U.S. patent application number 12/324509 was filed with the patent office on 2009-06-25 for waveguide sheet and methods for manufacturing the same.
Invention is credited to Shalom Luski, Noam Meir, Keren Regev, Micha Zimmermann.
Application Number | 20090161369 12/324509 |
Document ID | / |
Family ID | 40788371 |
Filed Date | 2009-06-25 |
United States Patent
Application |
20090161369 |
Kind Code |
A1 |
Regev; Keren ; et
al. |
June 25, 2009 |
WAVEGUIDE SHEET AND METHODS FOR MANUFACTURING THE SAME
Abstract
In one aspect, an illumination structure includes a
substantially non-fiber waveguide, which itself includes a discrete
in-coupling region for receiving light, a discrete propagation
region for propagating light, and a discrete out-coupling region
for emitting light.
Inventors: |
Regev; Keren; (Tel Aviv,
IL) ; Meir; Noam; (Hezlia, IL) ; Luski;
Shalom; (Tel Aviv-Yafo, IL) ; Zimmermann; Micha;
(Haifa, IL) |
Correspondence
Address: |
GOODWIN PROCTER LLP;PATENT ADMINISTRATOR
53 STATE STREET, EXCHANGE PLACE
BOSTON
MA
02109-2881
US
|
Family ID: |
40788371 |
Appl. No.: |
12/324509 |
Filed: |
November 26, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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61006110 |
Dec 19, 2007 |
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61064384 |
Mar 3, 2008 |
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61127095 |
May 9, 2008 |
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61076427 |
Jun 27, 2008 |
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61135098 |
Jul 16, 2008 |
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Current U.S.
Class: |
362/311.01 ;
264/1.24; 264/1.29; 362/551; 362/84; 385/129; 427/163.2 |
Current CPC
Class: |
G02B 6/0078 20130101;
G02B 6/0041 20130101; G02B 6/0065 20130101; G02B 6/0076
20130101 |
Class at
Publication: |
362/311.01 ;
264/1.24; 427/163.2; 264/1.29; 362/551; 362/84; 385/129 |
International
Class: |
F21V 8/00 20060101
F21V008/00; B29D 11/00 20060101 B29D011/00; F21V 9/16 20060101
F21V009/16; B05D 5/06 20060101 B05D005/06 |
Claims
1. An illumination structure comprising: a substantially non-fiber
waveguide; and a discrete light source disposed proximate a bottom
surface of a first portion of the waveguide, wherein light is
absorbed into the structure through the bottom surface of the first
portion and is emitted from a top surface of a second portion of
the waveguide having substantially no overlap with the first
portion of the waveguide.
2. The illumination structure of claim 1, wherein the first and
second portions of the waveguide are spaced apart from each other,
and light is emitted only from the second portion of the
waveguide.
3. An illumination structure comprising: a substantially non-fiber
waveguide; and a discrete light source disposed proximate a bottom
surface of a first portion of the waveguide, wherein a propagation
direction, within a second portion of the waveguide, of light from
the discrete light source is substantially perpendicular to an
in-coupling direction of the light.
4. The illumination structure of claim 3, wherein the propagation
direction of the light is substantially perpendicular to an
out-coupling direction of the light in a third portion of the
waveguide, the out-coupling direction being parallel to the
in-coupling direction.
5. The illumination structure of claim 3, further comprising a
phosphor material for converting some of the light to a different
wavelength, the converted light mixing with unconverted light to
form mixed light spectrally different from both the unconverted
light and the converted light.
6. The illumination structure of claim 5, wherein an out-coupling
direction of the mixed light is substantially perpendicular to the
propagation direction.
7. A method of forming a substantially non-fiber waveguide, the
method comprising forming a plurality of joined core structures, at
least one of which is substantially free of scattering
particles.
8. The method of claim 7, wherein at least some of the core
structures comprise a plurality of scattering particles, and
wherein at least one of a size, a concentration, or a type of the
scattering particles varies among at least two of the core
structures.
9. The method of claim 7, wherein forming the plurality of joined
core structures comprises at least one of co-injection molding,
coextrusion, coating, lamination, bonding, or welding.
10. The method of claim 7, further comprising forming a cladding
layer on at least one of a top surface or a bottom surface of the
plurality of joined core structures.
11. The method of claim 7, wherein, across a thickness thereof,
there is substantially no overlap between adjoining core
structures.
12. The method of claim 7, wherein the waveguide is substantially
planar.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to and the benefit of U.S.
Provisional Patent Application No. 61/006,110, filed on Dec. 19,
2007; U.S. Provisional Patent Application No. 61/064,384, filed on
Mar. 3, 2008; U.S. Provisional Patent Application No. 61/127,095,
filed on May 9, 2008; U.S. Provisional Patent Application No.
61/076,427, filed on Jun. 27, 2008; and U.S. Provisional Patent
Application No. 61/135,098/, filed on Jul. 16, 2008. The entire
disclosure of each of these applications is incorporated by
reference herein.
TECHNICAL FIELD
[0002] In various embodiments, the present invention relates to
optics, and in particular to optical waveguides.
BACKGROUND
[0003] The technology to transmit and guide light through optical
systems exploits a physical phenomenon in which light is confined
within a material surrounded by other materials with lower
refractive index. Such optical systems are generally referred to as
optical waveguides, and are employed to direct, diffuse, and/or
polarize light in many applications, e.g., optical communication
and illumination.
[0004] When a ray of light moves within a transparent substrate and
strikes one of its internal surfaces at a certain angle, the ray of
light is either reflected from the surface or refracted into the
open air in contact with the substrate. The condition according to
which the light is reflected or refracted is determined by Snell's
law, which relates the impinging angle, the refracting angle (in
the case of refraction) and the refractive indices of both the
substrate and the air. Broadly speaking, depending on the
wavelength of the light, for a sufficiently large impinging angle
(above the "critical angle") no refraction occurs, and the energy
of the light is trapped within the substrate. In other words, the
light is reflected from the internal surface as if from a mirror.
Under these conditions, total internal reflection is said to take
place.
[0005] Many optical systems operate according to the principle of
total internal reflection. Optical fiber represents one such
system. Optical fibers are transparent, flexible rods of glass or
plastic, basically composed of a core and cladding. The core is the
inner part of the fiber, through which light is guided, while the
cladding surrounds it completely. The refractive index of the core
is higher than that of the cladding, so that light in the core
impinging the boundary with the cladding at an angle equal to or
exceeding the critical angle is confined in the core by total
internal reflection. Thus, geometric optics may be used to derive
the largest angle at which total internal reflection occurs. An
important parameter of every optical fiber (or any other
light-transmitting optical system) is known as the "numerical
aperture," which is defined as the sine of the largest incident
light ray angle that is successfully transmitted through the
optical fiber, multiplied by the index of refraction of the medium
from which the light ray enters the optical fiber.
[0006] Another optical system designed for guiding light is the
graded-index optical fiber, in which the light ray is guided by
refraction rather than by total internal reflection. In this
optical fiber, the refractive index decreases gradually from the
center outwards along the radial direction, and finally drops to
the same value as the cladding at the edge of the core. As the
refractive index does not change abruptly at the boundary between
the core and the cladding, there is no total internal reflection.
However, the refraction nonetheless bends the guided light rays
back into the center of the core while the light passes through
layers with lower refractive indices.
[0007] Another type of optical system is based on photonic
materials, where light is confined within a bandgap material
surrounding the light. In this type of optical system, also known
as a photonic material waveguide, the light is confined in the
vicinity of a low-index region. One example of a photonic material
waveguide is a silica fiber having an array of small air holes
throughout its length.
[0008] International Patent Application Publication No.
WO2004/053531, the entire contents of which are hereby incorporated
by reference, discloses a waveguide for propagating and emitting
light. The waveguide is made of a flexible, multilayer waveguide
material in which the refractive index of one layer is larger than
the refractive index of the other layers to allow propagation of
light via total internal reflection. One layer of the waveguide
material comprises one or more impurities which scatter the light
to thereby emit a portion thereof through the surface of the
waveguide material.
[0009] Impurities for light scattering are also employed in light
diffusers (also known as light-scattering films or diffusing
films), which diffuse light from a source in order to attain a
uniform luminance. For example, in a liquid crystal display device
a light diffuser is placed between the light source or light
reflector and the liquid crystal panel so as to diffuse the
illuminating light, allowing the device to be used as a plane or
flat light source as well as enhancing the luminance on the front
side of the device.
[0010] Conventional illumination apparatuses capable of emitting
diffused light with uniform luminance are complicated to
manufacture and too large for many applications. They tend to be
unitary and large rather than small and scalable. Additionally,
such apparatuses often exhibit insufficient color mixing and
diffusion to emit light with a high degree of color and luminance
uniformity.
SUMMARY
[0011] The foregoing limitations of conventional illumination
apparatuses are herein addressed by utilizing a waveguide that
incorporates in-coupling, propagation, and out-coupling regions
and/or that is easily manufactured as a group of aligned core
structures.
[0012] Generally, embodiments of the invention propagate and
diffuse light until it exits though a surface of the waveguide
device or a portion thereof. The light path may involve two right
angles: in various embodiments, light is absorbed into the
structure through the bottom surface of one portion the waveguide
(e.g., the in-coupling region) and is emitted from a top surface of
a second portion of the waveguide (e.g., the out-coupling region).
These waveguide portions have substantially no overlap; they may be
separated, for example, by a propagation region from which light is
not emitted.
[0013] In various embodiments, light entering a waveguide's
in-coupling region is substantially retained within the waveguide
until it is emitted from the out-coupling region. The different
emission and retention behavior of the various waveguide portions
may be obtained using different concentrations of scattering
particles; for example, the propagation region may be devoid of
scattering particles altogether in order to keep light confined
therein.
[0014] Embodiments of the invention successfully provide an optical
waveguide device that may be tiled or overlapped. As further
detailed herein, the optical properties of the waveguide may be
tailored to the requirements of particular applications.
