U.S. patent application number 17/588061 was filed with the patent office on 2022-05-19 for liquid crystal reflective polarizer and pancake lens assembly having the same.
The applicant listed for this patent is Facebook Technologies, LLC. Invention is credited to Ying GENG, Jacques GOLLIER, Yuge HUANG, Yun-Han LEE, Lu LU, Fenglin PENG, Barry David SILVERSTEIN, Yusufu Njoni Bamaxam SULAI, Junren WANG, Yu-Jen WANG.
Application Number | 20220155513 17/588061 |
Document ID | / |
Family ID | |
Filed Date | 2022-05-19 |
United States Patent
Application |
20220155513 |
Kind Code |
A1 |
PENG; Fenglin ; et
al. |
May 19, 2022 |
LIQUID CRYSTAL REFLECTIVE POLARIZER AND PANCAKE LENS ASSEMBLY
HAVING THE SAME
Abstract
An illumination system is provided. The illumination system
includes a light source assembly configured to output a first
polarized light having a first handedness. The illumination system
also includes a light guide plate configured to guide the first
polarized light received from the light source assembly and output
a second polarized light having a second handedness opposite to the
first handedness. The light guide plate includes two wedges coupled
to one other at a slanted surface between the two wedges and a
reflective polarizer disposed at the slanted surface. The
illumination system also includes a reflective sheet arranged at a
first side surface of the light guide plate and configured to
reflect the first polarized light as the second polarized light.
The reflective polarizer includes a birefringent material having a
chirality, and is configured to selectively transmit the first
polarized light and reflect the second polarized light.
Inventors: |
PENG; Fenglin; (Redmond,
WA) ; WANG; Junren; (Kirkland, WA) ; HUANG;
Yuge; (Oviedo, FL) ; LU; Lu; (Kirkland,
WA) ; SULAI; Yusufu Njoni Bamaxam; (Snohomish,
WA) ; GENG; Ying; (Bellevue, WA) ; GOLLIER;
Jacques; (Sammamish, WA) ; SILVERSTEIN; Barry
David; (Kirkland, WA) ; WANG; Yu-Jen;
(Redmond, WA) ; LEE; Yun-Han; (Redmond,
WA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Facebook Technologies, LLC |
Menlo Park |
CA |
US |
|
|
Appl. No.: |
17/588061 |
Filed: |
January 28, 2022 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16820695 |
Mar 16, 2020 |
11269131 |
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17588061 |
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International
Class: |
F21V 8/00 20060101
F21V008/00; G02F 1/13363 20060101 G02F001/13363; G02F 1/1335
20060101 G02F001/1335; G02B 5/30 20060101 G02B005/30; G02F 1/13357
20060101 G02F001/13357 |
Claims
1. An illumination system, comprising: a light source assembly
configured to output a first polarized light having a first
handedness; a light guide plate configured to guide the first
polarized light received from the light source assembly and output
a second polarized light having a second handedness opposite to the
first handedness, the light guide plate including two wedges
coupled to one other at a slanted surface between the two wedges
and a reflective polarizer disposed at the slanted surface; and a
reflective sheet arranged at a first side surface of the light
guide plate and configured to reflect the first polarized light as
the second polarized light, wherein the reflective polarizer
includes a birefringent material having a chirality, and is
configured to selectively transmit the first polarized light and
reflect the second polarized light.
2. The illumination system of claim 1, wherein the light source
assembly is coupled to the light guide plate at a second side
surface of the light guide plate, and the first side surface and
the second side surface of the light guide plate are arranged
opposite to one another.
3. The illumination system of claim 1, wherein the light guide
plate is configured to guide the first polarized light received
from the light source assembly to the reflective sheet, the
reflective sheet is configured to reflect the first polarized light
as the second polarized light, the light guide plate is configured
to guide the second polarized light received from the reflective
sheet to the reflective polarizer, and the reflective polarizer is
configured to reflect the second polarized light to output from a
light outputting surface of the light guide plate to illuminate a
display panel.
4. The illumination system of claim 3, wherein the light outputting
surface is arranged between the first side surface and the second
side surface of the light guide plate.
5. The illumination system of claim 3, further comprising at least
one of a diffuser sheet or a prism sheet disposed at the light
outputting surface of the light guide plate.
6. The illumination system of claim 1, wherein the reflective
polarizer is a cholesteric liquid crystal ("CLC") reflective
polarizer.
7. The illumination system of claim 6, wherein the light source
assembly includes a narrowband monochromatic light source, and the
CLC reflective polarizer is a narrowband CLC reflective polarizer
with a constant helix pitch.
8. The illumination system of claim 6, wherein the light source
assembly includes a broadband light source, and the CLC reflective
polarizer is a broadband CLC reflective polarizer with a gradient
helix pitch.
9. The illumination system of claim 6, wherein the light source
assembly includes a plurality of narrowband monochromatic light
sources for different colors, and the CLC reflective polarizer
includes a plurality of CLC layers stacked together, the CLC layers
having at least two different helix pitches.
10. A system, comprising: a light guide plate including two wedges
having slanted surfaces coupled to one other; a reflective sheet
coupled to the light guide plate and configured to reflect a first
polarized light having a first handedness as a second polarized
light having a second handedness opposite to the first handedness;
and a reflective polarizer disposed between the slanted surfaces
and configured to selectively transmit the first polarized light
and reflect the second polarized light, wherein the light guide
plate is configured to guide the first polarized light to the
reflective sheet, and guide the second polarized light reflected
from the reflective sheet to the reflective polarizer.
11. The system of claim 10, wherein the reflective sheet is
disposed at a first side surface of the light guide plate, and the
system further comprises a light source assembly disposed at a
second side surface of the light guide plate opposite to the first
side surface, the light source assembly being configured to output
the first polarized light.
12. The system of claim 11, wherein the reflective polarizer is
configured to reflect the second polarized light guided by the
light guide plate toward a light outputting surface of the light
guide plate, and the second polarized light is output from the
light outputting surface to illuminate a display panel.
13. The system of claim 12, wherein the light outputting surface is
a surface connecting the first side surface and the second side
surface of the light guide plate.
14. The system of claim 12, wherein the light outputting surface is
perpendicular to the first side surface and the second side surface
of the light guide plate.
15. The system of claim 12, wherein the side surface and the second
side surface are parallel to one another.
16. The system of claim 12, further comprising at least one of a
diffuser sheet or a prism sheet disposed at the light outputting
surface of the light guide plate.
17. The system of claim 10, wherein the reflective polarizer is a
cholesteric liquid crystal ("CLC") reflective polarizer.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a division of U.S. patent application
Ser. No. 16/820,695, entitled "LIQUID CRYSTAL REFLECTIVE POLARIZER
AND PANCAKE LENS ASSEMBLY HAVING THE SAME," filed on Mar. 16, 2020.
Content of the above-mentioned application is incorporated herein
by reference in its entirety.
TECHNICAL FIELD
[0002] The present disclosure relates generally to optical devices
and, more specifically, to a liquid crystal reflective polarizer
and a pancake lens assembly having the same.
BACKGROUND
[0003] Birefringent materials having a chirality may be used in
various optical elements or devices. As a type of birefringent
material having a chirality, cholesteric liquid crystals ("CLCs"),
also known as chiral nematic liquid crystals, have been used in
optical elements to reflect or transmit circularly polarized light
depending on the handedness of the incident light. For example,
CLCs may be configured to primarily reflect a light having a
specific circular polarization and primarily transmit a light
having an opposite circular polarization. Due to the handedness
selectivity of the CLCs, a CLC layer (or a CLC film, a CLC plate,
etc.) or a CLC-layers stack may function as a circular reflective
polarizer. For example, a circular reflective polarizer including
left-handed CLCs ("LHCLCs") can be configured to reflect a
left-handed circularly polarized ("LHCP") light and transmit a
right-handed circularly polarized ("RHCP") light, and a circular
reflective polarizer including right-handed CLCs ("RHCLCs") can be
configured to reflect a right-handed circularly polarized ("RHCP")
light and transmit a left-handed circularly polarized ("LHCP")
light. CLCs can be configured to function over a broad bandwidth
such that lights having different wavelengths within the spectrum
can be reflected or transmitted. Circular reflective polarizers
based on CLCs may be used as multifunctional optical components in
a large variety of applications, such as polarization conversion
components, brightness enhancement components, or optical
path-folding components.
SUMMARY
[0004] Consistent with a disclosed embodiment of the present
disclosure, an optical device is provided. The optical device
includes a first optical element configured to output an
elliptically polarized light having one or more predetermined
polarization ellipse parameters. The optical device also includes a
second optical element including a birefringent material with a
chirality. The second optical element is configured to receive the
elliptically polarized light from the first optical element and
reflect the elliptically polarized light as a circularly polarized
light.
[0005] Consistent with a disclosed embodiment of the present
disclosure, an optical lens assembly is provided. The optical lens
assembly includes a first optical element. The first optical
element includes an optical waveplate configured to convert an
incident light into an elliptically polarized light having one or
more predetermined polarization ellipse parameters. The first
optical element also includes a mirror configured to transmit a
first portion of the elliptically polarized light and reflect a
second portion of the elliptically polarized light. The optical
lens assembly also includes a second optical element. The second
optical element includes a reflective polarizer configured to
receive the first portion of the elliptically polarized light from
the mirror and reflect the first portion of the elliptically
polarized light as a circularly polarized light having a first
handedness toward the mirror. The reflective polarizer includes a
birefringent material with a chirality.
[0006] Consistent with a disclosed embodiment of the present
disclosure, an illumination system is provided. The illumination
system includes a light source assembly configured to emit a first
polarized light having a first handedness. The illumination system
includes a light guide plate configured to guide the first
polarized light received from the light source assembly and output
the first polarized light. The light guide plate includes two
wedges coupled to each other at a slanted surface between the two
wedges and a reflective polarizer disposed at the slanted surface.
The illumination system includes a reflective sheet arranged at a
first side surface of the light guide plate and configured to
reflect the first polarized light having the first handedness as a
second polarized light having a second handedness opposite to the
first handedness. The reflective polarizer includes a birefringent
material having a chirality, and is configured to selectively
transmit the first polarized light having the first handedness and
reflect the second polarized light having the second
handedness.
[0007] Other aspects of the present disclosure can be understood by
those skilled in the art in light of the description, the claims,
and the drawings of the present disclosure. The foregoing general
description and the following detailed description are exemplary
and explanatory only and are not restrictive of the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The following drawings are provided for illustrative
purposes according to various disclosed embodiments and are not
intended to limit the scope of the present disclosure. In the
drawings:
[0009] FIG. 1A illustrates a schematic diagram of a director
configuration in cholesteric liquid crystals ("CLCs"), according to
an embodiment of the present disclosure;
[0010] FIG. 1B illustrates polarization selective reflectivity of
the CLCs, according to an embodiment of the present disclosure;
[0011] FIG. 2A illustrates a cross section of a cholesteric liquid
crystal ("CLC") reflective polarizer, according to an embodiment of
the present disclosure;
[0012] FIG. 2B illustrates a polarization ellipse diagram of a
polarized light, according to an embodiment of the present
disclosure;
[0013] FIG. 2C illustrates simulation results showing light leakage
versus thickness of a CLC layer for incident lights with different
polarization ellipse parameters, according to an embodiment of the
present disclosure;
[0014] FIG. 2D illustrates experimental results showing light
leakage of a CLC layer versus ellipticity of a light incident onto
the CLC layer, according to an embodiment of the present
disclosure;
[0015] FIG. 3A illustrates a cross section of a CLC reflective
polarizer, according to another embodiment of the present
disclosure;
[0016] FIG. 3B illustrates a cross section of a CLC reflective
polarizer, according to another embodiment of the present
disclosure;
[0017] FIG. 3C illustrates simulation results showing off-axis
incidence angle light leakage of a conventional CLC reflective
polarizer that does not include a positive C-plate;
[0018] FIG. 3D illustrates simulation results showing off-axis
incidence angle light leakage of a CLC reflective polarizer with
two positive C-plates, according to an embodiment of the present
disclosure;
[0019] FIG. 4 illustrates a cross section of a CLC reflective
polarizer, according to another embodiment of the present
disclosure;
[0020] FIG. 5A illustrates a schematic diagram of a pancake lens
assembly, according to an embodiment of the present disclosure;
[0021] FIG. 5B schematically illustrates a cross-sectional view of
an optical path of the pancake lens assembly shown in FIG. 5A,
according to an embodiment of the present disclosure;
[0022] FIG. 6A illustrates a schematic diagram of a pancake lens
assembly, according to another embodiment of the present
disclosure;
[0023] FIG. 6B schematically illustrates a cross-sectional view of
an optical path of the pancake lens assembly shown in FIG. 6A,
according to an embodiment of the present disclosure;
[0024] FIG. 7 illustrates a schematic diagram of an illumination
system including a CLC reflective polarizer, according to an
embodiment of the present disclosure;
[0025] FIG. 8A illustrates a diagram of a near-eye display ("NED"),
according to an embodiment of the present disclosure; and
[0026] FIG. 8B illustrates a cross sectional view of a front body
of the NED shown in FIG. 8A, according to an embodiment of the
present disclosure.
