U.S. patent application number 09/738607 was filed with the patent office on 2002-01-10 for optically integrating pixel microstructure.
This patent application is currently assigned to Gemfire Corporation. Invention is credited to Bischel, William K., Cockroft, Nigel J., Deacon, David A.G., Field, Simon J., Hehlen, Markus P., Tompane, Richard B., Wagner, David K..
Application Number | 20020003928 09/738607 |
Document ID | / |
Family ID | 23136861 |
Filed Date | 2002-01-10 |
United States Patent
Application |
20020003928 |
Kind Code |
A1 |
Bischel, William K. ; et
al. |
January 10, 2002 |
Optically integrating pixel microstructure
Abstract
An integrated optical microstructure includes a substrate
carrying an optical waveguide and supporting a medium disposed to
receive optical energy from the waveguide. The medium includes an
optical re-radiator such as a phosphor, which re-radiates optical
energy in response to optical energy received from the waveguide.
The structure further includes a reflector disposed to redirect
some of the input optical energy emanating from the medium back
into the medium, to achieve spatial confinement of the input light
delivered by the input waveguide. The structure can thereby
increase the efficiency of the light conversion processes of
re-radiating materials. An aperture in the reflector permits
optical energy emitted by the re-radiator to emerge from the
structure and to propagate in a preferred direction, such as toward
a viewer or sensor. The structure is useful for increasing the
brightness of various kinds of small emissive elements which are
excited by light delivered from an integrated optical waveguide,
including pixels in an information display.
Inventors: |
Bischel, William K.; (Menlo
Park, CA) ; Deacon, David A.G.; (Los Altos, CA)
; Cockroft, Nigel J.; (Los Gatos, CA) ; Hehlen,
Markus P.; (Los Gatos, CA) ; Wagner, David K.;
(San Jose, CA) ; Tompane, Richard B.; (Los Altos,
CA) ; Field, Simon J.; (Palo Alto, CA) |
Correspondence
Address: |
HAYNES BEFFEL & WOLFELD LLP
P O BOX 366
HALF MOON BAY
CA
94019
US
|
Assignee: |
Gemfire Corporation
|
Family ID: |
23136861 |
Appl. No.: |
09/738607 |
Filed: |
December 15, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09738607 |
Dec 15, 2000 |
|
|
|
09295244 |
Apr 19, 1999 |
|
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6208791 |
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Current U.S.
Class: |
385/39 ; 385/27;
385/47 |
Current CPC
Class: |
G02B 6/12004 20130101;
G02B 6/262 20130101; G02B 6/4214 20130101; G02B 2006/12104
20130101; G02B 6/122 20130101; G02B 6/10 20130101 |
Class at
Publication: |
385/39 ; 385/27;
385/47 |
International
Class: |
G02B 006/26 |
Claims
1. Optical apparatus comprising: a material having a pit; an
integrated optical waveguide in said material, said waveguide
having a core layer having top and bottom depths in said material
and said pit extending at least down to said bottom depth of said
core layer, said pit being disposed to receive optical energy from
said waveguide; a medium disposed at least partially in at least
part of said pit and including an optical re-radiator, said optical
re-radiator re-radiating optical energy in response to optical
energy received from said waveguide; and a reflector disposed to
redirect at least a portion of optical energy emanating from said
medium back into said medium.
2. Apparatus according to claim 1, wherein said waveguide further
has a top cladding layer above said core layer, wherein said top
cladding layer terminates at or upstream of said pit, and wherein
said core layer extends into said pit.
3. Apparatus according to claim 2, wherein said core layer
terminates part-way across said pit.
4. Apparatus according to claim 1, wherein said re-radiator in said
medium is disposed at least partially above said top depth of said
core layer.
5. Apparatus according to claim 4, wherein said waveguide further
has a top cladding layer having a top depth and wherein said
re-radiator in said medium is disposed entirely above said top
depth of said top cladding layer.
6. Apparatus according to claim 4, wherein said medium includes a
top volume superposing substantially all of said re-radiator in
said medium.
7. Apparatus according to claim 4, wherein said medium consists of
a lower volume disposed in said pit and an upper volume disposed
above said top depth of said top cladding layer, and wherein said
re-radiator is disposed entirely and uniformly in said upper
volume.
8. Apparatus according to claim 4, wherein said medium includes an
upper volume disposed above said top depth of said top cladding
layer, and wherein said re-radiator is concentrated within a
predetermined volume which is smaller than and entirely within said
upper volume.
9. Apparatus according to claim 8, wherein said predetermined
volume is less than 5% of the volume of said medium.
10. Apparatus according to claim 8, wherein said reflector is
shaped to redirect, preferentially toward said predetermined
volume, optical energy from said waveguide which is emanating from
said medium.
11. Apparatus according to claim 1, wherein said medium has a top
surface, and wherein said reflector includes a top portion at least
partially covering said top surface of said medium.
12. Apparatus according to claim 11, wherein said top portion of
said reflector is dome-shaped.
13. Apparatus according to claim 11, wherein said top portion of
said reflector includes a top aperture transmissive to optical
energy re-radiated by said re-radiator.
14. Apparatus according to claim 13, further comprising black
matrix material superposing regions of said top portion of said
reflector.
15. Apparatus according to claim 13, wherein said pit has a bottom
surface and said reflector includes a bottom portion at least
partially covering said bottom surface of said pit below said
medium, said bottom portion of said reflector including a bottom
aperture transmissive to optical energy re-radiated by said
re-radiator.
16. Apparatus according to claim 11, wherein said pit has a bottom
surface and said reflector includes a bottom portion at least
partially covering said bottom surface of said pit below said
medium.
17. Apparatus according to claim 1, wherein said pit has a bottom
surface and said reflector includes a bottom portion at least
partially covering said bottom surface of said pit below said
medium.
18. Apparatus according to claim 17, wherein said bottom portion of
said reflector includes a bottom aperture transmissive to optical
energy re-radiated by said re-radiator.
19. Apparatus according to claim 1, wherein said reflector includes
a first aperture through which said pit receives optical energy
from said waveguide, and further includes a second aperture,
different from said first aperture, which is transmissive to
optical energy re-radiated by said re-radiator.
20. Apparatus according to claim 19, further comprising an output
waveguide disposed to receive optical energy transmitted through
said second aperture.
21. Apparatus according to claim 1, wherein said reflector
comprises a reflector material which is at least partially
transmissive to optical energy re-radiated by said re-radiator.
22. Apparatus according to claim 1, wherein said optical energy
received by said pit from said waveguide propagates along a path in
an input plane, wherein said reflector includes an input aperture
through which said pit receives said optical energy from said
waveguide, and further includes a sidewall portion on a wall of
said pit opposite said input aperture, said sidewall portion being
disposed and oriented to reflect optical energy received by said
pit through said input aperture, out of said input plane and toward
said re-radiator.
23. Apparatus according to claim 22, wherein said medium contains
substantially no re-radiator in said input plane.
24. Apparatus according to claim 1, wherein said optical energy
received by said pit from said waveguide is concentrated primarily
in an input plane parallel to said core layer of said waveguide,
wherein said reflector includes a sidewall substantially
perpendicular to said input plane and forming an intersection with
said input plane which substantially surrounds said pit.
25. Apparatus according to claim 24, wherein said pit includes a
raised region substantially surrounded by said side wall and
underlying at least part of said medium, said raised region having
a core layer with the same top and bottom depths as the core layer
of said waveguide.
26. Apparatus according to claim 25, wherein said sidewall forms a
circle having an input aperture through which said optical energy
from said waveguide passes, said optical energy from said waveguide
entering said circle with a primary propagation direction that is
off-center with respect to said circle.
27. Apparatus according to claim 26, further comprising a baffle
reflector portion disposed and oriented to reduce optical energy
emission back out through said input aperture.
28. Apparatus according to claim 25, wherein said waveguide further
has a top cladding layer above the core layer of said waveguide,
wherein said raised region further comprises a top cladding layer
above said core layer and below said medium, said top cladding
layer being thinner than the top cladding layer of said
waveguide.
29. Apparatus according to claim 28, wherein said top cladding
layer in said pit is sufficiently thin to permit evanescent
coupling of optical energy out of said core layer and into said
medium in said pit.
30. Apparatus according to claim 1, wherein said reflector
redirects into said medium substantially all optical energy which
reaches said reflector from said waveguide.
31. Apparatus according to claim 1, wherein said re-radiator
comprises a luminescent substance.
32. Apparatus according to claim 1, wherein said re-radiator
comprises an upconversion phosphor.
33. Apparatus according to claim 1, wherein said re-radiator
comprises a medium consisting of scattering centers.
34. Apparatus according to claim 1, wherein said reflector includes
an input aperture through which said pit receives optical energy
from said waveguide, said medium superposing at least said input
aperture.
35. Apparatus according to claim 1, wherein said reflector has a
single aperture through which said pit receives optical energy from
said waveguide, and through which optical energy generated by said
re-radiator escapes said pit.
36. Apparatus according to claim 1, wherein said material further
comprises a second pit, said medium further being disposed at least
partially in said second pit.
37. Apparatus according to claim 1, comprising a first optical path
through which said pit receives optical energy from said waveguide,
further comprising a second optical path through which said pit
receives optical energy not from said waveguide.
38. Apparatus according to claim 1, further comprising a lens
disposed to refract optical energy re-radiated by said
re-radiator.
39. Apparatus according to claim 1, further comprising a further
reflector disposed below at least part of said core layer.
40. Apparatus comprising: a substrate carrying an optical waveguide
and supporting a medium disposed to receive optical energy from
said waveguide, said medium including an optical re-radiator which
re-radiates optical energy in response to optical energy received
from said waveguide; and a reflector disposed to redirect a first
portion of optical energy emanating from said medium back into said
medium, at least a second portion of optical energy re-radiated by
said optical re-radiator being permitted to escape said medium
primarily in a direction not parallel to said substrate.
41. Apparatus according to claim 40, wherein said integrated
optical waveguide has a top cladding layer and a core layer below
said top cladding layer, said core layer having top and bottom
depths in said substrate and wherein said medium is at least partly
disposed in at least part of a pit, at least part of said pit
extending down at least to said bottom depth of said core
layer.
42. Apparatus according to claim 41, wherein said top cladding
layer terminates at or upstream of said pit, and wherein said core
layer extends into said pit.
43. Apparatus according to claim 42, wherein said core layer
terminates at a partial distance across said pit.
44. Apparatus according to claim 41, wherein said optical energy
from said waveguide is received into said pit from an input
aperture in a sidewall of said pit, wherein said reflector includes
a sidewall portion disposed on a sidewall of said pit opposite said
input aperture, said sidewall portion being disposed and oriented
to reflect optical energy received from said input aperture toward
said re-radiator.
