U.S. patent application number 16/783019 was filed with the patent office on 2020-08-06 for methods for compensating for optical surface nonuniformity.
This patent application is currently assigned to DigiLens Inc.. The applicant listed for this patent is DigiLens Inc.. Invention is credited to Shibu Abraham, Milan Momcilo Popovich, Jonathan David Waldern.
Application Number | 20200247017 16/783019 |
Document ID | / |
Family ID | 1000004644866 |
Filed Date | 2020-08-06 |
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United States Patent
Application |
20200247017 |
Kind Code |
A1 |
Waldern; Jonathan David ; et
al. |
August 6, 2020 |
Methods for Compensating for Optical Surface Nonuniformity
Abstract
Systems and methods for compensating for nonuniform surface
topography features in accordance with various embodiments of the
invention are illustrated. One embodiment includes a method for
manufacturing waveguide cells, the method including providing a
waveguide including first and second substrates and a layer of
optical recording material, and applying a surface forming process
to at least one external surface of the first and second
substrates. In another embodiment, applying the surface forming
process includes applying a forming material coating to the at
least one external surface, providing a forming element having a
forming surface, bringing the forming element in physical contact
with the forming material coating, curing the forming material
coating while it is in contact with the forming element, and
releasing the forming material coating from the forming
element.
Inventors: |
Waldern; Jonathan David;
(Los Altos Hills, CA) ; Abraham; Shibu;
(Sunnyvale, CA) ; Popovich; Milan Momcilo;
(Leicester, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DigiLens Inc. |
Sunnyvale |
CA |
US |
|
|
Assignee: |
DigiLens Inc.
Sunnyvale
CA
|
Family ID: |
1000004644866 |
Appl. No.: |
16/783019 |
Filed: |
February 5, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62801528 |
Feb 5, 2019 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B29C 35/0805 20130101;
B29C 2035/0827 20130101; G02F 1/1334 20130101; G02B 2006/12166
20130101; G02F 1/1326 20130101 |
International
Class: |
B29C 35/08 20060101
B29C035/08; G02F 1/13 20060101 G02F001/13; G02F 1/1334 20060101
G02F001/1334 |
Claims
1. A method for manufacturing waveguide cells, the method
comprising: providing a waveguide comprising first and second
substrates and a layer of optical recording material; and applying
a surface forming process to at least one external surface of said
first and second substrates.
2. The method of claim 1, wherein applying said surface forming
process comprises: applying a forming material coating to said at
least one external surface; providing a forming element having a
forming surface; bringing said forming element in physical contact
with said forming material coating; curing said forming material
coating while it is in contact with said forming element; and
releasing said forming material coating from said forming
element.
3. The method of claim 1, wherein said surface forming process
provides surface planarization said at least one external
surface.
4. The method of claim 2, wherein applying said surface forming
process further comprises depositing at least one of a release
layer or a hard coat layer.
5. The method of claim 2, wherein curing said forming material
coating comprises applying UV curing radiation via a curing
configuration selected from the group consisting of: one or more UV
sources distributed above said forming material coating, a fixture
comprising UV sources spatially distributed around the waveguide,
and one or more UV sources coupled into an internal reflection path
within at least one of said forming element or said waveguide.
6. The method of claim 2, wherein curing said forming material
coating comprises a curing configuration selected from the group
consisting of: applying radiation having more than one wavelength,
applying UV radiation having more than one wavelength within the UV
spectrum, applying a thermal process, applying pressure, immersing
said forming material coating in a vacuum, immersing said forming
material coating in a gas, immersing said forming material coating
in a liquid, applying radiation having a wavelength within the
visible spectrum, applying radiation having a wavelength within the
infrared spectrum, and exposing said forming material coating to a
humid atmosphere.
7. The method of claim 2, wherein said forming material coating
comprises a material selected from the group consisting of:
photoresists, resins, polymers, thermosets, thermoplastic polymers,
polyepoxies, polyamides, low viscosity planarization materials,
materials with viscosity between 10 and 15 cps at 20.degree. C.,
materials with viscosity below 2 cps at 20.degree. C., and ethylene
glycol diacrylate.
8. The method of claim 2, wherein said release layer is a
fluorocarbon silylating agent.
