U.S. patent application number 11/046586 was filed with the patent office on 2006-08-03 for apparatus having a photonic crystal.
Invention is credited to Herbert Thomas III Etheridge, Henry Lewis, Carol McConica.
Application Number | 20060171016 11/046586 |
Document ID | / |
Family ID | 36710584 |
Filed Date | 2006-08-03 |
United States Patent
Application |
20060171016 |
Kind Code |
A1 |
Etheridge; Herbert Thomas III ;
et al. |
August 3, 2006 |
APPARATUS HAVING A PHOTONIC CRYSTAL
Abstract
An apparatus, including a substrate, where at least a portion of
the substrate has a convex surface, and a photonic crystal disposed
over the convex surface. The photonic crystal is substantially
conformal to at least a portion of the convex surface.
Inventors: |
Etheridge; Herbert Thomas III;
(Corvallis, OR) ; Lewis; Henry; (Corvallis,
OR) ; McConica; Carol; (Corvallis, OR) |
Correspondence
Address: |
HEWLETT PACKARD COMPANY
P O BOX 272400, 3404 E. HARMONY ROAD
INTELLECTUAL PROPERTY ADMINISTRATION
FORT COLLINS
CO
80527-2400
US
|
Family ID: |
36710584 |
Appl. No.: |
11/046586 |
Filed: |
January 28, 2005 |
Current U.S.
Class: |
359/321 |
Current CPC
Class: |
G02B 1/005 20130101;
G02B 1/00 20130101; H01K 1/04 20130101; H01K 1/14 20130101; B82Y
20/00 20130101; H01K 3/02 20130101 |
Class at
Publication: |
359/321 |
International
Class: |
G02F 1/00 20060101
G02F001/00 |
Claims
1. An apparatus, comprising: a substrate, wherein at least a
portion of said substrate has a convex surface; and a photonic
crystal disposed over said convex surface, wherein said photonic
crystal is substantially conformal to at least a portion of said
convex surface.
2. An apparatus, comprising: a substrate, wherein at least a
portion of said substrate has a convex surface: and a colloidal
photonic crystal disposed over said convex surface, wherein said
colloidal crystal is substantially conformal to at least a portion
of said convex surface.
3. The apparatus in accordance with claim 2, wherein said colloidal
crystal further comprises: a plurality of first spheres having a
first diameter; and a plurality of second spheres having a second
diameter.
4. The apparatus in accordance with claim 3, wherein said colloidal
crystal further comprises a first layer having said plurality of
first spheres, and a second layer having said plurality of second
spheres.
5. The apparatus in accordance with claim 3, wherein said colloidal
crystal further comprises a first layer having said plurality of
first spheres and an n th layer having said plurality of second
spheres, wherein n is an integer greater than one.
6. The apparatus in accordance with claim 3, wherein said colloidal
crystal further comprises a first layer having said plurality of
first spheres alternating with a second layer having said plurality
of second spheres.
7. The apparatus in accordance with claim 3, wherein said colloidal
crystal further comprises a first group of layers having said
plurality of first spheres alternating with a second group of
layers having said plurality of second spheres.
8. The apparatus in accordance with claim 3, wherein said plurality
of first spheres and said plurality of second spheres form a binary
colloidal crystal.
9. The apparatus in accordance with claim 2, wherein said colloidal
crystal further comprises metal spheres.
10. The apparatus in accordance with claim 2, wherein said
colloidal crystal further comprises spheres having a differential
solubility over an infiltration material.
11. The apparatus in accordance with claim 2, wherein said
colloidal photonic crystal further comprises a layer of
spheres.
12. The apparatus in accordance with claim 2, wherein said
colloidal photonic crystal further comprises a photonic band gap
crystal.
13. The apparatus in accordance with claim 2, wherein said
colloidal photonic crystal further comprises a spatially periodic
structure.
14. An apparatus, comprising: a substrate, wherein at least a
portion of said substrate has a convex surface; and an inverse opal
crystal structure disposed over said convex surface, wherein said
inverse opal crystal structure is substantially conformal to at
least a portion of said convex surface.
15. The apparatus in accordance with claim 14, wherein said inverse
opal crystal structure includes a refractory metal.
16. The apparats in accordance with claim 2, wherein said convex
surface further comprises a substantially cylindrically shaped
surface.