45. Apparatus according to claim 44, wherein substantially all of
the re-radiator in said medium is disposed at a depth in said
medium which is above the optical energy path from said input
aperture to said sidewall portion of said reflector.
46. Apparatus according to claim 40, wherein said substrate has a
top surface, wherein said reflector includes a sidewall portion
substantially perpendicular to said substrate top surface and
substantially surrounding an underlying confinement region below
said re-radiator in said medium, said sidewall portion having an
input aperture for receiving optical energy from said
waveguide.
47. Apparatus according to claim 46, wherein said sidewall portion
forms a circle having said input aperture therein, said optical
energy from said waveguide entering said confinement region with a
propagation direction that is off-center with respect to said
circle.
48. Apparatus according to claim 46, wherein said reflector further
comprises a baffle portion disposed and oriented to reduce optical
energy emission from said confinement region back through said
input aperture.
49. Apparatus according to claim 46, further comprising an optical
core material in said confinement region below said re-radiator,
and a cladding material superposing said optical core material
within said confinement region and below said re-radiator.
50. Apparatus according to claim 49, wherein said cladding material
is sufficiently thin to permit evanescent coupling of optical
energy out of said optical core material and into said medium.
51. Apparatus according to claim 40, wherein said medium has a top
surface, and wherein said reflector includes a top portion at least
partially covering said top surface of said medium.
52. Apparatus according to claim 51, wherein said top portion of
said reflector is dome-shaped.
53. Apparatus according to claim 51, wherein said top portion of
said reflector includes a top aperture transmissive to optical
energy re-radiated by said re-radiator, said second portion of
optical energy escaping said medium through said top aperture.
54. Apparatus according to claim 53, further comprising black
matrix material superposing at least a portion of said top portion
of said reflector.
55. Apparatus according to claim 40, further comprising an optical
output path through said substrate for optical energy re-radiated
by said re-radiator.
56. Apparatus according to claim 55, wherein said reflector
comprises a bottom portion between said medium and said substrate,
said bottom portion being at least partially reflective of optical
energy received from said waveguide and at least partially
transmissive to optical energy re-radiated by said re-radiator.
57. Apparatus according to claim 56, wherein said bottom portion
includes a portion which is reflective of optical energy received
from said waveguide and also of optical energy re-radiated by said
re-radiator, said bottom portion including an aperture which is
transmissive to optical energy re-radiated by said re-radiator.
58. Apparatus according to claim 40, wherein said reflector
comprises a material which is at least partially transmissive to
optical energy re-radiated by said re-radiator.
59. Apparatus according to claim 58, wherein said reflector is
further partially transmissive to optical energy received from said
waveguide.
60. Apparatus according to claim 40, wherein said reflector
redirects into said medium substantially all optical energy receive
from said waveguide.
61. Apparatus according to claim 40, wherein said re-radiator
comprises a luminescent material.
62. Apparatus according to claim 40, wherein said re-radiator
comprises an upconversion phosphor.
63. Apparatus according to claim 40, wherein said re-radiator
comprises scattering centers.
64. Apparatus according to claim 40, wherein said reflector is
shaped to redirect preferentially into a predetermined volume of
said medium, smaller than said entire medium, optical energy from
said waveguide which is emanating from said medium.
65. Apparatus according to claim 40, wherein said medium is at
least partly disposed in at least part of a well in said
substrate.
66. Apparatus according to claim 65, wherein said substrate
includes an optical core material underlying said well, optical
energy coupling out of said optical core material and into said
medium in said well.
67. Apparatus according to claim 66, wherein said substrate further
includes a top cladding material between said well and said optical
core material, said top cladding material being sufficiently thin
to permit evanescent coupling of optical energy out of said optical
core material and into said medium in said well.
68. Apparatus according to claim 66, wherein said substrate
includes a pit disposed to intersect said core material downstream
of said well along a propagation direction of said optical energy
from said waveguide.
69. Apparatus according to claim 68, wherein said pit is spaced
from said well in said propagation direction of said optical energy
from said waveguide.
70. Apparatus according to claim 68, further comprising an optical
absorber material in said pit.
71. Apparatus according to claim 68, wherein said pit contains a
material forming an index of refraction boundary with said core
material at said intersection.
72. Apparatus according to claim 66, wherein said reflector
includes a portion disposed to intersect said core material
downstream of said well along a propagation direction of said
optical energy from said waveguide.
73. Apparatus according to claim 65, wherein said substrate has a
top surface level, said well extending below said substrate top
surface level, and wherein said re-radiator in said medium is
disposed at a depth which is at least partially above said
substrate top surface level.
74. Apparatus according to claim 73, wherein said re-radiator in
said medium is disposed entirely above said substrate top surface
level.
75. Apparatus according to claim 73, wherein said medium includes a
top volume superposing substantially all of said re-radiator in
said medium.
76. Apparatus according to claim 73, wherein said re-radiator is
concentrated within a predetermined volume in said medium above
substrate top surface level.
77. Apparatus according to claim 76, wherein said predetermined
volume is less than 5% of the volume of said medium.
78. Apparatus according to claim 76, wherein said reflector is
shaped to redirect into said predetermined volume, optical energy
from said waveguide which is emanating from said medium.
79. Apparatus according to claim 40, wherein said medium includes
an upper volume and a lower volume separated by said reflector, at
least part of said re-radiator being disposed in said upper volume,
said reflector permitting optical energy received from said
waveguide to pass from said lower volume to said upper volume.
80. Apparatus according to claim 40, further comprising a lens
disposed to refract said second portion of optical energy.
81. Optical apparatus comprising: a material including an
integrated optical waveguide, said waveguide having a top cladding
layer, said top cladding layer having top and bottom levels in said
material; a medium including an optical re-radiator disposed to
receive optical energy from said waveguide, said optical
re-radiator re-radiating optical energy in response to optical
energy received from said waveguide, said medium including at least
a portion which is above said bottom level of said top cladding
layer; and a reflector disposed to redirect at least a portion of
optical energy emanating from said medium back into said
medium.
82. Apparatus according to claim 81, wherein said waveguide further
has a core layer below said top cladding layer, said core layer
having top and bottom depths in said material, and wherein said
material includes a pit extending at least down to said bottom
depth of said core layer.
83. Apparatus according to claim 81, wherein said re-radiator in
said medium is disposed entirely above said top depth of said top
cladding layer.
84. Apparatus according to claim 83, wherein said medium includes a
top volume superposing substantially all of said re-radiator in
said medium.
85. Apparatus according to claim 83, wherein said medium consists
of an upper volume disposed above said top level of said top
cladding layer, and a lower volume disposed below said upper
volume, and wherein said re-radiator is disposed entirely and
uniformly in said upper volume.
86. Apparatus according to claim 83, wherein said medium includes
an upper volume disposed above said top level of said top cladding
layer, and wherein said re-radiator is concentrated within a
predetermined volume which is smaller than and entirely within said
upper volume.
87. Apparatus according to claim 86, wherein said reflector is
shaped to redirect preferentially into said predetermined volume,
optical energy from said waveguide which is emanating from said
medium.
88. Apparatus according to claim 81, wherein said medium has a top
surface, and wherein said reflector includes a top portion at least
partially covering said top surface of said medium.
89. Apparatus according to claim 88, wherein said top portion of
said reflector includes a top aperture transmissive to optical
energy re-radiated by said re-radiator.
90. Apparatus according to claim 81, wherein said reflector
includes a bottom portion at least partially underlying said
medium.
91. Apparatus according to claim 90, wherein said bottom portion of
said reflector includes a bottom aperture transmissive to optical
energy re-radiated by said re-radiator.
92. Apparatus according to claim 81, wherein said reflector
includes a first aperture through which said medium receives
optical energy from said waveguide, and further includes a second
aperture, different from said first aperture, which is transmissive
to optical energy re-radiated by said re-radiator.
93. Apparatus according to claim 81, wherein said re-radiator
comprises a luminescent substance.
94. Apparatus according to claim 81, wherein said re-radiator
comprises an upconversion phosphor.
95. Apparatus according to claim 81, wherein said re-radiator
comprises scattering centers.
96. Apparatus according to claim 81, further comprising a lens
disposed to refract optical energy re-radiated by said
re-radiator.
97. Optical apparatus for use with input optical energy,
comprising: a medium including an optical re-radiator, said optical
re-radiator re-radiating optical energy in response to said input
optical energy; a sidewall reflector substantially surrounding a
confinement region in a plane below said re-radiator, said sidewall
reflector having an input path for receiving said input optical
energy into said confinement region and directed within said plane,
said sidewall reflector being oriented to redirect back into said
confinement region, optical energy directed outwardly from said
confinement region, optical energy being transferrable from said
confinement region into said re-radiator.
98. Apparatus according to claim 97, wherein said optical
re-radiator comprises a luminescent material.
99. Apparatus according to claim 97, wherein said optical
re-radiator comprises a medium consisting of scattering
centers.
100. Apparatus according to claim 97, further comprising an input
optical waveguide carrying said input optical energy, said
waveguide having a core layer and top and bottom cladding layers,
at least said core layer extending into said confinement region and
at least partially defining said input path.
101. Apparatus according to claim 100, further comprising a top
cladding material superposing said core layer in said confinement
region below said re-radiator, said top cladding material being
sufficiently thin to permit evanescent coupling of optical energy
out of said confinement region and into said medium.
102. Apparatus according to claim 97, wherein said confinement
region is below said medium, further comprising a top cladding
material superposing said core layer in said confinement region
below said medium, said top cladding material being sufficiently
thin to permit evanescent coupling of optical energy out of said
confinement region and into said medium.
103. Apparatus according to claim 102, further comprising a trench
substantially surrounding said confinement region except for said
input path, said sidewall reflector being formed on a surface of
said trench.
104. Apparatus according to claim 103, further comprising a ridge
of top cladding material substantially surrounding said confinement
region and substantially surrounded by said trench, said ridge of
top cladding material being thicker than said top cladding material
superposing said core layer in said confinement region below said
re-radiator.
105. Apparatus according to claim 103, further comprising an
optical absorber disposed in said trench.
106. Apparatus according to claim 103, further comprising an
optical re-radiator disposed in said trench.
107. Apparatus according to claim 97, further comprising a
reflector superposing said medium and redirecting at least a
portion of optical energy emanating from said medium back into said
medium.
108. Apparatus according to claim 107, wherein optical energy
re-radiated from said re-radiator is permitted to escape said
medium primarily in a direction not parallel to said plane.
109. Apparatus according to claim 107, wherein said reflector has
an aperture which is transmissive to optical energy re-radiated by
said re-radiator.