DETAILED DESCRIPTION
[0027] Embodiments consistent with the present disclosure will be
described with reference to the accompanying drawings, which are
merely examples for illustrative purposes and are not intended to
limit the scope of the present disclosure. Wherever possible, the
same reference numbers are used throughout the drawings to refer to
the same or similar parts, and a detailed description thereof may
be omitted.
[0028] Further, in the present disclosure, the disclosed
embodiments and the features of the disclosed embodiments may be
combined. The described embodiments are some but not all of the
embodiments of the present disclosure. Based on the disclosed
embodiments, persons of ordinary skill in the art may derive other
embodiments consistent with the present disclosure. For example,
modifications, adaptations, substitutions, additions, or other
variations may be made based on the disclosed embodiments. Such
variations of the disclosed embodiments are still within the scope
of the present disclosure. Accordingly, the present disclosure is
not limited to the disclosed embodiments. Instead, the scope of the
present disclosure is defined by the appended claims.
[0029] As used herein, the terms "couple," "coupled," "coupling,"
or the like may encompass an optical coupling, a mechanical
coupling, an electrical coupling, an electromagnetic coupling, or a
combination thereof. An "optical coupling" between two optical
elements refers to a configuration in which the two optical
elements are arranged in an optical series, and a light output from
one optical element may be directly or indirectly received by the
other optical element. An optical series refers to optical
positioning of a plurality of optical elements in a light path,
such that a light output from one optical element may be
transmitted, reflected, diffracted, converted, modified, or
otherwise processed or manipulated by one or more of other optical
elements. In some embodiments, the sequence in which the plurality
of optical elements are arranged may or may not affect an overall
output of the plurality of optical elements. A coupling may be a
direct coupling or an indirect coupling (e.g., coupling through an
intermediate element).
[0030] The phrase "at least one of A or B" may encompass all
combinations of A and B, such as A only, B only, or A and B.
Likewise, the phrase "at least one of A, B, or C" may encompass all
combinations of A, B, and C, such as A only, B only, C only, A and
B, A and C, B and C, or A and B and C. The phrase "A and/or B" may
be interpreted in a manner similar to that of the phrase "at least
one of A or B." For example, the phrase "A and/or B" may encompass
all combinations of A and B, such as A only, B only, or A and B.
Likewise, the phrase "A, B, and/or C" has a meaning similar to that
of the phrase "at least one of A, B, or C." For example, the phrase
"A, B, and/or C" may encompass all combinations of A, B, and C,
such as A only, B only, C only, A and B, A and C, B and C, or A and
B and C.
[0031] When a first element is described as "attached," "provided,"
"formed," "affixed," "mounted," "secured," "connected," "bonded,"
"recorded," or "disposed," to, on, at, or at least partially in a
second element, the first element may be "attached," "provided,"
"formed," "affixed," "mounted," "secured," "connected," "bonded,"
"recorded," or "disposed," to, on, at, or at least partially in the
second element using any suitable mechanical or non-mechanical
manner, such as depositing, coating, etching, bonding, gluing,
screwing, press-fitting, snap-fitting, clamping, etc. In addition,
the first element may be in direct contact with the second element,
or there may be an intermediate element between the first element
and the second element. The first element may be disposed at any
suitable side of the second element, such as left, right, front,
back, top, or bottom.
[0032] When the first element is shown or described as being
disposed or arranged "on" the second element, term "on" is merely
used to indicate an example relative orientation between the first
element and the second element. The description may be based on a
reference coordinate system shown in a figure, or may be based on a
current view or example configuration shown in a figure. For
example, when a view shown in a figure is described, the first
element may be described as being disposed "on" the second element.
It is understood that the term "on" may not necessarily imply that
the first element is over the second element in the vertical,
gravitational direction. For example, when the assembly of the
first element and the second element is turned 180 degrees, the
first element may be "under" the second element (or the second
element may be "on" the first element). Thus, it is understood that
when a figure shows that the first element is "on" the second
element, the configuration is merely an illustrative example. The
first element may be disposed or arranged at any suitable
orientation relative to the second element (e.g., over or above the
second element, below or under the second element, left to the
second element, right to the second element, behind the second
element, in front of the second element, etc.).
[0033] The term "processor" used herein may encompass any suitable
processor, such as a central processing unit ("CPU"), a graphics
processing unit ("GPU"), an application-specific integrated circuit
("ASIC"), a programmable logic device ("PLD"), or a combination
thereof. Other processors not listed above may also be used. A
processor may be implemented as software, hardware, firmware, or a
combination thereof
[0034] The term "controller" may encompass any suitable electrical
circuit, software, or processor configured to generate a control
signal for controlling a device, a circuit, an optical element,
etc. A "controller" may be implemented as software, hardware,
firmware, or a combination thereof. For example, a controller may
include a processor, or may be included as a part of a
processor.
[0035] The term "non-transitory computer-readable medium" may
encompass any suitable medium for storing, transferring,
communicating, broadcasting, or transmitting data, signal, or
information. For example, the non-transitory computer-readable
medium may include a memory, a hard disk, a magnetic disk, an
optical disk, a tape, etc. The memory may include a read-only
memory ("ROM"), a random-access memory ("RAM"), a flash memory,
etc.
[0036] The present disclosure provides an optical device that may
include a first optical element configured to output an
elliptically polarized light having one or more predetermined
polarization ellipse parameters. The optical device may also
include a second optical element including a birefringent material
with a chirality, and configured to receive the elliptically
polarized light from the first optical element and reflect the
elliptically polarized light as a circularly polarized light. The
one or more predetermined polarization ellipse parameters may
include at least one of an ellipticity or an orientation angle. In
some embodiments, the first optical element may be a transmissive
type optical element, a reflective type optical element, an
absorptive type optical element, or a combination thereof. For
example, the first optical element may be an optical waveplate,
which may be configured to convert a linearly polarized light or a
circularly polarized light into the elliptically polarized light
having the one or more predetermined polarization ellipse
parameters. In some embodiments, the first optical element may be a
light source assembly. In some embodiments, the light source
assembly may generate and output the elliptically polarized light
having the one or more predetermined polarization ellipse
parameters. In some embodiments, the optical waveplate may be a
part of the light source assembly. In some embodiments, the optical
waveplate may be separately provided from the light source
assembly. The second optical element may be configured to transmit
the elliptically polarized light having one or more predetermined
polarization ellipse parameters at a light transmittance of
substantially zero, resulting a substantially zero light leakage of
the optical device for the elliptically polarized light having one
or more predetermined polarization ellipse parameters. In some
embodiments, the second optical element may be a reflective
polarizer based on the birefringent material with a chirality. The
light leakage of the reflective polarizer may be suppressed through
configuring properties (e.g., one or more predetermined
polarization ellipse parameters) of an incident light of the
reflective polarizer using the first optical element.
[0037] In some embodiments, the chirality of the birefringent
material may be a property of the birefringent material itself,
e.g., the birefringent material may include chiral crystal
molecules, or molecules of the birefringent material may include a
chiral functional group. In some embodiments, the chirality of the
birefringent material may be introduced by chiral dopants doped
into the birefringent material. In some embodiments, the
birefringent material with a chirality may include twist-bend
nematic LCs (or LCs in twist-bend nematic phase), in which the LC
directors may exhibit periodic twist and bend deformations forming
a conical helix with doubly degenerate domains having opposite
handedness. The LC directors in twist-bend nematic LCs may be
tilted with respect to the helical axis and, thus, twist-bend
nematic phase may be considered as the generalized case of the
conventional nematic phase in which the LC directors are orthogonal
with respect to the helical axis. Cholesteric liquid crystals
("CLCs") are a type of birefringent material with a chirality. In
the following descriptions, for illustrative purposes, CLCs are
used as an example of the birefringent material with a chirality.
CLC reflective polarizers (i.e., reflective polarizers based on
CLCs) are used as an example of the reflective polarizer based on
the birefringent material with a chirality. In some embodiments,
optical elements (e.g., reflective polarizers) with suppressed
light leakage may also be configured based on another suitable
birefringent material with a chirality, following the same design
principles for the CLC reflective polarizer described below.
[0038] Cholesteric liquid crystals ("CLCs") are liquid crystals
that have a helical structure and, thus, exhibit chirality, i.e.,
handedness. CLCs are also known as chiral nematic liquid crystals.
For an incidence wavelength within the reflection band of the CLCs,
a circularly polarized light with a handedness that is the same as
the handedness of the helical structure of the CLCs may be
primarily or substantially reflected, and a circularly polarized
light with a handedness that is different from (e.g., opposite to)
the handedness of the helical structure of the CLCs may be
primarily or substantially transmitted. Due to the handedness
selectivity of the CLCs, a CLC layer (or a CLC film, a CLC plate,
etc.) may function as a CLC reflective polarizer. In some
embodiments, for both of the reflected light and transmitted light
of the CLCs, their polarization states may remain unchanged. In
some embodiments, due to the waveplate effect of the CLCs, the
polarization states of the reflected and/or the transmitted lights
may be changed, which may result in a light leakage of the CLC
layer and, accordingly, degrade the extinction ratio of the CLC
reflective polarizer. Further, the light leakage of the CLC layer
may increase as the incidence angle increases.
[0039] The present disclosure provides an optical device configured
to reduce the light leakage of a CLC layer. In some embodiments,
the light leakage of the CLC layer may be reduced by controlling
the ellipticity of a polarized incident light and/or a clocking
angle (e.g., an orientation angle) between the CLC layer and the
polarized incident light. In some embodiments, the property (e.g.,
polarization ellipse parameters) of the polarized incident light
may be adjusted or modified to match the property of the CLC layer
(e.g., through ellipticity matching), such that the output of the
CLC layer is primarily or substantially a reflected circularly
polarized light, with reduced light transmittance (e.g., light
transmittance of the CLC layer is substantially zero). To modify
optical properties of the light incident onto the CLC layer, the
optical device may include an optical element disposed upstream of
the CLC layer in a light path, and configured to convert the light
into an elliptically polarized light having one or more
predetermined polarization ellipse parameters, before the light is
incident onto the CLC layer. In some embodiments, the optical
element may be a transmissive type optical element, a reflective
type optical element, an absorptive type optical element, or a
combination thereof. In some embodiments, the optical device may
include an optical element disposed upstream of the CLC layer in a
light path, and configured to output an elliptically polarized
light having one or more predetermined polarization ellipse
parameters toward the CLC layer as an incident light of the CLC
layer.
[0040] In some embodiments, the optical element disposed upstream
of the CLC layer in a light path may be an optical waveplate. The
optical waveplate may be a quarter-wave plate ("QWP"). The
quarter-wave plate may be oriented relative to the polarization
direction of an incident light (e.g., a linearly polarized incident
light) onto the QWP or otherwise configured based on the property
of the incident light to convert the incident light into the
elliptically polarized light having one or more predetermined
polarization ellipse parameters. The one or more predetermined
polarization ellipse parameters of the elliptically polarized light
may be determined or selected, e.g., through an optimization, such
that a transmitted portion of the elliptically polarized light
incident onto the CLC layer is significantly reduced or is
substantially zero. In some embodiments, the light transmittance
(or light leakage) of the CLC layer for the elliptically polarized
light may be reduced to be below 0.05%. Improved optical
performance of the optical device may be achieved due to the
reduction in the light leakage.
[0041] FIG. 1A illustrates a schematic diagram of a director
configuration 100 of cholesteric liquid crystals ("CLCs") and FIG.
1B illustrates polarization selective reflectivity of the CLCs
shown in FIG. 1A. CLCs are liquid crystals that have a helical
structure and, thus, exhibit chirality, i.e., handedness. CLCs are
also known as chiral nematic liquid crystals. In the schematic
diagram shown in FIG. 1A, nematic LC molecules are represented by
solid rods. CLCs may be organized in one or more layers 111, 112,
113, 114, 115 with no positional ordering within the layers. For
illustrative purposes, in the schematic diagram shown in FIG. 1A,
the layers are separated apart from one another to better
illustrate the structure. Although five layers are shown, the
number of layers is not limited by the present disclosure, which
may be any suitable number, such as 1, 2, 3, 4, 6, 7, etc. The
nematic LC directors (e.g., long axes of the CLC molecules) may
rotate along an axial direction (e.g., z-direction shown in FIG.