[0015] The design of waveguide-based light structures in accordance
with the invention also facilitates convenient manufacture. The
light structure may, for example, be assembled by joining a
plurality of core structures, each of which has a different
concentration of scattering particles (or no scattering particles
at all). Forming the joined core structures may be accomplished by,
e.g., co-injection molding, coextrusion, coating, lamination,
bonding, and/or welding.
[0016] In an aspect, embodiments of the invention feature an
illumination structure including a substantially non-fiber
waveguide and a discrete light source disposed proximate a bottom
surface of a first portion of the waveguide. Light is absorbed into
the illumination structure through the bottom surface of the first
portion and is emitted from a top surface of a second portion of
the waveguide; the second portion has substantially no overlap with
the first portion of the waveguide. The first and second portions
of the waveguide may be spaced apart from each other. In general,
light is emitted only from the second portion of the waveguide.
[0017] In another aspect, embodiments of the invention feature a
substantially non-fiber waveguide and a discrete light source
disposed proximate a bottom surface of a first portion of the
waveguide. A propagation direction, within a second portion of the
waveguide, of light from the discrete light source is substantially
perpendicular to an in-coupling direction of the light. The
propagation direction of the light may be substantially
perpendicular to an out-coupling direction of the light in a third
portion of the waveguide. The illumination structure may include a
phosphor material for converting some of the light to a different
wavelength, the converted light mixing with unconverted light to
form mixed light spectrally different from both the unconverted
light and the converted light. An out-coupling direction of the
mixed light may be substantially perpendicular to the propagation
direction of light from the discrete light source.
[0018] In yet another aspect, embodiments of the invention feature
a method of forming a substantially non-fiber waveguide. The method
includes forming a plurality of joined core structures, at least
one of which is substantially free of scattering particles. At
least some of the core structures may include pluralities of
scattering particles, and the size, the concentration, and/or the
type of the scattering particles may vary among at least two of the
core structures. Forming the plurality of joined core structures
may include or consist essentially of at least one of co-injection
molding, coextrusion, coating, lamination, bonding, or welding. The
method may include forming a cladding layer on the top surface
and/or the bottom surface of the plurality of joined core
structures. There may be substantially no overlap between adjoining
core structures across a thickness thereof. The waveguide may be
substantially planar.
[0019] These and other objects, along with advantages and features
of the present invention herein disclosed, will become more
apparent through reference to the following description, the
accompanying drawings, and the claims. Furthermore, it is to be
understood that the features of the various embodiments described
herein are not mutually exclusive and may exist in various
combinations and permutations.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] In the drawings, like reference characters generally refer
to the same parts throughout the different views. Also, the
drawings are not necessarily to scale, emphasis instead generally
being placed upon illustrating the principles of the invention. In
the following description, various embodiments of the present
invention are described with reference to the following drawings,
in which:
[0021] FIG. 1a is a schematic illustration showing a perspective
view of an optical waveguide device which comprises a plurality of
core structures joined in a side-by-side configuration, according
to some embodiments of the present invention;
[0022] FIG. 1b is a schematic illustration showing a
cross-sectional view along the line A-A of FIG. 1a, according to
some embodiments of the present invention;
[0023] FIG. 1c is a schematic illustration showing a perspective
view of the device optical waveguide device in embodiments in which
the device comprises one or more cladding layers;
[0024] FIGS. 1d and 1e are schematic illustrations showing cross
sectional views along line B-B of FIG. 1c;
[0025] FIGS. 1f and 1g are schematic illustrations showing
perspective views of the optical waveguide device without (FIG. 1f)
and with (FIG. 1g) claddings, in an embodiment in which the core
layer of the device is formed of core structures in the shape of
plaques;
[0026] FIG. 1h is a schematic illustration showing a perspective
view of an optical waveguide device which comprises a plurality of
core structures joined in a nested configuration, according to some
embodiments of the present invention;
[0027] FIGS. 2a and 2b show representative examples of an optical
mean free path as a function of a lateral direction, according to
some embodiments of the present invention;
[0028] FIGS. 3a-3d are schematic illustrations showing fragmentary
cross-sectional views of the device, according to some embodiments
of the present invention;
[0029] FIGS. 4a-4d are schematic illustrations showing
cross-sectional views of an optical funnel, according to some
embodiments of the present invention;
[0030] FIGS. 4e-4g are cross-sectional views of an optical
waveguide device having substantially no line-of-sight between a
photoluminescent material and a light-emitting element in an
optical funnel, according to some embodiments of the present
invention;
[0031] FIGS. 4h-4j are cross-sectional views of an optical
waveguide device having substantially no line-of-sight between a
photoluminescent material and a light-emitting element embedded
within the waveguide device, according to some embodiments of the
present invention;
[0032] FIG. 5 is a schematic illustration of a coextrusion
apparatus for forming a core layer, according to some embodiments
of the present invention;
[0033] FIG. 6 is a schematic illustration of a coextrusion
apparatus for forming a core layer and one or more cladding layers,
according to some embodiments of the present invention;
[0034] FIGS. 7a and 7b are schematic illustrations of a process for
forming a core layer and optionally one or more cladding layers
using extrusion coating technique, according to various exemplary
embodiments of the present invention;
[0035] FIGS. 8a-8c are schematic illustrations of a process for
forming a core layer and optionally one or more cladding layers
using lamination technique, according to various exemplary
embodiments of the present invention;
[0036] FIGS. 9a-9c are schematic illustrations of a process for
forming a core layer and optionally one or more cladding layers
using tiling technique, according to various exemplary embodiments
of the present invention;
[0037] FIGS. 10a-10c are schematic illustrations of a process for
manufacturing a core layer by co-injection technique, according to
various exemplary embodiments of the present invention;
[0038] FIG. 11 is a schematic illustration showing a perspective
view of a multilayer optical waveguide device, according to some
embodiments of the present invention;
[0039] FIG. 12a is a plan view of an illumination panel
incorporating multiple optical waveguide devices, according to some
embodiments of the present invention;
[0040] FIG. 12b is an exploded view of a display device
incorporating the illumination panel depicted in FIG. 12a; and
[0041] FIG. 13 is a schematic illustration of a light-emitting
element that includes a phosphor layer.
DETAILED DESCRIPTION
[0042] FIGS. 1a-1h illustrate an optical waveguide device 10
according to various exemplary embodiments of the present
invention. Device 10 generally has an open shape (i.e.,
non-tubular) such as the shape of a sheet, e.g., a planar sheet.
Typically, device 10 is a non-fiber device, i.e., not a
substantially cylindrical waveguide in which a light-conducting
core is surrounded by a layer of cladding, and is solid (i.e., not
hollow). In various exemplary embodiments of the invention the
sheet is flexible and hence may be also assume a non-planar shape.
For example, when the sheet is placed on a curved surface, the
sheet may acquire the curvature of the surface. Device 10 may also
have a certain degree of elasticity. Thus, one or more of the
layers of device 10 may be made, for example, from an elastomer. In
some embodiments, device 10 is substantially rigid.
[0043] Device 10 includes a core layer 16 formed of a plurality of
core structures 18 joined in, e.g., a side-by-side or nested
configuration. Core structures 18 (designated in FIGS. 1a-1h by
reference numerals 18-1, 18-2, . . . , 18-n) may take the form of
elongated bands arranged side-by-side (see, e.g., FIG. 1a), or may
instead have a nested configuration (see, e.g., FIG. 1h) with their
common ends joined. The width of structures 18 (along the x
direction in FIGS. 1a-1h) may vary.
[0044] For clarity of presentation device 10 is shown as planar,
with layer 16 being parallel to the x-y plane, and each elongated
core structure 18 extending along the y direction. The ordinarily
skilled person would know how to tailor the following description
for non-planar devices. For example, each section of a non-planar
sheet may be described using a Cartesian x-y-z coordinate system
which is rotated such that the section is tangential to the x-y
plane and normal to the z direction. The x, y and z directions are
referred to herein as the "lateral," "longitudinal" and "normal"
directions, respectively.
[0045] Although core structures 18 are shown in FIGS. 1a-1g as
having a rectangular cross-section, this need not necessarily be
the case, depending on the application.
[0046] With more specific reference to FIGS. 1a and 1b, FIG. 1a is
a perspective view of device 10 and FIG. 1b is a cross-sectional
view along the line A-A of FIG. 1a in embodiments in which core
layer 16 is at least partially surrounded by air. FIG. 1b is a
cross-sectional view along the line A-A of a device similar to that
illustrated FIGS. 1a and 1h in embodiments in which core layer 16
is at least partially surrounded by air.
[0047] In embodiments in which core layer 16 is at least partially
surrounded by air, structures 18 are characterized by a refractive
index which is larger than the refractive index of the surrounding
air. In such configuration, when light strikes the internal surface
of layer 16 at an angle larger than the critical angle,
.theta..sub.c.ident.sin.sup.-1(n.sub.1/n.sub.2), where n.sub.1 and
n.sub.2 are the refractive indices of the air and the core layer,
respectively, the light energy is trapped within core layer 16 and
propagates therethrough via total internal reflection. Light may
also propagate through device 10 when the impinging angle is
smaller than the critical angle, in which case one portion of the
light is emitted and the other portion thereof continues to
propagate. The difference between the indices of refraction the
core layer and surrounding air may be selected in accordance with
the desired propagation angle of the light.
[0048] Typically, the refractive index of air is about 1; hence,
core structures 18 typically include or consist essentially of a
waveguide material having a refractive index greater than 1.
Representative examples of waveguide materials suitable for the
core structures include, without limitation, a thermoplastic such
as a polycarbonate, polymethyl methacrylate (PMMA), and/or
polyurethane (TPU) (aliphatic) with a refractive index of about
1.50, TPU (aromatic) with a refractive index of from about 1.58 to
about 1.60, amorphous nylon such as GRILAMID supplied by EMS
Grivory (e.g., GRILAMID TR90 with refractive index of about 1.54),
polymethylpentene, e.g., TPX supplied by Mitsui with a refractive
index of about 1.46, polyvinylidene fluoride (PVDF) with a
refractive index of about 1.34, or other thermoplastic fluorocarbon
polymers, and/or STYROLUX (UV stabilized) supplied by BASF with
refractive index of about 1.58.