9. The method of claim 4, wherein said forming surface of said
forming element has a surface characteristic for compensating for
shrinkage of said forming material coating.
10. The method of claim 2, further comprising correcting a wedge
characteristic of the forming material coating after completion of
said surface forming process.
11. The method of claim 2, where said first substrate is curved;
and said forming element surface has a curvature matching the
curvature of said first substrate.
12. The method of claim 2, wherein said forming surface of said
forming element has a degree of planarization less than 98%.
13. The method of claim 1, wherein said first substrate is a
plastic.
14. The method of claim 1, wherein said substrates have a
birefringence calculated to provide smoothing of non-uniformity
after a predefined number of TIR beam reflections.
15. The method of claim 2, further comprising employing an
apparatus for monitoring at least one selected from the group of
thickness, composition, and uniformity of said forming material
during deposition.
16. The method of claim 1, wherein providing said waveguide
comprises: providing said first substrate; depositing said layer of
optical recording material onto said first substrate using at least
one deposition head, wherein said optical recording material
deposited over a grating region is formulated to achieve a
predefined grating characteristic selected from the group
consisting of: refractive index modulation, refractive index,
birefringence, liquid crystal director alignment, grating layer
thickness, and a spatial variation of said characteristic;
providing said second substrate; placing said second substrate onto
said deposited layer of optical recording material; and laminating
said first substrate, said layer of optical recording material, and
said second substrate.
17. The method of claim 16, wherein providing said waveguide
further comprises depositing at least one of release layer or a
hard coat layer using said at least one deposition head.
18. The method of claim 2, wherein said forming element is an
optical flat, a refractive optical element, or an optical element
with at least one optical surface providing optical power.
19. The method of claim 2, wherein said forming element is
supported by a substrate providing an optical path from a light
source for curing.
20. The method of claim 1, wherein said layer of optical recording
material comprises a polymer dispersed liquid crystal mixture.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The current application claims the benefit of and priority
under 35 U.S.C. .sctn. 119(e) to U.S. Provisional Patent
Application No. 62/801,528 entitled "Methods for Compensating for
Optical Surface Nonuniformity," filed Feb. 5, 2019. The disclosure
of U.S. Provisional Patent Application No. 62/801,528 is hereby
incorporated by reference in its entirety for all purposes.
FIELD OF THE INVENTION
[0002] The present invention generally relates to methods for
compensating for nonuniform surface topography features in
substrates and, more specifically, in waveguide substrates.
BACKGROUND
[0003] Surface flatness is a common requirement in the manufacture
of various semiconductor devices, including but not limited to
display backplanes. In holographic waveguides used for conveying
image data, tight planarity tolerances are desirable to avoid image
artifacts that can result from light path deviations caused by
surface nonuniformities. Industry methods for planarization of
semiconductor substrates include low pressure chemical vapor
deposition (LPCVD), etch-back of a sacrificial layer (typically a
photoresist), simultaneous etch and deposition, chemical mechanical
polishing (CMP), reflow of SiO.sub.2 doped with phosphorus and
boron glass, and other processes. Applications of such methods
cover the range from smooth partial planarization all the way to
complete global planarization. Existing processes of relevance to
the manufacture of holographic waveguides can include organic spin
coating, molding using a planar surface, and other coating
processes.
SUMMARY OF THE INVENTION
[0004] Systems and methods for compensating for nonuniform surface
topography features in accordance with various embodiments of the
invention are illustrated. One embodiment includes a method for
manufacturing waveguide cells, the method including providing a
waveguide including first and second substrates and a layer of
optical recording material, and applying a surface forming process
to at least one external surface of the first and second
substrates.
[0005] In another embodiment, applying the surface forming process
includes applying a forming material coating to the at least one
external surface, providing a forming element having a forming
surface, bringing the forming element in physical contact with the
forming material coating, curing the forming material coating while
it is in contact with the forming element, and releasing the
forming material coating from the forming element.
[0006] In a further embodiment, the surface forming process
provides surface planarization the at least one external
surface.
[0007] In still another embodiment, applying the surface forming
process further includes depositing at least one of a release layer
or a hard coat layer.
[0008] In a still further embodiment, curing the forming material
coating includes applying UV curing radiation via a curing
configuration selected from the group consisting of one or more UV
sources distributed above the forming material coating, a fixture
including UV sources spatially distributed around the waveguide,
and one or more UV sources coupled into an internal reflection path
within at least one of the forming element or the waveguide.