110. Apparatus according to claim 97, wherein said sidewall
reflector forms a circle having an input aperture therein for said
input path, said input optical energy entering said confinement
region with a propagation direction that is off-center with respect
to said circle.
111. Apparatus according to claim 97, further comprising a baffle
reflector disposed and oriented to reduce optical energy emission
from said confinement region back through said input aperture.
Description
FIELD OF THE INVENTION
[0001] The invention concerns means of improving the optical
efficiency of optically excited light emitting structures such as
pixels in flat-panel displays.
BACKGROUND OF THE INVENTION
[0002] Many commercial emissive display devices generate visible
light using electron beam or ultraviolet radiation incident upon a
phosphor, such as in cathode ray tube (CRT) or AC plasma visual
displays. A less well known display technology, typified in Bischel
et al. U.S. Pat. No. 5,544,268, incorporated herein by reference,
uses optical waveguides to convey light from a light source onto a
display screen. Waveguide-based flat panel displays generally
utilize planar and/or channel waveguides. They typically include
several parallel channel waveguides to be formed on a substrate.
Optical switches are located either in or on the channel waveguides
at predetermined matrix locations across the display screen.
Optical energy injected into the channel waveguides is extracted at
these predetermined positions by the optical switches and directed
toward pixel structures which may, in certain embodiments described
in the '268 patent, include re-radiators to emit light from the
pixel structure towards a viewer. Such re-radiators can include
out-of-plane reflectors, scattering materials, or luminescent
materials which emit at a wavelength which may differ from the
wavelength of the input optical energy.
[0003] Metal reflectors on or near the visible light emitting
pixels are used in a variety of ways in different display
architectures to redirect visible light emitted by phosphors into a
preferred direction to achieve enhanced brightness at the viewer
location. For example, Thomas U.S. Pat. No. 5,097,175, incorporated
herein by reference, describes a pixel structure for CRT displays,
where a material that emits visible light upon excitation with an
electron beam is deposited on a transparent substrate in the form
of a parabolic shaped cell that is coated with a reflective metal
layer to redirect visible light emitted inside the cell through the
substrate toward a viewer.
[0004] In another example of the use of reflectors to direct light
for a visual display, Murata U.S. Pat. No. 5,055,737, incorporated
herein by reference, describes a luminescent screen which contains
a material that emits visible light when excited by light incident
from the viewing direction. This screen contains a reflective
structure that redirects light from the emitting material, that
otherwise would propagate in undesired directions, back toward the
viewer, thereby enhancing brightness.
[0005] Thus the conventional function of reflectors used in
displays is to direct the light generated in the pixel toward the
viewer. Such reflectors do not serve to enhance the efficiency of
conversion to visible light of pump energy such as that from an
electron beam in a CRT or from the ultra-violet light in a plasma
display. Optical performance, including the conversion efficiency,
brightness, and chromaticity, of display pixels containing certain
optically activated luminescent materials such as phosphors,
glasses, or crystals would benefit from increasing the amount of
absorbed pump radiation. Therefore a different kind of reflective
pixel structure is needed which confines the pump radiation while
allowing for the emission of generated light.
SUMMARY OF THE INVENTION
[0006] The present invention provides a means of increasing the
efficiency of the light conversion processes of re-radiating
materials in integrated structures. Roughly described, this is
achieved by using a reflective coating deposited on or near the
light emitting material to achieve spatial confinement of the input
light delivered by an integrated waveguide. The fraction of the
input light that contributes to the generation of useful output
light is thereby increased. It will be apparent to those skilled in
the art that the structures described herein pertain not only to
pixels in information displays but more generally to any
reflectively enclosed light emitting structure that is optically
excited by light from an integrated optical waveguide.
[0007] In one embodiment, the optical performance, including
conversion efficiency, of an upconversion phosphor contained in
such a device is improved by the enhanced absorption of infrared
pump light resulting from multiple passes through the absorber by
reflection of otherwise unabsorbed pump light off the reflective
coating of the confinement structure. Apertures in the reflective
coating of the confinement structure allow for the visible light
generated in the upconversion process to emerge from the pixel
structure and to propagate in a preferred direction, such as toward
a viewer or sensor. The efficiency of visible light generation upon
infrared excitation of an upconversion phosphor material generally
increases as the infrared power absorbed per unit volume is
increased, because the probability of non-radiative energy transfer
processes involved in the generation of the visible light increases
as the average distance between excited optically active ions
decreases.
[0008] At a fundamental materials level, the invention enables the
use of re-radiator materials that have small absorption
coefficients for input light due to a small concentration of active
dopant ions that absorb light. It is well known that the conversion
efficiency of such phosphors often decreases as the concentration
of absorbing ions is increased (see "Luminescent Materials", by G.
Blasse and B. C. Grabmaier, 1994, incorporated herein by
reference). The use of reflectors on a pixel designed to increase
the absorption of input light helps ensure utility for such
materials that may have low absorption but high conversion
efficiency.
[0009] The invention provides a means for increasing the brightness
of small emissive structures such as pixels in information displays
which are excited using light delivered by integrated optical
waveguides. The advantage of the invention is significant in the
example of an information display where the dimensions of the pixel
feature are constrained according to display resolution
requirements and the pixel cannot be increased to an arbitrarily
large size to achieve larger single pass absorption of input
light.
[0010] Furthermore, in the case of upconversion phosphor grains in
an optically transparent polymer binder, the mixture may comprise
phosphor as perhaps only 5% by volume of the total volume enclosed
by a pit/mound structure. Confinement of the input light by the
reflective surfaces increases the total input light energy that is
absorbed per upconversion phosphor particle. The resultant increase
in excitation density within the phosphors can provide a higher
efficiency of conversion of infrared to visible light within the
phosphor grains.
[0011] An additional advantage gained from the use of reflectors
that confine the pump light delivered to a pixel is that the
variation of efficiency with pump light wavelength of a
wavelength-converting phosphor, for example, can be reduced. In
such a structure, for example, a NaYF.sub.4 upconversion phosphor
doped with ytterbium and erbium ions having an absorption peak
around 977 nm may be pumped at a variety of wavelengths in, say,
the 960 nm to 990 nm range and produce comparable green light
emission intensity despite a significant variation in the
absorption coefficient of the phosphor over that wavelength range.
This increase in wavelength tolerance relaxes the specification of
lasers used with such a device and can improve device performance
uniformity as the wavelengths of pump lasers tend to vary with
temperature.
[0012] This invention will be better understood upon reference to
the following detailed description in connection with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a schematic cross-sectional view of a mound of
re-radiator material that is deposited in a pit that terminates an
optical waveguide integrated on a substrate.
[0014] FIGS. 2A, 2B, 3 and 4 illustrate various views of various
embodiments that include a mound of re-radiator material superposed
by a reflective layer with an aperture, all integrated with an
optical waveguide terminated by a pit on a substrate.
[0015] FIG. 5 illustrates an embodiment in which a mound of
re-radiator material is completely enclosed by a reflector except
for the input aperture.
[0016] FIG. 6 illustrates an embodiment in which a mound of
re-radiator material has a fully reflectively coated top surface
and an aperture in a reflective coating at the base of the
mound.
[0017] FIG. 7 illustrates an embodiment that uses more than one
optical waveguide for light input into and/or output from the
re-radiator material.
[0018] FIGS. 8 and 9 illustrate embodiments in which the
re-radiator material is substantially above the level in the pit at
which input optical energy is received.
[0019] FIGS. 10 and 11 illustrate embodiments in which a
re-radiator material is embedded with spatial non-uniformity in a
medium also containing other material(s).
[0020] FIG. 12 illustrates an embodiment in which the core layer of
the input optical waveguide extends into a mound of medium
containing a re-radiator material.
[0021] FIGS. 13-15 illustrate other embodiments including offset
pits, half-filled pits and more than one pit.
[0022] FIGS. 16 and 17 illustrate embodiments in which the medium
containing the re-radiator material is disposed in a separate well
allowing it to interact with the evanescent field of the input
light.
[0023] FIGS. 18A-C illustrate various views of an embodiment of a
device based on the structure shown in FIG. 17.
[0024] FIG. 19 illustrates an embodiment of the present invention
incorporating a black matrix layer.
[0025] FIGS. 20 and 21 illustrate other embodiments incorporating
alternative black matrix layers and output lenses.
DETAILED DESCRIPTION
[0026] FIG. 1 shows a cross-sectional view of a device comprising a
medium 106 which includes a re-radiator material 105 partially
located in a pit 110 which terminates an optical waveguide 115 that
is integrated in an optical waveguide structure 125 on a substrate
120. The termination of an optical waveguide by the pit is defined
as the pit intersecting with and capturing substantially all the
light propagating towards the pit in the portion of the integrated
optical waveguide that terminates at the pit. Even though the
waveguide may not actually meet the pit, the pit may still be able
to capture substantially all the light propagating in the waveguide
in a downstream direction towards the pit. The optical waveguide
structure 125 may be a multilayer stack, or part of the substrate
120 incorporating ion-diffused or ion-exchanged channel or planar
waveguides formed from, for instance, titanium, zinc or protons in
lithium niobate; silver in glass; or one of many other techniques
of waveguide fabrication which are well known in the art. The
medium 106 in this example comprises a re-radiator material 105
which protrudes above the top surface of the optical waveguide
structure 125 and can be of any shape and may extend laterally
beyond the confines of the pit 110 onto the top surface of the
waveguide structure 125 or onto any other layer deposited on this
top surface of the waveguide structure 125. The medium may be added
to the pit by many methods including stencil printing,
photolithographic definition, or ink jet printing. A re-radiator
material may be any single or multi-component material that alters
the properties of input light and from which output light emanates.
The input light and the output light emerging may be of single or
multiple wavelengths. Generated light is that portion of output
light whose wavelength is altered from that of the input light as a
result of interaction with the re-radiator. For example, the
re-radiator material may include a luminescent material (refer to
"Luminescent Materials" by Blasse and Grabmaier referenced earlier)
or a phosphor that absorbs radiation at wavelengths shorter than
the wavelength(s) of emission, henceforth referred to as
down-conversion phosphor, or it may include a phosphor that
generates light at wavelengths shorter than the input light
wavelength at which it is excited, henceforth referred to as an
upconversion phosphor. Examples of down-conversion phosphors
include BaMgAl.sub.10O.sub.17:Eu.sup.2+ and SrS:Cu.sup.+. Examples
of upconversion phosphors include
BaY.sub.2F.sub.8:Yb.sup.3+,Tm.sup.3+ and
YF.sub.3:Yb.sup.3+,Er.sup.3+. The wavelengths referred to above
imply the spectral range extending from the far-infrared to the
deep UV. Another example of a re-radiator material is a material
that scatters input radiation without changing wavelength, in this
case there is no generated light.