17. The apparatus in accordance with claim 16, wherein said
substantially cylindrically shaped surface further comprises a
filament.
18. The apparatus in accordance with claim 17, wherein said
filament further comprises a metal wire.
19. The apparatus in accordance with claim 17, wherein said metal
wire further comprises a refractory metal wire.
20. The apparatus in accordance with claim 17, wherein said
filament further comprises an optical fiber.
21. The apparatus in accordance with claim 16, wherein said
substantially cylindrically shaped surface further comprises a
tubularly-shaped structure having an outer surface, wherein said
colloidal photonic crystal is disposed over and conformal to at
least a portion of said outer surface of said tube.
22. The apparatus in accordance with claim 21, wherein said
tubularly shaped substrate is substantially optically transparent
in the visible portion of the electromagnetic spectrum.
23. The apparatus in accordance with claim 21, further comprising a
metal wire disposed at least partially within said tubularly shaped
substrate.
24. The apparatus in accordance with claim 23, wherein said metal
wire further comprises a spirally wound metal wire filament.
25. The apparatus in accordance with claim 24, wherein said
spirally wound metal wire filament further comprises a photonic
crystal conformal to and disposed on at least a portion of said
spirally wound metal wire filament.
26. The apparatus in accordance with claim 2, wherein said convex
surface forms at least a portion of an optical component such as a
lens.
27. The apparatus in accordance with claim 26, where in said lens
further comprises a rod lens.
28. The apparatus in accordance with claim 2, wherein said
substrate further comprises a tubularly shaped substrate having at
least a portion of an external surface of said tubularly shaped
substrate forming said convex surface.
29. The apparatus in accordance with claim 28, wherein said
colloidal photonic crystal is disposed over and conformal to said
external surface of said tubularly shaped substrate.
30. The apparatus in accordance with claim 29, further comprising a
metal wire disposed at least partially within said tubularly shaped
substrate.
31. The apparatus in accordance with claim 30, wherein said metal
wire further comprises a spirally wound metal wire filament.
32. The apparatus in accordance with claim 31, wherein said
spirally wound metal wire filament further comprises a photonic
crystal conformal to and disposed on at least a portion of said
spirally wound metal wire filament.
33. The apparatus in accordance with claim 2, wherein said
substrate further comprises a rod-like substrate.
34. The apparatus in accordance with claim 33, wherein said
rod-like structure further comprises a filament.
35. The apparatus in accordance with claim 34, wherein said
filament further comprises a metal wire.
36. The apparatus in accordance with claim 35, wherein said metal
wire further comprises a refractory metal wire.
37. The apparatus in accordance with claim 34, wherein said metal
wire further comprises a spirally wound metal wire.
38. The apparatus in accordance with claim 37, wherein said
spirally wound metal wire further comprises a photonic crystal
conformal to and disposed on at least a portion of said spirally
wound metal wire.
39. The apparatus in accordance with claim 2, wherein said
substrate further comprises said substrate having an external
closed surface.
40. The apparatus in accordance with claim 2, wherein said
substrate further comprises a conically-shaped substrate.
41. The apparatus in accordance with claim 2, wherein said
substrate further comprises a spherically-shaped substrate.
42. The apparatus in accordance with claim 2, wherein said
substrate further comprises cylindrically-shaped substrate having a
cylindrical axis, wherein said colloidal photonic crystal
substantially encircles said cylindrical axis.
43. The apparatus in accordance with claim 42, further comprising
an inner photonic crystal disposed on an internal surface of said
cylindrically shaped substrate, wherein said inner photonic crystal
substantially encircles said cylindrical axis.
44. The apparatus in accordance with claim 42, further comprising a
metal wire disposed in said cylindrically-shaped substrate and
substantially coaxial with said cylindrical axis.
45. A method of manufacturing a photonic crystal, comprising
forming an inverse opal photonic crystal over at least a portion of
a convex surface, wherein the inverse opal photonic crystal is
conformal to at least a portion of said convex surface.
46. A method of manufacturing an apparatus, comprising forming at
least one layer of spheres over a convex surface of a substrate,
wherein said at least one layer of spheres is conformal to said
convex surface.