1A) of the layers due to the presence of chiral dopants. In the
same layer, the nematic LC directors may be oriented in the same
direction. In some embodiments, the variation of the nematic LC
directors may be periodic. The period of the variation of the
nematic LC directors, i.e., an axial length over which the nematic
LC directors rotate by 360.degree., is known as a helix pitch P. In
some embodiments, the variation of the nematic LC directors may
repeat at every half pitch (P/2), as the nematic LC directors at
0.degree. and .+-.180.degree. may be equivalent. The helix pitch P
may determine a reflection band of the CLCs, i.e., a band of
incidence wavelengths that may be reflected by the CLCs via Bragg
Reflection. In some embodiments, the helix pitch P may be of the
same order as wavelengths of visible lights. The reflection band of
the CLCs may be centered at a wavelength .lamda..sub.0=n*P, where n
may be an average refractive index of the CLCs that may be
calculated as n=(n.sub.e+n.sub.o)/2. In these equations, no and no
represent the extraordinary and ordinary reflective indices of the
nematic LCs, respectively, and P represents the helix pitch of the
CLCs. A reflection bandwidth .DELTA..lamda. of the CLCs may be
calculated as .DELTA..lamda.=.DELTA.n*P, which may be proportional
to the birefringence .DELTA.n of the CLCs, where
.DELTA.n=n.sub.e=n.sub.o.
[0042] For an incidence wavelength within the reflection band of
the CLCs, a circularly polarized light with a handedness that is
the same as the handedness of the helical structure of the CLCs may
be primarily or substantially reflected, and a circularly polarized
light with a handedness that is different from (e.g., opposite to)
the handedness of the helical structure of the CLCs may be
primarily or substantially transmitted. For example, as shown in
FIG. 1B, left-handed CLCs ("LHCLCs") 150 may exhibit a high
reflection characteristic (e.g., a high reflectance) for a
left-handed circularly polarized ("LHCP") incident light and a high
transmission characteristic (e.g., a high transmittance) for a
right-handed circularly polarized ("RHCP") incident light. That is,
for a light having an incidence wavelength within the reflection
band of the LHCLCs 150, when the light is an LHCP light (or
includes an LHCP light portion), the LHCLCs 150 may primarily or
substantially reflect the LHCP light (or the LHCP light portion).
When the light is an RHCP light (or includes an RHCP light
portion), the LHCLCs 150 may primarily or substantially transmit
the RHCP light (or the RHCP light portion). Due to the handedness
selectivity of the CLCs, a thin film of CLCs may be used to realize
a reflective polarizer. In some embodiments, for both of the
reflected light and transmitted light of the CLCs 150, their
polarization states may remain unchanged. In some embodiments, due
to the waveplate effect of the CLCs 150, the polarization states of
at least one of the reflected light or the transmitted light may be
changed, which may result in a light leakage. When the incidence
wavelength is outside of the reflection band of the LHCLCs 150, a
circularly polarized light may be transmitted by the LHCLCs 150
regardless of the handedness. An unpolarized light or a linearly
polarized light can be decomposed into a RHCP light (or a RHCP
component or portion) and an LHCP light (or an LHCP component or
portion), where each component may be selectively reflected or
transmitted depending on the handedness of the component and the
handedness of the helical structure of the CLCs.
[0043] FIG. 2A illustrates a y-z cross section of a CLC reflective
polarizer 200, according to an embodiment of the present
disclosure. As shown in FIG. 2A, the CLC reflective polarizer 200
may include a CLC layer 215 having a helical structure that
includes a constant helix pitch (e.g., repeat of a same, fixed
helix pitch). An axis of the helix may be normal (e.g.,
perpendicular) to the surface of the CLC layer 215. In some
embodiments, the CLC reflective polarizer 200 may further include
one or more substrates 205 for support and protective purposes. Two
substrates 205 are shown in FIG. 2A for illustrative purposes. The
number of substrates is not limited to two and may be any suitable
number. The substrates 205 may be optically transparent in the
visible band (about 380 nm to about 700 nm). In some embodiments,
the substrates 205 may also be optically transparent in some or all
of the infrared ("IR") band (e.g., about 700 nm to about 1 mm, or
any portion thereof). For example, the substrate 205 may include a
glass, a plastic, a sapphire, etc. The substrate 205 may be rigid,
semi-rigid, flexible, or semi-flexible. In some embodiments, the
substrate 205 may be a part of another optical device or another
optoelectrical device. For example, the substrate 205 may be a part
of a functional device, such as a display screen. In some
embodiments, the substrate 205 may be a part of an optical lens
assembly, such as a lens substrate of the optical lens assembly. In
some embodiments, at least one of the substrates 205 may be
provided with an alignment layer 210, which may be configured to
provide an initial alignment of the CLCs. In the embodiment shown
in FIG. 2A, two alignment layers 210 are provided for illustrative
purposes, with each alignment layer 210 being coupled (e.g.,
stacked) with each substrate 205. The number of the alignment
layers 210 is not limited to two, and may be any suitable number.
The number of the alignment layers may or may not be the same as
the number of the substrates. In some embodiments, the alignment
layer 210 may provide anti-parallel homogeneous alignments of the
CLCs.
[0044] In some embodiments, the helix pitch of the CLCs may be of
the same order as the wavelengths of visible lights. Accordingly,
the CLC layer 215 may have a reflection band in the visible
spectrum. When the incidence wavelength is within the reflection
band of the CLC layer 215, a circularly polarized light having a
handedness that is the same as that of the helical structure of the
CLC layer 215may be primarily or substantially reflected, and a
circularly polarized light having a handedness that is different
from (e.g., opposite to) that of the helix structure of the CLC
layer 215 may be primarily or substantially transmitted. Due to the
waveplate effect of the CLC layer 215, the polarization states of
at least one of the reflected light or the transmitted light may be
changed to an elliptical polarization. This phenomenon may be
referred to as depolarization. Depolarization may result in a light
leakage of the CLC layer 215, which may degrade an extinction ratio
of the CLC reflective polarizer 200.
[0045] In the disclosed embodiments, the CLC layer 215 may be
coupled to an optical waveplate 220. The optical waveplate 220 may
be configured to convert an incident light 221 into an elliptically
polarized light 204 having one or more predetermined polarization
ellipse parameters, and direct the elliptically polarized light 204
toward the CLC layer 215. In some embodiments, the optical
waveplate 220 may be a quarter-wave plate ("QWP"). In some
embodiments, the incident light 221 may be a linearly polarized
light that is substantially normally incident onto the QWP, and the
polarization axis of the QWP may be oriented or configured relative
to a polarization direction of the linearly polarized light 221 to
output an elliptically polarized light 204 having one or more
predetermined polarization ellipse parameters toward the CLC layer
215. In some embodiments, the CLC layer 215 may be coupled to a
light source 230 configured to emit an unpolarized light 222. In
some embodiments, a linear polarizer 225 may be disposed between
the optical waveplate 220 and the light source 230. The linear
polarizer 225 may be configured to convert the unpolarized light
222 emitted by the light source 230 into a linearly polarized light
221 incident onto the optical waveplate 220. In some embodiments,
the light source 230 may directly emit a linearly polarized light
(e.g., light 222 may be a linearly polarized light). In such
embodiments, the linear polarizer 225 may be omitted. In some
embodiments, the light source 230 may emit a circularly polarized
light (e.g., the light 222 may be a circularly polarized light). In
such embodiments, the optical waveplate 220 may be a first optical
waveplate. A second optical waveplate (not shown) may be disposed
between the first optical waveplate 220 and the light source 230 to
convert the circularly polarized light into a linearly polarized
light incident onto the first optical waveplate 220.
[0046] In some embodiments, the light incident onto the optical
waveplate 220 may be a circularly polarized light. The optical
waveplate 220 may be a QWP, or may be any other suitable waveplate.
The optical waveplate 220 may be configured (e.g., properties of
the optical waveplate 220 such as the optical axis, thickness,
materials, etc. may be configured) such that the light output from
the optical waveplate 220 is an elliptically polarized light having
the one or more predetermined polarization ellipse parameters. The
elliptically polarized light output from the optical waveplate 220
having the one or more predetermined polarization ellipse
parameters may be directed onto the CLC layer 215, and may be
substantially reflected by the CLC layer 215 as a circularly
polarized light, with the light transmittance being substantially
suppressed (e.g., the light transmittance may be significantly
reduced or may be substantially zero). Configuration of the optical
waveplate 220 may be performed relatively statically or relatively
dynamically. For example, when the property of the CLC layer 215 is
fixed and the light incident onto the optical waveplate 220 is
fixed, the property of the optical waveplate 220 may be suitably
determined or configured such that an elliptically polarized light
having the one or more predetermined polarization ellipse
parameters is output by the optical waveplate 220, and directed
toward the CLC layer 215. When the elliptically polarized light
having the one or more predetermined polarization ellipse
parameters is incident onto the CLC layer 215, the elliptically
polarized light may be substantially converted into and reflected
as a circularly polarized light, with a reduced light transmittance
(or light leakage) through the CLC layer 215. During operations,
the property of the optical waveplate 220 may remain substantially
the same. In some embodiments, when the light incident onto the
optical waveplate 220 may change over time, and/or when the
property of the CLC layer 215 may change over time, the property of
the optical waveplate 220 may be dynamically adjusted (e.g., by
adjusting an electric field applied to the optical waveplate 220
such that the optical waveplate 220 outputs an elliptically
polarized light having the one or more predetermined polarization
ellipse parameters toward the CLC layer 215.
[0047] In some embodiments, the polarization ellipse parameters of
the elliptically polarized light may include at least one of an
orientation angle .PSI. or an ellipticity E. Due to the waveplate
effect of the CLC layer 215, the elliptically polarized light
having one or more of the predetermined orientation angle .PSI. and
ellipticity .epsilon. (the value(s) or ranges of which may be
determined or calculated through optimization) may be substantially
or primarily reflected as a circularly polarized light by the CLC
layer 215, thereby reducing the amount of light transmitted through
the CLC layer 215. As a result, the light leakage caused by the
transmitted light may be significantly reduced or suppressed. In
some embodiments, the optical waveplate 220 may be a part of the
CLC reflective polarizer 200. In some embodiments, the optical
waveplate 220 may be a part of another element or device other than
the CLC reflective polarizer 200.
[0048] FIG. 2B illustrates a polarization ellipse diagram 240 of a
polarized light. The Electric Field of a plane wave can be
described as the vector sum of two orthogonal components, e.g., a
horizontal component and a vertical component. The two components
may be characterized by their respective amplitudes and the
relative phase between the two components. When viewed along a
direction of wave propagation, the tip of the Electric Field vector
of a fully polarized wave traces out a regular pattern. In a
general form, the pattern may be represented by an ellipse, which
may be referred to as a polarization ellipse as shown in FIG. 2B.
The ellipse has a semi-major axis x' of length a, and a semi-minor
axis y' of length b, where a and b correspond to the amplitudes of
the two orthogonal components, respectively. The angle of the
semi-major axis x', as measured counter-clockwise from a positive
horizontal axis x (when coupled to the CLC layer 215, the positive
horizontal axis xis the alignment direction of the CLC layer 215)
is the orientation angle .PSI. of the plane wave, where
0.degree..ltoreq..PSI..ltoreq.180.degree.. The degree to which the
ellipse is oval may be represented by a shape parameter named
eccentricity or ellipticity .epsilon., defined as .epsilon.=b/a,
which is a ratio of the length of the semi-minor axis y' to that of
the semi-major axis x', where -1.ltoreq..epsilon..ltoreq.1. An LHCP
light may have .epsilon.=-1, and an RHCP light may have
.epsilon.=1. A left-handed elliptically polarized ("LHEP") light
may have -1<.epsilon.<0 and
0.degree..ltoreq..PSI..ltoreq.180.degree., and a right-handed
elliptically polarized ("RHEP") light may have 0<.epsilon.<1
and 0.degree..ltoreq..PSI..ltoreq.180.degree.. A linearly polarized
light may have .epsilon.=0 and
0.degree..ltoreq..PSI..ltoreq.180.degree..
