Title: Optical substrate and method of making
Abstract: An optical surface substrate. The optical substrate features a three-dimensional surface having a correlation length of about 1 cm or less. The optical substrate is defined by a first surface structure function modulated by a second surface structure function, the first surface structure function producing at least one specular component from a first input beam of light. The optical substrate is suitable for use in a variety of applications, including brightness enhancement and projection devices.
Patent Number: 6,862,141 Issued on 03/01/2005 to Olczak
| Inventors:
|
Olczak; Eugene George (Glenville, NY)
|
| Assignee:
|
General Electric Company (Schenectady, NY)
|
| Appl. No.:
|
150958 |
| Filed:
|
May 20, 2002 |
| Current U.S. Class: |
359/621; 359/561 |
| Intern'l Class: |
G02B 027//10; G02B 027//46 |
| Field of Search: |
359/621,625,626,559-561,599,239-240
|
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Other References
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1994, pp. 49-58.
Machine Design, "Plastic Film Reflects Around the Corner," p. 52, Aug.
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S.G. Saxe, Solar Energy Materials, Prismatic Film Light Guides: Performance
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pp. 95-109, 1989.
|
Primary Examiner: Epps; Georgia
Assistant Examiner: Harrington; Alicia M.
Attorney, Agent or Firm: Foley & Lardner LLP
Claims
What is claimed is:
1. A method of modeling a surface of an optical substrate, the method
comprising:
defining a first window in a coordinate system;
defining a master function within the first window;
defining a second window as a segment of the first window at a first
location within the first window;
selecting a set of points within the second window;
defining a modulation path interconnecting the selected set of points;
defining a surface function along the modulation path;
modulating the surface function along the modulation path;
combining the modulated surface function with the master function,
generating thereby a three dimensional structural pattern over the extent
of the modulation path.
2. The method as set forth in claim 1 wherein selecting a set of points
within the second window includes randomly selecting a set of points
within the second window.
3. The method as set forth in claim 1 wherein modulating the surface
function along the modulation path includes randomly modulating the
surface function along the modulation path.
4. The method as set forth in claim 1 further comprising moving the second
window to a new location within the first window.
5. The method as set forth in claim 4 further comprising repeating
selecting a set of points within the second window;
defining a modulation path interconnecting the selected set of points;
defining a surface function along the modulation path;
modulating the surface function along the modulation path;
combining the modulated surface function with the master function,
generating thereby a three dimensional structural pattern over the extent
of the modulation path until the second window has been coextensive with
all of the points in the first window.
6. The method as set forth in claim 5 further comprising:
returning the second window to the first location within the first window;
and
repeating selecting a set of points within the second window;
defining a modulation path interconnecting the selected set of points;
defining a surface function along the modulation path;
modulating the surface function along the modulation path;
combining the modulated surface function with the master function,
generating thereby a three dimensional structural pattern over the extent
of the first window until the second window has been coextensive with all
of the points in the first window.
7. The method as set forth in claim 6 further comprising:
generating a mask function from a set of morphologic operators;
convolving the mask function with the surface function; and
performing the Boolean union of the convolution of the mask function and
the modulation function with the master function.
8. The method as set forth in claim 1 wherein combining the modulated
surface function with the master function comprises performing the Boolean
union of the modulated surface function with the master function.
9. The method as set forth in claim 1 further comprising placing a
plurality of three dimensional structural patterns generated over the
extent of the first window side-by-side with one another to form an array
of three dimensional structural patterns.
10. An optical substrate generated by the method as set forth in claim 1,
wherein the three-dimensional structural pattern has a surface, the
surface of the three-dimensional structural pattern defined by a first
surface structure function and a second surface structure function, the
first surface structure function having a length, width and peak angle
with optical characteristics to produce at least one output specular
component from an input beam of light, and the second surface structure
function having a geometry with at least pseudo-random characteristics to
modulate the first surface structure function in at least a phase along
the length of the first surface structure function, the phase being a
horizontal peak position along the width.
11. The optical substrate as set forth in claim 10 having a correlation
function value of 1/e within a prescribed distance from a first location
within the three dimensional structural pattern in a first direction in
the coordinate system.
12. The optical substrate as set forth in claim 11 wherein the correlation
function is an auto correlation function.
13. The optical substrate as set forth in claim 11 wherein the correlation
function is a cross correlation function.
14. The optical substrate as set forth in claim 11 having minimized Moire
patterns.
