U.S. patent application number 12/730264 was filed with the patent office on 2010-07-15 for display device uniforming light distribution throughout areas and method for manufacturing same.
This patent application is currently assigned to SEKONIX CO. LTD.. Invention is credited to Gyuhwan HWANG, Hyunsoo LEE, Youngbin YU.
Application Number | 20100178019 12/730264 |
Document ID | / |
Family ID | 35451015 |
Filed Date | 2010-07-15 |
United States Patent
Application |
20100178019 |
Kind Code |
A1 |
HWANG; Gyuhwan ; et
al. |
July 15, 2010 |
DISPLAY DEVICE UNIFORMING LIGHT DISTRIBUTION THROUGHOUT AREAS AND
METHOD FOR MANUFACTURING SAME
Abstract
Disclosed are an optical display device producing uniform light
distribution and a method of fabricating such devices. The optical
display device has waveguides arranged in vertical and horizontal
directions. The waveguide has a conical shape whose cross-section
decreases towards the light-projection side thereof. At least one
of the size, height, spacing, and refraction index of the waveguide
is designed to be different for each section, depending on an
incident angle and/or intensity of light inputted from a light
source. Therefore, the intensity of projected light can be made
uniform over all sections of the optical device.
Inventors: |
HWANG; Gyuhwan;
(Gyeonggi-do, KR) ; YU; Youngbin;
(Gyeongsangnam-do, KR) ; LEE; Hyunsoo; (Seoul,
KR) |
Correspondence
Address: |
DR. MARK M. FRIEDMAN;C/O BILL POLKINGHORN - DISCOVERY DISPATCH
9003 FLORIN WAY
UPPER MARLBORO
MD
20772
US
|
Assignee: |
SEKONIX CO. LTD.
Gyeonggi-do
KR
|
Family ID: |
35451015 |
Appl. No.: |
12/730264 |
Filed: |
March 24, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11569807 |
Nov 30, 2006 |
7711231 |
|
|
PCT/KR05/00419 |
Feb 16, 2005 |
|
|
|
12730264 |
|
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|
Current U.S.
Class: |
385/131 ;
385/146 |
Current CPC
Class: |
G02F 1/133562 20210101;
G02B 6/0065 20130101; G02B 6/0053 20130101; G02F 1/133524
20130101 |
Class at
Publication: |
385/131 ;
385/146 |
International
Class: |
G02B 6/04 20060101
G02B006/04 |
Foreign Application Data
Date |
Code |
Application Number |
May 31, 2004 |
KR |
10-2004-0039310 |
Jan 8, 2005 |
KR |
10-2005-0001957 |
Claims
1. A optical display device uniforming light distribution
throughout areas, the optical display device including waveguides
each having a sidewall inclined from the bottom side thereof,
imaging light rays incident from a light source placed rearwards of
the center of the optical device being reflected inside the
waveguide to be projected to the outside of the waveguide, wherein
the waveguides arranged over the whole section of a screen have a
same bottom side and a same height, and simultaneously the sidewall
gradient in the waveguides is gradually decreased, within an angle
range within which a total reflection occurs, towards the
peripheral area of the screen from the central area thereof, such
that the imaging light rays are less frequently reflected in the
waveguide in the peripheral area of the screen, as compared with
the waveguides in the central area of the screen.
2. The optical display device according claim 1, wherein the
sidewall gradient of the waveguide placed in the center of the
screen is within a range of 10 to 12 with respect to the normal
line to a light input surface of the waveguide.
3. The optical display device according to claim 1, wherein the
sidewall gradient of the waveguide placed in the peripheral area of
the screen is within a range of 6 to 8 with respect to the normal
line to a light input surface of the waveguide.
4. The optical display device according to claim 1, wherein a
light-absorbing material is filled in a space between the
waveguides, the light-absorbing material absorbing external light
flowing into the screen.
5. The optical display device according to claim 4, wherein the
refraction index of the inside of the waveguide is within a range
of 1.4-1.6, the refraction index of the light projection surface of
the waveguide is within a range of 1.0-1.2, and the refraction
index of the light-absorbing material is within a range of
1.2-1.3.
6. The optical display device according to claim 5, wherein the
waveguide is further provided with a diffusion plate at the front
face thereof.
7. The optical display device according to claim 6, wherein, in a
case where the diffusion plate is employed, the refraction index of
the inside of the waveguide is 1.6, the refraction index of the
light projection surface is 1.0, and the refraction index of the
light-absorbing material is 1.2.