47. The method in accordance with claim 46, forming at least one
layer of spheres further comprises forming multiple layers of
spheres over and conformal to said convex surface of said
substrate, wherein said multiple layers include void spaces between
said spheres.
48. A method of manufacturing a photonic apparatus, further
comprising: forming two or more layers of spheres over and
conformal to a convex surface of a substrate; and forming a second
material in said void spaces.
49. The method in accordance with claim 48, further comprising
substantially filling said void spaces with said second
material.
50. The method in accordance with claim 49, further comprising
removing said spheres to form an inverse opal crystal.
51. The method in accordance with claim 48, wherein said spheres
have a sphere dielectric constant and said second material has a
dielectric constant different from said sphere dielectric
constant.
52. The method in accordance with claim 48, further comprising
immersing said convex surface in a mixture of spheres and a
solvent.
53. The method in accordance with claim 52, wherein immersing said
convex surface further comprises immersing said convex surface so
that a long axis of said convex surface is substantially
perpendicular to a meniscus formed by said mixture.
54. The method in accordance with claim 48, further comprising
suspending said convex surface in a mixture of spheres and a
solvent.
55. The method in accordance with claim 54, wherein suspending said
convex surface further comprises suspending said convex surface so
that a long axis of said convex surface is substantially
perpendicular to a meniscus formed by said mixture.
56. The method in accordance with claim 48, further comprising
cleaning said convex surface.
57. The method in accordance with claim 48, wherein forming at
least one layer of spheres further comprises forming at least one
layer of spheres utilizing a mixture of spheres in a solvent.
58. The method in accordance with claim 57, further comprising
removing said solvent.
59. The method in accordance with claim 58, wherein removing said
solvent further comprises evaporating said solvent.
60. The method in accordance with claim 48, further comprising
forming a sacrificial layer over at least a portion of a substrate
that forms said convex surface.
61. The method in accordance with claim 48, further comprising
etching a substrate that forms said convex surface.
62. A method of using an inverse opal photonic crystal, comprising
transmitting at least a portion of the electromagnetic spectrum
through a convex surface forming at least a portion of the inverse
opal photonic crystal.
63. The method in accordance with claim 62, further comprising
heating an incandescent filament, wherein at least a portion of the
inverse opal photonic crystal encircles said incandescent
filament.
64. The method in accordance with claim 63, wherein the inverse
opal photonic crystal is disposed on said incandescent
filament.
65. The method in accordance with claim 64, wherein said
incandescent filament includes a refractory metal.
66. The method in accordance with claim 63, wherein the inverse
opal photonic crystal further comprises a tubularly-shaped inverse
opal photonic crystal, and said incandescent filament is disposed
within said tubularly-shaped inverse opal photonic crystal.
67. A method of using a photonic crystal, comprising heating an
incandescent filament disposed within a tubularly-shaped photonic
crystal substantially encircling said incandescent filament.
68. An apparatus, comprising: substrate, wherein at least a portion
of said substrate has a convex surface, and means for forming a
colloidal photonic crystal disposed over and substantially
conformal to said convex surface.
69. The apparatus in accordance with claim 68, wherein said means
for forming said colloidal photonic crystal further comprises
forming a polymeric colloidal crystal.
70. The apparatus in accordance with claim 68, wherein said means
for forming said colloidal photonic crystal further comprises
forming a photonic band gap crystal.
71. The apparatus in accordance with claim 70, wherein said means
for forming said colloidal photonic crystal further comprises
forming a refractory metal colloidal photonic crystal.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is related to co-pending and commonly
assigned application Ser. No.______ filed on the same day herewith
(attorney docket no. 20050418 by Herbert T. Etheridge III, Henry D.
Lewis and Carol M. McConica and entitled "Apparatus Having a
Photonic Crystal."
BACKGROUND
Description of the Art
[0002] As the demand for cheaper and higher performance electronic
devices continues to increase there is a growing need to develop
higher yield lower cost manufacturing processes for electronic
devices especially in the area of optical devices. In particular
there is a demand for higher performance as well as improved
efficiency in lighting technology.