[0049] FIGS. 1c-1e are perspective (FIG. 1c) and cross-sectional
(FIGS. 1d and 1e) views along line B-B of device 10 in embodiments
in which device 10 further comprises one or more cladding layers.
Although the core layer of the device shown in FIG. 1c is
illustrated as having the core structures in a side-by-side
configuration, this need not necessarily be the case, since, for
some applications, it may be desired to have the core layer
arranged in a nested configuration (e.g., the configuration
schematically illustrated in FIG. 1h).
[0050] As shown in FIGS. 1c-1e, device 10 includes a first cladding
layer 12, a second cladding layer 14, and core layer 16 interposed
between cladding layers 12, 14. Typically, the elongated structures
of core 16 extend along the length of the cladding layers.
[0051] The refractive index of the cladding layers is typically
smaller than the refractive index of the core layer. As a result,
when light strikes the internal surface of the cladding layers at
an impinging angle larger than the critical angle
(.theta..sub.c.ident.sin.sup.-1(n.sub.1/n.sub.2), where n.sub.1 and
n.sub.2 are the refractive indices of the cladding and core layers,
respectively), the light energy is trapped within core layer 16,
and the light propagates therethrough. The light may also propagate
through device 10 when the impinging angle is smaller than the
critical angle, in which case one portion of the light is emitted
and the other portion continues to propagate. The difference
between the indices of refraction of the layers is preferably
selected in accordance with the desired propagation angle of the
light.
[0052] In the embodiments in which the cladding layers are
employed, core structures 18 include or consist essentially of a
waveguide material such as those identified above for the
embodiment lacking cladding layers, and preferably have relatively
high refractive indices.
[0053] In accordance with embodiments of the present invention, the
indices of refraction are selected such that propagation angle is
from about 2.degree. to about 55.degree.. For example, core layer
16 may be made of GRILAMID TR90 with a refractive index of about
1.54, and cladding layers 12, 14 may be made of TPX with refractive
index of about 1.46, so that
.DELTA.n.ident.n.sub.2-n.sub.1.apprxeq.0.08 and
n.sub.1/n.sub.2.apprxeq.0.948, corresponding to a propagation angle
of 90.degree.-sin.sup.-1(0.948), or approximately .+-.19.degree..
In another example, a core layer 16 made of TPU (aromatic) with a
refractive index of about 1.60 without cladding has a corresponding
propagation angle of 90.degree.-sin.sup.-1(1/1.6), or approximately
.+-.51.degree..
[0054] In some embodiments of the invention, core structures 18 do
not have elongated shapes. FIGS. 1f and 1g are perspective views of
device 10 without (FIG. 1f) and with (FIG. 1g) claddings, in an
embodiment in which core structures 18 are in the shape of plaques
(e.g., polygonal plaques such as squares or rectangles). The
ordinarily skilled person will know how to construct a
cross-sectional view of these illustrations, which may be similar
to FIGS. 1b, 1d and 1e.
[0055] The partitioning of core layer 16 into core structures 18
(elongated or shaped as plaques) may be accomplished by any process
known in the art, such as, but not limited to, coextrusion,
extrusion, coating, coinjection molding, lamination, tiling, and
the like. For example, two adjacent structures may be welded at
their joined ends, bonded by an adhesive material disposed along
their length and/or width, etc. A process for forming core layer 16
according to some embodiments of the present invention is provided
below.
[0056] Whether or not device 10 includes cladding layers, and
irrespectively of the shape and arrangement of the core structures
forming layer 16, some of the core structures include additives
selected to provide the individual core structures with a
predetermined effective refractive index. The effective refractive
index depends on the type and concentration of the additive.
Typically, higher additive concentrations provide higher effective
refractive indices. The additives may take the form of
light-scattering particles 20 embedded in one or more of the core
structures. In various exemplary embodiments of the invention, the
size, concentration, refractive index, and/or type of
light-scattering particles 20 varies among at least two of the core
structures.
[0057] Particles 20 are dispersed within core structures 18 and
facilitate emission of the light from a surface 23 of core layer 16
and/or a surface 24 of cladding layer 14 (in the embodiments in
which cladding layer 14 is employed). Particles 20 serve as
scatterers and typically scatter optical radiation in more than one
direction. When light is scattered by a particle 20 such that the
impinging angle is below the critical angle, no total internal
reflection occurs and the scattered light is emitted through
surface 23 and/or surface 24.
[0058] The light-scattering particles may be beads, e.g., glass
beads, or other ceramic particles, rubber particles, silica
particles, particles including or consisting essentially of
inorganic materials such as BaSO.sub.4 or TiO.sub.2, particles
including or consisting essentially of a phosphor material (as
further described below), and the like. In an embodiment, the
light-scattering particles are substantially or even completely
non-phosphorescent. Such non-phosphorescent particles merely
scatter light without converting the wavelength of any of the light
striking the particles. The term "light-scattering particles" may
also refer to non-solid objects embedded in the waveguide material
from which core structure are made, provided that such objects are
capable of scattering the light. Representative example of suitable
non-solid objects include, without limitation, closed voids within
the core structures, e.g., air bubbles, and/or droplets of liquid
embedded within the core structures. The light-scattering particles
may also be organic or biological particles, such as, but not
limited to, liposomes. In some embodiments, optical elements such
as microlenses are utilized in conjunction with, or even instead
of, light-scattering particles. In other embodiments, optical
elements include or consist essentially of structures such as
hemispheres or diffusive dots. In such embodiments, the optical
elements function to out- couple light propagating through device
10. As utilized herein, "optical elements" may generically refer to
elements such as microlenses as well as light-scattering particles,
e.g., non-photoluminescent particles.
[0059] In accordance with various embodiments of the present
invention, the concentration, size and/or type of particles is
selected such as to provide illumination at a predetermined profile
(e.g., intensity profile) from predetermined regions of surface 23
or 24. For example, in regions of device 10 where a larger portion
of the propagated light is to be emitted through the surface, the
concentration of particles 20 may be large and/or the particles may
have a type and/or size which provides them with high scattering
properties; in regions where a smaller portion of the light is to
be emitted the concentration of particles 20 may be smaller and/or
the particles may have a type and/or size which provides them with
lower scattering properties; and in surface regions from which no
light is to be emitted, substantially no particles are embedded in
core structures 18.
[0060] As will be appreciated by one ordinarily skilled in the art,
the energy trapped in waveguide device 10 decreases each time a
light ray is emitted through surface 23 or 24. On the other hand,
it may be desired to use device 10 to provide a uniform surface
illumination. Thus, as the overall amount of energy decreases with
each emission, a uniform surface illumination may be achieved by
gradually increasing the ratio between the emitted light and the
propagated light. According to some embodiments of the present
invention, the increasing ratio of emitted light to propagated
light is achieved by an appropriate selection of the distribution,
type, refractive index, and/or size of particles 20 in the core
layer 16. For example, at regions in which it is desired to have
uniform surface illumination, the concentration of particles 20 may
be an increasing function of the optical distance traversed by the
propagated light.
[0061] Generally, the optical output at specific and predetermined
regions may be controlled by arranging the core structures 18 such
that different core structures have different concentrations,
sizes, refractive indices, and/or types of particles 20.
[0062] In various exemplary embodiments of the invention, the core
structures 18 are arranged to define a first zone 26 and a second
zone 28. First and second zones 26, 28 may include portions of core
layer 16 such that a profile of an optical mean free path
characterizing core layer 16 is generally flat across the first
zone 26 and monotonically varying across the second zone 28.
[0063] The optical mean free path may be measured directly by
positioning a bulk material in front of a light-emitting element
and measuring the optical output through the bulk at a given
direction as a function of the thickness of the bulk. Typically,
when a bulk material, t mm in thickness, reduces the optical output
of a light source at the forward direction by 50%, the material is
said to have a mean free path of t mm.
[0064] FIG. 2a shows a representative example of an optical mean
free path as a function of the lateral direction x. As shown, the
optical mean free path is substantially constant in zone 26, and is
a decreasing function of x in zone 28. The decrement of the optical
mean free path in region 28 facilitates an increasing ratio between
the emitted portion and propagated portions of the light.
[0065] Zone 26 may include one or more core structures and is
typically devoid of light-scattering particles 20. In this
embodiment, zone 26 propagates light with minimal or no emissions
from surfaces 23 or 24, i.e., zone 26 is a propagation region. Zone
28 may include a plurality, e.g., three or more, of core structures
18 each having particles 20 embedded therein. In such an
embodiment, zone 28 provides illumination by out-coupling light
from core 16 (i.e., zone 28 is an out-coupling region for light
propagated through zone 26). The brightness of the illumination
from zone 28 may be substantially uniform.
[0066] Brightness uniformity may be calculated by considering the
luminance deviation across the range of azimuthal angles as a
fraction of the average luminance across that range. A more simple
definition of the brightness uniformity BU is
BU==1-(L.sub.MAX-L.sub.MIN)/(L.sub.MAX+L.sub.MIN), where L.sub.MAX
and L.sub.MIN are, respectively, the maximal and minimal luminance
values across the predetermined range of azimuthal angles.
[0067] The term "substantially uniform brightness" refers to a BU
value which is at least 0.8 when calculated according to the above
formula. In some embodiments of the invention the value of BU is at
least 0.85, more preferably at least 0.9, and still more preferably
at least 0.95.
[0068] To achieve a decreasing optical mean free path, the
concentration of particles 20 in the core structures 18 of zone 28
may be an increasing function of the distance from zone 26.
Alternatively or additionally, the type and/or size of the
particles in the individual core structures 18 of zone 28 may vary
to achieve the desired profile. As shown in FIG. 1b, the
concentration, type, size, and/or refractive index of particles 20
in zone 28 may change in a direction of light propagation through
device 10 (denoted as the x direction in FIG. 1b). However, for any
cross-section through zone 28, the concentration, type, size,
and/or refractive index of particles 20 may be substantially
constant in at least one of the directions perpendicular to the
light-propagation direction (e.g., they and z directions in FIG.