[0027] An integrated optical waveguide 115 is any structure that
provides for optical confinement of an input light beam in at least
one dimension by careful choice of refractive index of composite
materials and appropriate choice of physical dimensions. Examples
include planar waveguides or channel waveguides. The parameters
necessary to design an optical waveguide structure to guide light
at a particular wavelength are well known in the art and may be
found for instance in Nishihara et al. "Optical Integrated
Circuits," McGraw Hill 1989, incorporated herein by reference in
its entirety. The waveguide may be imbedded directly in the
interior or top surface of a substrate or may be contained in a
layered stack of materials of appropriate refractive index (core
and/or top and/or bottom cladding) that is deposited, or otherwise
attached, to the top surface of the substrate. It will be apparent
that the bottom cladding may be the substrate in a case for example
where the waveguide structure is a multilayered stack. A waveguide
is considered herein to concentrate optical energy "primarily"
within the core of the waveguide, although since evanescent tails
extend out into the cladding layers, some energy nevertheless
travels outside the core.
[0028] The pit 110 may be of any shape that includes a surface that
intersects the optical energy from the integrated optical waveguide
115. This surface of intersection includes a waveguide aperture 130
through which input light may be delivered from the integrated
optical waveguide 115 into the medium 106 comprising re-radiator
material 105. The surfaces of the pit are coated with a reflector
135, 140, 145 such as a multilayer dielectric film or a layer of a
metal such as silver, gold, aluminum or any metal or metallic alloy
reflector, or any other material or combination of materials that
reflect the input wavelength. Preferably the reflector will exhibit
a high degree of reflectivity for at least the input light. The
waveguide aperture 130 is at least partially transparent at the
wavelength of the input light to allow passage of light launched
from the waveguide into the pit. In some cases, this aperture may
also provide a means for escape of some of the light re-radiated
from the re-radiator material 105.
[0029] At least the portion of the top surface of the optical
waveguide structure 125 that is underneath the medium of
re-radiator material 105 may also be coated with a metallic,
dielectric or other reflector 150. Input light delivered to the pit
by a waveguide 115 enters the pit 110 through the waveguide
aperture 130. Subsequently it propagates through the medium 106
containing re-radiator material 105, undergoing wavelength
conversion and/or scattering. Input, scattered or generated light
reaching the reflective coatings on the surface of the pit or
optical waveguide structure at the base of the medium are reflected
back into the medium, to be wavelength converted or to emerge from
the top surface of the medium or to escape through the waveguide
aperture 130.
[0030] FIGS. 2A and 2B (sometimes referred to herein collectively
as "FIG. 2") show a further embodiment of the invention with the
addition of an optical reflector structure over part of the top
surface of the medium. FIG. 2A is a perspective view of the
structure, and FIG. 2B is a cross section in the plane defined by
A-A' in FIG. 2A. FIGS. 2A and 2B also indicate the definitions of
the bottom side and top side of all the embodiments and their
variants shown in the figures hereof, in which it can be seen that
all levels are described relative to a substrate at the "bottom" of
the structure. The terms above, below, top, bottom and
superposition as used herein are not intended to change their
meanings if the structure is turned upside down or tilted. In
addition, the term "superposition" refers to aboveness, and is not
limited to superadjacency.
[0031] The preferred use of the embodiment of FIG. 2 is as an
emissive pixel in a visual display, where the medium may comprise,
for example, phosphors that generate optical radiation upon
excitation with light at a different wavelength as described above.
Generated light emitted from the medium is directed towards a
viewer, a screen or perhaps an optical scanning device. For an
embodiment that uses upconversion phosphor, infrared laser light
propagates along an optical beam path 204 in an integrated optical
waveguide structure 240, disposed on or integrated directly into a
substrate 245, and enters the medium 210 through the waveguide
aperture 215. An optical beam path is defined as the direction of
propagation of a light beam in a planar or channel waveguide, or in
a bulk material. In a display, many pixels (such as any one or more
of those described herein) are arranged in an array and are
selectively excited with modulated input optical energy to produce
an image.
[0032] The top surface of the medium 210 is coated with a
reflective material 230, henceforth referred to as a top reflector,
that may have an optically transmissive aperture 235, henceforth
referred to as the top aperture, which allows the emission of light
from the structure. The top aperture substantially transmits at
least the generated light. The top reflector can be any kind of
reflective material including metallic or dielectric coatings that
reflects radiation at one or more wavelengths. There may be more
than one top aperture in the top reflector and the top aperture(s)
may be at any location on the top surface of the medium 210 and
have any shape. This allows for the design of the spatial intensity
distribution of the output light. Preferably, the top reflector
desirably should directly confront the bottom reflectors 250, 255
and 260 disposed on the surfaces of the pit 275 and optical
waveguide structure 240, to minimize the number or area of unwanted
optical apertures in the device. The top reflector may consist for
instance of a multi-layer dielectric coating (as know in the art of
optics) which is designed to preferentially reflect the input/pump
light and transmit part or all of the generated light. Thus a
defined aperture may not be necessary. Equally, the dielectric
coating may highly reflect both input/pump and generated
wavelengths and the aperture(s) may be formed by a hole in the
coating layers at one or more position(s) on the medium. A further
arrangement is a combination of the metallic and dielectric
reflectors where the metallic reflector may provide the confinement
for the generated light and the dielectric coating the confinement
for the input light. In this way, an aperture may be opened in the
metallic coating to allow emission of the generated light without
allowing emission of the input/pump light, as the dielectric
coating remains continuous across the surface of the medium.
[0033] The presence of the top reflector results in
un-wavelength-converted input light emanating from the medium,
being reflected back into the medium instead of emerging. This
increases the fraction of the input light that is confined to the
medium and is available for wavelength conversion and thus
increases the amount of generated light produced by the re-radiator
medium, compared to the structure of FIG. 1 which has no top
reflector. The optical performance of many re-radiator materials
will be enhanced through increased absorption in such a structure.
For example, input light at 300-400 nm will be absorbed by a
re-radiator material comprising BaMgAl.sub.10O.sub.17 doped with
divalent europium ions resulting in the efficient generation of
light in the 450 nm region. For some materials such as
BaY.sub.2F.sub.8 doped with trivalent ytterbium and trivalent
thulium ions, an upconversion material that has an efficiency of
infrared-to-blue conversion that increases super-linearly as the
excited ytterbium ion density increases, the increase in the amount
of light absorbed in the upconversion particles translates into an
increased conversion efficiency per absorbed photon when using the
pixel structure of FIG. 2.
[0034] In one embodiment, the medium 210 comprises a polymeric
binder material, such as an acrylate or epoxy that contains
upconversion phosphor particles 225 of, for instance, yttrium
fluoride doped with ytterbium and erbium, that absorbs input light
of wavelength around 980 nm and converts part of it to shorter
wavelengths in the visible spectral region to create red, green,
and blue light. As such, the binder material serves several
functions including (i) being a host that binds together the
upconversion phosphor particles 225 and providing a vehicle for
deposition, (ii) providing a means to define a desired shape to the
medium 210 and (iii) defining a refractive index boundary between
the binder material and the upconversion phosphor which allows
design of a specific optical scattering coefficient for the medium
210. In the latter function, for example, a binder can be chosen
that has a refractive index that closely matches that of the
phosphor material, glass or crystal so that input light and/or
output light exhibits essentially no optical scattering. Input
light propagates through the medium undergoing scattering and
absorption due to interaction with the re-radiator material and
undergoing reflection at the top reflector 230 or the reflective
coatings 250, 255, and 260 at the base of the medium, until it is
absorbed by the phosphor particles 225, or escapes through the top
aperture 235, or escapes through the waveguide aperture 215, or is
absorbed by any of the reflective coatings, or is absorbed by a
residual absorption of the polymeric binder material. Optical
absorption of the polymeric binder is preferably very low at the
input and generated wavelengths.
[0035] Preferably the decrease in input light intensity within the
medium due to absorption by the upconversion phosphor should
dominate other absorption and loss effects, such as due to the
binder material and reflector material, in order to maximize the
efficiency of emission of useful generated light by the structure.
The output light generated by the re-radiator material then
propagates through the medium, which preferably should have a small
absorption coefficient at this wavelength relative to the
absorption coefficient at the input light wavelength, and, after
possibly many reflections inside the medium from the reflective
coatings, emerges from the top aperture 235, or escapes through the
waveguide aperture 215, or is absorbed by the reflective coatings
or by the re-radiator or polymeric binder.
[0036] Of course, the device of FIG. 2 may contain other
re-radiator materials such as downconversion phosphors designed for
example to absorb blue light and generate, say, red or green light.
Alternatively, the re-radiator material may comprise a material
that scatters light but does not have a significant absorption at
the wavelength of the input light delivered via the waveguide.
[0037] It will be apparent to those skilled in the art that the
number, location, and shape of the top apertures 235, the type of
reflector material, as well as the type of re-radiator materials
and the spatial distribution of the re-radiator particles 225 in
the medium significantly influence the device performance as a
pixel for a display application, and that different material
choices and/or different applications lead to variations in
embodiment. For example, if a reflector material of relatively low
reflectivity at the generated light wavelength is used, the top
aperture may need to be of larger total area than if a high
reflectivity reflector is used so as to minimize cumulative losses
at the reflector interface within the device, by minimizing the
average number of reflections experienced by a ray of generated
light before it escapes through the top aperture.
[0038] A device of the type illustrated in FIG. 2 can in one
example use as a re-radiator an upconversion phosphor doped with
ytterbium and erbium ions mixed with a polymeric binder. It can be
fabricated by depositing a mound of the medium in a pit that
intersects a channel waveguide on a substrate. The mound is cured
then coated with a layer of metal to create the top reflector, and
a top aperture is created on the top surface. Upon excitation with
radiation of wavelength around 980 nm delivered through the
waveguide, a four-fold increase in the optical performance (visible
power emerging from the top aperture divided by power input into
the mound) of the device can be observed relative to a device of
similar design without the top reflector metal coating. Other
designs will provide either more or less enhancement.
[0039] The embodiment of FIGS. 2A and 2B may be fabricated as
follows. A planar optical waveguide structure is disposed on the
top surface of a substrate material. This structure may consist of
a series of separately deposited layers, for instance glasses or UV
curing polymers, each with a different refractive index dependent
on their position in the structure. For instance, a low index lower
cladding layer 265 may be deposited and cured (if necessary) on the
substrate surface (for instance by spin/spray/dip coating, slot-die
extrusion or vacuum deposition for polymer and spin-on-glass
materials, sputtering, evaporation or chemical vapor deposition for
hard oxides and glasses).