[0003] Although incandescent lamps are inexpensive and the most
widely utilized lighting technology in use today, they are also the
most inefficient lighting source in regards to the amount of light
generated per unit of energy consumed. An incandescent lamp works
by heating a filament, typically tungsten, to a very high
temperature so that it radiates in the visible portion of the
electromagnetic spectrum. Unfortunately, at such high temperatures
the filament radiates a considerable amount of energy in the
non-visible infrared region of the electromagnetic spectrum.
[0004] If these problems persist, the continued growth and
advancements in the use of opto-electronic devices, especially in
the area of photonic crystals, in various electronic products, will
be reduced. In areas like consumer electronics, the demand for
cheaper, smaller, more reliable, and higher performance electronics
constantly puts pressure on improving and optimizing performance of
ever more complex and integrated devices. The ability to optimize
lighting performance efficiency will open up a wide variety of
applications that are currently either impractical, or are not cost
effective.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1a is a perspective view of a portion of a substrate
having spheres disposed thereon according to an embodiment of the
present invention.
[0006] FIG. 1b is a cross-sectional view of a portion of the
substrate shown in FIG. 1a.
[0007] FIG. 1c is a cross-sectional view of a portion of a
substrate according to an alternate embodiment of the present
invention.
[0008] FIG. 2a is a perspective view of a colloidal crystal formed
on a cylindrically shaped substrate according to an alternate
embodiment of the present invention.
[0009] FIG. 2b is a cross-sectional view along 2b-2b of the
colloidal crystal shown in FIG. 2a.
[0010] FIG. 3a is a perspective view of a colloidal crystal formed
on the outer surface of a tubular shaped substrate according to an
alternate embodiment of the present invention.
[0011] FIG. 3b is a cross-sectional view along 3b-3b of the
colloidal crystal shown in FIG. 3a.
[0012] FIG. 3c is a cross-sectional view of a colloidal crystal
according to an alternate embodiment of the present invention.
[0013] FIG. 4 is a perspective view of an incandescent source
according to an embodiment of the present invention.
[0014] FIG. 5 is a perspective view of an incandescent source
according to an alternate embodiment of the present invention.
[0015] FIG. 6a is a perspective view of a portion of a colloidal
crystal according to an embodiment of the present invention.
[0016] FIG. 6b is a perspective view of a portion of an inverse
opal crystal according to an alternate embodiment of the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0017] This invention is directed to various photonic structures
utilizing colloidal crystals. The present invention includes a wide
variety of photonic structures formed on, over or both on and over
curved surfaces including, for example, wires and fiber optic
cables. Photonic crystals, typically, are spatially periodic
structures having useful electromagnetic wave properties, such as
photonic band gaps. Photonic crystals, for example, having the
proper lattice spacing, offer the potential of improving the
luminous efficacy of an incandescent lamp by modifying the
emissivity of the tungsten filament. Such a filament, incorporated
into a photonic crystal or encircled or surrounded by a photonic
crystal, would emit a substantial fraction of its radiation in the
visible portion of the spectrum and little or no light in the
non-visible portions such as the infrared portion of the
electromagnetic spectrum. Since many filaments, including spirally
wound filaments, utilized as incandescent sources have a large
degree of cylindrical symmetry the ability to form photonic
crystals on curved surfaces provides for simpler manufacturing
processes to make incandescent light sources, having a lower cost,
and a higher luminous efficiency. In addition, such a colloidal
crystal may also be formed on an optical fiber to deter loss of
light at desired wavelengths.
[0018] It should be noted that the drawings are not true to scale.
Further, various elements have not been drawn to scale. Certain
dimensions have been exaggerated in relation to other dimensions in
order to provide a clearer illustration and understanding of the
present invention. In particular, vertical and horizontal scales
may differ and may vary from one drawing to another. In addition,
although some of the embodiments illustrated herein are shown in
two dimensional views with various regions having height and width,
it should be clearly understood that these regions are
illustrations of only a portion of a device that is actually a
three dimensional structure. Accordingly, these regions will have
three dimensions, including length, width, and height, when
fabricated on an actual device.
[0019] Moreover, while the present invention is illustrated by
various embodiments, it is not intended that these illustrations be
a limitation on the scope or applicability of the present
invention. Further, it is not intended that the embodiments of the
present invention be limited to the physical structures
illustrated. These structures are included to demonstrate the
utility and application of the present invention to presently
preferred embodiments.