1b). For example, each core structure 18 in zone 28 may have a
substantially constant concentration, type, size, and/or refractive
index of particles 20 therewithin, but this value may change in at
least one (or every) other core structure 18 in zone 28.
[0069] Some embodiments of the present invention include a third
zone 30. As shown in FIG. 1a, third zone 30 may be proximate or in
direct contact with first zone 26 and away from second zone 28.
Third zone 30 may comprise or consist essentially of one or more
core structures 18 having light-scattering particles 20 embedded
therein. A representative example of an optical mean free path in
the embodiment in which three zones are defined is illustrated in
FIG. 2b.
[0070] Zone 30 may be an in-coupling region for facilitating the
entry of light into device 10. Light enters device 10 at zone 30,
propagates through zone 26 and exits (i.e., is out-coupled) at zone
28. One or more of the core structures 18, typically the first and
last structures (i.e., structures 18-1 and 18-n in the illustration
of FIG. 1d) may be made light-reflective so as to prevent or reduce
optical losses through the side(s) of device 10. The characteristic
refractive index of such light-reflective core structures 18 is
preferably above 2. A representative example of a material having a
sufficiently high refractive index suitable for the present
embodiment is TiO.sub.2, which has a refractive index of about 2.5.
Alternatively, light-reflective structures 22 may be disposed
proximate the entire height of device 10 as shown in FIG. 1e.
[0071] Coupling of light into device 10 may be facilitated using an
optical funnel 32 positioned adjacent to layer 12 or layer 16 at
zone 30. Funnel 32 is preferably configured to receive light from
one or more light-emitting elements and to transmit the light into
layer 12 or layer 16. The principle of operation of funnel 30
according to some embodiments of the present invention is further
detailed herein under with reference to FIG. 4.
[0072] To prevent or reduce optical losses through the portion of
cladding layer 14 which overlaps zone 30, device 10 may further
include one or more light reflectors 36 adjacent to cladding layer
14 at the region of cladding layer 14 which overlaps zone 30.
Reflector(s) 36 reduce illumination in any direction other than a
circumferential direction.
[0073] In various exemplary embodiments of the invention, zone 30
of device 10 includes one or more components that cause the light
exiting zone 30 (into zone 26) to have a predetermined optical
profile, such as, but not limited to, a substantially uniform color
profile or substantially uniform white light. This embodiment may
be implemented by color mixing, optical means, or may be
implemented via luminescence, a phenomenon in which energy is
absorbed by a substance, commonly called a luminescent, and is
emitted in the form of light. The wavelength of the emitted light
differs from the characteristic wavelength of the absorbed energy
(the characteristic wavelength equals hc/E, where h is the Plank's
constant, c is the speed of light and E is the energy absorbed by
the luminescent). Luminescence is a widely occurring phenomenon
which may be classified according to the excitation mechanism as
well as according to the emission mechanism. Examples of such
classifications include photoluminescence and electroluminescence.
Photoluminescence is sub-classified to fluorescence and
phosphorescence.
[0074] A photoluminescent is generally a material which absorbs
energy is in the form of light. A fluorescent material is a
material which emits light upon return to the base state from a
singlet excitation, and a phosphorescent materials is a material
which emits light upon return to the base state from a triplet
excitation. In fluorescent materials, or fluorophores, the electron
de-excitation occurs almost spontaneously, and the emission ceases
when the source of the energy exciting the fluorophore is removed.
In phosphor materials, or phosphors, the excitation state involves
a change of spin state, which decays only slowly. In
phosphorescence, light emitted by an atom or molecule persists
after the excitation source is removed.
[0075] Photoluminescent materials are used according to various
embodiments of the present invention for altering the color of
light. Since blue light has a short wavelength (compared, e.g., to
green or red light), and since the light emitted by a
photoluminescent material has a longer wavelength than the absorbed
light, blue light generated by a blue light-emitting element such
as a light-emitting diode (LED) may be readily converted to visible
light having a longer wavelength. Accordingly, in various exemplary
embodiments of the invention a specific light profile on the exit
of light into zone 26 is provided using one or more
photoluminescent layers disposed on or embedded in device 10.
[0076] The term "photoluminescent layer" is commonly used herein to
describe one photoluminescent layer or a plurality of
photoluminescent layers. Additionally, a photoluminescent layer may
include one or more types of photoluminescent species. In any
event, a photoluminescent layer is characterized by an absorption
spectrum (i. e., a range of wavelengths of light absorbed by the
photoluminescent molecules to effect quantum transition to a higher
energy level) and an emission spectrum (i.e., a range of
wavelengths of light emitted by the photoluminescent molecules as a
result of quantum transition to a lower energy level). The emission
spectrum of the photoluminescent layer is typically wider and
shifted relative to its absorption spectrum. The difference in
wavelength between the apex of the absorption and emission spectra
of the photoluminescent layer is referred to as the Stokes shift of
the photoluminescent layer.
[0077] The absorption spectrum of the photoluminescent layer
preferably overlaps, at least partially, the emission spectrum of
the light source which feeds device 10. More preferably, for each
characteristic emission spectrum of the light source, there is at
least one photoluminescent layer having an absorption spectrum
overlapping the characteristic emission spectrum. According to some
embodiments of the present invention, the apex of the source's
emission spectrum lies in the spectrum of the photoluminescent
layer, and/or the apex of the photoluminescent layer's absorption
spectrum lies in the spectrum of the light source.
[0078] The photoluminescent layer may "convert" the wavelength of a
portion of the light emitted by the light source. More
specifically, for each photon which is successfully absorbed by the
layer, a new photon is emitted. Depending on the type of
photoluminescent, the emitted photon may have a wavelength which is
longer or shorter than the wavelength of the absorbed photon.
Photons which do not interact with the photoluminescent layer
propagate therethrough. The combination of converted light and
non-converted light forms the profile of light entering zone 26.
This "mixed" light is preferably spectrally different from each of
the converted light and the non-converted light. Since the mixed
light is formed by the superposition of the converted light and the
non-converted light, the spectrum of the mixed light generally
contains all of the wavelengths of the converted light and the
non-converted light.
[0079] In preferred embodiments, the photoluminescent material is
disposed neither on an outer surface of device 10 nor directly on a
light-emitting element 34. Rather, as described further below, the
photoluminescent material (e.g., in the form of particles and/or a
layer or layers) is disposed within device 10 some distance away
from light-emitting element 34.
[0080] FIGS. 3a-d are fragmentary schematic illustrations of device
10 showing a cross-section of zone 30 parallel to the z-x plane.
Several components of device 10 are omitted from FIGS. 3a-d for
clarity of presentation. FIG. 3a illustrates an embodiment in which
the elongated structures at the ends of zone 30 (structures 18-1
and 18-3, in the present example) include or consist essentially of
photoluminescent material, e.g., a phosphor or a fluorophore. FIG.
3b illustrates an embodiment in which one or more of the inner
elongated structures of zone 30 (structure 18-2, in the present
example) include or consist essentially of photoluminescent
material. FIG. 3c is a schematic illustration of an embodiment in
which a photoluminescent layer 38, which may include or consist
essentially of a photoluminescent material such as a phosphor or a
fluorophore, is disposed on the surface of layer 12 and/or layer
14. In this embodiment, the wavelength of the light is changed via
the multiple impingements of the light on surface of layer 12
and/or 14. In an embodiment, only one of the surfaces is coated by
the photoluminescent layer 38. For example, the surface of layer 14
may be coated by the photoluminescent layer 38 and the surface of
layer 12 may be left exposed for better light coupling between
layer 12 and the light-emitting element or funnel 32.
[0081] Photoluminescent material may also be incorporated in the
form of particles, as illustrated in FIG. 3d. A plurality of
photoluminescent particles 128 may be distributed within one or
more of the core structures 18 in accordance with the desired light
output profile. For example, in one embodiment, the particles 128
are uniformly distributed in all the core structures 18. In another
embodiment, the particles are distributed such that there are core
structures 18 with a higher population of the particles 128 and
core structures 18 with a lower population of the particles 128,
depending on the desired profile in or near each core
structure.
[0082] A cross-sectional view of an exemplary embodiment of optical
funnel 32 is illustrated in FIG. 4a. Optical funnel 32 receives the
light from one or more light-emitting elements 34 and distributes
it prior to entry of the light into layer 12 (not shown in FIG. 4,
see FIGS. 1d and 1e) so as to establish a plurality of entry
locations within zone 30 (hence improving the uniformity of light
distribution within zone 30). Light-emitting elements 34 may be
arranged near funnel 32 or they may be embedded in funnel 32.
Efficient optical transmission between funnel 32 and layer 12 is
preferably ensured by impedance matching therebetween. Each
light-emitting element 34 may be a discrete light source, e.g., an
LED. In various embodiments, each light-emitting element 34 is a
substantially unpackaged (or "bare") LED die. In such embodiments,
funnel 32 or other portions of device 10 (such as zone 30, as
described further below) function as the "package" for
light-emitting element 34. In preferred embodiments of the
invention, bare LED dies do not include a phosphor or other
photoluminescent material as a portion thereof (e.g., on a common
substrate therewith or incorporated into or onto the LED
semiconductor layer structure). Where a single light-emitting
element 34 is described herein, more than one light-emitting
element 34 could generally also be utilized, and vice versa.
Generally, light is emitted from light-emitting element 34 upon
supply of electrical current thereto.
[0083] Funnel 32 may be made as a surface-emitting waveguide or
surface-emitting optical cavity which receives the light generated
by light-emitting elements 34 through an entry surface 142,
distributes it within an internal volume 148, and emits it through
an exit surface 144, which is typically opposite to the entry
surface 142.
[0084] In some embodiments of the present invention, funnel 32
comprises one or more light reflectors 146, which are typically
arranged peripherally about volume 148 so as to form an optical
cavity or an optical resonator within volume 148. One or more light
reflectors 146 may also be formed on or attached to the entry
surface 142 of funnel 32. In this embodiment, one or more openings
150 are formed on the reflectors 146 at the entry surface, thus
allowing light to enter volume 148. Openings 150 may be
substantially aligned, e.g., in the x-y plane, with light-emitting
elements 34.