8. The optical display device according to claim 5, wherein, in a
case where the diffusion plate is not employed, the refraction
index of the inside of the waveguide is 1.6, the refraction index
of the light projection surface is 1.1, and the refraction index of
the light-absorbing material is 1.2.
9. The optical display device according to claim 6, wherein the
critical angle for total reflection inside the waveguide is within
a range of 48-70.degree. and the critical angle of total reflection
on the light projection surface of the waveguide is within a range
of 35-60.degree.
10. The optical display device according to claim 9, wherein, in a
case where the diffusion plate is employed, the critical angle for
total reflection inside the waveguide is within a range of
45-50.degree. and the critical angle of total reflection on the
light projection surface of the waveguide is within a range of
40-45'.
11. The optical display device according to claim 5, wherein, in a
case where the diffusion plate is not employed, the critical angle
for total reflection inside the waveguide is within a range of
45-50.degree. and the critical angle of total reflection on the
light projection surface of the waveguide is within a range of
35-40.degree.
12. The optical display device according to claim 1, wherein the
optical display device is applied to a projection screen, an
advertisement board display, and a security screen.
Description
[0001] This application is a Divisional of pending U.S. application
Ser. No. 11/569,807, filed Nov. 30, 2006, which claim priority of
PCT/KR2005/00419, filed Feb. 16, 2005 and which claims priority of
KR 10-2004-0039310 filed May 31, 2005 and KR 10-2004-001957 filed
Jan. 8, 2005
TECHNICAL FIELD
[0002] The present invention relates to an optical display device
producing a uniform light distribution over the entire area. More
specifically, the invention relates to such devices and a method of
fabricating the same, in which the size, the height, the spacing,
and the refraction index of waveguides are all designed to be
different for each section, depending on an incident angle and/or
light intensity inputted from a light source, and thus a uniform
light distribution can be achieved over the whole area of the
optical device while maintaining a desired viewing angle, and the
luminance in the peripheral area of the device can be avoided from
being degraded.
BACKGROUND ART
[0003] In general, a projection device such as a projection TV, a
projection monitor, or the like is equipped with a rear projection
screen projecting images toward the viewer's side. This rear
projection screen is one of the optical display devices designed
such that the images projected from the rear side of the screen
pass through a viewing space. The viewing space may be relatively
large (for example, a projection TV), or may be relatively small
(for example, a projection monitor). The performance of a rear
projection screen can be described by various characteristics of
the screen. The screen performance typically includes gain, viewing
angle, resolution, contrast ratio, color, and undesirable artifacts
such as specks. The rear projection screen needs to have a high
resolution, a high contrast ratio, and a high gain.
[0004] In addition, it is preferable that the rear projection
television has a wide viewing angle capable of covering all the
viewers within a broad range of angle. In order to achieve this
wide viewing angle, the screen is provided with waveguides
thereinside. In a rear projection screen, inherently, a point light
source is positioned rearwards of the screen center and thus the
incident angles of the light are different in the central area and
the peripheral area of the screen. If the entire screen is formed
of waveguides of the same structure, the reflection angles inside
the waveguides are different from one section of the screen to
another, due to their different incident angles. Some waveguides
may not experience total reflection, depending on the position
thereof. Usually, the waveguides, specially designed for a wide
viewing angle, come to be placed in the central area of the screen.
Therefore, in a case where the screen is designed with identically
structured waveguides, the intended wide viewing angle can be
achieved on the whole since the peripheral area of the screen is
provided with the same waveguides. However, the luminance in the
peripheral area is considerably degraded relative to the central
area of the screen. For this reason, the image distinctiveness and
clarity are made different in the central and peripheral areas of
the screen, and homogeneity in the image is consequently degraded,
thereby failing to achieve a high quality image.
[0005] In particular, a large-scale display device employs a
plurality of unit light sources or a single diffusive light source,
and the light intensity thus becomes non-uniform throughout the
screen. More specifically, in the case where a plurality of light
sources is used, the light intensity is lowered in the boundary
area between the light sources. When a single diffusion light
source is employed, the central and peripheral areas of the screen
exhibit different luminance, due to different incident angles and
different light-paths. For the above reasons, the brightness is not
uniform over the entire screen, consequently resulting in
non-uniform image distinctiveness and clarity, and degraded image
resolution.