[0020] An embodiment of apparatus 100 employing the present
invention is illustrated, in a perspective view, in FIG. 1a. In
this embodiment, apparatus 100 includes substrate 120 that includes
at least a portion of the substrate forming convex surface 112 over
which photonic crystal 102 is disposed. In addition, the photonic
crystal is formed substantially conformal to convex surface 112 as
illustrated in the cross-sectional view along 1b-1b in FIG. 1b. In
this embodiment, spheres 122 may be disposed on any substrate
having essentially a convex surface. Examples of such substrate
structures include, but are not limiting as to the nature of the
present invention, rod-like substrates, cylindrically shaped
substrates, tubularly shaped substrates, conically shaped
substrates, and substrates having a closed surface such as the
outer surface of a sphere. In still other embodiments, various
layers such as an adhesive layer or other layer having particular
optical or dielectric properties may be disposed between substrate
120 and photonic crystal 102. Photonic crystal 102, as illustrated
in FIGS. 1a-1c is what is commonly referred to as a colloidal
crystal or opaline crystalline array. The colloidal crystal is
formed utilizing spheres 122. In alternate embodiments, photonic
crystal 102 may also form what is commonly referred to as an
inverse opal structure where interstitial volume 124 between the
spheres is infiltrated and filled with a second material with the
optional subsequent removal of spheres 122. Typically, the optional
removal of the spheres after infiltration is completed will depend
on whether the interstitial material has a higher refractive index
than the spheres. In those cases where it is higher then the
spheres need not, but may, still be removed. Generally, photonic
crystal 102 will be formed utilizing multiple layers of spheres
having typically a close-packed geometry, as illustrated in a cross
sectional view in FIG. 1c, forming a face centered cubic
crystalline structure (FCC), a hexagonal close packed structure
(HCP), or other randomly stacked polycrystalline structure with
each sphere predominantly touching six other spheres in one layer.
However, in alternate embodiments other structures also may be
utilized including, for example, simple cubic, body centered cubic
and tetragonal packing. Further, in some embodiments, a single
layer of spheres may be desirable. In those embodiments, utilizing
multiple layers photonic crystal 102', as shown in FIG. 1c, may
also form a photonic band gap crystal. Substrate 120, in this
embodiment, may be formed from any material that has the desired
optical, chemical, and mechanical properties for utilization in
apparatus 100. For example, in one embodiment, substrate 120 may be
formed from various glasses for those applications desiring
substantial transparency in the visible portion of the
electromagnetic spectrum. In a second embodiment, substrate 120 may
be a metal wire such as tungsten or a tungsten alloy for those
applications desiring substantial emission in the infrared or
visible portion of the electromagnetic spectrum (e.g. an
incandescent source heated to a high temperature). Any metal or
alloy may be utilized the particular material chosen will depend on
the particular portion of the spectrum to be used and the desired
intensity. In still other embodiments, substrate 120 may be a fiber
in, for example, a fiber optic application or substrate 120 may be
utilized as an optical component such as a rod lens. Such fibers
and optical components may be formed from various glasses, polymers
or any other appropriate material having the desired optical
properties for the particular application in which it will be
utilized. Spheres 122, in this embodiment, may be formed from any
material that is formable into spheres and provides the desired
dielectric constant for the particular application in which the
photonic crystal is utilized. The size of the spheres generally
ranges from a few microns in diameter to a few nanometers in
diameter. Both the particular material utilized to form spheres 122
and the size of the spheres will depend on the particular optical
properties of the photonic crystal utilized in apparatus 100. For
example, silica or polymer spheres may be utilized in those
applications desiring a reduction in light lost as it propagates
along an optical fiber. Another example is the use of metal spheres
to form high temperature filaments for emitting light in the
infrared and/or visible portions of the electromagnetic spectrum.
Still another example is to use spheres having a differential
solubility over an infiltration material to form inverse opal
structures such as silica spheres removed by hydrofluoric acid in a
tungsten inverse opal structure. Further, the photonic crystal may
be formed utilizing spheres having different sizes. A wide variety
of combinations of different sphere sizes may be used in the
present invention. For example, each successive layer of spheres
may increase or decrease in size, or the size of spheres may
alternate in successive layers or every nth layer may vary or an
alternating group of layers may be varied. In addition, spheres of
different sizes also may be utilized to form a single layer such as
in the formation of a binary (AB.sub.2) colloidal crystal.
