tops of the polymer regions and the tops of the optical
layer.
[0332] Item 85: The waveguide device of Item 84, wherein the
coating comprises an atomic layer deposition (ALD) deposited
metallic layer or dielectric layer to enhance evanescent coupling
between the waveguide and the polymer grating structure.
[0333] Item 86: The waveguide device of Item 84, wherein the
coating comprises an atomic layer deposition (ALD) deposited
metallic layer or dielectric layer to enhance the effective
refractive index of the polymer grating structure.
[0334] Item 87: The waveguide device of Item 84, wherein the
coating comprises an atomic layer deposition (ALD) deposited
metallic layer or dielectric layer to enhance adhesion and/or
perform as a bias layer.
[0335] Item 88: The waveguide device of Item 84, wherein the
coating comprises an atomic layer deposition (ALD) conformally
deposited metallic layer or dielectric layer disposed over the
entirety of the polymer regions and the exposed tops of the optical
layer.
[0336] Item 89: The waveguide device of Item 84, wherein the
coating comprises an atomic layer deposition (ALD) deposited
metallic layer or dielectric layer disposed over one or more facets
of the polymer regions including one or more of the upper, lower,
or sidewall facets of the polymer regions.
[0337] Item 90: The waveguide device of Item 84, wherein a
passivation coating is applied to the surfaces of the polymer
grating structure.
[0338] Item 91: The waveguide device of Item 84, wherein the
polymer regions include a slant angle with respect to the
waveguide.
[0339] Item 92: The waveguide device of Item 84, wherein the
thickness of optical layer is designed to selectively modify
diffraction efficiency vs angle characteristics within a defined
angular range.
[0340] Item 93: The waveguide device of Item 84, wherein the
polymer grating structure further comprises an isotropic material
between adjacent portions of the polymer network, wherein the
isotropic material has a refractive index higher or lower than the
refractive index of the polymer network.
[0341] Item 94: The waveguide device of Item 93, wherein the
isotropic material occupies a space at a bottom portion of the
space between adjacent portions of the polymer network and the air
occupies the space from above the top surface of the isotropic
material to the modulation depth.
[0342] Item 95: The waveguide device of Item 93, wherein the
isotropic material comprises a birefringent crystal material.
[0343] Item 96: The waveguide device of Item 95, wherein the
birefringent crystal material comprises a liquid crystal
material.
[0344] Item 97: The waveguide device of Item 84, wherein the
polymer grating structure has a modulation depth greater than a
wavelength of visible light.
[0345] Item 98: The waveguide device of Item 84, wherein the
polymer grating structure comprises a modulation depth and a
grating pitch and wherein the modulation depth is greater than the
grating pitch.
[0346] Item 99: The waveguide device of Item 84, wherein the
waveguide comprises two substrates and the polymer grating
structure is either sandwiched between the two substrates or
positioned on an external surface of either substrate.
[0347] Item 100: The waveguide device of Item 84, wherein the Bragg
fringe spacing of the polymer network is 0.35 .mu.m to 0.8 .mu.m
and the grating depth of the polymer network is 1 .mu.m to 3
.mu.m.
[0348] Item 101: The waveguide device of Item 84, wherein the ratio
of grating depth of the polymer network to the Bragg fringe spacing
is 1:1 to 5:1.
[0349] Item 102: The waveguide device of Item 84, further
comprising a picture generating unit, and wherein the polymer
grating structure comprises a waveguide diffraction grating.
[0350] Item 103: The waveguide device of Item 102, wherein the
waveguide diffraction grating is configured as a multiplexing
grating.
[0351] Item 104: The waveguide device of Item 103, wherein the
waveguide diffraction grating is configured to accept light from
the picture generating unit which includes multiple images.
[0352] Item 105: The waveguide device of Item 104, wherein the
waveguide diffraction grating is configured to outcouple light from
the waveguide.
[0353] Item 106: The waveguide device of Item 102, wherein the
waveguide diffraction grating is configured as a beam expander.
[0354] Item 107: The waveguide device of Item 102, wherein the
waveguide diffraction grating is configured to incouple light
including image data generated from the picture generating
unit.
[0355] Item 108: The waveguide device of Item 107, wherein the
waveguide diffraction grating is further configured to incouple
S-polarized light with a high degree of efficiency.
[0356] Item 109: The waveguide device of Item 108, wherein the
diffraction grating is further configured to incouple S-polarized
light at an efficiency of 70% to 95% at a Bragg angle.
[0357] Item 110: The waveguide device of Item 108, wherein the
diffraction grating is further configured to incouple P-polarized
light at an efficiency of 25% to 50% at a Bragg angle.
[0358] Item 111: The waveguide device of Item 84, wherein the
refractive index difference between the polymer network and the air
gaps is 0.25 to 0.4.
[0359] Item 112: The waveguide device of Item 95, wherein the
refractive index difference between the polymer network and the
birefringent crystal material is 0.05 to 0.2.