[0085] Funnel 32 may include or consist essentially of a waveguide
material, or it may be filled with a medium having a small
absorption coefficient to the spectrum or spectra emitted by the
light-emitting elements 34. For example, funnel 32 may be filled
with air, or be made of a waveguide material which is similar or
identical to the material of the cladding layers 12 and/or 14. The
advantage of using air is its low absorption coefficient, and the
advantage of a waveguide material identical to material of the
cladding layers 12, 14 is impedance matching therewith.
[0086] When funnel 32 is filled with medium having a small
absorption coefficient (e.g., air), there may be no impedance
matching at exit surface 144 of funnel 32. Thus, some reflections
and refraction events may occur upon the impingement of light on
the interface between funnel 32 and the cladding layer 12. Neither
refraction nor reflection events cause significant optical losses;
refraction events contribute to the distribution of light within
zone 30, and reflection events contribute to the distribution of
light within volume 148.
[0087] In various exemplary embodiments of the invention, funnel 32
is supplemented by photoluminescent material for controlling the
output profile of the light, as schematically illustrated in FIGS.
4b-4d. For clarity of presentation, the reflectors 146 are not
shown in FIGS. 4b-4d. In any of the embodiments, funnel 32 may
include one or more light reflectors 146 as detailed above. In the
embodiment illustrated in FIG. 4b, a photoluminescent layer 38 is
interposed between layer 12 and funnel 32; in the embodiment
illustrated in FIG. 4c, photoluminescent layer 38 is embedded in
funnel 32; and in the embodiment illustrated in FIG. 4d a plurality
of photoluminescent particles 128 is distributed within funnel
32.
[0088] Various embodiments of the present invention feature one or
more light-emitting elements 34 embedded within zone 30 of device
10 and/or photoluminescent material (e.g., photoluminescent layer
38 and/or particles 128) disposed within device 10 outside of the
direct "line-of-sight" from light-emitting elements 34. That is, in
such embodiments, there is no direct, straight-line optical path
between the light-emitting elements 34 and the photoluminescent
material; rather, light emitted from light-emitting elements 34
reflects from a reflector, a surface, or an interface within device
10 before reaching the photoluminescent material. Thus, any light
striking and being back-reflected from the photoluminescent
material will not propagate directly back into light-emitting
element 34 (where it could be absorbed, thus reducing overall light
output and efficiency of device 10). Rather, light reflecting from
the photoluminescent material will tend to remain within device 10
and eventually reflected back toward zone 28 to be out-coupled. In
some embodiments, there is substantially no direct line-of-sight
between light-emitting element 34 and the photoluminescent
material, i.e., less than approximately 5% of the light from
light-emitting element 34 has a direct line-of-sight to the
photoluminescent material; any losses thereof are therefore
negligible.
[0089] Whether or not the photoluminescent material is within a
direct line-of-sight of light-emitting element 34, the
photoluminescent material may advantageously be located remotely in
relation to light-emitting element 34, i.e., it may be present in
zone 26 and/or zone 28 rather than proximate light-emitting element
34 (in zone 30 or in funnel 32, for example). The quantum
efficiency (or other performance metric) of the photoluminescent
material may degrade when the material is exposed to elevated
temperatures, e.g., temperatures greater than approximately
50.degree. C. Remote placement of the photoluminescent material
prevents the temperature of the material from rising during
operation due to, e.g., heat given off by light-emitting element
34. Instead, the temperature of remotely placed luminescent
material will generally remain at the ambient temperature of the
surroundings of device 10. Generally, the temperature of the
luminescent material may remain at least approximately 30.degree.
C., or even at least 100.degree. C. less than the temperature of
light-emitting element 34 during operation.
[0090] During assembly of device 10, elevated temperatures capable
of damaging (e.g., degrading the quantum efficiency of) the
photoluminescent material are often required when affixing or
embedding light-emitting element 34 into device 10. Remote
placement of the photoluminescent material enables the
photoluminescent material to be provided within device 10 prior to
the addition of light-emitting element 34--the distance
therebetween prevents the elevated temperatures from damaging the
photoluminescent material.
[0091] A remotely placed photoluminescent material may be located
in any one or more of a variety of locations, as depicted in FIGS.
4e-4j. FIG. 4e depicts a photoluminescent layer 38 within zone 26
and outside the direct line-of-sight of light-emitting element(s)
in funnel 32 (e.g., as illustrated in FIG. 4a). At least a portion
of the light propagating through zone 26 is converted by
photoluminescent layer 38 to light of a different wavelength, and
then the converted and unconverted light components enter zone 28
where they are out-coupled together to form, e.g., substantially
white light. In this and similar configurations, the propagating
light converted by the photoluminescent material travels in a
direction substantially perpendicular to the direction of the
eventual out-coupled light. Such configurations may enable superior
uniformity, brightness, and color of the out-coupled light.
[0092] FIG. 4f depicts potential locations in zone 28 for the
photoluminescent material, which are also outside the direct
line-of-sight of light-emitting element(s) in funnel 32. First,
photoluminescent particles 128 may be utilized in conjunction with
(or instead of) particles 20; at least a portion of light striking
particles 128 is converted to light of a different wavelength, and
the light out-coupled from zone 28 is, e.g., substantially white.
Additionally (or instead), photoluminescent layer 38 may be
disposed within zone 28, e.g., proximate a top edge thereof. In
this configuration, at least a portion of the light already being
out-coupled (i.e., on its way out of device 10) is converted to
light of a different wavelength. The exiting converted and
unconverted light mix to form, e.g., substantially white light. In
configurations featuring particles 20 (or other optical element(s))
disposed between light-emitting element 34 and a photoluminescent
material (e.g., photoluminescent layer 38 disposed along the top
edge of zone 28), the uniformity of the light striking the
photoluminescent material may be greater than the uniformity of the
light striking particles 20. That is, the scattering by particles
20 increases the uniformity of the light, which then strikes the
photoluminescent material and is out-coupled from device 10 with a
high level of uniformity. The line of sight between light-emitting
element 34 and the photoluminescent material may not be eliminated
by placement of particles 20 therebetween, as some light may
propagate through the region populated with particles 20 without
being scattered thereby.
[0093] FIG. 4g depicts possible locations for a photoluminescent
material described with reference to FIGS. 4e and 4f, any of which
(or any combination of which) may be utilized in conjunction with a
device 10 shaped to eliminate the direct line-of-sight between the
light-emitting element(s) in funnel 32 and photoluminescent layer
38 and/or particles 128. As shown in FIG. 4g, device 10 may include
a bend, curve, or other geometry in zone 26 (or even in zone 28)
which facilitates the elimination of a direct line-of-sight between
the light-emitting element(s) and the photoluminescent material.
This geometry may also facilitate subsequent "tiling" of multiple
devices 10 to form an illumination panel, e.g., a panel in which
the zones 28 of devices 10 overlie zones 26 and/or 30 of adjacent
devices 10 (as further described below with reference to FIGS. 12a
and 12b). The shape depicted in FIG. 4g is exemplary, and many
other configurations are possible.
[0094] FIGS. 4h-4j are analogous to FIGS. 4e-4g, respectively, but
depict one or more light-emitting elements 34 embedded within
device 10 (here shown embedded within a core structure 18 of zone
30) rather than coupled to device 10 via funnel 32. As shown by the
schematic break within zone 26 in FIGS. 4h-4j, zone 26 may be
elongated and/or be sized and shaped so as to substantially or
completely eliminate the direct line-of-sight between
light-emitting element(s) 34 and photoluminescent layer 38 and/or
particles 128. Each device 10 depicted in FIGS. 4e-4j may also
incorporate cladding layers 12,14, e.g., as illustrated in FIGS.
1c-1e.
[0095] In a preferred embodiment, light from light-emitting element
34 (whether embedded within device 10 or operated in conjunction
with funnel 32) generally enters zone 30 in an "in-coupling
direction," i.e., along the z axis indicated in FIG. 1b. Once
in-coupled into device 10 by scattering from particles 20 and/or
reflector 36, the light generally propagates through device 10
(e.g., through zone 26) in a "propagation direction" that is
substantially perpendicular to the in-coupling direction. As
illustrated in FIG. 1b, the propagation direction is generally
along the x axis. After the light enters zone 28, it is generally
out-coupled from device 10 (i.e., emitted from surface 23 and/or
24) in an "out-coupling direction" that is substantially
perpendicular to the propagation direction (e.g., along the z axis
indicated in FIG. 1b). Thus, the in-coupling direction and the
out-coupling direction may be substantially parallel. In some
embodiments in which photoluminescent layer 38 and/or particles 128
are present, at least a portion of the light propagating in device
10 in the propagation direction is stimulated by photoluminescent
layer 38 and/or particles 128, giving rise to the mixed light that
is out-coupled from device 10 in an out-coupling direction
substantially perpendicular to the propagation direction. This
configuration may enable better brightness and/or color uniformity
than devices in which stimulated light (i.e., light before or as it
strikes a photoluminescent material) propagates in a direction that
is not substantially perpendicular (e.g., a substantially parallel
direction) to an out-coupling direction of the mixed light
resulting from stimulation by the photoluminescent material.
[0096] Phosphors are widely used for coating individual LEDs,
typically to obtain white light therefrom. However,
photoluminescent layers incorporated in waveguide devices as
described herein have not been employed. The advantage of providing
photoluminescent layer 38 and/or particles 128 (in layer 16 and/or
funnel 32) as opposed to on each individual light-emitting element,
is that waveguide device 10 diffuses the light before emitting it.
Thus, instead of collecting light from a point light source (e.g.,
a LED), photoluminescent layer 38 and/or particles 128 collects
light having a predetermined extent. This configuration allows a
better control on the light profile provided by device 10.