15. The method as set forth in claim 1 wherein combining the modulated
surface function with the master function comprises performing a boolean
union of the modulated surface function with the master function.
16. The optical substrate of claim 11, wherein the surface is characterized
by a correlation function value of less than about 37 percent of an
initial value within a correlation length of about 1 cm or less.
17. The optical substrate as set forth in claim 10 wherein the optical
substrate is generated by photolithograpy, gray-scale lithography,
microlithography, electrical discharge machining or micromachining using
hard tools to form molds.
18. The optical substrate as set forth in claim 17 wherein the optical
substrate includes a surface having characteristic dimension from 100 mm
to 1 nm.
19. The optical substrate as set forth in claim 10 wherein the first
surface function is a triangle with a width of approximately 40 .mu.m and
a height of between 1 .mu.m and 200 .mu.m.
20. The optical substrate as set forth in claim 10 wherein the first
surface function is a triangle with a width of approximately 40 .mu.m and
a height of approximately 18 .mu.m.
21. The optical substrate as set forth in claim 20 wherein the surface of
the optical substrate is formed with an optically transparent material
with an index of refraction of approximately 1.75.
22. The optical substrate as set forth in claim 10 wherein the first
surface function is a triangle with a base to height ratio of between 40
to 1 and 1 to 10.
23. The optical substrate as set forth in claim 10 wherein the first
surface function is a triangle with a base to height ratio approximately
40 to 18.
24. The optical substrate as set forth in claim 10 wherein the surface of
the optical substrate is formed with an optically transparent material
with an index of refraction of between 1.1 and 3.0.
25. The optical substrate as set forth in claim 10 wherein the surface of
the optical substrate is formed with an optically transparent material
with an index of refraction of approximately 1.75.
26. The method as set forth in claim 1, wherein the three-dimensional
structural pattern is defined by a first surface structure function and a
second surface structure function, the first surface structure function
having a length, width and peak angle with optical characteristics to
produce at least one output specular component from an input beam of
light, and the second surface structure function having a geometry with at
least pseudo-random characteristics to modulate the first surface
structure function in at least a phase along the length of the first
surface structure function, the phase being a horizontal peak position
along the width.
27. An optical substrate, comprising:
a surface characterized by a correlation function value of less than about
37 percent of an initial value within a correlation length of about 1 cm
or less, wherein the surface is defined by a first surface structure
function modulated by a second surface structure function, the surface of
the optical substrate producing specular and diffuse light from a first
input beam of light, the first surface structure function having a length,
width and peak angle with optical characteristics to produce at least one
output specular component from an input beam of light, and the second
surface structure function having a geometry with at least pseudo-random
characteristics to modulate the first surface structure function in at
least a phase along the length of the first surface structure function,
the phase being a horizontal peak position along the width.
28. The optical substrate as set forth in claim 27, wherein the first
surface structure function extends a length from a first end to a second
end of the substrate.
29. The optical substrate as set forth in claim 28, wherein the first
surface structure function has a sawtooth or triangular cross section.
30. The optical substrate as set forth in claim 27, wherein the surface of
the optical substrate comprises a shape that turns and diffuses light to
form a plurality of diffusion ellipses each with a power half angle
between about 0.1 and about 60 degrees.
31. The optical substrate as set forth in claim 30, wherein the power half
angle is between about 1 and about 5 degrees.
32. The optical substrate as set forth in claim 30, wherein first input
beam of light has a first angle of incidence and the surface of the
optical substrate is shaped so that the first input beam of light is
transmitted through the optical substrate and turned by the surface of the
optical substrate to an output angle different from the first angle of
incidence.
33. The optical substrate as set forth in claim 32, wherein the output
angles of the specular components are determined by the first surface
structure function.
34. The optical substrate as set forth in claim 33, wherein a second input
beam of light normal to the optical substrate is substantially reflected
by the surface of the optical substrate and forms output specular
components with a power half angle between about 0.1 and 60 degrees.
35. The optical substrate as set forth in claim 27, wherein the correlation
length of about 200 microns or less.
36. The optical substrate as set forth in claim 27, wherein the second
surface structure function has a geometry with at least pseudo-random
characteristics to modulate the first surface structure function in one or
more of frequency and peak angle along the length of the first surface
structure function.
37. The optical substrate of claim 27, wherein the optical substrate
comprises a brightness enhancement film.