[0049] In some embodiments, the CLC layer 215 may include LCs
having a birefringence in a range of about 0.15 to about 0.4. To
reduce the light leakage (e.g., to reduce the light transmittance)
of the CLC layer 215 for an elliptically polarized incident light
having the same handedness as the helical structure of the CLC
layer 215, the orientation angle of the elliptically polarized
incident light may be configured to be a value in a range of about
75.degree..ltoreq..PSI..ltoreq.90.degree., about
75.degree..ltoreq..PSI..ltoreq.85.degree., about
75.degree..ltoreq..PSI..ltoreq.80.degree., about
80.degree..ltoreq..PSI..ltoreq.90.degree., about
80.degree..ltoreq..PSI..ltoreq.85.degree., about
85.degree..ltoreq..PSI..ltoreq.90.degree., about
76.degree..ltoreq..PSI..ltoreq.89.degree., about
77.degree..ltoreq..PSI..ltoreq.88.degree., about
78.degree..ltoreq..PSI..ltoreq.87.degree., or about
79.degree..ltoreq..PSI..ltoreq.86.degree.. In some embodiments, the
orientation angle .PSI. may be in a range of
n.sub.1.degree..ltoreq..PSI..ltoreq.n.sub.2.degree., where n.sub.1
may be any suitable value equal to or greater than 75, and n.sub.2
may be any suitable value equal to or less than 90 and greater than
n.sub.1. In some embodiments, the ellipticity .epsilon. of the
elliptically polarized incident light may be configured to be a
value in a range of about -1<.epsilon..ltoreq.-0.85 when the
chirality of the birefringent material is left-handed, e.g., when
the CLC layer 215 includes LHCLCs (referred to as an LHCLC layer).
For example, when the CLC layer 215 is an LHCLC layer, the
ellipticity .epsilon. of the elliptically polarized incident light
may be configured to be a value in a range of about
-0.95.ltoreq..epsilon..ltoreq.-0.85, about
-0.9.ltoreq..epsilon..ltoreq.-0.85, about
-0.95.ltoreq..epsilon..ltoreq.-0.9, about
-1<.epsilon..ltoreq.-0.9, or about -1<.epsilon..ltoreq.-0.95.
The ellipticity .epsilon. of the elliptically polarized incident
light may be configured to be a value in a range of about
0.85.ltoreq..epsilon.<1 when the chirality of the birefringent
material is right-handed, e.g., when the CLC layer 215 includes
RHCLCs (referred to an RHCLC layer). For example, when the CLC
layer 215 is an RHCLC layer, the ellipticity .epsilon. of the
elliptically polarized incident light may be configured to be a
value in a range of about 0.85.ltoreq..epsilon..ltoreq.0.95, about
0.85.ltoreq..epsilon..ltoreq.0.9, about 0.9.ltoreq..epsilon.23
0.95, about 0.9.ltoreq..PSI.<1, or about
0.95.ltoreq..epsilon..ltoreq.1. The values of the orientation angle
.PSI. and ellipticity .epsilon. of the elliptically polarized
incident light may vary as the birefringence of the LCs included in
the CLC layer 215 varies.
[0050] FIG. 2C illustrates simulation results showing a light
leakage versus the thickness of the CLC layer 215 for substantially
normally incident lights with different polarization ellipse
parameters. For illustrative purposes, the CLC layer 215 including
LHCLCs (referred to as an LHCLC layer 215) is used in the
simulation. As shown in FIG. 2C, the horizontal axis is the
thickness the CLC layer 215 (in a unit of pitch), and the vertical
axis is the light leakage, which is the light transmittance of the
CLC layer 215 for a polarized incident light having the same
handedness (e.g., left-handedness) as that of the helical structure
of the CLC layer 215. The light leakage of the CLC layer 215 is
evaluated for five normally incident lights with different
polarization ellipse parameters, respectively. Referring to FIG. 2A
and FIG. 2C, curve 260 shows the thickness dependent light leakage
of the CLC layer 215 for an LHCP incident light 202 (.epsilon.=-1),
curve 270 shows the thickness dependent light leakage for a first
LHEP incident light 204 (.epsilon.=-0.95 and .PSI.=80.degree.),
curve 275 shows the thickness dependent light leakage for a second
LHEP incident light 206 (.epsilon.=-0.97 and .PSI.=170.degree.),
curve 280 shows the thickness dependent light leakage for a third
LHEP incident light 208 (.epsilon.=-0.95 and .PSI.=170.degree.),
and curve 285 shows the thickness dependent light leakage for a
fourth LHEP incident light 212 (.epsilon.=-0.90 and
.PSI.=170.degree.. In FIG. 2A, the first LHEP incident light 204
refers to the light output by the optical waveplate 220, according
to an embodiment of the present disclosure. The LHCP incident
lights 202 and the LHEP incident lights 206, 208 and 212 are
hypothetical incident lights for comparison with the LHEP incident
light 204, and hence are shown with dotted arrows in FIG. 2A.
[0051] As shown in FIG. 2A, the CLC layer 215 may reflect the LHCP
incident light 202 (.epsilon.=-1) as an LHEP light 202' due to the
waveplate effect of the CLC layer 215. Referring to FIG. 2C, as
shown in curve 260, the light leakage of the CLC layer 215 is about
0.55% when the thickness the CLC layer 215 is about 9 pitches. As
the thickness the CLC layer 215 gradually increases to about 14
pitches, the light leakage of the CLC layer 215 gradually decreases
to a minimum value of about 0.1%. As the thickness the CLC layer
215 further increases to about 20 pitches, the light leakage of the
CLC layer 215 remains substantially the same, which is about
0.1%.
[0052] As shown in FIG. 2A, the CLC layer 215 may reflect the first
LHEP incident light 204 (.epsilon.=-0.95 and .PSI.=80.degree.) as
an LHCP light 204'. Comparing curves 260 and 270 shown in FIG. 2C,
the CLC layer 215 exhibits a lower light leakage for the first LHEP
incident light 204 (.epsilon.=-0.95 and .PSI.=80.degree.) than for
the LHCP incident light 202 (.epsilon.=-1) at the same thickness.
As shown in curve 270, the light leakage of the CLC layer 215 is
about 0.45% when the thickness the CLC layer 215 is about 9
pitches. As the thickness the CLC layer 215 gradually increases to
about 14 pitches, the light leakage of the CLC layer 215 gradually
decreases to a minimum value that is substantially 0. As the
thickness the CLC layer 215 further increases to about 20 pitches,
the light leakage of the CLC layer 215 remains substantially the
same, which is about 0. In some applications, the thickness of the
CLC layer 215 may be in a range of 10 pitches to 11 pitches. In
this thickness range, as shown in the curve 260, for the LHCP light
202 (.epsilon.=-1), the leakage ranges from about 0.3% (10 pitches)
to about 0.18% (11 pitches). In the same thickness range, as shown
in the curve 270, for the first LHEP light 204 (.epsilon.=-0.95 and
.PSI.=80.degree.), the leakage ranges from about 0.2% (10 pitches)
to about 0.08% (11 pitches). Thus, the leakage for the first LHEP
incident light 204 (.epsilon.=-0.95 and .PSI.=80.degree.)is reduced
by about 0.1% in the thickness range of 10 pitches to 11 pitches.
In other applications where a thicker CLC 215 layer may be used
(e.g., thickness greater than 11 pitches), the leakage for the
first LHEP incident light 204 is consistently reduced by about
0.1%. In some applications of the CLC layer 215, such as in virtual
reality ("VR") devices including one or more CLC reflective
polarizers, even a 0.1% light leakage may significantly degrade the
optical performance of the VR devices.
[0053] As shown in FIG. 2A, the CLC layer 215 may reflect the
second LHEP incident light 206 (.epsilon.=-0.97 and
.PSI.=170.degree.) as an LHEP light 206'. Referring to FIG. 2C,
comparing curve 275 (.epsilon.=-0.97 and .PSI.=170.degree.) and
curves 260 (.epsilon.=-1) and 270 (.epsilon.=-0.95 and
.PSI.=80.degree.), at the same thickness, the CLC layer 215
exhibits the highest light leakage for the second LHEP incident
light 206 (.epsilon.=-0.97 and .PSI.=170.degree.) among the three
incident lights. As shown in curve 275, the light leakage of the
CLC layer 215 is about 0.65% when the thickness of the CLC layer
215 is about 9 pitches. As the thickness the CLC layer 215
gradually increases to about 14 pitches, the light leakage of the
CLC layer 215 gradually decreases to a minimum value of about 0.2%.
As the thickness the CLC layer 215 further increases to about 20
pitches, the light leakage of the CLC layer 215 remains
substantially the same, which is about 0.2%.
[0054] As shown in FIG. 2A, the CLC layer 215 may reflect the third
LHEP incident light 208 (.epsilon.=-0.95 and .PSI.=170.degree.) as
an LHEP light 208'. Referring to FIG. 2C, comparing curve 280
(.epsilon.=-0.95 and .PSI.=170.degree.) with curves 260
(.epsilon.=-1), 270 (.epsilon.=-0.95 and .PSI.=80.degree.), and 275
(.epsilon.=-.97 and .PSI.=80.degree.), at the same thickness, the
CLC layer 215 exhibits the highest light leakage for the third LHEP
incident light 208 (.epsilon.=-0.95 and .PSI.=170.degree.) among
the four incident lights. As shown in curve 280, the light leakage
of the CLC layer 215 is about 0.75% when the thickness of the CLC
layer 215 is about 9 pitches. As the thickness the CLC layer 215
gradually increases to about 14 pitches, the light leakage of the
CLC layer 215 gradually decreases to a minimum value of about 0.3%.
As the thickness the CLC layer 215 further increases to about 20
pitches, the light leakage of the CLC layer 215 remains
substantially the same, which is about 0.3%.
[0055] As shown in FIG. 2A, the CLC layer 215 may reflect the
fourth LHEP incident light 212 (.epsilon.=-0.90 and
.PSI.=170.degree.)as an LHEP light 212'. Referring to FIG. 2C,
comparing curve 285 (.epsilon.=-0.90 and .PSI.=170.degree.) with
curves 260 (.epsilon.=-1), 270 (.epsilon.=-0.95 and
.PSI.=80.degree.), and 275 (.epsilon.=-0.97 and .PSI.=80.degree.),
and 280 (.epsilon.=-0.95 and .PSI.=170.degree.), at the same
thickness, the CLC layer 215 exhibits the highest light leakage for
the fourth LHEP incident light 212 (.epsilon.=-0.90 and
.PSI.=170.degree.) among the five incident lights. As shown in
curve 285, the light leakage of the CLC layer 215 is greater than
0.8% when the thickness of the CLC layer 215 is about 9 pitches.
The light leakage of the CLC layer 215 is decreased to about 0.75%
when the thickness of the CLC layer 215 increases to about 11
pitches. As the thickness the CLC layer 215 gradually increases to
about 14 pitches, the light leakage of the CLC layer 215 gradually
decreases to a minimum value of about 0.7%. As the thickness the
CLC layer 215 further increases to about 20 pitches, the light
leakage of the CLC layer 215 remains substantially the same, which
is about 0.7%.
[0056] Referring to FIG. 2A and FIG. 2C, for a polarized light
having the same handedness as that of the helical structure of the
CLC layer 215, one or more of the orientation angle and the
ellipticity .epsilon. of the polarized light may affect the light
leakage of the CLC layer 215, thereby affecting an extinction ratio
of the CLC reflective polarizer 200. The CLC layer 215 may have a
reduced light leakage for an elliptically polarized incident light
having one or more of predetermined orientation angle .PSI. and
ellipticity .epsilon. as compared to a circularly polarized
incident light. The orientation angle of the elliptically polarized
incident light may affect the light leakage of the CLC layer 215.
When the ellipticity .epsilon. (e.g., -0.95) is the same, different
orientation angles of elliptically polarized incident lights may
result in significantly different light leakages. Comparing curves
270 and 280 as shown in FIG. 2C, a 90-degree difference in the
orientation angle .PSI. may lead to a 0.3% difference in the
minimum light leakage. The ellipticity .epsilon. of the
elliptically polarized incident light may affect the light leakage
of the CLC layer 215. When the orientation angle (e.g.,
.PSI.=170.degree.) is the same, different ellipticities .epsilon.
of elliptically polarized incident lights may result in
significantly different light leakages. Comparing curves 275, 280,
and 285 as shown in FIG. 2C, at the same thickness, the CLC layer
215 exhibits the highest light leakage for the fourth LHEP incident
light 212 (.epsilon.=-0.90) and the lowest light leakage for the
second LHEP incident light 206 (.epsilon.=-0.97) among the three
incident lights. A difference of about 0.7 in the ellipticity
.epsilon. (e.g., .epsilon.=-0.97 and .epsilon.=-0.90) may lead to a
0.55% difference in the minimum light leakage.