[0009] In yet another embodiment, curing the forming material
coating includes a curing configuration selected from the group
consisting of applying radiation having more than one wavelength,
applying UV radiation having more than one wavelength within the UV
spectrum, applying a thermal process, applying pressure, immersing
the forming material coating in a vacuum, immersing the forming
material coating in a gas, immersing the forming material coating
in a liquid, applying radiation having a wavelength within the
visible spectrum, applying radiation having a wavelength within the
infrared spectrum, and exposing the forming material coating to a
humid atmosphere.
[0010] In a yet further embodiment, the forming material coating
includes a material selected from the group consisting of
photoresists, resins, polymers, thermosets, thermoplastic polymers,
polyepoxies, polyamides, low viscosity planarization materials,
materials with viscosity between 10 and 15 cps at 20.degree. C.,
materials with viscosity below 2 cps at 20.degree. C., and ethylene
glycol diacrylate.
[0011] In another additional embodiment, the release layer is a
fluorocarbon silylating agent.
[0012] In a further additional embodiment, the forming surface of
the forming element has a surface characteristic for compensating
for shrinkage of the forming material coating.
[0013] In another embodiment again, the method further includes
correcting a wedge characteristic of the forming material coating
after completion of the surface forming process.
[0014] In a further embodiment again, the first substrate is
curved, and the forming element surface has a curvature matching
the curvature of the first substrate.
[0015] In still yet another embodiment, the forming surface of the
forming element has a degree of planarization less than 98%.
[0016] In a still yet further embodiment, the first substrate is a
plastic.
[0017] In still another additional embodiment, the substrates have
a birefringence calculated to provide smoothing of non-uniformity
after a predefined number of TIR beam reflections.
[0018] In a still further additional embodiment, the method further
includes employing an apparatus for monitoring at least one
selected from the group of thickness, composition, and uniformity
of the forming material during deposition.
[0019] In still another embodiment again, providing the waveguide
includes providing the first substrate, depositing the layer of
optical recording material onto the first substrate using at least
one deposition head, wherein the optical recording material
deposited over a grating region is formulated to achieve a
predefined grating characteristic selected from the group
consisting of refractive index modulation, refractive index,
birefringence, liquid crystal director alignment, grating layer
thickness, and a spatial variation of the characteristic, providing
the second substrate, placing the second substrate onto the
deposited layer of optical recording material, and laminating the
first substrate, the layer of optical recording material, and the
second substrate.
[0020] In a still further embodiment again, providing the waveguide
further includes depositing at least one of release layer or a hard
coat layer using the at least one deposition head.
[0021] In yet another additional embodiment, the forming element is
an optical flat, a refractive optical element, or an optical
element with at least one optical surface providing optical
power.
[0022] In a yet further additional embodiment, the forming element
is supported by a substrate providing an optical path from a light
source for curing.
[0023] In yet another embodiment again, the layer of optical
recording material includes a polymer dispersed liquid crystal
mixture.
[0024] Additional embodiments and features are set forth in part in
the description that follows, and in part will become apparent to
those skilled in the art upon examination of the specification or
may be learned by the practice of the invention. A further
understanding of the nature and advantages of the present invention
may be realized by reference to the remaining portions of the
specification and the drawings, which forms a part of this
disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] 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.
[0026] FIG. 1 shows a flow diagram conceptually illustrating a
method of providing a planarized waveguide in accordance with an
embodiment of the invention.
[0027] FIGS. 2A-2E conceptually illustrate a series of process
steps for planarizing a waveguide in accordance with an embodiment
of the invention.
[0028] FIG. 3 conceptually illustrates a curing configuration
utilizing a curing source disposed above a transparent forming
element in accordance with an embodiment of the invention.
[0029] FIG. 4 conceptually illustrates a curing configuration
utilizing a curing source optically coupled to a forming element in
accordance with an embodiment of the invention.
[0030] FIG. 5 conceptually illustrates a curing configuration
utilizing a curing source optically coupled to a waveguide in
accordance with an embodiment of the invention.
DETAILED DESCRIPTION
[0031] 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.