[0360] Item 113: The waveguide device of Item 84, wherein the
polymer grating structure comprises a two-dimensional lattice
structure or a three-dimensional lattice structure.
[0361] Item 114: The waveguide device of Item 84, further
comprising another grating structure.
[0362] Item 115: The waveguide device of Item 114, wherein the
polymer grating structure comprises an incoupling grating and the
other grating structure comprises a beam expander or an outcoupling
grating.
[0363] Item 116: A waveguide device comprising:
[0364] a waveguide supporting a polymer grating structure for
diffracting light propagating in total internal reflection in said
waveguide,
[0365] wherein the polymer grating structure comprises: [0366] a
polymer regions; [0367] air gaps between adjacent portions of the
polymer regions; and [0368] an optical layer disposed between the
polymer regions and the waveguide.
[0369] Item 117: The waveguide device of Item 116, wherein the
thickness of optical layer is designed to selectively modify
diffraction efficiency vs angle characteristics within a defined
angular range.
[0370] Item 118: The waveguide device of Item 116, wherein the
polymer grating structure further comprises an isotropic material
between adjacent portions of the polymer network, wherein the
isotropic material has a refractive index higher or lower than the
refractive index of the polymer network.
[0371] Item 119: The waveguide device of Item 118, wherein the
isotropic material occupies a space at a bottom portion of the
space between adjacent portions of the polymer network and the air
occupies the space from above the top surface of the isotropic
material to the modulation depth.
[0372] Item 120: The waveguide device of Item 118, wherein the
isotropic material comprises a birefringent crystal material.
[0373] Item 121: The waveguide device of Item 120, wherein the
birefringent crystal material comprises a liquid crystal
material.
[0374] Item 122: The waveguide device of Item 118, wherein the
polymer grating structure has a modulation depth greater than a
wavelength of visible light.
[0375] Item 123: The waveguide device of Item 118, wherein the
polymer grating structure comprises a modulation depth and a
grating pitch and wherein the modulation depth is greater than the
grating pitch.
[0376] Item 124: The waveguide device of Item 118, wherein the
waveguide comprises two substrates and the polymer grating
structure is either sandwiched between the two substrates or
positioned on an external surface of either substrate.
[0377] Item 125: The waveguide device of Item 118, wherein the
Bragg fringe spacing of the polymer network is 0.35 .mu.m to 0.8
.mu.m and the grating depth of the polymer network is 1 .mu.m to 3
.mu.m.
[0378] Item 126: The waveguide device of Item 118, wherein the
ratio of grating depth of the polymer network to the Bragg fringe
spacing is 1:1 to 5:1.
[0379] Item 127: The waveguide device of Item 118, further
comprising a picture generating unit, and wherein the polymer
grating structure comprises a waveguide diffraction grating.
[0380] Item 128: The waveguide device of Item 127, wherein the
waveguide diffraction grating is configured as a multiplexing
grating.
[0381] Item 129: The waveguide device of Item 128, wherein the
waveguide diffraction grating is configured to accept light from
the picture generating unit which includes multiple images.
[0382] Item 130: The waveguide device of Item 127, wherein the
waveguide diffraction grating is configured to outcouple light from
the waveguide.
[0383] Item 131: The waveguide device of Item 130, wherein the
waveguide diffraction grating is configured as a beam expander.
[0384] Item 132: The waveguide device of Item 127, wherein the
waveguide diffraction grating is configured to incouple light
including image data generated from the picture generating
unit.
[0385] Item 133: The waveguide device of Item 132, wherein the
waveguide diffraction grating is further configured to incouple
S-polarized light with a high degree of efficiency.
[0386] Item 134: The waveguide device of Item 133, wherein the
diffraction grating is further configured to incouple S-polarized
light at an efficiency of 70% to 95% at a Bragg angle.
[0387] Item 135: The waveguide device of Item 133, wherein the
diffraction grating is further configured to incouple P-polarized
light at an efficiency of 25% to 50% at a Bragg angle.
[0388] Item 136: The waveguide device of Item 116, wherein the
refractive index difference between the polymer network and the air
gaps is 0.25 to 0.4.
[0389] Item 137: The waveguide device of Item 120, wherein the
refractive index difference between the polymer network and the
birefringent crystal material is 0.05 to 0.2.
[0390] Item 138: The waveguide device of Item 116, wherein the
polymer grating structure comprises a two-dimensional lattice
structure or a three-dimensional lattice structure.
[0391] Item 139: The waveguide device of Item 116, further
comprising another grating structure.
[0392] Item 140: The waveguide device of Item 139, wherein the
polymer grating structure comprises an incoupling grating and the
other grating structure comprises a beam expander or an outcoupling
grating.
[0393] Item 141: The waveguide device of Item 116, wherein the
optical is sandwiched by the waveguide and the polymer grating
structure and wherein the polymer grating structure extends all the
way to the optical layer to directly contact the optical layer.