[0097] Many types of phosphorescent and fluorescent substance are
contemplated. Representative examples include, without limitation,
the phosphors disclosed in U.S. Pat. Nos. 5,813,752, 5,813,753,
5,847,507, 5,959,316, 6,155,699, 6,351,069, 6,501,100, 6,501,102,
6,522,065, 6,614,179, 6,621,211, 6,635,363, 6,635,987, 6,680,004,
6,765,237, 6,853,131, 6,890,234, 6,917,057, 6,939,481, 6,982,522,
7,015,510, 7,026,756, 7,045,826, and 7,005,086, the entire
disclosures of which are hereby incorporated by reference. In an
embodiment, the quantum efficiency of photoluminescent layer 38
and/or particles 128 is only stable up to a temperature of
approximately 50.degree. C. However, in many configurations the
temperature of such materials remains lower than this level due to
spatial separation of photoluminescent layer 38 and/or particles
128 from the light-emitting element(s). In various embodiments,
layer 38 and/or particles 128 include or consist essentially of one
or more electroluminescent materials rather than (or in addition
to) photoluminescent materials. Such electroluminescent materials
may include or consist essentially of quantum dot materials and/or
organic LED (OLED) materials. Suitable quantum dots may include or
consist essentially of cadmium selenide.
[0098] There is more than one configuration in which
photoluminescent layer 38 may be used. In one embodiment,
photoluminescent layer 38 complements the light emitted by
light-emitting elements 34 to create a white light, e.g., using
dichromatic, trichromatic, tetrachromatic or multichromatic
approach. For example, a blue-yellow dichromatic approach may be
employed, in which case blue light-emitting elements (e.g., InGaN
LEDs with a peak emission wavelength at about 460 nm) are used, and
photoluminescent layer 38 may include or consist essentially of
phosphor molecules with an absorption spectrum in the blue range
and an emission spectrum extending to the yellow range (e.g.,
cerium-activated yttrium aluminum garnet, or strontium silicate
europium). Since the scattering angle of light sharply depends on
the frequency of the light (fourth-power dependence for Rayleigh
scattering, or second-power dependence for Mie scattering), the
blue light generated by the blue light-emitting elements 34 is
efficiently diffused in the waveguide material before interacting
with photoluminescent layer 38 and/or particles 128. Layer 38
and/or particles 128 emit light in its emission spectrum and
complement the blue light which is not absorbed by photoluminescent
layer 38 and/or particles 128 to white light.
[0099] In another dichromatic configuration, ultraviolet
light-emitting elements (e.g., LEDs of GaN, AlGaN, and/or InGaN
with a peak emission wavelength between 360 nm and 420 nm) are
used. Light of such ultraviolet light-emitting elements is
efficiently diffused in the waveguide material. To provide
substantially white light, two photoluminescent layers 38 and/or
two types of photoluminescent particles 128 are preferably
employed. One such photoluminescent layer and/or type of particles
may be characterized by an absorption spectrum in the ultraviolet
range and emission spectrum in the orange range (with peak emission
wavelength from about 570 nm to about 620 nm), and another
photoluminescent layer and/or type of particles may be
characterized by an absorption spectrum in the ultraviolet range
and emission spectrum in the blue-green range (with peak emission
wavelength from about 480 nm to about 500 nm). The orange light and
blue-green light emitted by the two photoluminescent layers 38
and/or two types of photoluminescent particles 128 blend to appear
as white light to an observer. Since the light emitted by the
ultraviolet light-emitting elements is above or close to the end of
the visual range, it is not discerned by the observer. When two
photoluminescent layers 38 are employed, they may be deposited one
on top of the other so as to improve the uniformity. Alternatively,
a single photoluminescent layer 38 having two types of
photoluminescent material with the above emission spectra may be
utilized.
[0100] In another embodiment a trichromatic approach is employed.
For example, blue light-emitting elements may be employed as
described above, with two photoluminescent layers 38 and/or two
types of photoluminescent particles 128. A first photoluminescent
layer 38 and/or type of photoluminescent particles 128 may include
or consist essentially of phosphor molecules with an absorption
spectrum in the blue range and an emission spectrum extending to
the yellow range as described above, and a second photoluminescent
layer 38 and/or type of photoluminescent particles 128 may include
or consist essentially of phosphor molecules with an absorption
spectrum in the blue range and an emission spectrum extending to
the red range (e.g., cerium-activated yttrium aluminum garnet doped
with a trivalent ion of praseodymium, or europium-activated
strontium sulphide). The unabsorbed blue light, the yellow light,
and the red light blend to appear as white light to an
observer.
[0101] Also contemplated is a configuration is which light-emitting
elements 34 with different emission spectra are employed and
several photoluminescent layers 38 are deposited and/or several
types of photoluminescent particles 128 are distributed, such that
the absorption spectrum of each photoluminescent layer 38 and/or
type of photoluminescent particles 128 overlaps one of the emission
spectra of the light-emitting elements 34, and all the emitted
colors (of the light-emitting elements 34 and the photoluminescent
layers 38 and/or particles 128) blend to appear as white light. The
advantage of such a multi-chromatic configuration is that it
provides a high-quality white balance because it allows better
control of the various spectral components of the light in a
localized manner, e.g., along an edge or surface of device 10.
[0102] The color composite of the white output light depends on the
intensities and spectral distributions of the emanating light
emissions. These depend on the spectral characteristics and spatial
distribution of the light-emitting elements 34, and, in the
embodiments in which one or more photoluminescent components
(layers 38 and/or particles 128) are employed, on the spectral
characteristics of the photoluminescent components and on the
amount of unabsorbed light. The amount of light unabsorbed by the
photoluminescent components is, in turn, a function of the
characteristics of the components, e.g., thickness of the
photoluminescent layer(s) 38, density of photoluminescent
material(s), and the like. By judiciously selecting the emission
spectra of light-emitting element 34 and optionally the thickness,
density, and spectral characteristics (absorption and emission
spectra) of photoluminescent layer 38 and/or particles 128, device
10 may provide substantially uniform white light.
[0103] In any of the above embodiments, the "whiteness" of the
light may be tailored according to the specific application for
which device 10 is intended. For example, when device 10 is
incorporated as backlight of an LCD device, the spectral components
of the light provided by device 10 may be selected in accordance
with the spectral characteristics of the color filters of the
liquid crystal panel. In other words, since a typical liquid
crystal panel includes an arrangement of color filters operating at
a plurality of distinct colors, the white light provided by device
10 includes at least at the distinct colors of such filters. This
configuration significantly improves the optical efficiency as well
as the image quality provided by the LCD device, because the
optical losses due to mismatch between the spectral components of
the backlight unit and the color filters of the liquid crystal
panel are reduced or eliminated.
[0104] Thus, in the embodiment in which the white light is achieved
by light-emitting elements 34 emitting different colors of light
(e.g., red light, green light and blue light), the emission spectra
of the light-emitting elements 34 are preferably selected to
substantially overlap the characteristic spectra of the color
filters of an LCD panel. In the embodiment in which device 10 is
supplemented by one or more photoluminescent components (layers 38
and/or particles 128), the emission spectra of the photoluminescent
components and optionally the emission spectrum (or spectra) of the
light-emitting elements are preferably selected to overlap the
characteristic spectra of the color filters of an LCD panel.
Typically, the overlap between a characteristic emission spectrum
and a characteristic filter spectrum is about 70% spectral overlap,
more preferably about 80% spectral overlap, and even more
preferably about 90%.
[0105] The following is a description of a production process for
the core layer 16 and the optical waveguide device 10 according to
various exemplary embodiments of the present invention.
[0106] In some embodiments, the core layer is formed by
coextrusion. As used herein, the term "coextrusion" refers to the
process of simultaneous extrusion of several die outputs which are
welded together before chilling to form an extrudate having an open
shape, e.g., a non-tubular sheet. An extrudate formed by a
coextrusion process according to some embodiments of the present
invention may be a single-layer structure or a laminate structure
having two or more layers. In some embodiments of the present
invention the coextrusion process is employed in an extrusion
coating process in which an extrudate formed by the coextrusion
process is applied so as to coat one or more existing layers.
[0107] Thus, a plurality of light-transmissive compositions in a
molten or plastic state may be coextruded to form the elongated
core structures of core layer 16. Each light-transmissive
composition may be extruded to form a single core structure 18, and
may be a polymeric material mixed with light-scattering particles
of type, size and concentration selected to provide the core
structure 18 with the desired optical properties (e.g., mean free
path).
[0108] A coextrusion apparatus 50 which may be used according to
some embodiments of the present invention is schematically
illustrated in FIG. 5. As shown therein, several melt or
plasticized streams 52 (three in the illustration) are individually
extruded from a plurality of extruders 54. The melt streams
comprise light-transmissive compositions in accordance with the
respective core structures 18 to be formed. Extruders 54 discharge
the compositions, which are conveyed by conventional conduits (not
shown) to a coextrusion die or feedblock 56. Die 56 combines and
arranges the compositions and issues a composite flat stream 58 in
which the various compositions flow side-by-side. A chill roller
system 60 quenches stream 58 to form core layer 16 which includes
or consists essentially of a plurality of core structures 18 as
described above. The formed core structures 18 may have any shape
or cross-section, e.g., rectangular or triangular.
[0109] One or more of the extruded core structures 18 (e.g., the
sidemost elongated structure 18-1 and 18-n, see FIG. 1a) may be
made reflective. This may be achieved by judicious selection of the
composition from which these core structures are formed. For
example, a composition characterized by high refractive index
(e.g., 2 or more) may be fed to the respective extruder 54. A
representative example of a material having a sufficiently high
refractive index for reflectivity is TiO.sub.2, which has a
refractive index of about 2.5. Also contemplated, is the use or
incorporation of a substantially opaque composition or the
incorporation of reflective particles at a sufficiently high
density to make core structure 18 reflective.
[0110] Coextrusion apparatus 50 may be adapted to simultaneously
form the core layer 16 as well as the cladding layers 12, 14. This
approach is illustrated in FIG. 6, which shows apparatus 50 with a
die 56 configured to combine and arrange the compositions into a
laminated flat stream 58 in which the intermediate layer of stream
58 is composed of side-by-side flow of the various compositions of
the core layer 16 and the outer layers of the stream are composed
of the compositions of the cladding layers 12, 14. In an
embodiment, additional layers are formed above and below the
cladding layers 12, 14, e.g., for the purpose of protecting or
reenforcing the cladding layers 12, 14.