[0032] Planarization processes in accordance with various
embodiments of the invention includes processes that can enable low
cost products and lightweight designs. In many embodiments, a
planarization process is implemented for planarizing plastic
substrates for use in waveguides. Such processes can be utilized to
mitigate or eliminate undesirable surface characteristics of the
plastic substrates. Undesirable defects can include wedge shapes,
bending of the substrate, and high total thickness variation. In
some embodiments, the planarization process is compatible with
deposition and printing processes that can be used in the
manufacturing of holographic waveguides. Such processes are
described in further detail in U.S. application Ser. No. 16/203,071
filed Nov. 28, 2018 entitled "Systems and Methods for Manufacturing
Waveguide Cells," the disclosure of which is hereby incorporated by
reference in its entirety for all purposes. In some embodiments, a
planarization process is implemented for curved waveguides, which
can be integrated into various applications such as but not limited
to helmet visors and car windshields. In such cases, the
planarization process can compensate for deviations from the
desired curvature of the waveguide. In several embodiments, a
planarization process is implemented for correcting nonuniformity
in waveguides, including curved waveguides. Although planarization
processes in accordance with various embodiments of the invention
apply to the compensation of surface nonuniformities of waveguide
substrates of any geometry, to simplify the description of such
embodiments, the discussions below will generally address
applications directed at planarizing nominally flat waveguide
substrates.
[0033] In many embodiments, the planarization process is performed
on the outer surfaces of a fabricated waveguide. In some
embodiments, the planarization process is performed on a substrate
before it is used to fabricate a waveguide. The planarization
process can include coating the faces of a waveguide or substrate
with a deformable material (referred to as a forming material) and
then bringing it into contact with an element (referred to as a
forming element) having a forming surface with a desired surface
profile, typically a surface with a high degree of flatness. The
forming material can be cured, and the outer surfaces of the
finished waveguide or substrate can achieve flatness specifications
substantially equal to those of the forming surface. The process
can be applied to one or both of the external surfaces of the
waveguide. In the case of a curved waveguide or substrate, the
process can include using a curved forming surface instead of a
flat forming surface. In a number of embodiments, the curved
forming surface has a curvature matching that of the waveguide or
substrate. Waveguide structures, planarization processes, and
planarization materials utilized for such processes are described
below in further detail.
Optical Waveguides and Grating Structures
[0034] Optical structures recorded in waveguides can include many
different types of optical elements, such as but not limited to
diffraction gratings. In many embodiments, the grating implemented
is a Bragg grating (also referred to as a volume grating). Bragg
gratings can have high efficiency with little light being
diffracted into higher orders. The relative amount of light in the
diffracted and zero order can be varied by controlling the
refractive index modulation of the grating, a property that can be
used to make lossy waveguide gratings for extracting light over a
large pupil.
[0035] One class of gratings used in holographic waveguide devices
is the Switchable Bragg Grating (SBG). SBGs can be fabricated by
first placing a thin film of a mixture of photopolymerizable
monomers and liquid crystal material between substrates, forming a
waveguide cell. Waveguide cells are described in the sections below
in further detail. The substrates can be made of various types of
materials, such glass and plastics. In many cases, the substrates
are in a parallel configuration. One or both substrates can support
electrodes, typically transparent tin oxide films, for applying an
electric field across the film. The grating structure in an SBG can
be recorded in the liquid material (often referred to as the syrup)
through photopolymerization-induced phase separation using
interferential exposure with a spatially periodic intensity
modulation. Factors such as but not limited to control of the
irradiation intensity, component volume fractions of the materials
in the mixture, and exposure temperature can determine the
resulting grating morphology and performance. As can readily be
appreciated, a wide variety of materials and mixtures can be used
depending on the specific requirements of a given application. In
many embodiments, HPDLC material is used. During the recording
process, the monomers polymerize, and the mixture undergoes a phase
separation. The LC molecules aggregate to form discrete or
coalesced droplets that are periodically distributed in polymer
networks on the scale of optical wavelengths. The alternating
liquid crystal-rich and liquid crystal-depleted regions form the
fringe planes of the grating, which can produce Bragg diffraction
with a strong optical polarization resulting from the orientation
ordering of the LC molecules in the droplets.