[0394] Item 142: A waveguide device comprising:
[0395] a waveguide supporting a polymer grating structure for
diffracting light propagating in total internal reflection in said
waveguide,
[0396] wherein the polymer grating structure comprises: [0397] a
polymer regions; and [0398] air gaps between adjacent portions of
the polymer regions, [0399] wherein the polymer regions and air
gaps directly contact the waveguide.
[0400] Item 143: The waveguide device of Item 142, wherein the
thickness of optical layer is designed to selectively modify
diffraction efficiency vs angle characteristics within a defined
angular range.
[0401] Item 144: The waveguide device of Item 142, wherein the
polymer surface relief grating extends all the way to directly
contact the waveguide.
[0402] Item 145. The waveguide device of claim 142, wherein there
is no bias layer between the polymer surface relief grating and the
substrate.
[0403] Item 146: The waveguide device of Item 142, wherein the
polymer grating structure further comprises an isotropic material
between adjacent portions of the polymer network, wherein the
isotropic material has a refractive index higher or lower than the
refractive index of the polymer network.
[0404] Item 147: The waveguide device of Item 146, wherein the
isotropic material occupies a space at a bottom portion of the
space between adjacent portions of the polymer network and the air
occupies the space from above the top surface of the isotropic
material to the modulation depth.
[0405] Item 148: The waveguide device of Item 146, wherein the
isotropic material comprises a birefringent crystal material.
[0406] Item 149: The waveguide device of Item 148, wherein the
birefringent crystal material comprises a liquid crystal
material.
[0407] Item 150: The waveguide device of Item 142, wherein the
polymer grating structure has a modulation depth greater than a
wavelength of visible light.
[0408] Item 151: The waveguide device of Item 142, wherein the
polymer grating structure comprises a modulation depth and a
grating pitch and wherein the modulation depth is greater than the
grating pitch.
[0409] Item 152: The waveguide device of Item 142, wherein the
waveguide comprises two substrates and the polymer grating
structure is either sandwiched between the two substrates or
positioned on an external surface of either substrate.
[0410] Item 153: The waveguide device of Item 142, wherein the
Bragg fringe spacing of the polymer network is 0.35 .mu.m to 0.8
.mu.m and the grating depth of the polymer network is 1 .mu.m to 3
.mu.m.
[0411] Item 154: The waveguide device of Item 142, wherein the
ratio of grating depth of the polymer network to the Bragg fringe
spacing is 1:1 to 5:1.
[0412] Item 155: The waveguide device of Item 142, further
comprising a picture generating unit, and wherein the polymer
grating structure comprises a waveguide diffraction grating.
[0413] Item 156: The waveguide device of Item 155, wherein the
waveguide diffraction grating is configured as a multiplexing
grating.
[0414] Item 157: The waveguide device of Item 156, wherein the
waveguide diffraction grating is configured to accept light from
the picture generating unit which includes multiple images.
[0415] Item 158: The waveguide device of Item 155, wherein the
waveguide diffraction grating is configured to outcouple light from
the waveguide.
[0416] Item 159: The waveguide device of Item 155, wherein the
waveguide diffraction grating is configured as a beam expander.
[0417] Item 160: The waveguide device of Item 155, wherein the
waveguide diffraction grating is configured to incouple light
including image data generated from the picture generating
unit.
[0418] Item 161: The waveguide device of Item 160, wherein the
waveguide diffraction grating is further configured to incouple
S-polarized light with a high degree of efficiency.
[0419] Item 162: The waveguide device of Item 160, wherein the
waveguide diffraction grating is further configured to incouple
S-polarized light at an efficiency of 70% to 95% at a Bragg
angle.
[0420] Item 163: The waveguide device of Item 160, wherein the
diffraction grating is further configured to incouple P-polarized
light at an efficiency of 25% to 50% at a Bragg angle.
[0421] Item 164: The waveguide device of Item 142, wherein the
refractive index difference between the polymer network and the air
gaps is 0.25 to 0.4.
[0422] Item 165: The waveguide device of Item 164, wherein the
refractive index difference between the polymer network and the
birefringent crystal material is 0.05 to 0.2.
[0423] Item 166: The waveguide device of Item 142, wherein the
polymer grating structure comprises a two-dimensional lattice
structure or a three-dimensional lattice structure.
[0424] Item 167: The waveguide device of Item 142, further
comprising another grating structure.
[0425] Item 168: The waveguide device of Item 167, wherein the
polymer grating structure comprises an incoupling grating and the
other grating structure comprises a beam expander or an outcoupling
grating.