38. A brightness enhancement film, comprising:
surface characterized by a correlation length of about 1 cm or less, the
surface having a shape to turn and diffuse incident light to produce at
least a 30 percent brightness increase on-axis to a viewer, wherein the
surface produces diffused components of light with a power half angle
between about 0.1 and 60 degrees, the surface defined by a first surface
structure function and a second surface structure function, the first
surface structure function having a length, width and peak angle with
optical characteristics to produce at least one output specular component
from an input beam of light, and the second surface structure function
having a geometry with at least pseudo-random characteristics to modulate
the first surface structure function in at least a phase along the length
of the first surface structure function, the phase being a horizontal peak
position along the width.
39. The film as set forth in claim 38, wherein the surface is characterized
by a correlation length of about 200 microns or less.
40. The film as set forth in claim 38, wherein the brightness increase
on-axis is about 30 percent to about 300 percent.
41. The film as set forth in claim 38, wherein the brightness increase
on-axis is about 50 percent to about 200 percent.
42. The brightness enhancement film as set forth in claim 38, wherein the
second surface structure function has a geometry with at least
pseudo-random characteristics to modulate the first surface structure
function in one or more of frequency and peak angle along the length of
the first surface structure function.
43. An optical substrate, comprising:
a three-dimensional surface defined by a first surface structure function
and a second surface structure function, the first surface structure
function having a geometry with optical characteristics to produce at
least one output specular component from an input beam of light;
the second surface structure function having a geometry with at least
pseudo-random characteristics to modulate the first surface structure
function;
wherein the three-dimensional surface has a correlation function value of
less than about 37 percent of an initial correlation function value in a
correlation length of about 1 cm or less, the first surface structure
function having a length, width and peak angle with optical
characteristics to produce at least one output specular component from an
input beam of light, and the second surface structure function having a
geometry with at least pseudo-random characteristics to modulate the first
surface structure function in at least a phase along the length of the
first surface structure function, the phase being a horizontal peak
position along the width.
44. The optical substrate as set forth in claim 43, wherein the surface is
characterized by a correlation length of about 200 microns or less.
45. The optical substrate as set forth in claim 43, wherein the first
surface structure function is characterized by a series of first surface
structure functions, each first surface structure function having a
length, width and peak angle.
46. The optical substrate as set forth in claim 45, wherein the phase
modulation includes modulating a horizontal position of at least one of
the first surface structure functions along the length of that first
surface structure function.
47. The optical substrate as set forth in claim 45, wherein the frequency
modulation includes modulating the width of at least one of the first
surface structure functions along the length of that first surface
structure function.
48. The optical substrate as set forth in claim 45, wherein the peak angle
modulation includes modulating a peak angle of at least one of the first
surface structure functions along the length of that first surface
structure function.
49. The optical substrate as set forth in claim 43, wherein the surface
diffuses and turns the input beam of light to form a plurality of
diffusion ellipses each with a power half angle between about 0.1 and
about 60 degrees.
50. The optical substrate as set forth in claim 49, wherein the power half
angle is between about 1 and about 5 degrees.
51. The optical substrate as set forth in claim 49, wherein the input beam
of light has an angle of incidence and the surface is structured so that
the input beam of light is transmitted through the optical substrate and
turned by the surface to form output angles of the specular components
that are different from the angle of incidence.
52. The optical substrate as set forth in claim 51, wherein the output
angles of the specular components are determined by the first surface
structure function.
53. The optical substrate as set forth in claim 43, wherein the second
surface structure function has a geometry with at least pseudo-random
characteristics to modulate the first structure function in one or more of
frequency and peak angle along the length of the first surface structure
function.
54. A method for modeling a three-dimensional surface of an optical film,
the method comprising:
modulating a plurality of first surface structure functions with a second
surface structure function to produce irregular, modulated waveforms, each
one of the first surface structure functions having a length, width and
peak angle with optical characteristics to produce at least one output
specular component from an input beam of light, the second surface
structure function having a geometry with at least pseudo-random
characteristics to modulate the first surface structure function in at
least a phase along the length of the first surface structure function,
the phase being a horizontal peak position along the width;
placing a first set of the plurality of modulated waveforms at intervals on
a work surface, each of the modulated waveforms of the first set being
superimposed over adjacent modulated waveforms; and
placing a second set of the plurality of modulated waveforms at intervals
on the work surface, the second set of modulated waveforms being
superimposed over the first set of modulated waveforms.
55. The method as set forth in claim 54, wherein the waveforms, prior to
modulating, are shaped as sawtooth or triangular functions in cross
section.