[0036] The resulting volume phase grating can exhibit very high
diffraction efficiency, which can be controlled by the magnitude of
the electric field applied across the film. When an electric field
is applied to the grating via transparent electrodes, the natural
orientation of the LC droplets can change, causing the refractive
index modulation of the fringes to lower and the hologram
diffraction efficiency to drop to very low levels. Typically, the
electrodes are configured such that the applied electric field will
be perpendicular to the substrates. In a number of embodiments, the
electrodes are fabricated from indium tin oxide (ITO). In the OFF
state with no electric field applied, the extraordinary axis of the
liquid crystals generally aligns normal to the fringes. The grating
thus exhibits high refractive index modulation and high diffraction
efficiency for P-polarized light. When an electric field is applied
to the HPDLC, the grating switches to the ON state wherein the
extraordinary axes of the liquid crystal molecules align parallel
to the applied field and hence perpendicular to the substrate. In
the ON state, the grating exhibits lower refractive index
modulation and lower diffraction efficiency for both S- and
P-polarized light. Thus, the grating region no longer diffracts
light. Each grating region can be divided into a multiplicity of
grating elements such as for example a pixel matrix according to
the function of the HPDLC device. Typically, the electrode on one
substrate surface is uniform and continuous, while electrodes on
the opposing substrate surface are patterned in accordance to the
multiplicity of selectively switchable grating elements.
[0037] Typically, the SBG elements are switched clear in 30 .mu.s
with a longer relaxation time to switch ON. The diffraction
efficiency of the device can be adjusted, by means of the applied
voltage, over a continuous range. In many cases, the device
exhibits near 100% efficiency with no voltage applied and
essentially zero efficiency with a sufficiently high voltage
applied. In certain types of HPDLC devices, magnetic fields can be
used to control the LC orientation. In some HPDLC applications,
phase separation of the LC material from the polymer can be
accomplished to such a degree that no discernible droplet structure
results. An SBG can also be used as a passive grating. In this
mode, its chief benefit is a uniquely high refractive index
modulation. SBGs can be used to provide transmission or reflection
gratings for free space applications. SBGs can be implemented as
waveguide devices in which the HPDLC forms either the waveguide
core or an evanescently coupled layer in proximity to the
waveguide. The substrates used to form the HPDLC cell provide a
total internal reflection (TIR) light guiding structure. Light can
be coupled out of the SBG when the switchable grating diffracts the
light at an angle beyond the TIR condition.
[0038] Waveguides can be constructed using a variety of processes,
including but not limited to those described in U.S. application
Ser. No. 16/203,071. In many embodiments, the waveguide is
fabricated with a grating having a predefined grating
characteristic. One manufacturing process capable of fabricating
such waveguides includes a deposition technique where a layer of
optical recording material is deposited onto a first substrate
using at least one deposition head. In some embodiments, the
optical recording material is a polymer dispersed liquid crystal
mixture. In a number of embodiments, the optical recording material
does not include liquid crystals. As can readily be appreciated,
any type of recording material can be utilized as appropriate
depending on the specific requirements of a given application. The
optical recording material deposited over the grating region can be
formulated to form a grating having a predefined grating
characteristic. In a number of embodiments, the predefined grating
characteristic is at least one of: refractive index modulation,
refractive index, birefringence, liquid crystal director alignment,
grating layer thickness, and combinations thereof. In further
embodiments, the grating is formed with a spatially varying
predefined grating characteristic. A second substrate can be placed
on the deposited layer of optical recording material, and an
exposure process can be performed to form gratings within the
optical recording material layer.
[0039] In some embodiments, LC can be extracted or evacuated from
the SBG to provide a surface relief grating (SRG) that has
properties very similar to a Bragg grating due to the depth of the
SRG structure (which is much greater than that practically
achievable using surface etching and other conventional processes
commonly used to fabricated SRGs). The LC can be extracted using a
variety of different methods, including but not limited to flushing
with isopropyl alcohol and solvents. In many embodiments, one of
the transparent substrates of the SBG is removed, and the LC is
extracted. In further embodiments, the removed substrate is
replaced. The SRG can be at least partially backfilled with a
material of higher or lower refractive index. Such gratings offer
scope for tailoring the efficiency, angular/spectral response,
polarization, and other properties to suit various waveguide
applications.