[0426] Item 169. A method for fabricating a grating, the method
comprising:
[0427] providing a mixture of monomer and a nonreactive
material;
[0428] providing a substrate;
[0429] coating a layer of the mixture on a surface of the
substrate;
[0430] applying holographic recording beams to the layer to form a
holographic polymer dispersed grating comprising alternating
polymer rich regions and nonreactive material rich regions;
[0431] removing at least a portion of the nonreactive material in
the nonreactive material rich regions to form a polymer surface
relief grating including alternating polymer regions and air
regions; and
[0432] applying a coating to the top surfaces of the polymer
regions and the top surfaces of the substrate in the air
regions.
[0433] Item 170: The method of Item 169, wherein applying the
coating comprises an atomic layer deposition (ALD) process.
[0434] Item 171: The method of Item 169, wherein the coating
comprises TiO.sub.2 or ZnO.sub.2.
[0435] Item 172: The method of Item 169, wherein the monomer
comprises acrylates, methacrylates, vinyls, isocyanates, thiols,
isocyanate-acrylate, and/or thiolene.
[0436] Item 173: The method of Item 172, wherein the mixture
further comprises at least one of a photoinitiator, a coinitiator,
or additional additives.
[0437] Item 174: The method of Item 172, wherein the thiols
comprise thiol-vinyl-acrylate.
[0438] Item 175: The method of Item 173, wherein the photoinitiator
comprises photosensitive components.
[0439] Item 176: The method of Item 175, wherein the photosensitive
components comprise dyes and/or radical generators.
[0440] Item 177: The method of Item 169, wherein providing a
mixture of monomer and liquid crystal comprises:
[0441] mixing the monomer, liquid crystal, and at least one of a
photoinitiator, a coinitiator, multifunctional thiol, or additional
additives;
[0442] storing the mixture in a location absent of light at a
temperature of 22.degree. C. or less;
[0443] adding additional monomer;
[0444] filtering the mixture through a filter of 0.6 .mu.m or less;
and
[0445] storing the filtered mixture in a location absent of
light.
[0446] Item 178: The method of Item 169, wherein the substrate
comprises a glass substrate or plastic substrate.
[0447] Item 179: The method of Item 169, wherein the substrate
comprises a transparent substrate.
[0448] Item 180: The method of Item 169, further comprising
sandwiching the mixture between the substrate and another substrate
with one or more spacers for maintaining internal dimensions.
[0449] Item 181: The method of Item 180, further comprising
applying a non-stick release layer on one surface of the other
substrate.
[0450] Item 182: The method of Item 181, wherein the non-stick
release layer comprises a fluoropolymer.
[0451] Item 183: The method of Item 169, further comprising
refilling the liquid crystal rich regions with a liquid crystal
material.
[0452] Item 184: The method of Item 183, wherein the liquid crystal
material has a different molecular structure than the previously
removed liquid crystal.
[0453] Item 185: The method of Item 169, wherein removing at least
a portion of the liquid crystal comprises removing substantially
all of the liquid crystal in the liquid crystal rich regions.
[0454] Item 186: The method of Item 169, wherein removing at least
a portion of the liquid crystal further comprises leaving at least
a portion of the liquid crystal in the polymer rich regions.
[0455] Item 187: The method of Item 169, further comprising
applying a protective layer over the deep SRG.
[0456] Item 188: The method of Item 187, wherein the protective
layer comprises an anti-reflective layer.
[0457] Item 189: The method of Item 187, wherein the protective
layer comprises silicate or silicon nitride.
[0458] Item 190: The method of Item 187, wherein applying a
protective layer comprises depositing the protective layer on the
deep SRG.
[0459] Item 191: The method of Item 190, wherein depositing the
protective layer comprises chemical vapor deposition.
[0460] Item 192: The method of Item 191, wherein the chemical vapor
deposition is a nanocoating process.
[0461] Item 193: The method of Item 190, wherein the protective
layer comprises a parylene coating.
[0462] Item 194: The method of Item 169, wherein the liquid crystal
rich regions comprise air gaps after removing at least a portion of
the liquid crystal in the liquid crystal rich regions.
[0463] Item 195: The method of Item 194, further comprising
creating a vacuum in the air gaps or filling the air gaps with an
inert gas.
[0464] Item 196: The method of Item 169, wherein removing at least
a portion of liquid crystal comprises washing the holographic
polymer dispersed liquid crystal grating with a solvent.
[0465] Item 197: The method of Item 196, wherein washing the
holographic polymer dispersed liquid crystal grating comprises
immersing the holographic polymer dispersed liquid crystal grating
in the solvent.
[0466] Item 198: The method of Item 196, wherein the solvent
comprises isopropyl alcohol.
[0467] Item 199: The method of Item 196, wherein the solvent is
kept at a temperature lower than room temperature while washing the
holographic polymer dispersed liquid crystal grating.
[0468] Item 200: The method of Item 196, wherein removing at least
a portion of the liquid crystal further comprises drying the
holographic polymer dispersed liquid crystal grating with a high
flow air source.
[0469] Item 201: The method of Item 169, further comprising curing
the holographic polymer dispersed liquid crystal grating.