[0040] A waveguide core layer 205 is deposited and cured on top of
the lower cladding layer (or alternatively directly on top of the
substrate), using a technique compatible with both the core layer
and lower cladding materials. The refractive index of the core
layer must be greater than that of the lower cladding layer (or the
substrate if there is no lower cladding layer), and the combination
of the refractive index difference and the core layer thickness
should be sufficient to provide optical confinement for at least
one transverse mode in the waveguide structure. This combination
can readily be computed by a person skilled in the art based on the
mathematical waveguide analysis found for instance in the "Optical
Integrated Circuits" reference incorporated above. The thickness of
the lower cladding layer (if used) should be great enough to ensure
that the evanescent field of the guided mode has decayed to
substantially zero before it reaches the substrate-lower cladding
interface to prevent coupling of light into the substrate and
potentially high optical propagation losses.
[0041] A channel waveguide, or array of channel waveguides may be
disposed over all or part of the planar optical waveguide structure
by any of the methods known in the art compatible with the
materials system chosen. For instance, for a polymer waveguide
system, channel waveguides may be defined by reactive ion etching
or laser ablation of the core or cladding layers to provide rib
waveguides, photodefinition of the core or cladding layers or by
photobleaching. For glass based, or other hard oxide materials
(e.g. SiO, dopants can be incorporated into the core layer (e.g.
Ge) and wet or dry (e.g. RIE) etching used to pattern ridge
waveguides. Patterned indiffusion of dopants (e.g. metals, Ti, Zn,
Ag) into a uniform core layer, or into the surface of the substrate
itself can also be used to provide a localized refractive index
increase and a channel or planar waveguide structure. Channel
waveguide segments may terminate at or upstream of the input
waveguide aperture of a pit.
[0042] The pattern of channel and planar waveguides may be
registered to alignment marks to enable accurate relative placement
of the waveguides and the pixel pit structure, and of other
features not related to the pit, as necessary. The channel
waveguide pattern provides a light distribution structure and may
form an optical beam path to deliver light to the pixel
structures.
[0043] A third layer 270, termed the top cladding or buffer layer,
may be disposed over the top surface of the core layer. The
function of this layer is to isolate the optical mode in the core
of the waveguide from features later deposited on the surface of
the device, so that the optical mode propagates in the waveguide
structure without interference except at carefully selected
locations, such as the pixel pit. The refractive index of the top
cladding must be less than that of the core layer, and the
combination of the index difference (core-top cladding) and the
cladding thickness should be sufficient to cause the evanescent
field of the waveguide mode to have decayed substantially to zero
before it reaches the top surface of the top cladding layer.
[0044] Alternatively, the waveguide can be formed directly in the
top surface of the substrate by an indiffusion technique, such as
metal indiffusion (e.g. Ti, Zn) in lithium niobate or tantalate, or
ion exchange (e.g. Ag) in glass. Other waveguide fabrication
methods are well known in the art, and can be tailored for
application to different substrate materials. Top cladding (buffer)
layers may be applied as described above to protect the waveguide
mode from unwanted interference from elements on the top surface of
the device, above the cladding layer.
[0045] The pit can be formed at pre-selected locations, aligned to
the waveguide pattern described above, by one or a combination of
several methods. The pit itself can be formed by any of the surface
micro-machining or etching methods known in the art which are
compatible with the materials used in the waveguide structure
construction. For instance, a polymer optical structure may be
etched by excimer laser ablation, RIE (Reactive Ion Etching,
typically using fluorine based chemistries), or in some instances
wet chemical etching. Other optical materials such as glasses and
crystals can be etched using broadly the same techniques, but with
detailed changes to the etching chemistry, or wavelength in the
case of excimer laser ablation, to match the specific properties of
the material. The exact parameters of the etch process will depend
on the chemistry of the materials used in the waveguide structure.
For instance, the wavelength used for laser ablation must be
strongly absorbed in the material (e.g. wavelengths around 248 nm
or 193 nm are commonly used), or the RIE process must use the
appropriate chemistry to provide volatile by-products which can
remove the etched material (e.g. fluorine based gases are often
used for etching polymer materials).
[0046] The shape and location of the pit can be defined by
lithographic masking and patterning processes aligned to the
waveguide structures. The depth of the pit may, if desired, vary
across the width and length of the pit. The pit may extend
completely or partially through the optical waveguide structure,
and may even penetrate the substrate. In the embodiment of FIG. 2
the pit cuts through the waveguide core layer in at least one point
that intersects the optical path of light propagating in the
waveguide structure, such that the waveguide delivers light to the
re-radiator material disposed in the pit. For an etch process such
as excimer laser ablation, the pit depth may be controlled by
applying only a certain number of ablation pulses to the material.
The pit shape in the depth direction, (e.g. the angles of the side
walls) can be controlled by the detailed process parameters used to
perform the etching. For instance with excimer laser ablation, the
wall profile may be varied by altering the beam dimension and
fluence as a function of etch depth into the structure. Vertical
and angled walls (e.g. 45.degree.) can be created in this manner.
The base of the pit may be flat or curved as desired for the pixel
structure. For instance a curved base to the pit may be used to
preferentially reflect generated light directly through the top
aperture without undergoing further reflections from the reflector
disposed at the surface of the medium. This may decrease the amount
of generated light lost to absorption within the medium or on the
reflectors, and provide some directionality to the output light
emerging from the top aperture. The curved base may be fabricated
via laser ablation in a manner analogous to the controlled profile
of the pit walls, that is, by changing the laser beam dimension or
intensity profile as a function of the depth of the pit, the amount
of material ablated by each laser pulse will vary across the pit
dimensions, resulting in a non-planar profile to the base.
[0047] After etching the pit, a reflective coating is preferably
deposited on the surface of the pit structure, for instance by
sputtering of a thin metal layer (e.g. Ag), or by the deposition of
a multi-layer-dielectric thin-film coating. Lithographic patterning
(e.g. photoresist masking followed by a wet chemical etch or RIE,
or excimer laser ablation) can be used to remove the reflector from
unwanted locations, such as the waveguide aperture where the pit
intersects the optical beam path of the waveguide structure. The
lithographic pattern used is aligned to the intersection of the
optical beam path and the pit so as to form the optically
transparent waveguide aperture for delivering light to the medium
in the pit.
[0048] An alternative fabrication technique may use a directional
deposition process such as e-beam evaporation (as opposed to the
generally non-directional deposition obtained from a sputtering
system) to deposit the reflective coating on the surfaces of the
pit. Here, a deposition may be performed whereby the pit is
oriented relative to the direction of the deposition source such
that the face of the pit containing the waveguide aperture is
substantially shadowed from the deposition and remains uncoated
with reflective material. This avoids a later lithographic
processing of the reflective material in order to define the
optically transparent waveguide aperture and align it with the
intersection between the optical path and the pit, thus reducing
the overall number of steps in the fabrication process and in
particular reducing the number of steps that require accurate
alignment procedures.
[0049] The medium which may for instance comprise an upconversion
phosphor mixed with (suspended in) a curable polymer binder, is
then deposited into the pit. The binder may be cured by exposure to
UV, visible or IR light, by heat, or by evaporation of solvents.
The medium comprising the re-radiator material should be chemically
compatible with the materials used for the waveguide structure
fabrication. The medium may be deposited into the pit by a variety
of techniques including, but not limited to, stencil printing,
volumetric dispensing with a syringe, inkjet printing or
rotogravure printing. The material (i.e. polymer binder) may then
be cured to achieve structural integrity of the medium. The medium
may overlie the top surface of the waveguide structure outside of
the dimensions of the pit, or it may incompletely fill the pit. No
constraint is set as to the shape of the medium in the vertical
direction. The shape of the medium in the plane of the waveguide
structure may be controlled by the deposition technique, for
instance by the volume of medium dispensed from a syringe. Note
that for some deposition techniques, additional components such as
surfactants or fillers may be required in the binder to achieve
uniform deposition. In some manifestations, the binder may comprise
inorganic material, such as phosphoric acid or an alkaline metal
silicate solution.
[0050] In certain embodiments it may be preferable for the pit to
be significantly smaller than the medium. In this case the pit can
act primarily as an out-of-plane mirror to redirect the input light
up into the body of the medium where it interacts with the majority
of the re-radiator.
[0051] A second reflector is preferably deposited on the top
surface of the medium, for instance by the sputter or evaporation
of a thin layer of metal (e.g. Ag). Lithographic patterning (e.g.
wet etching or laser ablation) may again be performed to remove the
reflector from unwanted areas, such as the top aperture on the top
surface of the medium, providing an optically transparent emission
aperture for output light created by the re-radiator material
within the medium. Additionally, other coating methods may be used
to apply the reflector, which does not have to be a thin film. The
functionality of the reflector is to provide a high reflectivity at
the interface between the medium and the reflector. Thus the
reflector may be composed of a thin metallic film, but equally it
may consist of a thick layer, of for instance solder or silver
paste, deposited by dip coating, spray coating or stencil or screen
printing, as indicated by reflector 305 in FIG. 3. The reflector
305 could even planarize the top surface 310 of the device,
eliminating the surface topography of the medium 315 disposed on
the waveguide structure 320. Whatever the form, thickness or
material of the reflector, an aperture 325 is preferably created at
some position to enable output light to emerge from the medium.
[0052] The use of laser ablation to define the top aperture in the
reflector also enables the creation of a hole (a depression or a
crevice) 405 in the top of the medium 410, as indicated in FIG. 4.
This can be created simply by exposing the medium to further pulses
from the excimer laser ablation system after the reflective layer
has been removed. Provided that the medium 410 absorbs the excimer
laser radiation the hole can be ablated in the same way as
described above to create the pit. This hole in the top of the
medium may be used to enhance the amount of output light emerging
from the medium, while maintaining confinement of the input light.
In the case of the generated light being of shorter wavelength than
the input light, the generated light will be more strongly
scattered at the surfaces of the etched hole and thus is more
likely to exit the medium through the top aperture in the reflector
than is the input light. In addition, a transparent material 415
could be applied to fill the hole thus providing a lensing effect
to give directionality to the generated light.
[0053] The optical performance of the structures described herein
depends on a series of design parameters. For different uses of the
structures, different choices for one or more of these parameters
may be required to achieve the desired optical performance of the
structure. These factors include, but are not limited to, device
dimensions, absorption coefficient of the medium, the volume
fraction of the re-radiator in the medium, the volume fractions of
the phosphor/binder in the re-radiator, reflectivity at pump and
generated light wavelengths of the reflectors, divergence of input
light from the waveguide as it enters the pit, refractive index
mismatch between the phosphor and binder, and the size of the
waveguide aperture. The number, size, shape and position of top
apertures in the reflector may be optimized for a given set of
values for the device dimension and other aforementioned
parameters.