[0057] Referring to FIG. 2A and FIG. 2C, by specifically
configuring one or more of the orientation angle kif and
ellipticity .epsilon. of the elliptically polarized light incident
onto the CLC layer 215, the disclosed optical device may reduce the
light leakage of the CLC layer 215. As shown in FIG. 2C, for a
polarized incident light, the minimum light leakage of the CLC
layer 215 may vary with the thickness of the CLC layer 215. For
example, by specifically configuring one or more of the orientation
angle .PSI. and ellipticity .epsilon. of the elliptically polarized
light incident onto the CLC layer 215, the disclosed optical device
may reduce the minimum light leakage of the CLC layer 215 to be
below or equal to 0.05% when the thickness is above about 12
pitches. When the thickness of the CLC layer 215 is in a range of
about 10 pitches to 11 pitches, by specifically configuring one or
more of the orientation angle .PSI. and ellipticity .epsilon. of
the elliptically polarized light incident onto the CLC layer 215,
the disclosed optical device may reduce the minimum light leakage
of the CLC layer 215 to be below or equal to 0.1%.
[0058] FIG. 2D illustrates experimental results showing a light
leakage of a CLC layer (e.g., the CLC layer 215) versus the
ellipticity .epsilon. of a light incident onto the CLC layer,
according to an embodiment of the present disclosure. As shown in
FIG. 2D, the horizontal axis is the ellipticity of a light incident
onto a CLC layer, and the vertical axis is the light leakage of the
CLC layer, i.e., the light transmittance of the CLC layer. In some
embodiments, the CLC layer may include LHCLCs. Curve 290 shows the
light leakage at different ellipticities. As shown in the curve
290, when the incident light is an LHCP light (.epsilon.=-1), the
light leakage of the CLC layer is measured to be about 3.4%. For an
elliptically polarized incident light having an orientation angle
.PSI. of about 80.degree., as the ellipticity .epsilon. of the
elliptically polarized incident light gradually increases from -1
to -0.9, the light leakage of the CLC layer gradually decreases to
a minimum value, which is measured to be about 3%. As the
ellipticity .epsilon. of the elliptically polarized incident light
further increases to -0.6, the light leakage of the CLC layer
gradually increases to about 6%. The curve 290 indicates that the
light leakage of the CLC layer is reduced by about 0.4% when the
ellipticity .epsilon. of the incident light increases from -1 to
-0.9. That is, the light leakage of the CLC layer including LHCLCs
(referred to as an LHCLC layer) reaches a minimum value when the
incident light is configured as a left-handed elliptically
polarized light (.epsilon.=-0.9) rather than left-handed circularly
polarized light (.epsilon.=-1).
[0059] Referring to FIG. 2C and FIG. 2D, in some embodiments, a
minimum light transmittance of the LHCLC layer (e.g., the CLC layer
215) for an LHEP incident light with one or more of the
predetermined orientation angle .PSI. and ellipticity .epsilon. may
be reduced by at least 0.4% as compared to a minimum light
transmittance of the LHCLC layer for an LHCP light. In some
embodiments, a minimum light transmittance of the LHCLC layer for
an LHEP incident light with one or more of the predetermined
orientation angle .PSI. and ellipticity .epsilon. may be reduced by
at least 0.1% as compared to a minimum light transmittance of the
LHCLC layer for an LHCP light. In some embodiments, a minimum light
transmittance of the LHCLC layer for an LHEP incident light with
one or more of the predetermined orientation angle .PSI. and
ellipticity .epsilon. may be reduced by at least 0.3% as compared
to a minimum light transmittance of the LHCLC layer for an LHCP
incident light. In some embodiments, a minimum light transmittance
of the LHCLC layer for an LHEP incident light with one or more of
the predetermined orientation angle .PSI. and ellipticity .epsilon.
may be reduced by at least 0.2% as compared to a minimum light
transmittance of the LHCLC layer for an LHCP incident light.
Although left-handed elliptically polarized incident light and
left-handed circularly polarized light are used as examples in
describing the embodiments of the present disclosure, the
embodiments may be similarly implemented for right-handed
elliptically polarized incident light and the right-handed
circularly polarized light.
[0060] FIG. 3A illustrates a cross section of a CLC reflective
polarizer 300, according to another embodiment of the present
disclosure. The CLC reflective polarizer 300 shown in FIG. 3A may
include elements that are similar to those included in the CLC
reflective polarizer 200 shown in FIG. 2A. Detailed descriptions of
the similar elements may refer to the above descriptions rendered
in connection with FIG. 2A. As shown in FIG. 3A, the CLC reflective
polarizer 300 may include a plurality of layers of birefringent
materials (e.g., a plurality of single-pitch CLC layers) stacked
together, where each CLC layer may have a helical structure with a
constant helix pitch. The helix pitches may vary from layer to
layer (e.g., at least two helix pitches of the plurality of
single-pitch CLC layers may be different). The CLC layers may have
narrow reflection bandwidths and may be optically coupled to
corresponding narrowband (e.g., 30-nm bandwidth) light sources
emitting lights in different colors (e.g., different wavelengths).
In some embodiments, the reflection bands of the CLC layers may not
overlap with each other. In some embodiments, the reflection bands
of the CLC layers may overlap (e.g., slightly overlap) with each
other, such that an overall reflection band of the CLC reflective
polarizer 300 may be continuous and broad.
[0061] In some embodiments, each CLC layer may be disposed between
two substrates 305. One or more alignment layers 310 may be
disposed at one or more sides of each CLC layer, between the CLC
layer and a substrate. In some embodiments, each CLC layer may be
coupled with at least one substrate 305. In some embodiments, two
adjacent CLC layers may be coupled with the same substrate 305
disposed between the two adjacent CLC layers, as FIG. 3A shows. For
illustrative purposes, FIG. 3A shows that the CLC reflective
polarizer 300 includes three CLC layers 325, 330, and 335. At least
one of the three CLC layers 325, 330, and 335 (e.g., one, two, or
three) may include a helical structure having a constant helix
pitch (e.g., the helix pitches in the helical structure may be the
same). For example, in some embodiments, each of the three CLC
layers 325, 330, and 335 may include a helical structure having a
constant helix pitch (e.g., the helix pitches in the helical
structure may be the same).
[0062] In some embodiments, the helix pitches of the helical
structure of at least one of the CLC layers 325, 330, and 335 may
be different, e.g., gradually increasing or decreasing from one
side of the CLC reflective polarizer 300 to another side. In some
embodiments, the CLC layers 325, 330, and 335 may have narrow
reflection bandwidths. In some embodiments, one or more of the CLC
layers 325, 330, and 335 may be coupled to one or more
corresponding narrowband (e.g., 30-nm bandwidth) light sources
configured to emit lights in different colors (e.g., different
wavelengths). For example, in some embodiments, the CLC layers 325,
330, and 335 may have a reflection band in the wavelength ranges of
blue, green, and red lights, respectively. In some embodiments, the
CLC layers 325, 330, and 335 may be coupled to narrowband blue,
green, and red light sources having a central wavelength of about
450 nm, 530 nm, and 630 nm, respectively. The stack configuration
of the three CLC layers 325, 330, and 335 as shown in FIG. 3A is
for illustration only. Other suitable configurations may be used.
In addition, the number of CLC layers is not limited to three. Any
suitable number of CLC layers may be used.
[0063] A CLC layer may reflect a shorter wavelength as the
incidence angle of the light increases. This phenomenon may be
referred to as blue shift. In addition, due to the waveplate effect
of the CLCs included in the CLC layer, when a circularly polarized
light having the same handedness as that of the CLC layer is
incident onto the CLC layer, the polarization state of the
transmitted light may be changed to an elliptical polarization.
This phenomenon may be referred to as depolarization.
Depolarization of the transmitted light may result in a light
leakage of the CLC layer, which may degrade the extinction ratio of
the CLC reflective polarizer. The light leakage may increase as the
incidence angle increases. In addition, when a plurality of
single-pitch CLC layers are stacked to realize a broad reflection
band, the depolarization of the transmitted light caused by a CLC
layer may result in a lower reflectivity when the transmitted light
is incident onto a subsequent CLC layer. In view of the blue shift
and depolarization effect of the CLC layers, to achieve an optical
compensation at oblique incidence angles and to achieve a broad
reflection band, a CLC reflective polarizer consistent with the
disclosed embodiments may include a plurality of single-pitch CLC
layers and one or more compensation films arranged in a
predetermined order.
[0064] FIG. 3B illustrates a cross section of a CLC reflective
polarizer 350, according to another embodiment of the present
disclosure. The CLC reflective polarizer 350 may include elements
similar to those included in the CLC reflective polarizer 300 shown
in FIG. 3A. Description of the similar elements may refer to the
above descriptions rendered in connection with FIG. 3A. As shown in
FIG. 3B, the CLC reflective polarizer 350 may include a plurality
of single-pitch CLC layers and one or more compensation films
arranged in a predetermined order. To achieve a reflection band
covering the entire visible wavelength range, the CLC reflective
polarizer 350 may include a plurality of single-pitch CLC layers,
each configured for a specific wavelength. For example, in the
embodiment shown in FIG. 3B, the CLC reflective polarizer 350 may
include four single-pitch CLC layers: a first CLC layer 352 having
a reflection band in the wavelength range of blue lights (referred
to as a "B-CLC" layer 352), a second CLC layer 354 having a
reflection band in the wavelength range of red lights (referred to
as an "R-CLC" layer 354), a third CLC layer 356 having a reflection
band in the wavelength range of orange lights (referred to as an
"O-CLC" layer 356) and a fourth CLC layer 358 having a reflection
band in the wavelength range of green lights (referred to as a
"G-CLC" layer 358). To achieve an optical compensation at oblique
incidence angles, the CLC reflective polarizer 350 may further
include two or more compensation films. The compensation film may
be any suitable optical film, such as a positive C-plate. For
illustrative purposes, in the embodiment shown in FIG. 3B, the CLC
reflective polarizer 350 includes two compensation films: a first
positive C-plate 360 disposed between the O-CLC layer 356 and the
G-CLC layer 358, and a second positive C-plate 360 disposed between
the O-CLC layer 356 and the R-CLC layer 354. An off-axis light 351
(e.g., a light that is not normally incident onto the CLC
reflective polarizer 350) may be incident on the CLC reflective
polarizer 350 from the G-CLC layer 358 side. In some embodiments,
CLC layers 352, 354, 356, and 358 may also serve or function as
negative C-plates. The positive C-plate property of the
compensation films (e.g., positive C-plates 360) may compensate for
the negative C-plate property of the CLC layers 352, 354, 356, and
358. In some embodiments, the positive C-plate 360 may be a
retardation film having a substantially zero in-plane retardance
and a positive thickness-direction retardance. The positive C-plate
360 may include an optical axis aligned perpendicular to the plane
of the positive C-plate. An elliptically polarized light output
from a CLC layer may be transformed into a circularly polarized
light after passing through the positive C-plate. Through
respectively configuring the thickness-direction retardances of the
two positive C-plates 360, the depolarization of the transmitted
light may be compensated for, and the light leakage of the CLC
reflective polarizer 350 for off-axis incident lights may be
reduced.
[0065] The stack configuration and the number of the CLC layers and
positive C-plates shown in FIG. 3B are for illustration only. Other
suitable arrangements or suitable number (e.g., three or more than
four) of CLC layers may also be used. For example, in some
embodiments, the CLC reflective polarizer 350 may include the B-CLC
layer 352, the R-CLC layer 354, and the G-CLC layer 358, and may
not include the O-CLC layer 356. In some embodiments, one or more
additional CLC-layers for other colors may be added, such as a
yellow-CLC layer, a purple-CLC layer, etc. In addition, the number
of the positive C-plates may also be any suitable number, such as
one, three, four, etc. For example, in some embodiments, the CLC
reflective polarizer 350 may further include a positive C-plate 360
disposed between the B-CLC layer 352 and the R-CLC layer 354 in
addition to the positive C-plate 360 disposed between the O-CLC
layer 356 and the G-CLC layer 358 and the positive C-plate 360
disposed between the O-CLC layer 356 and the R-CLC layer 354. In
some embodiments, the CLC reflective polarizer 350 may include a
positive C-plate 360 disposed between the B-CLC layer 352 and the
R-CLC layer 354, and a positive C-plate 360 disposed between the
O-CLC layer 356 and the G-CLC layer 358, with no positive C-plate
disposed between the R-CLC layer 354 and the O-CLC layer 356. In
some embodiments, the CLC reflective polarizer 350 may include a
positive C-plate 360 disposed between the B-CLC layer 352 and the
R-CLC layer 354, and a positive C-plate 360 disposed between the
O-CLC layer 356 and the R-CLC layer 354, with no positive C-plate
disposed between the O-CLC layer 356 and the G-CLC layer 358. In
some embodiments, the order of the different CLC layers may be
different from the order shown in FIG. 3B. Any other suitable order
for the stacked CLC layers may be used.