[0470] Item 202: The method of Item 201, wherein curing the
holographic polymer dispersed liquid crystal grating comprises
exposing the holographic polymer dispersed liquid crystal grating
to a low intensity white light for a period of about an hour.
[0471] Item 203: The method of Item 169, wherein the polymer
surface relief grating is configured to incouple S-polarized light
at an efficiency of 70% to 95%.
[0472] Item 204: The method of Item 203, wherein the polymer
surface relief grating is further configured to incouple
P-polarized light at an efficiency of 25% to 50%.
[0473] Item 205: The method of Item 169, wherein the refractive
index difference between the polymer network and the air gaps is
0.25 to 0.4.
[0474] Item 206: The method of Item 183, wherein the refractive
index difference between the polymer network and the liquid crystal
material is 0.05 to 0.2.
[0475] Item 207: The method of Item 169, wherein the polymer
surface relief grating comprises a Bragg fringe spacing of 0.35
.mu.m to 0.8 .mu.m and the grating depth of 1 .mu.m to 3 .mu.m.
[0476] Item 208: The method of Item 169, wherein the polymer
surface relief grating comprises a ratio of Bragg fringe spacing to
grating depth of 1:1 to 5:1.
[0477] Item 209: The method of Item 169, wherein the liquid crystal
content in the mixture of monomer and liquid crystal is
approximately 20% to 50%.
[0478] Item 210: The method of Item 169, wherein the liquid crystal
in the mixture of monomer and liquid crystal comprises liquid
crystal singles.
[0479] Item 211: The method of Item 210, wherein the liquid crystal
singles comprise cyanobiphenyl and/or pentylcyanobiphenyl.
[0480] Item 212: A method for fabricating a grating, the method
comprising:
[0481] providing a mixture of monomer and a nonreactive
material;
[0482] providing a substrate;
[0483] coating a layer of the mixture on a surface of the
substrate;
[0484] applying holographic recording beams to the layer to form a
holographic polymer dispersed grating comprising alternating
polymer rich regions and nonreactive material rich regions;
[0485] removing at least a portion of the nonreactive material in
the nonreactive material rich regions to form a polymer surface
relief grating including alternating polymer regions and air
regions, wherein an optical layer is disposed between the polymer
regions and the substrate; and
[0486] applying a coating to the top surfaces of the polymer
regions and the top surfaces of the optical layer in the air
regions.
[0487] Item 213: The method of Item 212, wherein applying the
coating comprises an atomic layer deposition (ALD) process.
[0488] Item 214: The method of Item 212, wherein the coating
comprises TiO.sub.2 or ZnO.sub.2.
[0489] Item 215: The method of Item 212, wherein the monomer
comprises acrylates, methacrylates, vinyls, isocyanates, thiols,
isocyanate-acrylate, and/or thiolene.
[0490] Item 216: The method of Item 215, wherein the mixture
further comprises at least one of a photoinitiator, a coinitiator,
or additional additives.
[0491] Item 217: The method of Item 215, wherein the thiols
comprise thiol-vinyl-acrylate.
[0492] Item 218: The method of Item 216, wherein the photoinitiator
comprises photosensitive components.
[0493] Item 219: The method of Item 218, wherein the photosensitive
components comprise dyes and/or radical generators.
[0494] Item 220: The method of Item 212, wherein providing a
mixture of monomer and liquid crystal comprises:
[0495] mixing the monomer, liquid crystal, and at least one of a
photoinitiator, a coinitiator, multifunctional thiol, or additional
additives;
[0496] storing the mixture in a location absent of light at a
temperature of 22.degree. C. or less;
[0497] adding additional monomer;
[0498] filtering the mixture through a filter of 0.6 .mu.m or less;
and
[0499] storing the filtered mixture in a location absent of
light.
[0500] Item 221: The method of Item 212, wherein the substrate
comprises a glass substrate or plastic substrate.
[0501] Item 222: The method of Item 212, wherein the substrate
comprises a transparent substrate.
[0502] Item 223: The method of Item 212, further comprising
sandwiching the mixture between the substrate and another substrate
with one or more spacers for maintaining internal dimensions.
[0503] Item 224: The method of Item 223, further comprising
applying a non-stick release layer on one surface of the other
substrate.
[0504] Item 225: The method of Item 224, wherein the non-stick
release layer comprises a fluoropolymer.
[0505] Item 226: The method of Item 212, further comprising
refilling the liquid crystal rich regions with a liquid crystal
material.
[0506] Item 227: The method of Item 226, wherein the liquid crystal
material has a different molecular structure than the previously
removed liquid crystal.
[0507] Item 228: The method of Item 212, wherein removing at least
a portion of the liquid crystal comprises removing substantially
all of the liquid crystal in the liquid crystal rich regions.
[0508] Item 229: The method of Item 212, wherein removing at least
a portion of the liquid crystal further comprises leaving at least
a portion of the liquid crystal in the polymer rich regions.