[0040] Waveguides in accordance with various embodiments of the
invention can include various grating configurations designed for
specific purposes and functions. In many embodiments, the waveguide
includes an input grating optically coupled to a light source, a
fold grating for providing a first direction beam expansion, and an
output grating for providing beam expansion in a second direction,
which is typically orthogonal to the first direction, and beam
extraction towards the eyebox. As can readily be appreciated, the
grating configuration implemented waveguide architectures can
depend on the specific requirements of a given application. In some
embodiments, the grating configuration includes multiple fold
gratings. In several embodiments, the grating configuration
includes an input grating and a second grating for performing beam
expansion and beam extraction simultaneously. The second grating
can include gratings of different prescriptions, for propagating
different portions of the field of view, arranged in separate
overlapping grating layers or multiplexed in a single grating
layer. Furthermore, various types of gratings and waveguide
architectures can also be utilized.
[0041] 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, and 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, the gratings can be HPDLC gratings, switching gratings
recorded in HPDLC (such switchable Bragg Gratings), Bragg gratings
recorded in holographic photopolymer, or surface relief gratings.
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
grating.
[0042] Waveguides incorporating optical structures such as those
discussed above can be implemented in a variety of different
applications, including but not limited to waveguide displays. In
various embodiments, the waveguide display is implemented with an
eyebox of greater than 10 mm with an eye relief greater than 25 mm.
In some embodiments, the waveguide display includes a waveguide
with a thickness between 2.0-5.0 mm. 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.
The waveguide display can employ many different types of picture
generation units (PGUs). In several embodiments, the PGU can be a
reflective or transmissive spatial light modulator such as a liquid
crystal on Silicon (LCoS) panel or a micro electromechanical system
(MEMS) panel. In a number of embodiments, the PGU can be an
emissive device such as an organic light emitting diode (OLED)
panel. 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.
Waveguides implementing P-diffracting gratings (i.e., gratings with
high efficiency for P-polarized light) typically have a waveguide
efficiency of 5%-6.2%. Since P-diffracting or S-diffracting
gratings can waste half of the light from an unpolarized source
such as an OLED panel, many embodiments are directed towards
waveguides capable of providing both S-diffracting and
P-diffracting gratings to allow for an increase in the efficiency
of the waveguide by up to a factor of two. In some embodiments, the
S-diffracting and P-diffracting gratings are implemented in
separate overlapping grating layers. Alternatively, a single
grating can, under certain conditions, provide high efficiency for
both p-polarized and s-polarized light. In several embodiments, the
waveguide includes Bragg-like gratings produced by extracting LC
from HPDLC gratings, such as those described above, to enable high
S and P diffraction efficiency over certain wavelength and angle
ranges for suitably chosen values of grating thickness (typically,
in the range 2-5 .mu.m).
Planarization Processes
[0043] Planarization processes in accordance with various
embodiments of the invention can utilize a variety of different
types of substrates, including but not limited to glass and plastic
substrates of different thicknesses and geometries. Plastic
substrates can include but are not limited to polyvinyl butyral
(PVB), cyclo-olefinic polymers (COP), polymethyl methacrylate
(PMMA), polycarbonates (PC), clear polyimides, etc. In many
embodiments, the substrate can be injection molded. In some
embodiments, the substrate has low birefringence. In several
embodiments, the substrate has a birefringence calculated to
provide smoothing of illumination non-uniformities occurring in the
finished waveguide in normal operation. The planarization process
can be performed on individual substrates or the outer surfaces of
constructed waveguides. FIG. 1 shows a flow diagram conceptually
illustrating a method of providing a planarized waveguide in
accordance with an embodiment of the invention. Referring to the
flow diagram, the method 100 includes providing (101) a waveguide
having first and second substrates sandwiching a layer of optical
recording material. As described above, such waveguides can be
manufactured using a variety of different methods. In some
embodiments, the layer of optical recording material contains a
recorded grating. In other embodiments, the optical recording
material is uncured. A forming material can be applied (102) to one
or both surfaces of the waveguide. Various types of forming
materials and application processes can be utilized. For example,
inkjetting, spin coating, dip coating, or any other coating process
can be utilized. As can readily be appreciated, the application
technique can largely depend on the type of material utilized.