[0066] FIG. 3C illustrates simulation results showing off-axis
incidence angle light leakage of a conventional CLC reflective
polarizer that does not include a positive C-plate. FIG. 3D
illustrates simulation results showing off-axis incidence angle
light leakage of the CLC reflective polarizer 350 shown in FIG. 3B
that includes two positive C-plates. In each plot shown in FIG. 3C
and FIG. 3D, the horizontal axis is the incidence wavelength (unit:
nm), and the vertical axis is the normalized light intensity of the
transmitted light as represented by the Strokes parameter S0, i.e.,
the light leakage of a CLC reflective polarizer. Curve 370 shows
the light leakage of the CLC reflective polarizer 350 shown in FIG.
3B, in which two positive C-plates are included. Curve 380 shows
the light leakage of a CLC reflective polarizer having a B-CLC
layer, an R-CLC layer, an O-CLC layer, and a G-CLC layer (similar
to those shown in FIG. 3B) with no positive C-plate disposed
between the CLC layers. The light leakage of the two CLC reflective
polarizers is evaluated for a 40.degree. incidence angle (an
example of an off-axis incidence angle). As shown in curve 380, the
light leakage of the CLC reflective polarizer without a positive
C-plate is substantially zero merely in the blue wavelength range,
e.g., from 440 nm to 500 nm. In other wavelength ranges, e.g., from
500 nm to 640 nm, the light leakage is consistently large. In
comparison, as shown in curve 370, in addition to the blue
wavelength range (e.g., from 440 nm to 500 nm), the light leakage
of the CLC reflective polarizer 350 with two positive C-plates is
also substantially zero in other wavelength ranges, such as the
green wavelength range (e.g., from 530 nm to 560 nm) and the red
wavelength range (e.g., from 600 nm to 640 nm).
[0067] FIG. 4 illustrates a cross section of a CLC reflective
polarizer 400, according to another embodiment of the present
disclosure. The CLC reflective polarizer 400 may include elements
that are similar to those included in the CLC reflective polarizer
200 shown in FIG. 2A. Descriptions of the similar elements may
refer to the above descriptions rendered in connection with FIG.
2A. As shown in FIG. 4, the CLC reflective polarizer 400 may
include a CLC layer 415 having a helical structure of a varying
(e.g., non-constant) helix pitch (e.g., a gradient helix pitch). In
some embodiments, the helix pitch may gradually increase or
decrease in a predetermined direction (e.g., in a thickness
direction of the CLC layer 415). For illustrative purposes, in the
embodiment shown in FIG. 4, the varying helix pitch is shown as
gradually increasing along the thickness direction of the CLC layer
415, e.g., along the +z-axis direction as shown in FIG. 4. The
varying helix pitch configuration may result in a broad reflection
band for the CLC layer 415. In some embodiments, the CLC reflective
polarizer 400 may be coupled to a broadband polychromatic light
source (not shown), such as a 300-nm-bandwidth light source
covering the visible wavelength range. For discussion purposes, the
CLC reflective polarizer 400 is described as an LHCLC refractive
polarizer having a 300-nm-bandwidth reflection band covering the
visible wavelength range. In some embodiments, the CLC reflective
polarizer 400 may be configured as an RHCLC reflective polarizer. A
broadband LHCP light 402 may be substantially normally incident
onto a shorter pitch side (e.g., the lower side shown in FIG. 4) of
the CLC reflective polarizer 400. For discussion purposes, the
broadband LHCP light 402 may include components of LHCP blue,
green, and red lights having a central wavelength of about 450 nm,
about 530 nm, and about 630 nm, respectively. When propagating
substantially along the axial direction of the CLC layer 415, the
components of LHCP blue, green, and red lights may be primarily or
substantially reflected by the CLC layer 415 as an LHCP blue light,
an LHCP green light, and an LHCP red light, respectively, which are
subsequently combined to be visually observed as a broadband LHCP
light 402'.
[0068] The CLC refractive polarizers and the features of the CLC
refractive polarizers as described in various embodiments may be
combined. For example, the varying (e.g., gradient) pitch CLC layer
415 shown in FIG. 4 may be coupled to one or more positive C-plates
and an optical waveplate to reduce the light leakage at off-axis
incidence angles and at an on-axis incidence angle. In some
embodiments, the stack of single-pitch CLC layers shown in FIG. 3A
and FIG. 3B may be coupled to an optical waveplate to reduce the
light leakage at an on-axis incidence angle.
[0069] CLC reflective polarizers in accordance with an embodiment
of the present disclosure may have various applications in a number
of fields, which are all within the scope of the present
disclosure. Some exemplary applications in augmented reality
("AR"), virtual reality ("VR"), mixed reality ("MR)" fields or some
combinations thereof will be explained below. Near-eye displays
("NEDs") have been widely used in a large variety of applications,
such as aviation, engineering, science, medicine, computer gaming,
video, sports, training, and simulations. One application of NEDs
is to realize VR, AR, MR or some combination thereof. Desirable
characteristics of NEDs include compactness, light weight, high
resolution, large field of view ("FOV"), and small form factor. An
NED may include a display element configured to generate an image
light and a lens system configured to direct the image light toward
eyes of a user. The lens system may include a plurality of optical
elements, such as lenses, waveplates, reflectors, etc., for
focusing the image light to the eyes of the user. To achieve a
compact size and light weight and to maintain satisfactory optical
characteristics, an NED may adopt a pancake lens assembly in the
lens system to fold the optical path, thereby reducing a back focal
distance in the NED.
[0070] FIG. 5A illustrates a schematic diagram of a pancake lens
assembly 500 according to an embodiment of the present disclosure.
The pancake lens assembly 500 may be implemented in an NED to fold
the optical path, thereby reducing the back focal distance in the
NED. As shown in FIG. 5A, the pancake lens assembly 500 may focus a
light 521 emitted from an electronic display 550 (which may be
other suitable light source) to an eye-box located at an exit pupil
560. Hereinafter, the light 521 emitted by the electronic display
550 for forming images is also referred to as an "image light." The
exit pupil 560 may be at a location where an eye 570 is positioned
in an eye-box region when a user wears the NED. In some
embodiments, the electronic display 550 may be a monochromatic
display that includes a narrowband monochromatic light source
(e.g., a 30-nm-bandwidth light source). In some embodiments, the
electronic display 550 may be a polychromatic display (e.g., a
red-green-blue ("RGB") display) that includes a broadband
polychromatic light source (e.g., 300-nm-bandwidth light source
covering the visible wavelength range). In some embodiments, the
electronic display 550 may be a polychromatic display (e.g., an RGB
display) created by stacking a plurality of monochromatic displays,
which may include corresponding narrowband monochromatic light
sources respectively.
[0071] In some embodiments, the pancake lens assembly 500 may
include a first optical element 505 and a second optical element
510 coupled together to create, for example, a monolithic optical
element. In some embodiments, one or more surfaces of the first
optical element 505 and the second optical element 510 may be
shaped to compensate for field curvature. In some embodiments, one
or more surfaces of the first optical element 505 and/or the second
optical element 510 may be shaped to be spherically concave (e.g.,
a portion of a sphere), spherically convex, a rotationally
symmetric asphere, a freeform shape, or some other shape that can
mitigate field curvature. In some embodiments, the shape of one or
more surfaces of the first optical element 505 and/or the second
optical element 510 may be designed to additionally compensate for
other forms of optical aberration. In some embodiments, one or more
of the optical elements within the pancake lens assembly 500 may
have one or more coatings, such as an anti-reflective coating, to
reduce ghost images and enhance contrast. In some embodiments, the
first optical element 505 and the second optical element 510 may be
coupled together by an adhesive 515. Each of the first optical
element 505 and the second optical element 510 may include one or
more optical lenses.
[0072] The first optical element 505 may include a first surface
505_1 configured to receive an image light from the electronic
display 550 and an opposing second surface 505_2 configured to
output an altered image light. The first optical element 505 may
include a linear polarizer (or a linear polarizer surface) 502, a
waveplate (or a waveplate surface) 504, and a mirror (or a mirrored
surface) 506 arranged in optical series, each of which may be an
individual layer or coating bonded to or formed at the first
optical element 505. The linear polarizer 502, the waveplate 504,
and the mirror 506 may be bonded to or formed on the first surface
505_1 or the second surface 505_2 of the first optical element 505.
For discussion purposes, FIG. 5A shows that the linear polarizer
502 and the waveplate 504 are bonded to or formed at the first
surface 505_1, and the mirror 506 is bonded to or formed at the
second surface 505_2. In some embodiments, the mirror 506 may be a
partial reflector that is configured to reflect a portion of a
received light. In some embodiments, the mirror 506 may be
configured to transmit about 50% and reflect about 50% of a
received light, and may be referred to as a "50/50 mirror." In some
embodiments, the handedness of the reflected light may be reversed,
and the handedness of the transmitted light may remain
unchanged.
[0073] The second optical element 510 may have a first surface
510_1 facing the first optical element 505 and an opposing second
surface 510_2. The second optical element 510 may include a
reflective polarizer 508 (or a reflective polarizer surface 508),
which may be an individual layer or coating bonded to or formed at
the second optical element 510. The reflective polarizer 508 may be
bonded to or formed at the first surface 510_1 or the second
surface 510_2 of the second optical element 510 and may receive a
light output from the mirror 506. For discussion purposes, FIG. 5A
shows that the reflective polarizer 508 is bonded to or formed at
the first surface 510-1 of the second optical element 510. The
reflective polarizer 508 may include a reflective polarizing film
configured to primarily reflect a received light of a first
polarization and primarily transmit a received light of a second
polarization. The reflective polarizer 508 may be a CLC reflective
polarizer in accordance with an embodiment of the present
disclosure. For example, the reflective polarizer 508 may be any of
the CLC reflective polarizer 200, 300, 350, or 400.
[0074] Referring to FIG. 5A, in some embodiments, the image light
521 emitted from the electronic display 550 may be unpolarized. The
linear polarizer 502 may be configured to convert the unpolarized
image light 521 into a linearly polarized light. A polarization
axis (e.g., a fast axis) of the waveplate 504 may be orientated
relative to the transmission axis of the linear polarizer 502 to
convert the linearly polarized light into an elliptically polarized
light having one or more predetermined polarization ellipse
parameters toward the CLC reflective polarizer 508, such that the
elliptically polarized light may be substantially reflected by the
CLC reflective polarizer 508 with a reduced light leakage (e.g., a
portion of the elliptically polarized light that is transmitted by
the CLC reflective polarizer 508 may be reduced). In some
embodiments, the one or more predetermined polarization ellipse
parameters may include at least one of an orientation angle .PSI.
or an ellipticity .epsilon. described above in connection with FIG.
2B-FIG. 2D.
[0075] For example, the one or more predetermined polarization
ellipse parameters may include both of the orientation angle .PSI.
and the ellipticity .epsilon. described above in connection with
FIG. 2B-FIG. 2D. In some embodiments, the CLC reflective polarizer
508 may include LCs having a birefringence in a range of about 0.15
to about 0.4. To reduce the light leakage (e.g., to reduce the
light transmittance) of the CLC reflective polarizer 508 for an
elliptically polarized incident light having the same handedness as
the helical structure of the CLC reflective polarizer 508, the
orientation angle of the elliptically polarized incident light may
be configured to be a value in a range of about
75.degree..ltoreq..PSI..ltoreq.90.degree., about
75.degree..ltoreq..PSI..ltoreq.85.degree., about
75.degree..ltoreq..PSI..ltoreq.80.degree., about
80.degree..ltoreq..PSI..ltoreq.90.degree., about
80.degree..ltoreq..PSI..ltoreq.85.degree., about
85.degree..ltoreq..PSI..ltoreq.90.degree., about
76.degree..ltoreq..PSI..ltoreq.89.degree., about
77.degree..ltoreq..PSI..ltoreq.88.degree., about
78.degree..ltoreq..PSI..ltoreq.87.degree., or about
79.degree..ltoreq..PSI..ltoreq.86.degree.. In some embodiments, the
orientation angle .PSI. may be in a range of
n.sub.1.degree..ltoreq..PSI..ltoreq.n.sub.2.degree., where n.sub.1
may be any suitable value equal to or greater than 75, and n.sub.2
may be any suitable value equal to or less than 90 and greater than
n.sub.1. The ellipticity .epsilon. of the elliptically polarized
incident light may be configured to be a value in a range of about
-1<.epsilon..ltoreq.-0.85 when the CLC reflective polarizer 508
includes LHCLCs (referred to as an LHCLC reflective polarizer). For
example, when the CLC reflective polarizer 508 is an LHCLC
reflective polarizer, the ellipticity .epsilon. of the elliptically
polarized incident light may be configured to be a value in a range
of about -0.95 .ltoreq..epsilon..ltoreq.-0.85, about -0.9
.ltoreq..epsilon..ltoreq.-0.85, about
-0.95.ltoreq..epsilon..ltoreq.-0.9, about
-1<.epsilon..ltoreq.-0.9, or about -1<.epsilon..ltoreq.-0.95.