[0054] One embodiment includes a reflector material with high
reflectivity at the wavelengths of both the input and generated
light. The size of the input aperture is small compared to the top
aperture(s), while still allowing the desired amount of input light
to enter through it, in order to minimize input and generated light
escaping through the input aperture and to maximize the fraction of
generated light that escapes through the top aperture(s). The
volume fraction of upconversion phosphor in the polymeric binder
(or the re-radiator in the medium) is chosen such that the input
light will be substantially absorbed after only a few passes
through the re-radiator material. However, the choice of a phosphor
volume fraction, for example, depends on the reflectivity of the
reflector material. The use of a reflector with high reflectivity
allows for more reflections, compared to the use of a reflector
with lower reflectivity, for the same total optical loss to the
reflector material surfaces, and it therefore allows for a lower
phosphor volume fraction. This in turn may require smaller top
aperture size(s) in order to maintain confinement of the input
light. While the size of the phosphor pit and the aperture may vary
significantly in different embodiments, in one example the pit has
approximately a 200 micron diameter and the top aperture has a 50
micron diameter. It is apparent to those skilled in the art that
achieving the desired function with optimal optical performance
involves the optimization of one or more of the aforementioned
parameters.
[0055] Optical energy emitted by the pixel element has a primary
direction of emission, defined by a weighted center of the solid
angle of the emission. For display purposes at least, the primary
direction of emission should be some direction that is not parallel
to the plane of the substrate. Depending on the embodiment, the
primary direction of emission might be away from the substrate or
through the substrate, and need not be perpendicular to the
substrate. A pixel element can also have a second primary direction
of emission in certain embodiments, for example where the reflector
includes more than one aperture.
[0056] In a variation of FIG. 4 an optical fiber may be placed into
the hole 405 in the medium 410 in order to capture the output light
from the medium. The optical fiber may be glued in place to provide
permanent attachment to the medium. In this way the top reflector
and fiber assembly may completely enclose the medium, preventing
light loss from the medium around the edges of the fiber.
Alternatively, a top reflective layer may be applied after the
fiber attachment to cover the region around the hole admitting the
fiber.
[0057] The invention described herein has embodiments other than
the preferred form as a visual display pixel. For example the
devices of FIGS. 1 or 2 may be used as a light source in a data
storage device. Radiation delivered by the waveguide may be
re-radiated with different wavelength, emerge from the medium
towards a collection lens (optional) and be directed onto a data
storage medium, such as a hologram or compact disc.
[0058] In order to avoid unnecessary repetition, it should be
understood that the variations described in reference to FIG. 2
apply to the embodiments described below, and that the variations
described in reference to the figures below also apply to FIG.
2.
[0059] FIG. 5 indicates an embodiment of the invention where there
is no aperture in the top reflector 505 disposed on the medium 510
comprising re-radiator material. Input light propagating along an
optical beam path 515 in the optical waveguide structure 520 and
entering the medium 510 through the waveguide aperture 525 is
confined by reflection in this structure so that the only means for
input light and/or output light from the re-radiator material to
emerge from the structure is through the waveguide aperture 525. In
other embodiments, it may be desired that no light emerge from the
waveguide aperture and all the input light may be absorbed.
[0060] FIG. 6 indicates an embodiment of the invention where there
is no top aperture, but that contains an optically transmissive
aperture 605, henceforth referred to as a bottom aperture, in the
reflector 610 disposed on the surface of the pit 615 at the bottom
of the medium 620. There may be more than one bottom aperture, and
such apertures can be of any shape and at any location on the
surface of the pit 615. Alternatively these bottom apertures may be
located in the reflector on the side walls 625 of pit 615 and/or in
the reflective layer 630 on the top surface of the optical
waveguide structure 635. Input light propagates along an optical
beam path 640 in the optical waveguide structure and enters the
medium 620 through the waveguide aperture 645. The input light is
highly confined by the reflector 650 disposed on the surface of the
medium 620. Output light can emerge from the medium 620 either
through the bottom aperture 605 or the waveguide aperture 645. The
presence of the top reflector 650 will increase the efficiency of
light re-radiation of the structure by the mechanisms described
above, and at the same time provide for propagation of the
generated light through the bottom aperture 605, the optical
waveguide structure 635, and the substrate 655. This would be the
preferred propagation direction in an embodiment of the invention
used as a pixel in an emissive display that is viewed through the
substrate.
[0061] An alternative fabrication of the basic structure of FIG. 6
incorporates a multilayer dielectric coating reflector under the
medium, which can be designed to provide high reflectivity at the
input light wavelength and to transmit part or all of the generated
light. The dielectric coating may be disposed on the bottom surface
of the pit, or alternatively may be disposed directly on the
substrate before the optical waveguide structure is deposited and
patterned, or on some intermediate layer between the substrate and
the optical waveguide structure. The dielectric coating may, if
desired, be combined with a metallic reflector layer to
independently control the reflectivity and emission apertures for
the input light and the generated light, to optimize the efficiency
of the pixel structure and maximize the emission of the generated
light.
[0062] In the context of using the device described here as a pixel
in an emissive display, a manifestation which incorporates one or
more bottom apertures 605 in the bottom reflector 610 along with
one or more top apertures 235 (FIG. 2), can provide a structure
with apertures on opposing sides of the medium. Such a structure
will simultaneously provide high confinement of the input light and
increased optical efficiency, compared to a structure with no
reflector, and enable an emissive display that can be viewed from
both sides of the substrate 655.
[0063] FIG. 7 indicates a modification that can be applied to any
of the embodiments described herein, with two optical beam paths
705, 710 in the optical waveguide structure 715, through which
input light can be delivered to the medium 720 through waveguide
apertures 725, 730, respectively disposed at the intersection of
the pit 735 and the optical beam paths. Output light can also
escape through the waveguide apertures 725, 730 into the optical
waveguide structure 715. There may be more than two such optical
paths terminating at waveguide apertures in the pit 735, and these
optical paths may come from any direction in the plane of the
optical waveguide structure 715. Light from one or several light
sources may be delivered along these optical beam paths to the
medium. Thus, this embodiment may provide for further improvement
of the optical performance by, for example, delivering additional
input light from a second laser source (at the same or different
wavelength) through waveguide 710 and waveguide aperture 730 to
medium 720 for the purpose of increasing input power to the
re-radiator material. This embodiment may also enable the use of
two or more different types of input radiation, for example light
at different wavelengths, for the purpose of enhancing the
efficiency of the desired wavelength conversion process in the
re-radiator material.
[0064] FIG. 8 indicates another modification that can be applied to
any of the embodiments described herein and is demonstrated as a
variation applied to the device of FIG. 2 as an example. Input
light propagating along an optical beam path 805 enters the pit 810
through waveguide aperture 815. In this device, the medium in the
pit does not contain only the re-radiator material but rather, as
an example, also contains a portion of material that is optically
transparent to the input light. In this particular example, the
re-radiator is disposed uniformly through only an upper volume of
the medium, with substantially no re-radiator in the lower volume
of the medium. It will be apparent that the re-radiator may
alternatively be "clustered" in a predetermined location within the
upper volume of medium or otherwise distributed. Optically
transparent is defined as having minimal absorption at the
wavelength of input and generated light. This "transparent"
material may consist for instance of transparent glass, organic
resin, or a gas such as air, and may in particular be the binder
material containing no re-radiator material. It will be understood
that the term "medium" in this context is intended to include media
containing more than one substance, even if the substances are not
intermixed, and even if the substances are deposited in different
process steps.
[0065] The top surface of the transparent material may be above or
below the top surface of the optical waveguide structure and is not
necessarily planar or flat. Preferably the optically transparent
material is disposed adjacent to the waveguide aperture. After
entering the pit 810 through the waveguide aperture 815 the input
light propagates along the input plane within the optically
transparent material without interacting with the re-radiator
material, since there is substantially no re-radiator in this input
plane. The light may enter the portion of the medium containing the
re-radiator material 820 by means of scattering and/or refraction
at the interface 825 between the optically transparent material and
the re-radiator material 820. The interface 825 may be smooth or
rough. If the interface is sufficiently smooth, internal reflection
of at least part of the input light may occur as the light
traverses the pit. In combination with a reflective surface 830 at
the bottom of the pit 810, this allows for the input light to
preferentially propagate toward the side of the pit that is
opposite the waveguide aperture 815. If the refractive indices of
the optically transparent material and the re-radiator are chosen
correctly (as described in any text on optical waveguide design,
see for instance The Optical Integrated Circuits reference
incorporated above), the combination of the reflector disposed on
the surface of the pit and the interface 825 may act as an optical
waveguide. A reflective or diffractive (for instance, a grating)
outcoupling element on the distal side wall 835 of the pit may be
oriented (e.g. slanted) to direct input light from the pit into the
portion of the medium containing the re-radiator material 820. Such
reflective or refractive outcoupling elements may also be located
on the other walls or the bottom of the pit itself.
[0066] In an embodiment as a pixel that generates visible light for
a display application and where the re-radiator material includes a
binder material and/or a wavelength converting material such as an
upconversion or downconversion phosphor, the scheme shown in FIG. 8
offers the advantage, relative to the case of FIG. 2, of generating
less of the generated light in regions that are close to the
waveguide aperture 815. Therefore the generated light has an
increased probability of exiting the structure through the top
aperture 840 from where it can be directed towards the viewer. The
structure of FIG. 8 may also be fabricated using a multilayer thin
film dielectric coating (e.g. a multilayer stack of alternating
SiO.sub.2/TiO.sub.2 layers) as a dichroic filter deposited at the
interface 825 to allow input light at a first wavelength to enter
the portion of the medium containing the re-radiator material 820
and designed to reflect generated light emitted from the
re-radiator material back into the re-radiator material to emerge
from the re-radiator through the top aperture 840. This type of
interfacial reflector will prevent light generated in the
re-radiator material from escaping through the waveguide aperture
815. For example, if the re-radiator material includes an
upconversion material such as erbium-doped YF.sub.3 that generates
green light when excited with infrared light around 1500 nm, 980 nm
or 800 nm the interfacial dichroic filter may be designed to
transmit the infrared wavelengths and to reflect green light so
that the generated green light does not enter the transparent
region and then escape through the waveguide aperture.
[0067] The structure described above could be fabricated using a
two stage deposition process. The pit may be located and fabricated
as described above for the embodiment illustrated in FIG. 2. A
first deposition step may be used to deposit the optically
transparent material into the pit adjacent to the input aperture,
the material may over-fill the pit and protrude above the surface
and extend out onto the top surface of the optical waveguide
structure, or the material may incompletely fill the pit and lie
beneath or flush with the top surface of the waveguide structure.
The top surface of the optically transparent material is not
required to be planar or parallel to the top surface of the optical
waveguide structure. This first deposition step could consist for
instance of a screen or stencil printing process, or an inkjet or
volumetric (via syringe) deposition of the transparent material.