56. The method as set forth in claim 55, wherein the plurality of sawtooth
or triangular functions are modulated by one or more of phase, frequency,
and peak angle modulation.
57. The method as set forth in claim 54, wherein the second surface
structure function has a geometry with at least pseudo-random
characteristics to modulate the first surface structure function in one or
more of frequency and peak angle along the length of the first surface
structure function.
58. A method of modeling a surface of an optical substrate, the method
comprising:
defining a first window in a coordinate system;
defining a master function within the first window;
defining a second window at a first location within the first window;
randomly selecting a set of points within the second window;
defining a modulation path interconnecting the selected set of points;
defining a surface function along the modulation path;
randomly modulating the surface function along the modulation path;
combining the modulated surface function with the master function,
generating thereby a three dimensional structural pattern over the extent
of the modulation path;
moving the second window to a new location within the first window and
repeating
selecting a set of points within the second window;
defining a modulation path interconnecting the selected set of points;
defining a surface function along the modulation path;
modulating the surface function along the modulation path; and
combining the modulated surface function with the master function,
generating thereby a three dimensional structural pattern over the extent
of the modulation path until the second window has been coextensive with
all of the points in the first window.
59. An optical substrate, comprising:
a surface characterized by a correlation function value of less than about
37 percent of an initial value within a correlation length of about 1 cm
or less, wherein the surface is defined by a first surface structure
function having a sawtooth or triangular cross section extending a length
from a first end to a second end of the substrate modulated by a second
function, the surface of the optical substrate producing specular and
diffuse light from a first input beam of light, the first surface
structure function having a length, width and peak angle with optical
characteristics to produce at least one output specular component from an
input beam of light, and the second surface structure function having a
geometry with at least pseudo-random characteristics to modulate the first
surface structure function in at least a phase along the length of the
first surface structure function, the phase being a horizontal peak
position along the width.
60. The optical substrate as set forth in claim 59, wherein the second
surface structure function has a geometry with at least pseudo-random
characteristics to modulate the first surface structure function in one or
more of frequency and peak angle along the length of the first surface
structure function.
61. A brightness enhancement film, comprising:
a surface characterized by a correlation length of about 1 cm or less, the
surface having a shape to turn and diffuse incident light to produce a 50
percent to 200 percent brightness increase on-axis to a viewer, wherein
the surface produces diffused components of light with a power half angle
between about 0.1 and 60 degrees, the surface defined by a first surface
structure function and a second surface structure function, the first
surface structure function having a length, width and peak angle with
optical characteristics to produce at least one output specular component
from an input beam of light, and the second surface structure function
having a geometry with at least pseudo-random characteristics to modulate
the first surface structure function in at least a phase along the length
of the first surface structure function, the phase being a horizontal peak
position along the width.
62. The brightness enhancement film as set forth in claim 61, wherein the
second surface structure function has a geometry with at least
pseudo-random characteristics to modulate the first surface structure
function in one or more of frequency and peak angle along the length of
the first surface structure function.
63. An optical substrate, comprising:
a three-dimensional surface defined by a first surface structure function
and a second surface structure function, the first surface structure
function having a length, width and peak angle with optical
characteristics to produce at least one output specular component from an
input beam of light;
the second surface structure function having a geometry with at least
pseudo-random characteristics to modulate the first surface structure
function in at least a phase along the length of the first surface
structure function, the phase being a horizontal peak position along a
respective widths of the first surface structure functions;
wherein the three-dimensional surface has a correlation function value of
less than about 37 percent of an initial correlation function value in a
correlation length of about 1 cm or less.
64. The optical substrate as set forth in claim 63, wherein the second
surface structure function has a geometry with at least pseudo-random
characteristics to modulate the first surface structure function in one or
more of frequency and peak angle along the length of the first surface
structure function.
65. A method for modeling a three-dimensional surface of an optical film,
the method comprising:
modulating in at least a pseudo-random fashion at least a phase along
respective lengths of a plurality of first surface structure functions
shaped in cross section at sawtooth or triangular functions to produce
irregular, modulated waveforms, the phase being a horizontal peak position
along respective widths of the first surface structure functions;
placing a first set of the plurality of modulated waveforms at intervals on
a work surface, each of the modulated waveforms of the first set being
superimposed over adjacent modulated waveforms; and
placing a second set of the plurality of modulated waveforms at intervals
on the work surface, the second set of modulated waveforms being
superimposed over the first set of modulated waveforms.