DISCLOSURE OF INVENTION
Technical Problem
[0006] Accordingly, the present invention has been made in order to
solve the above problems in the prior art. It is an object of the
invention to provide an optical display device producing a uniform
light distribution, in which the sidewall gradient of waveguides is
designed to be different in the central and peripheral areas of a
screen in such a way as to be gradually decreased radially away
from the central area towards the peripheral area, thereby
preventing degradation in the peripheral luminance.
[0007] Another object of the invention is to provide an optical
display device producing a uniform light distribution, in which the
sidewall gradient of waveguides is gradually decreased from the
central area of a screen in a horizontal or vertical direction
towards the peripheral area, thereby achieving a uniform luminance
over the entire screen.
[0008] A further object of the invention is to provide a method of
fabricating such optical display devices, in which
ultraviolet-exposing time varies with each section of a screen
using a line-scanning mode, thereby enabling the formation of
waveguides having a sidewall gradient gradually decreasing toward
the peripheral area from the central area.
[0009] A further object of the invention is to provide an optical
display device producing a uniform light distribution, in which the
size, the height, the spacing, and the refraction index of
waveguides is designed to be different for each section, depending
on incident angle and/or intensity of light inputted from a light
source, thereby achieving a uniform light distribution over the
whole area of the optical device.
[0010] A further object of the invention is to provide an optical
display device, in which the line spacing of a photomask is set up
to be different, depending on incident angle and/or intensity of a
light inputted from a light source, thereby achieving a uniform
light distribution over the whole area of the optical device.
Technical Solution
[0011] In order to accomplish the above objects, according to one
aspect of the invention, there is provided an optical display
device producing a uniform light distribution, the optical display
device including waveguides each having a sidewall inclined from
the bottom side thereof, imaging light rays incident from a light
source placed rearwards of the center of the optical device being
reflected inside the waveguide to be projected to the outside of
the waveguide, wherein the waveguides arranged over the whole
section of a screen have a same bottom side and a same height, and
simultaneously the sidewall gradient in the waveguides is decreased
gradually, within an angle range within which a total reflection
occurs, towards the peripheral area of the screen from the central
area thereof, such that the imaging light rays are less frequently
reflected in the waveguide in the peripheral area of the screen, as
compared with the waveguides in the central area of the screen.
[0012] According to anther aspect of the invention, there is
provided an optical display device producing a uniform light
distribution, the optical display device including waveguides each
having a sidewall inclined from the bottom side thereof, imaging
light rays incident from a light source placed rearwards of the
center of the optical device being reflected inside the waveguide
to be projected to the outside of the waveguide, wherein the
waveguides arranged over the whole section of a screen have a same
bottom side and a same height, and simultaneously the sidewall
gradient in the waveguides is decreased gradually, within an angle
range within which a total reflection occurs, towards the radially
peripheral area of the screen from the central area thereof,
depending on the incident angle, such that the waveguides at a
radially same distance from the central area have a same sidewall
gradient in symmetrical fashion with respect to the central
area.
[0013] According to yet another aspect of the invention, there is
provided an optical display device producing a uniform light
distribution, the optical display device including waveguides each
having a sidewall inclined from the bottom side thereof, imaging
light rays incident from a light source placed rearwards of the
center of the optical device being reflected inside the waveguide
to be projected to the outside of the waveguide, wherein the
waveguides arranged over the whole section of a screen have a same
bottom side and a same height, and the sidewall gradient in the
waveguides is gradually decreased simultaneously within an angle
range within which a total reflection occurs, along either a
horizontal direction or a vertical direction, towards the
peripheral area of the screen from the central area thereof,
depending on the incident angle.
[0014] According to a further aspect of the invention, there is
provided a method of fabricating the above-described optical
display device. The method comprises: a first step of placing a
grid on a photomask and attaching a transparent substrate on the
grid; a second step of coating a photopolymer material on the
transparent substrate; a third step of radiating ultraviolet rays
in a line-scanning mode on the photopolymer material from below the
photomask, the exposure time of the ultraviolet rays being
controlled for each section of a screen so as to form waveguides
having a sidewall gradient decreasing gradually towards the
peripheral area along one direction from the central area of the
screen; and a fourth step of attaching a front transparent plate on
the waveguides.
[0015] According to a further aspect of the invention, there is
provided an optical display device producing a uniform light
distribution, the optical display device having waveguides arranged
in vertical and horizontal directions, the waveguide having a
conical shape whose cross-section decreases towards the
light-projection side thereof, wherein at least one of the size,
height, spacing, and refraction index of the waveguide is designed
to be different for each section, depending on incident angle
and/or intensity of a light inputted from a light source such that
the intensity of projected light can be made uniform over the
entire section of the optical device.