[0021] An alternate embodiment of the present invention is shown in
a perspective view in FIG. 2a. In this embodiment, apparatus 200
includes substrate 220 having generally a cylindrically shaped
outer surface. However, in alternate embodiments, substrate 220 may
have any curved shape forming a substantially rod-like substrate.
Substrate 220 includes multiple layers of spheres 222 disposed on
the outer or external surface of substrate 220 as illustrated in a
cross-sectional view in FIG. 2b; however, in alternate embodiments,
a single layer of spheres 222 also may be utilized. In this
embodiment, the spheres form photonic crystal 202; however, in
alternate embodiments, photonic crystal 202 may be formed utilizing
an inverse opal structure where interstitial volume 224 between the
spheres is infiltrated and filled with a second material with the
optional subsequent removal of spheres 222. In one particular
embodiment, photonic crystal 202 forms a photonic band gap crystal
including inverse opal band gap structures. In still other
embodiments, various layers such as an adhesive layer or other
layer having particular optical or dielectric properties may be
disposed between substrate 220 and photonic crystal 202. In this
embodiment, photonic crystal 202 is a coaxial, colloidal crystal
tuned to yield a band gap in a desired spectral region. In addition
in this embodiment, photonic crystal 202 fully encloses and/or
encircles the outer surface of substrate 220. For example, in those
embodiments, utilizing a metal wire, such as tungsten, the desired
spectral region may be in the infrared or visible portions of the
electromagnetic spectrum. In one embodiment, substrate 220 may be a
tungsten wire with a tungsten inverse opal structure disposed on
the outer surface of substrate 220 forming an incandescent
filament. In addition, the wire may be formed into various shapes,
such as a spiral shape. In a second embodiment, substrate 220 also
may be a tungsten wire with tungsten spheres or other metal with a
low vapor pressure at high temperatures forming the colloidal
crystal. In still other embodiments, substrate 220 may be an
optical fiber where photonic crystal 202 is tuned to reduce the
amount of light lost in the optical fiber during use, or substrate
220 may be a lens such as a rod lens.
[0022] An alternate embodiment of the present invention is shown in
a perspective view in FIG. 3a. In this embodiment, apparatus 300
includes substrate 320 having generally a cylindrically shaped
tubular structure. However, in alternate embodiments, substrate 320
may have any curved shape forming essentially a tubular-like
structure. Substrate 320 includes multiple layers of spheres 322
disposed on the outer or external surface of substrate 320 as
illustrated in a cross-sectional view, in FIG. 3b. In this
embodiment, the spheres form photonic crystal 302; however, in
alternate embodiments, photonic crystal 302 may be formed utilizing
an inverse opal structure. In one particular embodiment photonic
crystal 302 forms a photonic band gap crystal including inverse
opal band gap structures. In still other embodiments, various
layers such as an adhesive layer or other layer having particular
optical or dielectric properties may be disposed between substrate
320 and photonic crystal 302. In this embodiment, photonic crystal
302 is a colloidal crystal tuned to yield a band gap in a desired
spectral region. An alternate embodiment is illustrated in FIG. 3c
where substrate 320 includes multiple layers of spheres 322
disposed on both the external surface and the inner or internal
surface of substrate 320 to form photonic crystals 302 and 302'.
Photonic crystals 302 and 302' illustrated in FIG. 3c may also
include inverse opal structures as well as combinations of a
colloidal crystal and an inverse opal structure. In addition, the
photonic crystals may be formed utilizing spheres having different
sizes as previously described for the embodiments shown in FIGS.
1a-1c.