66. The method as set forth in claim 65, wherein the modulating comprises
modulating in a pseudo random fashion the plurality of first surface
structure functions in one or more of frequency and peak angle along the
length of the first surface structure functions.
67. A method of making an optical substrate comprising a surface
characterized by a correlation function value of less than about 37
percent of an initial value within a correlation length of about 1 cm or
less, wherein the surface is defined by a first surface structure function
modulated by a second function, the surface of the optical substrate
producing specular and diffuse light from a first input beam of light, the
method comprising:
photolithographically mastering the surface of the optical substrate to a
photoresist, a gray scale mask or a halftone mask; and
forming a mold of the surface of the optical substrate from the master by
hot embossing, cold calendaring, ultraviolet curing or thermal setting.
68. The method as set forth in claim 67 further comprising:
electroforming the master with a metal coating forming thereby a parent
electroform;
electroforming the parent electroform forming thereby a child electroform.
69. The method as set forth in claim 68 wherein electroforming the parent
and child electroforms includes electro-depositing nickel thereon.
70. The method as set forth in claim 67 wherein the substrate comprises
organic, inorganic or hybrid optically transparent material including
suspended diffusion, birefringent or index of refraction modifying
particles.
71. The method as set forth in claim 67 wherein the master is a negative of
the optical substrate.
72. The method as set forth in claim 67 wherein the master comprises glass,
crystalline metal or plastic.
73. A method of making an optical substrate comprising a surface
characterized by a correlation function value of less than about 37
percent of an initial value within a correlation length of about 1 cm or
less, wherein the surface is defined by a first surface structure function
modulated by a second function, the surface of the optical substrate
producing specular and diffuse light from a first input beam of light, the
first surface structure function having a length, width and peak angle
with optical characteristics to produce at least one output specular
component from an input beam of light, and the second surface structure
function having a geometry with at least pseudo-random characteristics to
modulate the first surface structure function in at least a phase along
the length of the first surface structure function, the phase being a
horizontal peak position along the width, the method comprising:
hard tool mastering the surface of the optical substrate; and
forming a mold of the surface of the optical substrate from the master by
hot embossing, cold calendaring, ultraviolet curing or thermal setting.
74. The method as set forth in claim 73, wherein the second surface
structure function has a geometry with at least pseudo-random
characteristics to modulate the first surface structure function in one or
more of frequency and peak angle along the length of the first surface
structure function.
75. A backlight display device comprising:
an optical source for generating light;
a light guide for guiding the light therealong including a reflective
surface for reflecting the light out of the light guide;
at least one optical substrate receptive of the light from the reflective
surface, the optical substrate comprising:
a three-dimensional surface defined by two surface structure functions,
the first surface structure function having a length, width and peak angle
with optical characteristics to produce at least one output specular
component from an input beam of light;
the second surface structure function having a geometry with at least
pseudo-random characteristics to modulate the first surface structure
function in at least a phase along the length of the first surface
structure function, the phase being a horizontal peak position along the
width;
wherein the three-dimensional surface has a correlation function value of
less than about 37 percent of an initial correlation function value in a
correlation length of about 1 cm or less.
76. The backlight display device as set forth in claim 75 wherein the at
least one optical substrate comprises a plurality of optical substrates.
77. The backlight display device as set forth in claim 76 wherein the
plurality of optical substrates include first and second surface functions
in a relative orientation from zero to ninety degrees with respect to one
another.
78. The backlight display device as set forth in claim 77 wherein the
relative orientation of the first and second surface function is parallel
or perpendicular with respect to one another.
79. A backlight display device comprising:
an optical source for generating light;
a light guide for guiding the light therealong including a reflective
surface for reflecting the light out of the light guide; and
an optical substrate receptive of the light from the reflective surface,
the optical substrate comprising:
a first three-dimensional surface defined by first and second surface
structure functions; the first surface structure function having a length,
width and peak angle with optical characteristics to produce at least one
output specular component from an input beam of light;
the second surface structure function having a geometry with at least
pseudo-random characteristic to modulate the first surface structure
function in at least a phase along the length of the first surface
structure function, the phase being a horizontal peak position along the
width of the first surface structure function;
a second three-dimensional surface opposing the first three-dimensional
surface and defined by a third surface structure function and a fourth
surface structure function; the third surface structure having a length,
width and peak angle with optical characteristics to produce at least one
output specular component from an input beam of light;
the fourth surface structure function having a geometry with at least
pseudo-random characteristics to modulate the third surface structure
function in at least a phase along the length of the third surface
structure function, the phase being a horizontal peak position along the
width of the third surface structure function;
wherein the first and second three-dimensional surface have a correlation
function value of less than about 37 percent of an initial correlation
function value in a correlation length of about 1 cm or less.