[0016] According to a further aspect of the invention, there is
provided an optical display device producing a uniform light
distribution, the optical display device having waveguides arranged
in vertical and horizontal directions, the waveguide having a
conical shape whose cross-section decreases towards the
light-projection side thereof, wherein the size of the waveguide is
designed to be different for each section, depending on incident
angle and/or intensity of light inputted from a light source such
that the intensity of projected light can be made uniform over the
entire section of the optical device.
[0017] According to a further aspect of the invention, there is
provided an optical display device producing a uniform light
distribution, the optical display device having waveguides arranged
in vertical and horizontal directions, the waveguide having a
conical shape whose cross-section decreases towards the
light-projection side thereof, wherein the refraction index of the
waveguide is designed to be different for each section, depending
on incident angle and/or intensity of light inputted from a light
source such that the intensity of projected light can be made
uniform over the entire section of the optical device.
[0018] According to a further aspect of the invention, there is
provided a method of fabricating an optical display device, the
optical display device having different-sized waveguides for
different sections. The method comprises the steps of: attaching a
photopolymer on a photomask having a grid structure whose line
spacing is non-uniform, radiating ultraviolet rays on the
photopolymer from outside of the photomask such that waveguides
having different sizes are formed in the photopolymer due to the
non-uniform line spacing of the grid structure of the photomask;
removing the photopolymer excepting the formed waveguide portions
through a development process; and filling a resin having a low
refraction index in a valley-like space between the waveguides
formed through the development process.
ADVANTAGEOUS EFFECTS
[0019] As described above, in the present invention, the sidewall
gradient of waveguides is designed to be different in the central
and peripheral areas of a screen in such a way as to be gradually
decreased radially away from the central area towards the
peripheral area. Thus, degradation in the peripheral luminance can
be avoided. In addition, the sidewall gradient of waveguides is
gradually decreased from the central area of a screen in a
horizontal or vertical direction towards the peripheral area,
thereby achieving uniform luminance over the entire screen.
[0020] Furthermore, the size, height, spacing, and refraction index
of waveguides are designed to be different for each section,
depending on incident angle and/or intensity of light inputted from
alight source. Therefore, a uniform light distribution can be
achieved over the whole area of the optical device, and homogeneity
in the projected image can be consequently enhanced.
[0021] In addition, a low index resin is filled in the valley-like
space between the waveguides and a light diffuser is added to the
low index region, thereby further improving the uniform light
distribution. Here, the material, particle size, and contents of
the light diffuser can be controlled to adjust the light
distribution.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] Further objects and advantages of the invention can be more
fully understood from the following detailed description taken in
conjunction with the accompanying drawings in which:
[0023] FIGS. 1 to 4 are schematic diagrams showing the reflection
of imaging light rays inside different waveguides having different
designs;
[0024] FIG. 5 is a sectional view of an optical display device
producing a uniform light distribution according to a first
embodiment of the invention, where the invention is applied to a
projection screen;
[0025] FIGS. 6 to 8 show one example for the configuration of the
waveguides in the optical display device in FIG. 5;
[0026] FIGS. 9 to 11 illustrate another embodiment of the waveguide
structure in the optical display device in FIG. 5;
[0027] FIG. 12 is a process diagram explaining a method of
fabricating the optical display device illustrated in FIGS. 9 to
11;
[0028] FIG. 13 is a schematic diagram showing the variation of the
sidewall gradient with the light-exposing time;
[0029] FIGS. 14 and 15 are a front and rear perspective view of an
optical display device producing a uniform light distribution
according to a second embodiment of the invention;
[0030] FIG. 16 is a sectional view taken along the line E-E in FIG.