[0509] Item 230: The method of Item 212, further comprising
applying a protective layer over the deep SRG.
[0510] Item 231: The method of Item 230, wherein the protective
layer comprises an anti-reflective layer.
[0511] Item 232: The method of Item 230, wherein the protective
layer comprises silicate or silicon nitride.
[0512] Item 233: The method of Item 230, wherein applying a
protective layer comprises depositing the protective layer on the
deep SRG.
[0513] Item 234: The method of Item 233, wherein depositing the
protective layer comprises chemical vapor deposition.
[0514] Item 235: The method of Item 234, wherein the chemical vapor
deposition is a nanocoating process.
[0515] Item 236: The method of Item 230, wherein the protective
layer comprises a parylene coating.
[0516] Item 237: The method of Item 212, wherein the liquid crystal
rich regions comprise air gaps after removing at least a portion of
the liquid crystal in the liquid crystal rich regions.
[0517] Item 238: The method of Item 237, further comprising
creating a vacuum in the air gaps or filling the air gaps with an
inert gas.
[0518] Item 239: The method of Item 212, wherein removing at least
a portion of liquid crystal comprises washing the holographic
polymer dispersed liquid crystal grating with a solvent.
[0519] Item 240: The method of Item 239, wherein washing the
holographic polymer dispersed liquid crystal grating comprises
immersing the holographic polymer dispersed liquid crystal grating
in the solvent.
[0520] Item 241: The method of Item 239, wherein the solvent
comprises isopropyl alcohol.
[0521] Item 242: The method of Item 239, wherein the solvent is
kept at a temperature lower than room temperature while washing the
holographic polymer dispersed liquid crystal grating.
[0522] Item 243: The method of Item 239, wherein removing at least
a portion of the liquid crystal further comprises drying the
holographic polymer dispersed liquid crystal grating with a high
flow air source.
[0523] Item 244: The method of Item 212, further comprising curing
the holographic polymer dispersed liquid crystal grating.
[0524] Item 245: The method of Item 244, wherein curing the
holographic polymer dispersed liquid crystal grating comprises
exposing the holographic polymer dispersed liquid crystal grating
to a low intensity white light for a period of about an hour.
[0525] Item 246: The method of Item 212, wherein the polymer
surface relief grating is configured to incouple S-polarized light
at an efficiency of 70% to 95%.
[0526] Item 247: The method of Item 246, wherein the polymer
surface relief grating is further configured to incouple
P-polarized light at an efficiency of 25% to 50%.
[0527] Item 248: The method of Item 212, wherein the refractive
index difference between the polymer network and the air gaps is
0.25 to 0.4.
[0528] Item 249: The method of Item 226, wherein the refractive
index difference between the polymer network and the liquid crystal
material is 0.05 to 0.2.
[0529] Item 250: The method of Item 212, wherein the polymer
surface relief grating comprises a Bragg fringe spacing of 0.35
.mu.m to 0.8 .mu.m and the grating depth of 1 .mu.m to 3 .mu.m.
[0530] Item 251: The method of Item 212, wherein the polymer
surface relief grating comprises a ratio of Bragg fringe spacing to
grating depth of 1:1 to 5:1.
[0531] Item 252: The method of Item 212, wherein the liquid crystal
content in the mixture of monomer and liquid crystal is
approximately 20% to 50%.
[0532] Item 253: The method of Item 212, wherein the liquid crystal
in the mixture of monomer and liquid crystal comprises liquid
crystal singles.
[0533] Item 254: The method of Item 253, wherein the liquid crystal
singles comprise cyanobiphenyl and/or pentylcyanobiphenyl.
[0534] Item 255: A method for fabricating a grating, the method
comprising:
[0535] providing a mixture of monomer and a nonreactive
material;
[0536] providing a substrate;
[0537] coating a layer of the mixture on a surface of the
substrate;
[0538] applying holographic recording beams to the layer to form a
holographic polymer dispersed grating comprising alternating
polymer rich regions and nonreactive material rich regions;
[0539] removing at least a portion of the nonreactive material in
the nonreactive material rich regions to form a polymer surface
relief grating including alternating polymer regions and air
regions; and
[0540] performing a plasma ashing process to remove at least a
portion of polymer from the polymer regions.
[0541] Item 256: The method of Item 255, wherein the mixture
contains chemical additives for enhancing the effectiveness of the
plasma ashing process.
[0542] Item 257: The method of Item 256, wherein the plasma ashing
process includes reactive species including oxygen and the mixture
includes nitrogen to control the plasma ashing rate.
[0543] Item 258: The method of Item 256, wherein the plasma ashing
process includes reactive species including oxygen, fluorine,
and/or hydrogen.
[0544] Item 259: The method of Item 258, wherein the plasma ashing
process includes a plasma mixture of nitrogen and hydrogen.
[0545] Item 260: The method of Item 259, wherein the plasma mixture
further includes fluorine.