[0111] An alternative embodiment is illustrated in FIGS. 7a and 7b.
In this embodiment, apparatus 50 performs an extrusion coating
process, whereby the core structures 18 of core layer 16 are
coextruded on a cladding layer 12 which is already in a
dimensionally stable (i.e., rigid) state. Once core layer 16 is
dimensionally stable (e.g., following cooling, or treatment with
roller system 60), cladding layer 14 may optionally be laminated on
core layer 16 to form a three-layer structure.
[0112] Once the core layer 16 and optionally the cladding layers
12, 14 are coextruded, the layer(s) may be further treated while
the compositions are in molten or plastic state. One example of
such treatment is application of heat and/or pressure so as to at
least partially mix respective compositions at common edges of
adjacent core structures 18. When the adjacent core structures 18
have different particle concentrations (including the case of two
adjacent structures in which one has a zero concentration and the
other has a non-zero concentration), the heat and/or pressure
treatment may result in a concentration gradient across the lateral
direction of the core structures 18. This embodiment is
particularly useful when it is desired to have a smooth profile
along the optical mean free path. Post-extrusion treatment of the
formed core structures 18 may be performed by roller system 60
(prior to the cooling of the extruded structures), or it may be
done using another roller system. When the compositions comprise
thermoplastic materials, the post- extrusion treatment may be
performed after the structures are cooled. In this embodiment, the
post-extrusion treatment may include reheating of the core
structures.
[0113] The optical waveguide device featured in embodiments of the
present invention may also be manufactured by a lamination process.
Suitable lamination processes may be employed on both thermoset and
theremoplastic materials. Any lamination technique suitable for the
materials from which core layer 16 and cladding layers 12, 14 are
formed may be employed. The lamination process may be executed with
or without a solid support. When a solid support (e.g., a metal
support or other rigid support) is employed, it is preferably
designed and constructed to allow lamination of individual core
structures 18 in a side-by-side fashion. Thus, the solid support
preferably fixes each individual core structure 18 to its place
sidewise with a previously laminated elongated structure.
[0114] A lamination technique according to various embodiments is
schematically illustrated in FIGS. 8a-8c. The process starts with a
substrate 62 (FIG. 8a), on which the lamination process is
executed. The process continues with the lamination of a plurality
of core structures 18 (e.g., elongated core structures) in a
side-by-side configuration on a substrate 62 to form core layer 16
(FIG. 8b). The lamination may be performed by heat-and-press, with
or without adhesives. Optionally, but not obligatorily, substrate
62 may serve as a cladding layer (e.g., layer 12 of FIGS. 1c-1e or
1g). In this embodiment, substrate 62 preferably includes or
consists essentially of a flexible cladding material and is
preferably laid on a support substrate (not shown), which is
desirably planar.
[0115] One or more light-reflective structures may be laminated
sidewise relative to core layer 16. This may be done in a similar
manner to the lamination of the other core structures 18.
[0116] Once laminated side-by-side, the core structures 18 may be
joined at their common ends using any technique known in the art,
including, without limitation, adhesive bonding, solvent bonding,
or welding (also known as fusion bonding). The lamination of core
16 on substrate 62 may be preceded by a step in which an adhesive
optical material is applied on substrate 62. If desired, substrate
62 may be removed following the lamination of the core structures
18. It this embodiment, the air serves as the "cladding" layer as
detailed above.
[0117] In various exemplary embodiments of the invention the
process continues by laminating cladding layer 14 on core layer 16
(FIG. 8c). Optionally, an optical adhesive may be applied on core
layer 16 prior to the lamination of cladding layer 14 thereon.
[0118] An additional technique for fabricating device 10 is
illustrated in FIGS. 9a-9c. The process starts with substrate 62
(FIG. 9a). A plurality of core structures 18 having the shape of
plaques are tiled in a side-by-side configuration on a substrate 62
to form core layer 16 (FIG. 9b). The tiling may be performed by
lamination techniques such as heat-and-press, with or without
adhesives. Optionally, but not obligatorily, substrate 62 may serve
as a cladding layer (e.g., layer 12 of FIGS. 1c-e or 1g). In this
embodiment, substrate 62 is made of a flexible cladding material
and is preferably laid on a support substrate (not shown), which is
preferably planar.
[0119] One or more light-reflective structures may be laminated
sidewise relative to core layer 16. This may be done in a similar
manner to the lamination of the other core structures 18.
[0120] Once laminated side-by-side, the core structures 18 may be
joined at their common ends using any technique known in the art,
including, without limitation, adhesive bonding, solvent bonding,
or welding. The lamination of core 16 on substrate 62 may be
preceded by a step in which an adhesive optical material is applied
on substrate 62. If desired, substrate 62 may be removed following
the lamination of the core structures 18. In this embodiment, the
air serves as the "cladding" layer as detailed above. In various
exemplary embodiments of the invention the process continues by
laminating cladding layer 14 on core layer 16 (FIG. 9c).
Optionally, an optical adhesive may be applied on core layer 16
prior to the lamination of cladding layer 14 thereon.
[0121] Following the lamination process of any of the above
embodiments, one or more additional layers (not shown) may be
attached to cladding layers 12 and/or 14. This may be achieved
using any procedure known in the art, including, without
limitation, printing, embossing, lamination, and the like. The
attachment of the additional layers may be performed using any
technique, including, without limitation, adhesive bonding, solvent
bonding, welding, mechanical fastening, co-consolidation, and the
like. The additional layer may cover the entire surface area of the
cladding or a portion thereof. For example, a reflective foil 36
(see, e.g., FIG. 1a) may be attached to cladding layer 14. Also
contemplated are jacket layers for protecting the cladding layers
12, 14.
[0122] An additional technique for fabricating device 10 according
to some embodiments of the present invention is illustrated in
FIGS. 10a-10c. In these embodiments co-injection molding is
employed. Co-injection molding is a variant of a process known as
injection molding. In injection molding thermoplastic polymers or
the like are fed from a hopper into a barrel, melted by a
reciprocating screw and/or electric heat, and are propelled forward
by a ram (piston, plunger) or the screw (used as a plunger) into a
mold cavity, which is cooled to below the heat-distortion
temperature of the resin.
[0123] Co-injection molding takes advantage of a characteristic of
injection molding called fountain flow. As the cavity is filled,
the material at the melt front moves from the center line of the
stream to the cavity walls. The walls are typically kept below the
transition temperature of the melt such that the material that
touches the walls cools rapidly and freezes in place. This provides
insulating layers through which new melt makes its way to the melt
front.
[0124] In some embodiments of the present invention, the
co-injection technique is employed for forming a core layer 16
having a plurality of core structures 18 in a nested configuration.
A co-injection molding system suitable for the present embodiments
is illustrated in FIG. 10a. The system typically includes a
co-injection manifold 230 mounted relative to a mold cavity 220,
and shaped according to the desired shape of the device. In various
exemplary embodiments of the invention, mold cavity 220 has a
substantially planar shape.
[0125] Manifold 230 includes a nozzle housing 234 having forward
and rearward ends. The illustrated nozzle housing 234 is generally
V-shaped, but any other shape suitable for co-injection may be
utilized. Nozzle housing 234 includes a plurality of arms 254, each
having a rearward end 262, and includes an outwardly extending
mounting portion 266. Arms 254 are supported by mounting columns
236, which are typically fixedly mounted on a horizontal surface of
a machine base sled (not shown).
[0126] Housing 234 has an outlet 270 in its forward end, as well as
a plurality of inlets 274 in the rearward end of each arm. Outlet
270 communicates with an inlet 226 of cavity 220. Inlets 274 of
housing 234 respectively communicate with a plurality of injection
nozzles 284 of respective injection units (not shown). Each
injection nozzle is typically fed by a different light-transmissive
composition as described above.
[0127] Manifold 230 also includes a valve 258 movable between a
plurality of positions. In each position, valve 258 open a fluid
communication channel between one of inlets 274 and outlet 270.
Also contemplated is a position in which valve 258 closes all
communication channels. Valve 258 may be moved relative to housing
234 by a hydraulic cylinder 278 mounted on the manifold 230.
[0128] The co-injection system may operate as follows. The nozzle
housing is oriented such that each injection nozzle provides one
type of light-transmissive composition. The co-injection process
begins with the valve 258 in a position selected such that a first
light-transmissive composition (e.g., a composition with low
concentration of light-scattering particles), in a molten or
plastic state, flows through the outlet 270. The selected
composition is injected into the mold cavity 220. The valve 258 is
then moved to another position to allow flow of a second
light-transmissive composition (e.g., a composition with a higher
concentration of light-scattering particles), in a molten or
plastic state, through the outlet 270. By the effect of fountain
flow described above, the second composition is nested into the
first composition. The process is optionally continued by
repositioning the valve 258 so as to inject into the mold a third
composition in a molten or plastic state. The third composition is
nested into the previously injected second composition. The third
composition may have a concentration of light-scattering particles
higher than that of the second composition.
[0129] Any number of light-transmissive compositions may be
serially injected into the mold so as to form a core layer 16 with
a plurality of core structures 18 (which may be flexible) joined in
a nested configuration. The melt fronts of the different
light-transmissive compositions are designated in FIG. 10a by
reference numerals 222-1, . . . , 222-n. The propagation of each
melt front nesting into previously injected light-transmissive
compositions is shown by arrows. An advantage of using a
co-injection manifold for manufacturing the core layer 16 is that
it allows more flexibility in selecting the characteristics of the
different core structures 18. A continuous or semi-continuous
control on the operation of the co-injection manifold may
facilitate formation of core structures 18 in a manner such that
the characteristic mean free path varies substantially smoothly
from one core structure 18 to the other. Since the effective
refractive index varies with the characteristic mean free path,
various embodiments of the present invention allow production of an
optical waveguide device 10 having a graded effective refractive
index along the lateral direction.