The ellipticity .epsilon. of the elliptically polarized incident
light may be configured to be a value in a range of about 0.85
.ltoreq..epsilon.<1 when the CLC reflective polarizer 508
includes RHCLCs (referred to an RHCLC reflective polarizer). For
example, when the CLC reflective polarizer 508 is an RHCLC
reflective polarizer, the ellipticity of the elliptically polarized
incident light may be configured to be a value in a range of about
0.85.ltoreq..epsilon..ltoreq.0.95, about
0.85.ltoreq..epsilon..ltoreq.0.9, about
0.9.ltoreq..epsilon..ltoreq.0.95, about
0.9.ltoreq..epsilon..ltoreq.1, or about 0.95.ltoreq..epsilon.<1.
With such configurations, ghost images caused by the light leakage
of the CLC reflective polarizer 508 may be suppressed, and the
optical performance of the pancake lens assembly 500 may be
improved.
[0076] FIG. 5B illustrates a schematic cross-sectional view of an
optical path of the pancake lens assembly 500 shown in FIG. 5A,
according to an embodiment of the present disclosure. In FIG. 5B,
the character "s" denotes that the corresponding light is
s-polarized, RHCP and LHCP denote right-handed circularly polarized
light and left-handed circularly polarized light, respectively, and
RHEP and LHEP denote right-handed elliptically polarized light and
left-handed elliptically polarized light, respectively. For
discussion purposes, as shown in FIG. 5B, the linear polarizer 502
may be configured to transmit an s-polarized light and block a
p-polarized light, and the reflective polarizer 508 may be a
left-handed CLC ("LHCLC") reflective polarizer. For illustrative
purposes, the electronic display 550, the linear polarizer 502, the
waveplate 504, the mirror 506, and the reflective polarizer 508 are
illustrated as flat surfaces in FIG. 5B. In some embodiments, one
or more of the electronic display 550, the linear polarizer 502,
the waveplate 504, the mirror 506, and the reflective polarizer 508
may include a curved surface.
[0077] As shown in FIG. 5B, the electronic display 550 may generate
the unpolarized image light 521 covering a predetermined spectrum,
such as a portion of the visible spectral range or the entire
visible spectral range. The unpolarized image light 521 may be
transmitted by the linear polarizer 502 as an s-polarized image
light 523, which may be transmitted by the waveplate 504 as an LHEP
light 525 having one or more predetermined polarization ellipse
parameters (e.g., one or both of the orientation angle .PSI. and
the ellipticity .epsilon. being within predetermined ranges or at
predetermined values). A first portion of the LHEP light 525 may be
reflected by the mirror 506 as an RHCP light 527 toward the
waveplate 504, and a second portion of the LHEP light 525 may be
transmitted through the mirror 506 as an LHEP light 528 toward the
CLC reflective polarizer 508.
[0078] The LHEP light 528 incident onto the CLC reflective
polarizer 508 may have the same handedness (e.g., the left
handedness) as that of the helical structure of the CLC reflective
polarizer 508. As a result, the LHEP light 528 may be reflected by
the CLC reflective polarizer 508 as an LHCP light 529 toward the
mirror 506. The LHCP light 529 may be reflected by the mirror 506
as an RHCP light 531, which may be transmitted through the CLC
reflective polarizer 508 as an RHCP light 533. The RHCP light 533
may be focused onto the eye 570.
[0079] In some embodiments, the linear polarizer 502 may be a first
linear polarizer and the waveplate 504 may be a first waveplate,
and the pancake lens assembly 500 may further include a second
linear polarizer and a second waveplate arranged between the CLC
reflective polarizer 508 and the eye 570 to enhance the performance
of the pancake lens assembly 500. FIG. 6A illustrates a schematic
diagram of a pancake lens assembly 600, according to another
embodiment of the present disclosure. The pancake lens assembly 600
may include elements similar to those included in the pancake lens
assembly 500 shown in FIG. 5A. Descriptions of the similar elements
can refer to the above descriptions rendered in connection with
FIG. 5A. As shown in FIG. 6A, the second optical element 510 may
include a second waveplate (or a second waveplate surface) 535 and
a second linear polarizer (or a second linear polarizer surface)
530 arranged in optical series, each of which may be an individual
film or coating bonded to or formed at the first surface 510_1 or
the second surface 510_2 of the second optical element 510. For
discussion purposes, FIG. 6A shows that the second waveplate 535
and the second linear polarizer 530 are bonded to or formed at the
second surface 510_2 of the second optical element 510.
[0080] The second waveplate 535 may receive a circularly polarized
light from the reflective polarizer 508. The second linear
polarizer 530 may be disposed between the second waveplate 535 and
the eye 570. This configuration is better illustrated in FIG. 6B.
In some embodiments, a polarization axis of the second waveplate
535 may be oriented relative to the transmission axis of the second
linear polarizer 530 to convert a linearly polarized light into a
circularly polarized light or vice versa for a visible spectrum
and/or infrared spectrum. In some embodiments, for an achromatic
design, the second waveplate 535 may include a multilayer
birefringent material (e.g., a polymer or liquid crystals) to
produce quarter wave birefringence across a wide spectral range.
For example, an angle between the polarization axis (e.g., the fast
axis) of the second waveplate 535 and the transmission axis of the
second linear polarizer 530 may be configured to be in a range of
35-50 degrees. The combination of the second waveplate 535 and the
second linear polarizer 530 may reduce the intensity of a ghost
image caused by unpolarized image lights directly received from the
electronic display 550. In addition, the combination of the second
waveplate 535 and the second linear polarizer 530 may also function
as an anti-narcissus film such that the user would not observe the
image of the eye(s) of the user.
[0081] FIG. 6B illustrates a schematic cross-sectional view of an
optical path of the pancake lens assembly 600 shown in FIG. 6A,
according to an embodiment of the present disclosure. Certain
elements shown in FIG. 6B are similar to or the same as those shown
in FIG. 5B. Descriptions of such elements can refer to the above
descriptions rendered in connection with FIG. 5B. In FIG. 6B, the
character "p" denotes that the corresponding light is p-polarized.
As shown in FIG. 6B, the optical path of the unpolarized image
light 521 propagating from the electronic display 550 to the
reflective polarizer 508 may be similar to that shown in FIG. 5B.
As shown in FIG. 6B, the RHCP light 533 may be converted into a
p-polarized light 538 by the second waveplate 535. The second
linear polarizer 530 arranged between the second waveplate 535 and
the eye 570 may be configured to transmit a p-polarized light and
block an s-polarized light. Accordingly, the p-polarized light 538
may be transmitted by the second linear polarizer 530 as a
p-polarized light 537 that may be focused onto the eye 570. In
addition, an unpolarized image light 521' incident onto the second
waveplate 535 directly from the electronic display 550 may be
transmitted as an unpolarized light 523' toward the second linear
polarizer 530. The unpolarized light 523' may be transmitted by the
second linear polarizer 530 as a p-polarized light 525', thereby
reducing the intensity of a ghost image caused by the image light
521' directly received from the electronic display 550.
[0082] The combination of the second waveplate 535 and the second
linear polarizer 530 may also function as an anti-narcissus film.
For example, as shown in FIG. 6B, the p-polarized light 537 and the
p-polarized light 525' may be reflected by the eye 570 as an
s-polarized light 539 and an s-polarized light 527' traveling in
the -z-direction, respectively. As the second linear polarizer 530
may be configured to transmit a p-polarized light and block an
s-polarized light, both the s-polarized light 539 and s-polarized
light 527' may be blocked by the second linear polarizer 530.
Accordingly, the narcissus may be suppressed, and the eye 570 of
the user may not observe the image of the eye.
[0083] Referring to FIG. 5A and FIG. 6A, the electronic display 550
may be any suitable display. In some embodiments, the electronic
display 550 may include a self-emissive panel, such as an organic
light-emitting diode ("OLED") display panel, a micro light-emitting
diode ("micro-LED") display panel, a quantum dot ("QD") display
panel, or some combination thereof. In some embodiments, the
electronic display 550 may include a non-emissive display, i.e., a
display panel that is illuminated by an external illumination
system, such as a liquid crystal display ("LCD") panel, a
liquid-crystal-on-silicon ("LCoS") display panel, or a digital
light processing ("DLP") display panel, or some combination
thereof. The external illumination system may include a light
source. Examples of light sources may include a laser, an LED, an
OLED, or some combination thereof. The light sources may be
narrowband or broadband. In some embodiments, the light source may
emit an unpolarized image light.
[0084] The present disclosure further provides an illumination
system including a CLC reflective polarizer. FIG. 7 illustrates a
schematic diagram of an illumination system 700 including a CLC
reflective polarizer, according to an embodiment of the present
disclosure. The illumination system 700 may be configured to
illuminate a display panel. As shown in FIG. 7, the illumination
system 700 may include a planar light guide plate 710 formed by two
or more wedges (e.g., a first wedge 705a and a second wedge 705b).
For illustrative purposes, FIG. 7 shows two wedges 705a and 705b in
the illumination system 700. Any other suitable number of wedges,
such as three, four, five, six, etc., may be included in other
embodiments of the illumination system 700. For example, at least
one of the wedges 705a and 705b may be formed by two or more
smaller wedges. In some embodiments, the illumination system 700
may include a reflective sheet 720 arranged or disposed at a first
side surface 710_1 of the light guide plate 710. In some
embodiments, as shown in FIG. 7, the reflective sheet 720 may be
disposed external to the first side surface 710_1. In some
embodiments, as shown in FIG. 7, the illumination system 700 may
include a light source assembly 715 arranged or disposed at a
second side surface 710_2 of the light guide plate 710. The first
side surface 710_1 and the second side surface 710_2 may be located
at opposite ends of the light guide plate 710. In some embodiments,
the illumination system 700 may include a reflective polarizer 725
arranged at a slanted surface 710_3 of at least one of the two
wedges 705a and 705b. In some embodiments, the slanted surface
710_3 may refer to a slanted surface of the first wedge 705a or a
slanted surface of the second wedge 705b. The slanted surface of
the first wedge 705a and the slanted surface of the second wedge
705b may fit with one another.
[0085] The light source assembly 715 may include a light source
configure to emit a light and an optical assembly configured to
conditioning the light. The light source may include one or more
light-emitting diodes ("LEDs"), an electroluminescent panel
("ELP"), one or more cold cathode fluorescent lamps ("CCFLs"), one
or more hot cathode fluorescent lamps ("HCFLs"), or one or more
external electrode fluorescent lamps ("EEFLs"), etc. The LED light
source may include a plurality of white LEDs or a plurality of RGB
("red, green, blue") LEDs, etc. The optical assembly may include
one or more optical components configured to condition the light
received from the light source. Conditioning the light emitted by
the light source may include, e.g., transmitting, attenuating,
expanding, collimating, adjusting orientation, and/or polarizing in
accordance with instructions from a controller. The light output
from the light source assembly 715 may be coupled into the light
guide plate 710 at the second side surface 710_2 of the light guide
plate 710. The side surface 710_2 may be referred to as a light
incident surface of the light guide plate 710.
[0086] At least one of the wedges 705a and 705b may include an
optically transparent material, such as an optically transparent
acryl resin or the like. The light entering from the light incident
surface (e.g., the second side surface 710_2) may propagate inside
the light guide plate 710 via total internal reflection ("TIR").