Different thicknesses of forming material can be applied as
appropriate depending on the application. Depending on the type of
material, thicker layers can result in more haze for waveguide
operation. In several embodiments, the layer of forming material
applied is less than .about.10 .mu.m. In further embodiments, the
layer of forming material applied is less than .about.5 .mu.m. A
forming element having a forming surface can be provided (103).
Various types of forming elements can be utilized. In many
embodiments, the forming element can be an optical flat or a more
general refractive optical element. The forming element can be
brought into physical contact (104) with the forming material. In
some embodiment, a process is applied to settle the forming element
into a desired position. For example, a vacuum process can be
applied to remove air pockets. The forming material can be cured
(105) while it is in contact with the forming element. In various
embodiments, curing of the planarization material (forming
material) can include the application of radiation of one or more
wavelengths to the material. In many embodiments, radiation of two
or more wavelengths is utilized. In several embodiments,
ultraviolet radiation can be used. In some embodiments, infrared
radiation or visible band light can be used. Sequential or
simultaneous curing steps based on any of the above procedures may
be used. Curing can include thermal processes which may include
infrared heating. In a number of embodiments, the curing process
can include the application of pressure. In some embodiments,
curing of the forming material can be carried out in a vacuum, a
gas, or in a liquid. The curing process can include exposure to a
humid atmosphere. The planarized waveguide can be released (106)
from the forming element. In many embodiments, the forming material
now includes a surface profile corresponding to the surface of the
forming element. In various embodiments, the planarization process
does not include the use of a forming element. In such cases, the
forming material is cured after it is applied to the substrate or
waveguide surface. The forming material can be chosen such that
gravity is sufficient for planarization. In a number of
embodiments, the forming element contains a previously applied
release layer. The coating can be applied using spray coating of
polytetrafluoroethylene (PTFE) or similar compounds. In several
embodiments, the release coating can be a fluorocarbon silylating
agent. To avoid wear of the forming element, a hard coating can be
applied to the forming surface of the forming element prior to
application of a release coating. In some embodiments, a release
coating may be applied to the forming material. Release layers and
hard coating layers can be applied using various techniques,
including but not limited to printing and coating techniques.
[0044] After the curing process, the external surfaces of the
waveguides can be coated with a hard coat. In a number of
embodiments, the hard coating process replaces the planarization
step with the hard coat acting as the forming material. In some
embodiments, the hard coat is a liquid resin material or an
acrylate. In many embodiments, the hard coat implemented is similar
to the ones used to protect plastic lenses. One example of a hard
coating material is the Nidek Co., Ltd (Japan) "Acier" hard coating
material, which is designed for hard coating lenses and transparent
plastic substrates. The coating thickness can vary widely. In some
embodiments, the coating thickness is about 30 micrometers. As can
readily be appreciated, the precise coating thickness can depend on
the average surface non-uniformity and shape. In several
embodiments, exposure of the waveguide gratings is carried out
after all of the above steps have been completed. In many
embodiments, exposure of the waveguide gratings can be carried out
before the application of the forming material (or hard coat
material). In such cases, it can be desirable that the forming
material and the application process are compatible with the
waveguide materials. For example, the forming material can be
chosen such that its application process occurs at a temperature
low enough to prevent any deformation of any formed waveguide
gratings. As can readily be appreciated, the choice of forming
material can depend on the material within which the waveguide
gratings are formed.
[0045] In many embodiments, planarization involves the application
of a reference flat (made from various materials). In some
embodiments, the planarization process can employ apparatus and
process steps for controlling the wedge of the planarized surface.
In several embodiments, surface flatness can be monitored during
the planarization process. In various embodiments, the
planarization process can employ an apparatus for monitoring at
least one selected from the group of thickness, composition, and
uniformity of the forming material during deposition. In a number
of embodiments, the forming element can be cut to match the
dimensions of the waveguide. In many embodiments, a tool fixture
for presenting the working surface of the forming element to the
forming material layer can be provided.
[0046] FIGS. 2A-2E conceptually illustrate a series of process
steps for planarizing a waveguide in accordance with an embodiment
of the invention. FIG. 2A shows a cross section of a first
waveguide substrate 200 in the XY plane 201. In the illustrative
embodiment, the surface of the substrate 200 has a deviation
.DELTA.Y in the XY plane 201 from its nominal planar geometry as
represented by the plot 202. In typical cases, the deviation
.DELTA.Y will vary across the surface of the substrate 200. FIG. 2B
shows a coating 203 of holographic recording material applied to
the first substrate 200. FIG. 2C shows a second substrate 204
placed over the holographic recording material layer 203. FIG. 2D
shows a layer of forming material 205 applied over the second
substrate 204. As described above, either or both outer surfaces of
the waveguide can be sequentially or simultaneously planarized.