[0130] Once the core layer 16 is formed, it is typically released
from the mold. A top view of the core layer 16 once released from
the mold is illustrated in FIG. 10b. The procedure optionally and
preferably continues by cutting the core layer 16 along the lateral
direction so as to remove one or more marginal regions 228
therefrom, thereby providing a core layer 16 in which the core
structures 18 are joined in a side-by-side configuration. Shown in
FIG. 10b are two cut lines 224 parallel to the lateral direction
along which the core layer may be cut. A top view of the core layer
16 once cut along cut lines 224 is illustrated in FIG. 10c. The
procedure may continue to form additional layers such as cladding
layers 12, 14, and/or photoluminescent layers 38 on the core
structure 16 as detailed above. In some embodiments of the present
invention, the co-injection system is configured to inject also the
cladding layers 12, 14.
[0131] Referring to FIG. 11, in various embodiments of the
invention, multilayer optical waveguide device 100 comprises
multiple waveguide devices 10, each of which may be fabricated as
described above. The devices 10 in multilayer device 100 may be
disposed in a vertically "stacked" configuration as depicted in
FIG. 11. A layer 1100 of low-refractive-index material may be
disposed between each "layer" 10 in order to prevent undesired
light propagation from one layer 10 to another. Light may be
coupled in to zone 30 of each layer 10 from a different light
source, or the same light source may be utilized for each layer 10.
In a particular embodiment, multilayer device 100 provides
controllable RGB illumination by including different types of
photoluminescent particles 128 in each layer 10. For example, a
bottom layer 10 may include photoluminescent particles 128 that
emit red light, a middle layer 10 may include photoluminescent
particles 128 that emit green light, and a top layer 10 may include
photoluminescent particles 128 that emit blue light. Such a
multicolor multilayer device 100 may be suitable for LCD backlight
applications. As shown in FIG. 11, the zones 28 of the layers 10
may be substantially vertically aligned such that light emitted
from the bottom layer 10 travels through the other layers 10 before
finally being emitted from multilayer device 100. In other words,
each zone 28 in multilayer device 100 may have substantially no
vertical overlap with zones 26, 30 of the other layers 10.
[0132] Referring to FIGS. 12a and 12b, in various embodiments of
the invention, multiple optical waveguide devices 10 are utilized
together to provide enhanced functionality. Illumination panel 1200
includes or consists essentially of a plurality of optical
waveguide devices 10 attached together at their edges (or
overlapped) in a "tiled" fashion. In order to provide substantially
uniform illumination across the entire surface of illumination
panel 1200, the waveguide devices 10 may be tiled together such
that only out-coupling region 28 of each device 10 is visible.
In-coupling region 30 and propagation region 26 of each device 10
may therefore be disposed beneath adjoining devices 10 and not
visible. While illumination panel 1200 is illustrated as
substantially planar, the flexibility of each waveguide device 10
enables illumination panel 1200 to be configured in a variety of
shapes, including curved sheets and even spheres.
[0133] Illumination panel 1200 may be utilized to provide
substantially uniform illumination in a variety of applications.
For example, illumination panel 1200 may itself be utilized as a
luminaire for lighting applications. In another embodiment,
illumination panel 1200 is utilized as a backlight unit for a
display device 1210, e.g., a liquid crystal display (LCD). Display
device 1210 may additionally include an LCD panel 1220 defining a
plurality of pixels, and may be actuated by signals received from
control circuitry 1230.
[0134] Referring to FIG. 13, a phosphor layer 1302 may be added to
a light-emitting element 1300. The phosphor layer 1302 converts
light emitted from the in-coupling region 1304 from the light
source 1306, such as an LED, into a different color (i.e., changes
the spectrum). For example, part of the light from a blue LED may
be converted to yellow light, which mixes with the remaining blue
light to provide white output illumination. In other embodiments,
phosphor material is placed at any location in the optical path,
including locations without any direct line of sight from any light
source.
[0135] The waveguide materials from which the waveguide device 10
is made may include or consist essentially of one or more polymeric
materials. The polymeric material may optionally include a rubbery
or rubber-like material. The material may be formed by dip-molding
in a dipping medium, for example, a hydrocarbon solvent in which a
rubbery material is dissolved or dispersed. The polymeric material
optionally and preferably has a predetermined level of
cross-linking, which is preferably between particular limits. The
cross-linking may optionally be physical cross-linking, chemical
cross-linking, or a combination thereof. A non-limiting
illustrative example of a chemically cross-linked polymer is
cross-linked polyisoprene rubber. Non-limiting illustrative
examples of physically cross-linked polymers include cross-linked
block co-polymers and segmented co-polymers, which may be
cross-linked due to, e.g., micro-phase separation. The material is
optionally cross-linked through application of radiation, such as,
but not limited to, electron beam radiation and/or electromagnetic
(e.g., ultraviolet) radiation.
[0136] Although not limited to rubber itself, the material
optionally and preferably has the physical characteristics (e.g.,
parameters relating to tensile strength and elasticity) of rubber.
For example, the waveguide material may be characterized by a
tensile set value which is below 5%. The tensile set value
generally depends on the degree of cross-linking and is a measure
of the ability of a flexible material, after having been stretched
either by inflation or by an externally applied force, to return to
its original dimensions upon deflation or removal of the applied
force.
[0137] The tensile set value may be determined by, for example,
placing two reference marks on a strip of the waveguide material
and noting the distance between them, stretching the strip to a
certain degree, for example, by increasing its elongation to 90% of
its expected ultimate elongation, holding the stretch for a certain
period of time, e.g., one minute, then releasing the strip and
allowing it to return to its relaxed length, and re-measuring the
distance between the two reference marks. The tensile set value is
then determined by comparing the measurements before and after the
stretch, subtracting one from the other, and dividing the
difference by the measurement taken before the stretch. In a
preferred embodiment, using a stretch of 90% of an expected
ultimate elongation and a holding time of one minute, the preferred
tensile set value is less than 5%. Also contemplated are materials
having about 30% plastic elongation and less than 5% elastic
elongation.
[0138] Other exemplary materials, which may optionally be used
alone or in combination with each other, or with one or more of the
above rubber materials, include but are not limited to, crosslinked
polymers such as: polyolefins, including but not limited to,
polyisoprene, polybutadiene, ethylene-propylene copolymers,
chlorinated olefins such as polychloroprene (neoprene) block
copolymers, including diblock-, triblock-, multiblock- or
star-block-, such as: styrene-butadiene-styrene copolymers, or
styrene-isoprene-styrene copolymers (preferably with styrene
content from about 1% to about 37%), segmented copolymers such as
polyurethanes, polyether-urethanes, segmented polyether copolymers,
silicone polymers, including copolymers, and fluorinated polymers
and copolymers. In some embodiments of the present invention, the
waveguide material may include or consist essentially of IOTEK.
[0139] The embedded particles may be glass beads, BaSO.sub.4
particles, and/or similar particles. The volume density of the
particles may be from about 0.1% to about 5%.
[0140] The number of extruders used to fabricate the core layer 16
may number from three to approximately 10. When the cladding layers
12, 14 are formed simultaneously with the core layer 16 the number
of extruders may number from three to approximately 15. The total
width of the coextrusion die may be about 400 mm to about 1200 mm,
and it may be constructed and designed to provide from about 20 to
about 100 side-by-side core structures 18.
[0141] The thickness of the cladding layers 12, 14 may be about 10
.mu.m to about 100 .mu.m. The thickness of the core layer 16 may be
about 400 .mu.m to about 1300 .mu.m. The number of core structures
18 in the core layer may be approximately 20 structures to
approximately 100 structures. The width of a single core structure
18 may be about 5 mm to about 30 mm.
EXAMPLES
[0142] The core structures 18 of an optical waveguide device 10
were fabricated from polyurethane. Two outer in-coupling zones 30
were each approximately 22 mm wide and included 0.5% volume density
of VELVOLUX M synthetic BaSO.sub.4 particles (available from
Sachtleben Chemie GmbH of Duisburg, Germany) having approximate
diameters of 5 .mu.m. Propagation zones 26 were each approximately
29 mm wide and were substantially particle-free. The center
out-coupling zone 28 was approximately 77 mm wide, and was composed
of three core structures 18. The outer core structures 18 were
approximately 26 mm wide and included 0.35% volume density of
VELVOLUX M synthetic BaSO.sub.4 particles. The middle core
structure 18 of out-coupling zone 28 was approximately 25 mm wide
and contained 0.2% volume density of BLANC FIXE F synthetic
BaSO.sub.4 particles (also available from Sachtleben Chemie GmbH of
Duisburg, Germany) having approximate diameters of 1 .mu.m.
Out-coupling region 28 exhibited a nine-point average brightness of
approximately 9078 Nits, with a uniformity of approximately
10%.
[0143] Another optical waveguide device 10 was fabricated from
IOTEK, and included a propagation zone 26 that was substantially
particle-free and had a width of approximately 11 mm. Out-coupling
zone 28 was composed of three core structures 18. In increasing
distance from propagation zone 26, these core structures 18 were 1)
a 17 mm-wide region having 0.75% volume density of 5 .mu.m-diameter
BaSO.sub.4 particles, 2) a 10 mm-wide region having 1.5% volume
density of 5 .mu.m-diameter BaSO.sub.4 particles, and 3) a 10
mm-wider region having 3% volume density of 5 .mu.m-diameter
BaSO.sub.4 particles. Illumination from this out-coupling zone 28
was approximately uniform across its width.
[0144] The terms and expressions employed herein are used as terms
and expressions of description and not of limitation, and there is
no intention, in the use of such terms and expressions, of
excluding any equivalents of the features shown and described or
portions thereof. In addition, having described certain embodiments
of the invention, it will be apparent to those of ordinary skill in
the art that other embodiments incorporating the concepts disclosed
herein may be used without departing from the spirit and scope of
the invention. Accordingly, the described embodiments are to be
considered in all respects as only illustrative and not
restrictive.
* * * * *