[0023] An alternate embodiment of the present invention is shown in
a perspective view in FIG. 4. In this embodiment, apparatus 400
includes filament 430 disposed within, and substantially coaxial
with, substrate 420 which has a cylindrically shaped tubular
structure. Substrate 420 includes multiple layers of spheres 422
disposed on the outer or external surface of substrate 420;
however, in alternate embodiments a single layer of spheres may be
utilized. However, in an alternate embodiment, spheres 422 may be
disposed on both the external surface and the inner or internal
surface of substrate 420 to form multiple photonic crystals. In
this embodiment, substrate 420 is sufficiently transparent to
provide the desired optical performance; however, in alternate
embodiments, substrate 420 may be removed after the formation of
the colloidal crystal, such as by etching, so that the optical
properties of the substrate would not be important. In this
embodiment, the spheres form photonic crystal 402; however, in
alternate embodiments, photonic crystal 402 may be formed utilizing
an inverse opal structure. In one particular embodiment photonic
crystal 402 forms a photonic band gap crystal including inverse
opal band gap structures where the photonic crystal is tuned to
yield a band gap in a desired spectral region in the infrared or
visible region of the electromagnetic spectrum as represented by
arrows 410. In one embodiment, filament 430 is a tungsten wire and
photonic crystal 402 is tuned to pass visible light providing for
an incandescent source having higher efficiency compared to
conventional incandescent sources. In alternate embodiments,
filament 430 may be formed from other metals, including other
refractory metals such as Ta, Mo, and Re, or cermets. In addition,
photonic crystal 402, may, for example, be tuned to pass infrared
radiation in a desired region. Again providing higher efficiency
compared to conventional sources. In still another embodiment of
the present invention apparatus 500 includes spiral filament 530
disposed within and substantially coaxial with substrate 520 as
illustrated in a perspective view in FIG. 5. Substrate 520 includes
multiple layers of spheres 522 disposed on the outer surface of
substrate forming photonic crystal 502; however in alternate
embodiments, photonic crystal 502 may also be formed utilizing a
single layer of spheres or an inverse opal structure. As described
previously for the embodiment shown in FIG. 4 the combination of
spiral filament 530 and photonic crystal 502 generally provides for
more efficient infrared and visible light sources as represented by
arrows 510. In still another embodiment, a photonic crystal may be
formed directly on the outside surface of the coiled filament where
the photonic crystal formed on the filament and the photonic
crystal formed on the tubular structure are optimized to provide a
more efficient light source.
[0024] The colloidal crystals shown in FIGS. 1-5 may be formed by a
variety of techniques. For example, sedimentation, and evaporation
may be utilized to deposit monolayer and multilayer spheres on a
substrate. Two exemplary techniques have been used to form
multilayer spheres on convex surfaces. The substrate is suspended
and/or immersed in a solution so that the longitudinal axis of the
substrate is essentially perpendicular to the meniscus formed by
the solution. The solution includes a mixture of spheres and a
solvent. For example the solution may include silica spheres or
polymeric spheres, such as polystyrene, suspended in an ethanol
solvent. Generally, the volume fraction of spheres is in the range
from about 1 percent to about 10 percent. A wide variety of
solvents may be utilized such as water, ethanol, methanol,
propanol, and hexanes. After suspending and/or immersing the
substrate in the solution the solution is allowed to evaporate.
Depending on the size of spheres and the material utilized to form
the spheres the evaporation may be carried out anywhere from room
temperature up to just below the boiling point of the solvent. For
example, for silica spheres having a diameter less than about 500
nanometers the solution may be evaporated at or near room
temperature, whereas for silica spheres having a diameter greater
than about 500 nanometers the solution may be evaporated at or near
its boiling point. Generally, when the solution is heated above
room temperature the vessel holding the solution is enclosed and
partially sealed so that the solution may evaporate in a controlled
manner and convection currents in the solvent substantially hinder
the spheres from settling. The thickness or number of layers of
spheres deposited may be controlled by varying the speed of
evaporation, the volume fraction of spheres in suspension, or
combinations of both. In addition, thicker colloidal crystals also
may be formed by carrying out multiple deposition cycles. To hinder
the peeling off or partial redispersion of the previously deposited
films during subsequent depositions it has been found to be
advantageous to sinter the spheres. For example, in those
embodiments utilizing silica spheres sintering may be carried out
utilizing tetramethyl orthosilicate for several minutes at about
80.degree. C. Another example is to heat silica spheres to about
600.degree. C. to improve the structural integrity of the colloidal
crystal without utilizing a sintering agent. In still other
embodiments, other sintering agents, times, and temperatures also
may be utilized. The particular, sintering agent, time, and
temperature is application specific because sintering may affect
the filling factor or optical properties of the photonic crystal or
various combinations of both. In addition, multilayer colloidal
crystals having different colloidal sphere sizes may be formed
utilizing multiple depositions. For example, AB, ABA, ABC
multilayer crystals may be formed where the letters A, B, and C
each represent at least one layer of spheres having a different
sphere diameter from the other letters. In still other embodiments,
multiple sized spheres also may be utilized in a single solution to
generate, for example, binary AB.sub.2 crystal structures. Further,
the spheres of different sizes may be formed utilizing different
materials have different dielectric constants generating a
colloidal crystal having a spatially varying dielectric constant.