FIG. 2E shows a forming element 206 with a forming surface 207
applied to the forming material 205. In many embodiments, the
forming element has a degree of planarization less than 98% wherein
the degree of planarization is defined as [1-(T'/T)].times.100%
where T is the surface deviation of the untreated surface and T' is
the resulting surface deviation after completion of the
planarization process.
[0047] In several embodiments, the forming element is supported by
a transparent substrate providing an optical path from one or more
sources of curing radiation. In various embodiments, the forming
element is a transparent refracting element with at least one
surface having optical power for controlling the intensity
distribution of the radiation presented to the forming material
layer. In many embodiments, the forming element can be an optical
flat or a more general refractive optical element. In such
embodiments, the curing radiation can be introduced to the forming
material via the forming element. In some embodiments, the curing
radiation is provided by a group of one or more UV sources
distributed above a transparent forming element. FIG. 3
conceptually illustrates a curing configuration utilizing a curing
source disposed above a transparent forming element in accordance
with an embodiment of the invention. As shown, a waveguide 300
supports a forming material coating 301 that is in contact with a
forming element 302. In the illustrative embodiment, a curing
source 303 provides curing radiation 304 that is transmitted in a
diverging beam via the forming element 302 to irradiate the forming
material coating 301. In some embodiments, the curing radiation can
be coupled from one or more sources spatially distributed around
the forming element into an internal reflection path within the
forming element. FIG. 4 conceptually illustrates a curing
configuration utilizing a curing source optically coupled to a
forming element in accordance with an embodiment of the invention.
As shown, a waveguide 400 supports a forming material coating 401
that is in contact with a forming element 402. Curing radiation
from a curing source 404 is optically coupled to the waveguide 400
and is introduced to the forming material coating 401 via total
internal reflection paths 405. In several embodiments, the curing
radiation is provided by sources spatially distributed around the
waveguide. FIG. 5 conceptually illustrates a curing configuration
utilizing a curing source optically coupled to a waveguide in
accordance with an embodiment of the invention. As shown, a
waveguide 500 supports a forming material coating 501 that is in
contact with a forming element 502. Curing radiation from a curing
source 504 is optically coupled to the waveguide 500 and is
introduced to the forming material coating 501 via total internal
reflection paths 505.
[0048] Although FIGS. 1-5 illustrate specific processes for
planarizing the surface of substrates and waveguides, such
processes can be modified as appropriate depending on the specific
requirements of a given application. Modifications of planarization
processes in accordance with various embodiments of the invention
can include the deletion or addition of various steps. For example,
in some embodiments, a forming element is not needed as the forming
material is capable of forming a desired flatness profile passively
using gravitational forces.
Planarization Materials
[0049] Many different materials can be used to provide a forming or
planarization material. For example, photoresists, resins,
polymers, thermosets, thermoplastic polymers, polyepoxies, and
polyamides may be used. In a number of embodiments, ethylene glycol
diacrylate may be used. In many embodiments, the forming material
has low shrinkage. Where use of a low shrinkage material is not
practical, shrinkage of the planarization material can be
compensated by modifying the topography of the forming surface. In
some embodiments, low viscosity forming materials may be used. In
several embodiments, low viscosity materials with viscosity below 1
cps (centipoise) at 20.degree. C. may be used. In many embodiments,
low viscosity materials with viscosity below 2 cps at 20.degree. C.
As can readily be appreciated, various materials having a wide
range of viscosity can be utilized as appropriate depending on the
specific requirements of a given application. For example, in some
embodiments, the forming material is applied using
deposition/printing techniques such as but not limited to inkjet
printing. In such cases, it can be desirable for the material to
have a viscosity compatible with the techniques used. In several
embodiments, the material has a viscosity between
.about.10-.about.15 cps at 20.degree. C.
DOCTRINE OF EQUIVALENTS
[0050] 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.
* * * * *