80. The backlight display device as set forth in claim 79 wherein the first
and second surface structure functions are in a relative orientation from
zero to ninety degrees with respect to one another.
81. The backlight display device as set forth in claim 80 wherein the
relative orientation of the first and third surface structure functions is
parallel or perpendicular with respect to one another.
82. The optical substrate as set forth in claim 79 wherein the second
surface is optically smooth or planar.
83. The optical substrate as set forth in claim 79 wherein the second
surface has a matte or diffuse finish.
84. The optical substrate as set forth in claim 83 wherein the second
surface has diffusion characteristics that are anamorphic or anisotropic.
85. The optical substrate as set forth in claim 79 wherein the second
surface is optically smooth or planar including a pattern of protrusions
formed either in the substrate or attached with an adhesive.
86. The backlight display device as set forth in claim 79, wherein the
second surface structure function has a geometry with at least
pseudo-random characteristics to modulate the first surface structure
function in one or more of frequency and peak angle along the length of
the first surface structure function, and wherein the fourth surface
structure function has a geometry with at least pseudo-random
characteristics to modulate the third surface structure function in one or
more of frequency and peak angle along the length of the third surface
structure function.
87. An optical substrate, comprising:
a surface characterized by a correlation function value of less than about
37 percent of an initial correlation function value within a correlation
length of about 1 cm or less, wherein the surface is defined by a first
surface structure function having a plurality of parameters modulated by a
plurality of random functions, the first surface structure function having
a length, width and peak angle with optical characteristics to produce at
least one output specular component from an input beam of light, and the
plurality of random functions each having a geometry with at least
pseudo-random characteristics to modulate the first surface structure
function in at least a phase along the length of the first surface
structure function, the phase being a horizontal peak position along the
width.
88. The optical substrate as set forth in claim 87 wherein the plurality of
random functions are spatially constant or spatially varying.
89. The optical substrate as set forth in claim 87, wherein the second
surface structure function has a geometry with at least pseudo-random
characteristics to modulate the first surface structure function in one or
more of frequency and peak angle along the length of the first surface
structure function.
Description
BACKGROUND OF THE INVENTION
This invention relates to optical substrates and, more specifically, to
optical substrates having a surface performing at least two optical
functions.
In backlight computer displays or other systems, films are commonly used to
direct light. For example, in backlight displays, brightness enhancement
films use prismatic structures to direct light along the viewing axis
(i.e., normal to the display), which enhances the brightness of the light
viewed by the user of the display and which allows the system to use less
power to create a desired level of on-axis illumination. Films for turning
light can also be used in a wide range of other optical designs, such as
for projection displays, traffic signals, and illuminated signs.
Backlight displays and other systems use layers of films stacked and
arranged so that the prismatic surfaces thereof are perpendicular to one
another and are sandwiched between other optical films known as diffusers.
Diffusers have highly irregular surfaces.
SUMMARY OF THE INVENTION
The invention features a multiple function optical substrate and a method
of making the same. Under one aspect of the invention, the optical
substrate includes a three-dimensional surface characterized by a function
such as a correlation function, R(x,y), having a value of less than about
37 percent (1/e) of the initial value of R within a correlation length,
l.sub.c, of about 1 cm or less. The three-dimensional surface is defined
by a first surface structure function modulated by a second, random, or at
least pseudo-random, function. The properties of the first surface
structure function produce a specular component from a first input beam of
light, and this light turning behavior is retained in the
three-dimensional surface. Generally, the pseudo-random function is a
signal that modulates any combination of the frequency, height, peak angle
or phase of the first surface structure function. A window is defined and
points are randomly selected within the window thereby creating a
modulation path connecting the randomly selected points. A master function
is defined and a surface function is generated along the modulation path
and repeatedly combined with a master function at successive locations
within the master function. The resulting three-dimensional surface of the
substrate retains the light turning characteristics of the first surface
structure function, but also diffuses light to, for example, reduce Moire
artifacts.