The material should then be cured if necessary before a second
deposition process, which may be the same or different to the
first, is used to add the second layer of material containing the
re-radiator. Following curing of the second layer (if necessary)
the top surface of the mound may be coated with a reflector as
previously described and an aperture created to allow the emission
of output light. If desired, a multi-layer dielectric coating may
be deposited, by for instance electron-beam evaporation, on the
surface of the transparent material before the deposition of the
re-radiator medium.
[0068] An alternative method of fabrication of the embodiment of
FIG. 8 is shown in FIG. 9. Here the upper volume of the medium has
been created in a separate layer structure 905 to the optical
waveguide structure 910 and then attached (for instance glued or
laminated) to the surface of the waveguide structure in alignment
to the pit(s) 915 therein. This fabrication route offers the
potential for the creation of taller medium 920 structures that
offer advantages in terms of single pass absorption efficiency of
the input light, minimization of reflection losses on the surface
of the medium, and increased directionality of the generated light
emission from the top aperture. One route to fabricate the
illustrated device would be as follows: A flexible (e.g.
Mylar.RTM.) (or non flexible) substrate 905 with a thickness
preferably greater than the desired height of the medium, is
patterned to provide a depression 925 with the desired shape of the
medium. This depression could be fabricated by embossing, molding,
wet etching, reactive ion etching or excimer laser ablation,
depending on the choice of substrate material (at least the latter
two processes would be suitable for a plastic (e.g. a Mylar
.RTM.)substrate). A reflective layer 930 is then disposed on the
interior surface of the depression, for instance by the sputtering
of a thin metal layer onto the structure. The non-directionality of
the sputtering process enables the 3-dimensional surface of the
depression to be covered with a continuous layer of material. The
reflective layer is then patterned to open an aperture 935 at the
bottom of the depression, either using lithographic exposure and
wet etching, or more simply by direct material removal using a
projection excimer laser ablation system. After patterning the
reflector, the medium 920 is deposited into the depression, for
instance by screen or stencil printing, or inkjet or volumetric
(syringe) deposition. Preferably the deposition process should
leave the medium flush with the surface of the substrate or
recessed slightly beneath the surface, rather than protruding from
the surface of the substrate. The medium filled substrate 905 is
then placed over the optical waveguide structure 910 as indicated
in FIG. 9 and aligned so that the entrance to the medium filled
depression is above the reflector 940 coated pit created in the
optical waveguide structure (which may be fabricated as described
in the embodiments detailed above). A suitable glue may be disposed
between the two substrates, for instance it may be screen printed
onto one or the other substrate before they are aligned and brought
into contact. The glue may, if desired, form the optically
transparent material described above and fill the pit adjacent to
the waveguide aperture. Thus, light propagating along an optical
beam path 950 within the optical waveguide structure 910 enters the
pit through the waveguide aperture 945 and is directed into the
medium by the reflector 940 coated pit structure. Output light
emerging from the medium is emitted from the top aperture 935
opened in the reflector layer 930 surrounding the medium.
[0069] FIG. 10 shows an embodiment of FIG. 2 in which the medium
comprises a spatially non-uniform distribution of re-radiator
material 1005, such as upconversion phosphor particles in a binder
material, disposed between two optically transparent materials 1010
and 1015 (which may or may not be same material). The re-radiator
may be placed in a particular location in the structure for several
reasons. For example, the re-radiator may be more efficient if
concentrated in a region within the structure where the input light
excitation density is higher than at other locations in the medium.
Alternatively, the re-radiator material 1005 may be preferentially
located close to the top aperture 1020 where the generated light
can more directly exit the top aperture 1020 in the top reflector
1025 thereby requiring fewer reflections from the reflective
coatings before exit. A further embodiment may comprise a
re-radiator material that itself comprises a spatially non-uniform
distribution of phosphor particles for the reasons explained
above.
[0070] Several methods may create a spatially non-uniform
distribution of re-radiator in the medium. For example, an
optically transparent polymeric binder material might first be
deposited by stencil printing, ink jet printing or spin coating,
and a second material comprising, for example a polymeric binder
containing upconversion phosphor might be stencil printed on top of
the first layer. If desired, additional optically transparent
material may be deposited on top of the re-radiator material and
part or all of the structure may be covered with reflector.
[0071] Of course, the spatial nonuniformity of re-radiator is not
restricted to the use of layers or to the use of one type of
re-radiator. For example, two or more small mounds of different
re-radiator materials may for example, be deposited in a pit and an
additional material may be deposited over the combination of
re-radiator mounds. A reflector may be deposited over the entire
structure. The reflector will ensure good absorption of light by
the appropriate re-radiators. Multiple layers of materials, or
small mounds of different re-radiator materials may be deposited
serially in a sequence of deposition steps. For instance, screen or
stencil printing and curing of the underlying transparent layer may
be followed by individual volumetric depositions (or inkjet or
stencil prints) to create layers or mounds of re-radiator
materials, followed by a final deposition of transparent material
to cap the re-radiator material.
[0072] FIG. 10 also demonstrates that the structure may, if
desired, contain only a small volume of one component and a larger
volume of a second. For example, the upconversion phosphor
particles in the re-radiator 1005 may occupy only a small fraction,
say 5% of the total volume of the medium. Confinement of the input
light by the reflective surfaces thereby increases the total input
light energy that is absorbed per upconversion phosphor particle.
The resultant increase in excitation density within the phosphors
will provide a higher efficiency of conversion of infrared to
visible light within the phosphor particles. This enhancement will
occur whether the phosphor particles are distributed evenly, as a
small volume fraction, or unevenly.
[0073] It is also within the scope of the invention to utilize a
specific shape to the medium and therefore the top reflector 1025
to create, by reflection, localized regions of higher intensity of
light within the medium. Preferably the shape will maximize the
intensity of input radiation at the same spatial location as the
re-radiator material thus maximizing the excitation density and
efficiency of the re-radiation process. Suitable shapes to perform
this function would include parabolic profiles, or generally
concave reflection surfaces.
[0074] FIG. 11 shows a further embodiment of the invention using
multiple depositions of different materials to create a mound of
optical re-radiator in a medium. In this case a portion of
optically transparent material 1105 is deposited and cured (if
necessary) over and in the reflector coated pit 1110 formed in the
optical waveguide structure 1115 (fabricated as described in the
embodiments above). A depression 1120 is created in the top surface
of the optically transparent material, for instance using excimer
laser ablation or reactive ion etching to remove material from a
desired area. The shape/profile of the depression may be controlled
during the etch process as described for the embodiment of FIG. 2,
leading preferably to a parabolic or near parabolic shape.
Following the etching of the depression, a reflective layer 1125 is
deposited over the mound of optically transparent material, and an
aperture 1130 is opened as described above. The aperture should
preferably be aligned relative to the reflector coated pit in the
optical waveguide structure, such that input light from an optical
beam path 1135 within the optical waveguide structure 1115 enters
the pit 1110 and is redirected through the aperture. Re-radiator
material 1140 is deposited into the depression formed in the top
surface of the mound of optically transparent material, superposing
the reflector layer, using any of the deposition methods previously
described. The re-radiator material may protrude above the top
surface of the transparent material, or it may be flush with or
recessed below the top surface. Preferably, a multilayer dielectric
mirror 1145 (e.g. a stack of alternating layers of SiO.sub.2 and
TiO.sub.2 is deposited over the top surface of the mound of
re-radiator to preferentially reflect the input light and transmit
light generated within the re-radiator.
[0075] FIG. 12 shows a structure which enables the design of a
controlled delivery of input light to desired locations in the
medium. At least part of the bottom of the pit 1205 does not extend
further down than to the plane defined by the top surface 1210 of
the integrated optical waveguide core 1215, and at least another
part of the bottom of the pit 1220 extends at least as far down as
the plane defined by the bottom surface 1225 of the integrated
optical waveguide core 1215. As a result, the optical waveguide
core layer 1215 may extend partially into the medium 1230 and input
light propagating through the optical waveguide core 1215 may be
only partially confined within the waveguide core and may outcouple
from the waveguide into the medium 1230. Optionally, a reflective
coating 1235, such as a metallic or dielectric reflector, may be
deposited onto the surface of the pit 1205 in the section where the
waveguide extends into the medium 1230.
[0076] Alternatively or additionally a metallic or dielectric
reflector 1240 may be disposed directly on the surface of the
substrate, or on some intermediate layer 1245 between the substrate
1250 and the optical waveguide structure 1255, before the
deposition of the optical waveguide structure. This reflector layer
can be designed to reflect one or both of the input light and
generated light that emerges from the medium towards the substrate
back into the medium for emission through the top aperture 1260.
The pit may extend from the top surface of the optical waveguide
structure 1255 completely through the structure to reach the
reflector disposed beneath the structure, such that a reflector
1265 disposed on the side walls of the pit abuts the reflector 1240
on the substrate leaving substantially no area for light to escape
the medium at this location.
[0077] Such a structure may be fabricated by several methods
including the following multi-step process. Firstly, a
lithographically defined etch technique is used to create a pit
that extends into the top surface of the waveguide structure as
described above. A multi-step etch process may be used to vary the
depth of the pit at different locations, for instance using two
lithographic masking steps for an RIE process, or using two
different projection exposure masks for a laser ablation etch. The
two masks used must of course be correctly aligned to ensure the
desired overlap of the different depth regions of the pit.
Deposition and patterning of a reflective layer 1235, 1265 on the
bottom and side surfaces of the pit may be performed for instance
by sputter coating and wet etching of a thin film metal layer. The
medium 1230 may be deposited into the pit by any of the techniques
previously described, and the top surface of the medium coated with
a reflector 1270 and provided with a top emission aperture as
previously described. Thus the structure of FIG. 12 may be created,
with an initial region where the pit is etched only partially into
the upper cladding or core layer, followed by a second section
where the pit extends deeper, to completely remove the core layer
in at least one location within the pit.
[0078] Additionally, FIGS. 13A and 13B show an alternative
technique for controlling the delivery position of input light to
desired locations in the medium 1305. In these embodiments, the
medium 1305 is positioned off center from the pit 1310. By
controlling the relative positions of the medium, input aperture
and distal reflecting surface 1315, the path of input light 1320
can be controlled within the medium. Thus it is possible to
preferentially direct the input light towards the front, center or
back of the medium (and similarly in the lateral dimension not
shown in the cross-sectional FIGS. 13A and 13B). As shown in FIG.
14 a further embodiment is such that the medium 1405 does not
superpose all the surfaces of the pit 1410 but at least superposes
the input face 1415 comprising the input aperture 1420.