It may also be desirable, depending on the particular application
in which the photonic crystal will be utilized, to generate or
create portions of the substrate surface free of the spheres. In
such embodiments, patterning of the substrate may be generated by
selectively applying a sacrificial layer in those areas where it is
desired that the spheres do not form. For example, in the
embodiment shown in FIG. 4, the internal surface of substrate 420
may be coated or filled with a polyamic acid solution which may be
removed at a later time utilizing a solvent such as
N,N-dimethylacetamide (DMAC) or N-methyl-2-pyrrolidone (NMP), or a
strong basic solution such as potassium hydroxide (KOH). A wide
variety of inorganic or organic sacrificial materials may be
utilized. The particular material chosen will depend on various
factors such as the particular spheres, solvent, and temperature
utilized to form the colloidal crystal.
[0025] For those embodiments utilizing an inverse opal crystal
structure a variety of deposition techniques may be utilized to
fill the interstitial volume formed between the spheres such as
atomic layer deposition (ALD), chemical vapor deposition (CVD),
electro-deposition, and electroless deposition and other wet
infiltration methods. An exemplary technique utilizes atomic layer
deposition to fill or infiltrate the interstitial volume of the
colloidal crystal. In one embodiment a tungsten inverse opal
structure may be generated utilizing alternating exposures of the
colloidal crystal to tungsten hexafluoride (WF.sub.6) and silicon
hydride (e.g. SiH.sub.4, Si.sub.2H.sub.6, Si.sub.3H.sub.8 and
mixtures of various silicon hydrides). The tungsten film growth may
be achieved utilizing an alternating sequence of exposures of
WF.sub.6 and Si.sub.2H.sub.6 in the temperature range from about
100.degree. C. to about 400.degree. C. It is believed that the
disilane reactant serves a sacrificial role to strip fluorine from
tungsten limiting the incorporation of silicon into the film;
however, the present invention is not limited to such a mechanism.
Other chemistries also may be utilized such as tungsten
hexacarbonyl as a tungsten precursor material and boron compounds
such as a boron hydride as a reducing agent. In alternate
embodiments, other silicon hydrides also may be utilized. In still
other embodiments a wide range of inorganic materials also may be
utilized. Tungsten nitride, titanium dioxide, graphite, diamond,
tungsten carbide, hafnium carbide, and indium phosphide are just a
few examples. After the interstitial volume in the crystal is
filled or substantially filled the silica spheres may then be
removed by soaking in a aqueous hydrofluoric acid solution (i.e.
typically about 2 weight percent) to form inverse opal photonic
crystal 604 as illustrated in FIG. 6b. FIGS. 6a and 6b illustrate
the differences between a colloidal crystal and an inverse opal
crystal. FIG. 6a represents a portion of colloidal crystal 604
which has a close-packed geometry; whether the structure is
face-centered cubic, hexagonal close-packed or randomly stacked
with each sphere 626 touching six other spheres in one layer.
Interstitial volume 624 is the volume of the crystal not occupied
by spheres 626. FIG. 6b represents a portion of an inverse opal
photonic crystal 604' where interstitial volume 624 has been
infiltrated or filled with an inorganic material and spheres 626
have been removed. The particular inorganic material utilized will
depend on the particular application in which the photonic crystal
is utilized. ALD provides an exemplary technique for thin film
deposition in deep structures, complex structures, or both. In
addition, ALD also provides control in the chemical composition of
the deposited film by selection of various precursors, various
deposition temperatures and pressures, and combinations of these
parameters. Further, the generally low deposition rates (i.e.
typically on the order of a few tenths of a nanometer per cycle)
allows for a more uniform growth rate and more uniform thickness
control in the narrow voids formed in the colloidal crystal
providing a cost-effective process to fabricating photonic band gap
structures.
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