The reflective polarizer 725 may be disposed at the slanted surface
710_3 of at least one of the two wedges 705a and 705b, where the
two wedges 705a and 705b may be coupled to each other (e.g., in
contact with each other) at their respective slanted surfaces to
form the planar light guide plate 710. In some embodiments, the
reflective polarizer 725 may be formed on, coated to, or otherwise
provided via a suitable manner at the slanted surface of the first
wedge 705a. In some embodiments, the reflective polarizer 725 may
be formed on, coated to, or otherwise provided via a suitable
manner at the slanted surface of the second wedge 705b. As shown in
FIG. 7, the reflective polarizer 725 may be disposed between the
slanted surface of the first wedge 705a and the slanted surface of
the second wedge 705b. The reflective polarizer 725 may be
configured to selectively transmit a light of a first polarization
and reflect a light of a second polarization different from the
first polarization. The reflective sheet 720 may be disposed at the
first side surface 710_1 of the light guide plate 710, such that
the light source assembly 715 and reflective sheet 720 may be
disposed opposite to each other. The reflective sheet 720 may have
a substantially high reflectivity (e.g., above 90%) and may convert
a light of the second polarization into a light of the first
polarization or vice versa when reflecting a received light.
[0087] In an operation, a first polarized light 702 emitted from
the light source assembly 715 may have the first polarization. The
first polarized light 702 may propagate inside the light guide
plate 710 via TIR until arriving at the reflective sheet 720, where
the first polarized light 702 may be reflected by the reflective
sheet 720 as a second polarized light 704 having the second
polarization. The second polarized light 704 may propagate inside
the light guide plate 710 via TIR until arriving at the reflective
polarizer 725. As the reflective polarizer 725 may be configured to
selectively transmit a light of the first polarization and reflect
a light of the second polarization, the second polarized light 704
having the second polarization may be reflected by the reflective
polarizer 725 as a third polarized light 706 having the second
polarization. The third polarized light 706 may be output from a
light outputting surface 710_4 of the light guide plate 710 to
illuminate display function materials, such as liquid crystals, in
a display panel coupled to the illumination system 700.
[0088] FIG. 7 shows the light source assembly 715 spaced apart from
the light guide plate 710 by a distance. This illustration is for
illustrative purposes and is not intended to limit the scope of the
present disclosure. In some embodiments, the light source assembly
715 may be directly coupled to the light guide plate 710 at the
second side surface 710_2 of the light guide plate 710. In some
embodiments, the illumination system 700 may include other
elements, such as a diffuser sheet and/or a prism sheet arranged at
the light outputting surface 710_4 of the light guide plate
710.
[0089] In some embodiments, the reflective polarizer 725 may be a
CLC reflective polarizer in accordance with an embodiment of the
present discourse, such as the CLC reflective polarizer 200 in FIG.
2A, the CLC reflective polarizer 300 in FIG. 3A, or the CLC
reflective polarizer 400 in FIG. 4, etc. For example, the CLC
reflective polarizer 725 may be an RHCLC reflective polarizer,
which may be configured to primarily or substantially reflect a
RHCP light and primarily or substantially transmit a LHCP light.
The first polarized light 702 emitted from the light source
assembly 715 may be an LHCP light, which may be transmitted by the
CLC reflective polarizer 725 and may propagate inside the light
guide plate 710 via TIR until arriving at the reflective sheet 720.
The reflective sheet 720 may reflect the first LHCP light 702 as a
second polarized light, i.e., an RHCP light 704, which may
propagate inside the light guide plate 710 via TIR until arriving
at the reflective polarizer 725. The RHCP light 704 may be
reflected by the reflective polarizer 725 as a third polarized
light, i.e., an RHCP light 706 that may be output at the light
outputting surface 710_4 of the light guide plate 710 to illuminate
display function materials, such as liquid crystals, in a display
panel coupled to the illumination system 700.
[0090] Returning to FIG. 7, the structure of the CLC reflective
polarizer 725 may be determined according to the characteristics of
the light source assembly 715. The reflection band of the CLC
reflective polarizer 725 may correspond to the wavelength of the
light source assembly 715. For example, when the light source
assembly 715 includes a narrowband monochromatic light source
(e.g., a 30-nm-bandwidth light source), the CLC reflective
polarizer 725 may be configured as a narrowband CLC reflective
polarizer with a constant helix pitch. When the light source
assembly 715 includes a broadband light source (e.g., a
300-nm-bandwidth light source covering the visible spectrum), the
CLC reflective polarizer 725 may be configured as a broadband CLC
reflective polarizer with a gradient helix pitch. When the light
source assembly 715 includes a plurality of narrowband
monochromatic light sources of different colors (e.g., narrowband
blue, green, and red light sources), the CLC reflective polarizer
725 may be configured to include a plurality of CLC layers stacked
together where the CLC layers may have at least two different helix
pitches. In some embodiments, each CLC layer may have a different
helix pitch.
[0091] FIG. 8A illustrates a diagram of a near-eye display ("NED")
800, according to an embodiment of the present disclosure. As shown
in FIG. 8A, the NED 800 may include a front body 805 and a band
810. The front body 805 may include one or more electronic display
elements of an electronic display and one or more optical elements
(not shown in detail in FIG. 8A), an inertial measurement unit
("IMU") 830, one or more position sensors 825, and one or more
locators 820. In the embodiment shown in FIG. 8A, the one or more
position sensors 825 may be located within the IMU 830. The
locators 820 may be located at various positions on the front body
805 relative to a reference point 815. In the embodiment shown in
FIG. 8A, the reference point 815 may be located at the center of
the IMU 830, or at any other suitable location. The locators 820,
or some of the locators 820, may be located on a front side 820A, a
top side 820B, a bottom side 820C, a right side 820D, and a left
side 820E of the front body 805.
[0092] FIG. 8B is a cross-sectional view of a front body of the NED
800 shown in FIG. 8A. As shown in FIG. 8B, the front body 805 may
include an electronic display 835 and a pancake lens assembly 840
configured to provide altered image lights to an exit pupil 845. In
some embodiments, the pancake lens assembly 840 may be a pancake
lens assembly in accordance with an embodiment of the present
disclosure, such as the pancake lens assembly 500 in FIG. 5A or the
pancake lens assembly 600 in FIG. 6A. In some embodiments, the
electronic display 835 may be an electronic display including a
display panel and an illumination system in accordance with an
embodiment of the present disclosure, such as the illumination
system 700 in FIG. 7. The exit pupil 845 may be at a location of
the front body 805 where an eye 850 of the user may be positioned.
For illustrative purposes, FIG. 8B shows a cross-section of the
front body 805 associated with a single eye 850, while another
electronic display, separate from the electronic display 835, may
provide image lights altered by another pancake lens assembly,
separate from the pancake lens assembly 835, to another eye of the
user.
[0093] The present disclosure also provides a method. The method
relates to providing an incident light having one or more
predetermined parameters to an optical element (e.g., a reflective
polarizer) including a birefringent material with a chirality, such
that the incident light may be substantially reflected by the
optical element with a reduced (e.g., substantially zero) light
transmittance. In some embodiments, the one or more predetermined
parameters may include one or more predetermined polarization
ellipse parameters, such as at least one of an ellipticity or an
orientation angle. In some embodiments, providing the incident
light having one or more predetermined parameters to the optical
element including a birefringent material with a chirality may
include, generating the incident light having the one or more
predetermined parameters and outputting the incident light having
the one or more predetermined parameters to the optical element. In
some embodiments, providing the incident light having the one or
more predetermined parameters to the optical element including a
birefringent material with a chirality may include, converting a
linearly polarized light into an elliptically polarized light
having the one or more predetermined parameters (e.g.,
predetermined polarization ellipse parameters) and outputting the
elliptically polarized light having the one or more predetermined
parameters to the optical element. In some embodiments, providing
the incident light having the one or more predetermined parameters
to the optical element including a birefringent material with a
chirality may include, converting a circularly polarized light into
an elliptically polarized light having the one or more
predetermined parameters (e.g., predetermined polarization ellipse
parameters) and outputting the elliptically polarized light having
the one or more predetermined parameters to the optical element. In
some embodiments, providing the incident light having the one or
more predetermined parameters to the optical element including a
birefringent material with a chirality may include, converting an
unpolarized light into an elliptically polarized light having the
one or more predetermined parameters (e.g., predetermined
polarization ellipse parameters) and outputting the elliptically
polarized light having the one or more predetermined parameters to
the optical element.
[0094] Any suitable devices (e.g., a waveplate, a light source
assembly) may be used to provide the incident light having one or
more predetermined parameters to an optical element including a
birefringent material with a chirality. The method may also include
receiving, by the optical element, the incident light having the
one or more predetermined parameters and reflecting the incident
light as a circularly polarized light. In some embodiments, the
incident light may be an elliptically polarized light having the
one or more predetermined polarization ellipse parameters. In some
embodiments, the elliptically polarized light may be substantially
reflected as the circularly polarized light with a reduced (e.g.,
substantially zero) light transmittance.
[0095] In some embodiments, the optical element including a
birefringent material with a chirality may be a cholesteric liquid
crystal ("CLC") reflective polarizer. In some embodiments,
providing the incident light having the one or more predetermined
polarization ellipse parameters may include, altering, by an
optical waveplate disposed upstream of the CLC reflective
polarizer, properties of the incident light such that the incident
light have the one or more predetermined polarization ellipse
parameters before the incident light is incident onto CLC
reflective polarizer. For example, the optical waveplate may
convert a linearly polarized light into an elliptically polarized
light having the one or more predetermined polarization ellipse
parameters, and output the elliptically polarized light to the CLC
reflective polarizer. In some embodiments, providing the incident
light having the one or more predetermined polarization ellipse
parameters may include, generating, by a light source assembly, the
incident light having the one or more predetermined polarization
ellipse parameters, and outputting, by the light source assembly,
the incident light having the one or more predetermined
polarization ellipse parameters to the CLC reflective polarizer. In
some embodiments, the light source assembly may directly generate
and output an elliptically polarized light having the one or more
predetermined polarization ellipse parameters as an incident light
for the CLC reflective polarizer. In some embodiments, the light
source assembly may include the optical waveplate. In some
embodiments, the optical waveplate may be provided separately from
the light source assembly. When the optical waveplate is provided
separately from the light source assembly, in some embodiments, the
light source assembly may output a linearly polarized light, and
the optical waveplate may convert the linearly polarized light into
an elliptically polarized light having the one or more
predetermined polarization ellipse parameters, and output the
elliptically polarized light to the CLC reflective polarizer. The
CLC reflective polarizer may receive the incident light having the
one or more predetermined parameters and reflect the incident light
as a circularly polarized light with a reduced (e.g., substantially
zero) light transmittance.
[0096] The foregoing description of the embodiments of the
disclosure have been presented for the purpose of illustration. It
is not intended to be exhaustive or to limit the disclosure to the
precise forms disclosed. Persons skilled in the relevant art can
appreciate that modifications and variations are possible in light
of the above disclosure.
[0097] Some portions of this description may describe the
embodiments of the disclosure in terms of algorithms and symbolic
representations of operations on information. These algorithmic
descriptions and representations are commonly used by those skilled
in the data processing arts to convey the substance of their work
effectively to others skilled in the art. These operations, while
described functionally, computationally, or logically, are
understood to be implemented by computer programs or equivalent
electrical circuits, microcode, or the like. Furthermore, it has
also proven convenient at times, to refer to these arrangements of
operations as modules, without loss of generality. The described
operations and their associated modules may be embodied in
software, firmware, hardware, or any combinations thereof.
[0098] Any of the steps, operations, or processes described herein
may be performed or implemented with one or more hardware or
software modules, alone or in combination with other devices. In
one embodiment, a software module is implemented with a computer
program product comprising a computer-readable medium containing
computer program code, which can be executed by a computer
processor for performing any or all of the steps, operations, or
processes described.
[0099] Embodiments of the disclosure may also relate to an
apparatus for performing the operations herein. This apparatus may
be specially constructed for the required purposes, and/or it may
comprise a general-purpose computing device selectively activated
or reconfigured by a computer program stored in the computer. Such
a computer program may be stored in a non-transitory, tangible
computer readable storage medium, or any type of media suitable for
storing electronic instructions, which may be coupled to a computer
system bus. Furthermore, any computing systems referred to in the
specification may include a single processor or may be
architectures employing multiple processor designs for increased
computing capability.
[0100] Embodiments of the disclosure may also relate to a product
that is produced by a computing process described herein. Such a
product may comprise information resulting from a computing
process, where the information is stored on a non-transitory,
tangible computer readable storage medium and may include any
embodiment of a computer program product or other data combination
described herein.
[0101] Finally, the language used in the specification has been
principally selected for readability and instructional purposes,
and it may not have been selected to delineate or circumscribe the
inventive subject matter. It is therefore intended that the scope
of the disclosure be limited not by this detailed description, but
rather by any claims that issue on an application based hereon.
Accordingly, the disclosure of the embodiments is intended to be
illustrative, but not limiting, of the scope of the disclosure,
which is set forth in the following claims.
* * * * *