[0079] Note that in all the embodiments described above there is no
limitation on the relative dimensions of the pit and the medium. In
certain embodiments it may be preferable for the pit to be
significantly smaller than the medium such as in FIG. 13A. In this
case the pit 1310 can act as an out-of-plane mirror to redirect the
input light up into the body of the medium where it interacts with
the majority of the re-radiator. In addition, consider the case of
FIG. 15 in crossectional view where at least two pits 1505 and 1510
are disposed to deliver input light propagating in one or more
optical beam paths 1515, 1520 to a common medium 1525.
[0080] FIGS. 16 and 17 indicate embodiments in which the pit (1605
in FIG. 16 and 1705 in FIG. 17) that terminates the optical energy
path from the waveguide 1610, 1710 does not also support the medium
containing the optical re-radiator. Instead the medium is supported
in a well (1615 in FIG. 16 and 1715 in FIG. 17) substantially above
the waveguide core, but close enough to the core such that input
light energy propagating within the waveguide is transferred to the
medium by evanescent coupling. The term "well", as used herein,
does not itself imply any particular depth relative to the core
layer. Optimizing evanescent coupling enables the design of
distributed energy delivery into the re-radiator material. The
separation between the bottom surface of the well and the core of
the waveguide is determined by a combination of the following
parameters: the desired strength of evanescent coupling, and the
difference in refractive indices between the medium or the
re-radiator material and the core and top cladding layer materials
of the waveguide structure. The closer the well approaches the
waveguide core, the stronger the optical coupling.
[0081] In FIG. 16, the pit 1605 which intersects the optical beam
path of light propagating within the waveguide core 1610 extends
below the waveguide core at a surface 1620. The pit 1705 in FIG. 17
similarly extends below the waveguide core 1710 and intersects the
optical beam path of the core 1710. A reflector 1725 may be
deposited on the intersecting surface as shown in FIG. 17, and/or,
as shown in FIG. 16, an absorber material 1625 may be deposited
within the pit 1605 to prevent further propagation of light along
the intersected optical path. An optical absorber material is one
that is opaque to light of at least the wavelength of the input
light and optionally the generated light. Note that if a reflector
is disposed on the surfaces of the pit 1605 or 1705, then the pit
1605 or 1705 may in some embodiments be filled, or partly filled,
with re-radiator material (rather than optical absorber) and may be
enclosed by the top reflector surmounting the medium.
[0082] In the particular embodiment of FIG. 16 an optional
reflector 1630 with an top aperture 1635 is shown disposed on the
top surface of the medium. Additionally, a dielectric reflector may
be disposed on the bottom surface 1640 of the well 1615 which
allows the evanescent transfer from the waveguide to the medium but
substantially reflects light generated by the re-radiator material
into a direction away from the waveguide core. Alternatively a
metallic or dielectric reflector may be disposed directly on the
surface of the substrate, or on some intermediate layer between the
substrate and the optical waveguide structure, before the
deposition of the optical waveguide structure. This reflector layer
can be designed to reflect one or both of the input light and
generated light that emerges from the medium towards the substrate,
back into the medium before emerging from the top aperture.
[0083] A further embodiment based on the structure shown in FIG. 17
and described above is shown in FIGS. 18A, 18B, and 18C. FIG. 18A
is a perspective view, FIG. 18B is atop view, and FIG. 18C is a
cross section in the plane defined by B-B' in FIG. 18A. In this
embodiment, as shown in FIG. 18A, the core termination surface 1805
of a pit 1810 describes a generally circular shape (a sidewall or
an enclosing shape) that leaves at least one section 1815 open for
the delivery of input light along an optical beam path in the
waveguide 1820 to the region 1825 of the waveguide that is bounded
by the core termination surface 1805; we henceforth refer to this
open section 1815 as the input aperture. There may be more than one
input aperture and the core termination surface 1805 of the pit may
describe any shape in the optical waveguide structure 1830 for
example an oval, quadrilateral or any other polygonal shape and,
optionally, may be coated with a reflector 1835. We henceforth
refer to the area bounded by the core termination section as the
confinement region 1825. The core termination surface 1805 may have
a shape that minimizes the amount of input light, that propagates
in the confinement region 1825, escaping through the input aperture
1815, thereby maximizing the fraction of input light that is
confined to the confinement region by the core termination surface.
This is achieved, for example, by a section of the core termination
surface 1805 acting as a baffle 1840 as shown in FIG. 18B. A well
1845 is located above the waveguide core layer in the confinement
region 1825. The evanescent interaction section 1850 of the well
1845 is that portion of the well 1845 that is disposed above the
waveguide core layer with a sufficiently thin top cladding layer
such that light is coupled from the waveguide into the superposing
medium 1855 by an evanescent coupling method. Deposited on top of
the evanescent interaction section 1850 is a medium 1855.
Optionally, a reflector may be added to the top surface of the
medium 1855. Additionally or alternatively, a reflector 1860 may be
added on the substrate or any surface between the substrate and the
bottom surface of the core layer 1820.
[0084] As shown by the rays 1860 in FIG. 18B, input light
propagating in the core layer 1820 and entering the input aperture
1815, undergoes multiple reflections at the core termination
surface 1805 and propagates in the plane of the waveguide core
layer within the confinement region until it is coupled into the
medium 1855 comprising re-radiator material by the evanescent
interaction, or escapes through the input aperture 1815, or is
absorbed by the reflective coatings. Adjustment of the thickness or
refractive index of the top cladding layer in the evanescent
interaction region 1850 allows for control of the interaction
process that couples input light into the re-radiator material. In
an embodiment of FIGS. 18A-18C where the re-radiator material
contains upconversion phosphor, the evanescent interaction achieved
by this device, for example, may allow for a very uniform
excitation of upconversion phosphor particles near the surface
1850. Output light generated by the upconversion phosphor particles
in the medium can then emerge from the structure and, in the
context of using the structure as a pixel in emissive displays,
provide for a uniform emission pixel on the display screen.
[0085] For applications of any of the embodiments of the invention
as pixels in emissive displays, it may be desirable to deposit a
black material in the regions from which no light is emitted from
the screen. One purpose of this so-called black matrix material is
to absorb ambient light incident on the viewing area of the display
and thereby to prevent ambient light reflected off the screen
toward the viewer from reducing the contrast ratio of pixels on the
display. FIG. 19 is an embodiment of the invention where a layer of
black material 1905 is deposited on top of the top reflector 1910
on the medium 1915. This embodiment provides coverage of
non-emissive areas with black material. In different embodiments
these non-emissive areas could include just the reflector-coated
top surface of the medium 1915 or the entire top surface of the
device except the optically transmissive top apertures 1920 on the
medium, or any other portion of the device top surface. In one
mode, the black material is deposited after the deposition of the
reflective material of the top reflector 1910 and before patterning
of the top aperture 1920. An etching or ablation technique, such as
laser-ablation, can then be used to remove the black material and
the reflective material on the medium in order to create an
optically clear aperture 1920 in a single manufacturing step.
[0086] The black material may be deposited for instance by
evaporating or sputtering an optically opaque (black) material
after depositing the reflective layer, or the black material may
consist of for instance a polymer binder material including a dye
such as Sudan black or carbon black particles, and be deposited by
screen or stencil printing, inkjet printing or spray or dip coating
Note that the aperture in the black material may be larger than
that formed in the reflective layer such that not all the
reflective layer is covered by black material. Alternatively, the
black material may be deposited and patterned if necessary after
the aperture has been formed in the reflective layer. In this case
the aperture in the black material may be smaller than, the same
size as or larger than the aperture in the reflective layer.
[0087] A further embodiment, shown in FIG. 20 allows for a
simplified deposition process of the black matrix by coating the
substrate 2005 with a layer of black material 2010 prior to
creating the various optical layers of the optical waveguide
structure 2015 and the components of the medium 2020. Alternatively
the black material may be deposited on some intermediate layer
between the substrate and the optical waveguide structure. FIG. 21
shows a further embodiment where the optically transmissive
aperture is created in the bottom surface of the medium through the
reflector 2105 and black material layers 2110. In this embodiment,
generated light is emitted through the substrate 2115.
[0088] In a further embodiment, a layer of material may be added to
a substantially planar medium in order to create an optically
smooth layer. If the refractive indices of the materials are
appropriately chosen it is possible to achieve a degree of optical
confinement within the multilayer structure as a result of total
internal reflection at the smooth top surface of the structure. In
this way the input light can be confined within the medium until it
is absorbed, without the requirement to add a further, highly
reflective, layer over the top surface of the medium. A smooth
layer may be created for instance by depositing a layer using one
of the techniques previously described, where the material can
undergo reflow to remove any surface topology induced by the
deposition process or the underlying layer. Following reflow the
layer should preferably be cured to provide a robust surface. A
true reflow process may not be required to achieve the aim of this
embodiment. The deposition of a low viscosity material will result
in a substantial smoothing of the surface topology of an underlying
layer as the low viscosity material is able to flow away from the
high points and into any depressions that may be present. The
degree of planarization achieved will be determined by a
combination of the roughness of the underlying layers and the flow
properties of the upper layer. It will be appreciated that there is
a limit to the minimum material viscosity that can be used before
the material simply flows over the entire surface of the
structure.
[0089] As shown in FIG. 20, an appropriately shaped lens element
2025 may be attached to the medium 2020 above the top aperture
2030. This lens will serve to control the direction and core angle
of light emitted from the device towards a viewer or other sensor.
Such a lens element may comprise for instance, a stencil printed or
inkjet printed transparent epoxy in a three-dimensional ellipsoidal
shape. Similarly, as shown in FIG. 21, for any embodiment
comprising a lower aperture 2120, such a lens 2125 may be added to
the substrate lower surface 2130.
[0090] Unless otherwise specified, the term "substantially" is used
herein to accommodate tolerances including manufacturing tolerances
and optical tolerances (for example, dielectric reflectors
physically can not reflect light at all angles). Omission of the
word "substantially", however, should not be taken to require that
such tolerances are not to be accommodated, since no real-world
manufacturing process can be perfect.
[0091] As used herein, the term "optical energy" is intended to
include energy extending from far infrared to deep ultraviolet
wavelengths.
[0092] As used herein, a given event is "responsive" to a
predecessor event if the predecessor event influenced the given
event. If there is an intervening processing element, step or time
period, the given event can still be "responsive" to the
predecessor event. If the intervening processing element or step
combines more than one event, the signal output of the processing
element or step is considered "responsive" to each of the event
inputs. "Dependency" of a given event upon another event is defined
similarly.
[0093] The specific embodiments of the invention described herein
are intended to be illustrative only, and many other variations and
modifications may be made thereto in accordance with the principles
of the invention. All such embodiments and variations and
modifications thereof are considered to be within the scope of the
invention, as defined in the following claims.
* * * * *