In another aspect of the invention, the optical substrate is applied to one
or more sides of a film used for brightness enhancement in a backlight
panel light guide. The optical substrate also produces an on-axis increase
in brightness of at least 30 percent in the brightness enhancement
application. In addition, the three-dimensional surface produces diffused
specular components of light with a power half angle of between about 0.1
and 60 degrees.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional view of a prior art film in which a series of
prismatic structures are used to turn light.
FIG. 2 is a top view of an optical substrate according to one embodiment of
the invention.
FIG. 3 is a top view of a second optical substrate according to another
embodiment of the invention.
FIG. 4 is a perspective view of the optical substrate of FIG. 3.
FIG. 5 is a graphical representation showing three cross-sectional views of
an optical substrate according to one embodiment of the invention.
FIG. 6 is a cross-sectional view of an optical substrate according to one
embodiment of the invention showing the turning and diffusing of light
beams.
FIG. 7 is a perspective view of a flat panel display.
FIG. 8 is a top view of a single waveform that can be used to model an
optical substrate according to one embodiment the invention.
FIG. 9 is a plot showing the variation in phase along the length of the
waveform depicted in FIG. 8.
FIG. 10 is a plot showing the variation in peak angle along the length of
the waveform depicted in FIG. 8.
FIG. 11 is a surface structure formed after performing a first iteration of
placing modulated waveform structures on a master image.
FIG. 12 is a surface structure formed after performing a second iteration
of placing modulated waveform structures on the structure of FIG. 11.
FIG. 13 is a representation of a randomized substrate surface.
FIG. 14 is a schematic representation of control points randomly located
within a window for generating a modulated waveform.
FIG. 15 is a representation of the modulated waveform of FIG. 14 applied to
a master function.
FIG. 16 is a flow chart of the method of generating a random substrate
surface.
FIG. 17 is a representation of the tiling of the random substrate surface
on a wafer.
FIG. 18 is the top view of a height map of a 40 um pitch prism array.
FIG. 19 is a normalized auto correlation function of a horizontal section
of the 40 um pitch prism array of FIG. 18.
FIG. 20 is the top view of a Moire map of the 40 um pitch prism array of
FIG. 18 with a 50 um pitch reference prism.
FIG. 21 is a profile of the Moire map of FIG. 20.
FIG. 22 is the top view of a height map of the 40 um pitch prism array of
FIG. 18 with randomization in the horizontal position of the prism
centers.
FIG. 23 is a normalized auto correlation function of a horizontal section
of the height map of FIG. 22.
FIG. 24 is the top view of a Moire map of the height map of FIG. 22.
FIG. 25 is a profile of the Moire map of FIG. 24.
FIG. 26 is the top view of a height map of the 40 um pitch prism array of
FIG. 18 with full cycle randomization in the horizontal position of the
prism centers with superimposed phase modulated prism wave forms.
FIG. 27 is a normalized auto correlation function of a horizontal section
of the height map of FIG. 26.
FIG. 28 is the top view of a Moire map of the height map of the 40 um pitch
prism array of FIG. 26.
FIG. 29 is a profile of the Moire map of FIG. 28.
FIG. 30 is the top view of a Moire map of a 40 um pitch prism array with a
44 um pitch prism array.
FIG. 31 is the top view of a Moire map of a 40 um pitch prism array with
randomization in the horizontal position of the prism centers with a 44 um
pitch prism array.
FIG. 32 is the top view of a Moire map of the height map of FIG. 26 against
a 44 um pitch reference prism array.
FIG. 33 is the vertical auto correlation of the height map of the 40 um
pitch prism array of FIG. 26.
FIG. 34 is the vertical auto correlation of the height map of the 40 um
pitch prism array of FIG. 22.
FIG. 35 is a graphical representation of a carrier wave, c(x) modulated in
amplitude by a random function.
FIG. 36 is a graphical representation of a carrier wave, c(x) modulated in
phase by a random function.
FIG. 37 is a first graphical representation of a carrier wave, c(x)
modulated in frequency by a random function.
FIG. 38 is a second graphical representation of a carrier wave, c(x)
modulated in frequency by a random function.
FIG. 39 is a graphical representation of frequency and amplitude modulation
with spatially varying carrier and noise functions.
FIG. 40 is an image of a skeleton mask function.
FIG. 41 is a sectional view of a backlight display device.
DETAILED DESCRIPTION OF THE INVENTION
The embodiments of the invention provide an optical substrate for turning
and diffusing light using the surface thereof. The substrate includes a
surface defined by a first surface structure function for turning light
and a second surface structure function for diffusing light. The
combination of these two surface functions results in a single
three-dimensional surface that both turns and diffuses light.