[0546] Item 261: The method of Item 255, wherein the monomer
comprises acrylates, methacrylates, vinyls, isocynates, thiols,
isocyanate-acrylate, and/or thioline.
[0547] Item 262: The method of Item 261, wherein the mixture
further comprises at least one of a photoinitiator, a coinitiator,
or additional additives.
[0548] Item 263: The method of Item 261, wherein the thiols
comprise thiol-vinyl-acrylate.
[0549] Item 264: The method of Item 262, wherein the photoinitiator
comprises photosensitive components.
[0550] Item 265: The method of Item 264, wherein the photosensitive
components comprise dyes and/or radical generators.
[0551] Item 266: The method of Item 255, wherein providing a
mixture of monomer and liquid crystal comprises:
[0552] mixing the monomer, liquid crystal, and at least one of a
photoinitiator, a coinitiator, multifunctional thiol, or additional
additives;
[0553] storing the mixture in a location absent of light at a
temperature of 22.degree. C. or less;
[0554] adding additional monomer;
[0555] filtering the mixture through a filter of 0.6 .mu.m or less;
and
[0556] storing the filtered mixture in a location absent of
light.
[0557] Item 267: The method of Item 255, wherein the substrate
comprises a glass substrate or plastic substrate.
[0558] Item 268: The method of Item 255, wherein the substrate
comprises a transparent substrate.
[0559] Item 269: The method of Item 255, further comprising
sandwiching the mixture between the substrate and another substrate
with one or more spacers for maintaining internal dimensions.
[0560] Item 270: The method of Item 265, further comprising
applying a non-stick release layer on one surface of the other
substrate.
[0561] Item 271: The method of Item 270, wherein the non-stick
release layer comprises a fluoropolymer.
[0562] Item 272: The method of Item 255, further comprising
refilling the liquid crystal rich regions with a liquid crystal
material.
[0563] Item 273: The method of Item 272, wherein the liquid crystal
material has a different molecular structure than the previously
removed liquid crystal.
[0564] Item 274: The method of Item 255, wherein removing at least
a portion of the liquid crystal comprises removing substantially
all of the liquid crystal in the liquid crystal rich regions.
[0565] Item 275: The method of Item 255, wherein removing at least
a portion of the liquid crystal further comprises leaving at least
a portion of the liquid crystal in the polymer rich regions.
[0566] Item 276: The method of Item 255, further comprising
applying a protective layer over the deep SRG.
[0567] Item 277: The method of Item 276, wherein the protective
layer comprises an anti-reflective layer.
[0568] Item 278: The method of Item 276, wherein the protective
layer comprises silicate or silicon nitride.
[0569] Item 279: The method of Item 276, wherein applying a
protective layer comprises depositing the protective layer on the
deep SRG.
[0570] Item 280: The method of Item 279, wherein depositing the
protective layer comprises chemical vapor deposition.
[0571] Item 281: The method of Item 280, wherein the chemical vapor
deposition is a nanocoating process.
[0572] Item 282: The method of Item 276, wherein the protective
layer comprises a parylene coating.
[0573] Item 283: The method of Item 255, wherein the liquid crystal
rich regions comprise air gaps after removing at least a portion of
the liquid crystal in the liquid crystal rich regions.
[0574] Item 284: The method of Item 283, further comprising
creating a vacuum in the air gaps or filling the air gaps with an
inert gas.
[0575] Item 285: The method of Item 254, wherein removing at least
a portion of liquid crystal comprises washing the holographic
polymer dispersed liquid crystal grating with a solvent.
[0576] Item 286: The method of Item 285, wherein washing the
holographic polymer dispersed liquid crystal grating comprises
immersing the holographic polymer dispersed liquid crystal grating
in the solvent.
[0577] Item 287: The method of Item 285, wherein the solvent
comprises isopropyl alcohol.
[0578] Item 288: The method of Item 285, wherein the solvent is
kept at a temperature lower than room temperature while washing the
holographic polymer dispersed liquid crystal grating.
[0579] Item 289: The method of Item 285, wherein removing at least
a portion of the liquid crystal further comprises drying the
holographic polymer dispersed liquid crystal grating with a high
flow air source.
[0580] Item 290: The method of Item 255, further comprising curing
the holographic polymer dispersed liquid crystal grating.
[0581] Item 291: The method of Item 290, wherein curing the
holographic polymer dispersed liquid crystal grating comprises
exposing the holographic polymer dispersed liquid crystal grating
to a low intensity white light for a period of about an hour.
[0582] Item 292: The method of Item 255, wherein the polymer
surface relief grating is configured to incouple S-polarized light
at an efficiency of 70% to 95%.
[0583] Item 293: The method of Item 292, wherein the polymer
surface relief grating is further configured to incouple
P-polarized light at an efficiency of 25% to 50%.
[0584] Item 294: The method of Item 255, wherein the refractive
index difference between the polymer network and the air gaps is
0.25 to 0.4.
[0585] Item 295: The method of Item 272, wherein the refractive
index difference between the polymer network and the liquid crystal
material is 0.05 to 0.2.
[0586] Item 296: The method of Item 255, wherein the polymer
surface relief grating comprises a Bragg fringe spacing of 0.35
.mu.m to 0.8 .mu.m and the grating depth of 1 .mu.m to 3 .mu.m.
[0587] Item 297: The method of Item 255, wherein the polymer
surface relief grating comprises a ratio of Bragg fringe spacing to
grating depth of 1:1 to 5:1.
[0588] Item 298: The method of Item 255, wherein the liquid crystal
content in the mixture of monomer and liquid crystal is
approximately 20% to 50%.
[0589] Item 299: The method of Item 255, wherein the liquid crystal
in the mixture of monomer and liquid crystal comprises liquid
crystal singles.
[0590] Item 300: The method of Item 299, wherein the liquid crystal
singles comprise cyanobiphenyl and/or pentylcynobiphenyl.
[0591] Item 301: The method of Item 255, for fabricating a grating,
further comprising:
[0592] immersing the grating in a refractive material to fill the
air regions and voids in the polymer rich regions formed by removal
of the nonreactive material to form alternating polymer regions and
refractive material regions; and
[0593] removing the refractive material in the refractive material
regions to leave alternating composite polymer and second
nonreactive material regions and air regions.
[0594] Item 302: The method of Item 301, wherein removing the
refractive material in the refractive materials is performed using
a plasma ashing process.
[0595] Item 303. A waveguide comprising:
[0596] an optical substrate supporting a polymer grating structure
for diffracting light propagating in total internal reflection in
said waveguide,
[0597] wherein the polymer grating structure comprises: [0598] a
polymer regions; [0599] air gaps between adjacent portions of the
polymer regions, wherein a portion of the polymer regions on the
same level as the air gaps along with the air gaps form a surface
relief grating; and [0600] backfill material regions below the air
gaps, wherein a portion of the polymer regions on the same level as
the backfill material regions along with the backfill material
regions form a volume grating, and [0601] wherein the polymer
grating structure comprises a dual interaction grating in which
total internal reflection light from the surface relief grating
formed by the polymer grating structure interacts with the volume
grating formed by the polymer grating structure to provide a first
diffraction efficiency versus angle characteristic and total
internal reflection light from an opposing face of the optical
substrate interacts with the volume grating formed by the polymer
grating structure to provide a second diffraction efficiency versus
angle characteristic.
[0602] Item 304: The waveguide of Item 303, wherein the polymer
grating structure is a fold grating.
[0603] Item 305: The waveguide of Item 303, wherein grating depth
of the polymer grating structure is less than the fringe spacing of
the polymer grating structure.
[0604] Item 306: The waveguide of Item 303, wherein grating depth
of the polymer grating structure is greater than the fringe spacing
of the polymer grating structure.
[0605] Item 307. The waveguide of Item 303, wherein total internal
reflection from the surface relief grating formed by the polymer
grating structure occurs when the reflected first order diffraction
from the surface relief grating formed by the polymer grating
structure has a diffraction angle equal to the TIR angle of the
waveguide.
[0606] Item 308: The waveguide of Item 303, wherein the polymer
grating structure provides no transmitted diffraction orders.
[0607] Item 309: The waveguide of Item 303, wherein the polymer
grating structure is a photonic crystal.
[0608] Item 310: The waveguide of Item 303, wherein the polymer
grating structure comprises a Raman Nath grating overlaying a Bragg
grating, wherein the Raman Nath grating has the same grating period
as the Bragg grating, and the minima of the Raman Nath grating
overlays the minima of the Bragg grating.
[0609] Item 311. The waveguide of Item 303, wherein the polymer
grating structure is a slanted grating.
[0610] Item 312: The waveguide of Item 303, wherein the polymer
grating structure is an unslanted grating.
[0611] Item 313. The waveguide of Item 303, wherein the backfill
material regions have a refractive index different from that of the
polymer rich regions.
[0612] Item 314. The waveguide device of Item 313, wherein the air
regions and the polymer rich regions on the same level of the air
regions comprise a Raman-Nath grating.
[0613] Item 315. The waveguide device of claim 314, wherein the
backfilled material regions and the polymer rich regions on the
same level as the backfilled material regions comprise a volume
Bragg grating.
DOCTRINE OF EQUIVALENTS
[0614] While the above description contains many specific
embodiments of the invention, these should not be construed as
limitations on the scope of the invention, but rather as an example
of one embodiment thereof. It is therefore to be understood that
the present invention may be practiced in ways other than
specifically described, without departing from the scope and spirit
of the present invention. Thus, embodiments of the present
invention should be considered in all respects as illustrative and
not restrictive. Accordingly, the scope of the invention should be
determined not by the embodiments illustrated, but by the appended
claims and their equivalents.
* * * * *