Embodiments of substrates will be described below with respect to
brightness enhancing films for use in backlight displays or the like. The
optical substrates, however, can be used in a wide variety of other
applications as well.
FIG. 1 depicts in cross section a prior art film in which a series of
prismatic structures 10 are used to turn light. In backlight displays,
light enters surface 20 and exits surface 30. In the film of FIG. 1, a
beam of light, A, having a zero degree angle of incidence to the
light-entering surface 20 is directed off the prism structures 10 and is,
essentially, reflected back toward the input. A second beam of light, B,
having an angle of incidence of .theta. is turned by the prismatic
structures 10 so that it is transmitted through the light-exiting surface
30 and exits substantially normal to the light-entering surface 20. Other
beams (not shown) will turn or reflect at other angles. The bulk
statistical properties of such a film are characterized by parameters such
as optical gain and viewing angle.
In this prior art film, the surface 30 can be described as a function. If
the height of the surface 30 relative to surface 20 is coordinate z and
the coordinates across the page and normal to the page are x, y
respectively, then the surface 30 can be defined by a function
z=.function.(x,y). In this case, .function.(x) is a repeating triangular
waveform, or sawtooth, with a constant offset relative to surface 20. In
this case, the function defining surface 30 has a special geometry that
both turns and reflects light as outlined above.
FIG. 2 is a top view of an optical substrate 40 according to a first
embodiment of the invention. The embodiment of FIG. 2 shows a portion of a
substrate 40 that has a length, l, of about 2,000 microns and a width, w,
of about 2,000 microns. FIG. 3 is a top view of an embodiment of a portion
of a substrate 42 that is about 500 microns by 500 microns in dimension,
and FIG. 4 shows a perspective view of a portion of the substrate 42 of
FIG. 3. The embodiments of FIGS. 3 and 4 have a three-dimensional surface
that is more highly irregular than the three-dimensional surface of FIG.
2. Generally, the substrates shown in FIGS. 2-4 have an irregular
three-dimensional surface structure on the light-exiting surface thereof.
Because of its geometry, the irregular three-dimensional surface
structure, turns light to produce output specular components, while at the
same time diffusing light and having a low correlation length, l.sub.c.
Because the embodiments of the substrates can turn and diffuse light on a
single surface, separate diffusion surfaces can be eliminated in some
applications.
The substrates shown in FIGS. 2-4 have an irregular three-dimensional
surface. This irregular surface, however, is not easily defined by well
known mathematical functions, as is the case for the light exiting surface
30 of FIG. 1. Instead, this surface function is better defined as the
result of modulating a first surface structure function by a second
surface function, and in some cases by taking such modulated functions and
superimposing them with other functions formed similarly. For example, the
first function can be similar to that defined by the light exiting surface
30 of FIG. 1. The first function may also be that of a single prism. The
second function can be a pseudo-random function of height, phase,
frequency or peak angle. Moreover, the combination can be accomplished by
way of modulating the first function by the second function so that the
resulting function z=.function.(x,y) of substrate 40 has a pseudo-randomly
varying height, phase, frequency or peak angle along the "l" direction of
the substrate 40 (FIG. 2). The first function provides the geometrical
properties to turn or reflect light and the second function provides the
geometrical properties to diffuse the turned light or reflected light. As
will be discussed below, other functions can be substituted and other
parameters can be relevant (e.g., the phase of an entity). If a prismatic
surface function is used as the first function, the height, h, width, s,
and peak angle, a, of the first surface function can vary depending on the
intended use of the substrate. In addition, the first surface function
need not be the symmetric structures as shown in FIG. 1.
In one embodiment, the first surface structure function is modulated in
phase, frequency, peak angle or height by the second surface structure
function. The second surface structure function defines the type of
modulation, to produce the three-dimensional surface of the film on the
light-exiting surface 41 (FIG. 2) of the substrate 40. The surface height
of the light-exiting surface 41 of the substrate 40 is therefore defined
by the combination of these two surface structure functions. For example,
the height of the peak of one or more of the first surface structure
functions, eg., prisms can be modulated along the length l of the
substrate 40. The height can be randomly or pseudo-randomly modulated
between certain limits at random or fixed intervals along the length, l,
of the substrate 40. As best understood, the term random means true
randomness or randomness to the extent possible when gene