14;
[0031] FIG. 17 is a partial sectional view of a modified example of
FIG. 16;
[0032] FIG. 18 is a process diagram explaining a method of
fabricating the optical device according to the second embodiment
of the invention, which is illustrated in FIGS. 14 to 16;
[0033] FIG. 19 is a plan view showing the grid structure of a
photomask used in the manufacturing process of FIG. 18;
[0034] FIG. 20 shows a display panel such as an LCD or an LED;
[0035] FIG. 21 is a graph showing the luminance for every section
of the display panel of FIG. 20;
[0036] FIG. 22 illustrates a display panel having an optical device
of the invention mounted thereon;
[0037] FIG. 23 is a graph showing the luminance for every section
of the display panel of FIG. 22;
[0038] FIG. 24 shows a conventional optical device using a
plurality of unit light sources;
[0039] FIG. 25 shows an optical device of the invention using a
plurality of unit light sources;
[0040] FIG. 26 depicts a conventional display device using a single
diffusion light source;
[0041] FIG. 27 illustrates an optical display device of the
invention using a single light source;
[0042] FIG. 28 is a graph contrasting the light characteristics of
the optical device of the invention in FIG. 21 with the
conventional one of FIG. 20;
[0043] FIGS. 29 and 30 are a front and rear perspective view of an
optical display device producing a uniform light distribution
according to a third embodiment of the invention;
[0044] FIG. 31 is a sectional view taken along the line F-F in FIG.
29;
[0045] FIG. 32 is a partial sectional view of another embodiment
modified from that of FIG. 31;
[0046] FIG. 33 is a process diagram explaining a method of
fabricating an optical device according to the third embodiment of
the invention and illustrated in FIGS. 29 to 31;
[0047] FIG. 34 is a partial sectional view of an optical display
device producing a uniform light distribution according to a fourth
embodiment of the invention;
[0048] FIGS. 35 and 36 explains a method of fabricating the optical
display device of FIG. 34; and
[0049] FIGS. 37 and 38 illustrate modifications for the fourth
embodiment of the invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0050] The preferred embodiments of the present invention will be
hereafter described in detail with reference to the accompanying
drawings. The embodiments of the invention will be explained,
illustrating a projection screen.
[0051] FIGS. 1 to 4 are schematic diagrams showing the reflection
of imaging light rays inside different waveguides having different
designs.
[0052] Referring to FIGS. 1 and 2, the principles for a waveguide
design in order to obtain uniform luminance will be explained.
FIGS. 1 and 2 are diagrams showing the reflection of imaging light
rays inside a waveguide, where the length of its bottom face is 40
mm and the gradient of its sidewall is 10.52.degree. Specifically,
FIG. 1 shows the reflection of imaging light rays in the case of an
incident angle of zero degree (0.degree. and FIG. 2 is in a case of
10 of incident angle. Here, the incident angle is measured with
respect to the normal line to the light input surface of the
waveguide.
[0053] In addition to the length of the bottom face and the
gradient of the sidewall, the refraction index of the waveguide is
1.6, the refraction index of the projection surface is 1, the
critical angle for total reflection inside the waveguide is
54.35.degree. and the critical angle for total reflection on the
projection surface (the tip of the waveguide) is 38.68.degree.
Typically, a point light source is positioned rearwards of the
screen center, and thus a waveguide placed in the screen center has
an incident angle q.sub.1 of zero degree (0.degree.), as in FIG. 1.
The imaging light rays L.sub.1 are reflected on the sidewall
S.sub.1 of the waveguide. With this incident angle q.sub.1, the
imaging light rays perform a total reflection until the second
reflection. The second-reflected imaging light rays L.sub.1 again
reach the sidewall S.sub.1 at the height of approximately 83 mm, as
illustrated in FIG. 1. In order to achieve a wide viewing angle,
commonly, at least one or two reflections are needed, and in order
to obtain a high luminance, a total reflection is required. Thus,
in the central area of the screen, the length of the waveguide
needs to be determined to be no more than a height corresponding to
three times that of the reflections to thereby meet the above
conditions. As the frequency of total reflections increases, the
viewing angle is widened. Preferably, the height of the waveguide
is determined to be within a range of from 73 mm (second
reflection) to 83 mm (third reflection).
[0054] On the other hand, since the point light source is placed
rearwards of the screen center, in the outer peripheral area of a
screen, the imaging light rays L.sub.2 are incident at a certain
angle, not vertically, as shown in FIG. 2. In the case where the
incident angle q.sub.2 is 10.degree. the imaging light rays perform
a total reflection on the sidewall S1 at the time of first
reflection only. At this time, as depicted in FIG. 2, the height of
the waveguide needs to be determined to be no more than about 51 mm
in order to obtain a high luminance. This is because, if a total
reflection does not occur inside a waveguide, light loss is caused
inside the waveguide, degrading the luminance.
[0055] In view of the above explanation in conjunction with FIGS. 1
and 2, if it is assumed that a waveguide has the same length of
bottom face and the same gradient of sidewall, waveguides in the
central area of the screen need to be designed to have a height of
73.about.83 mm. In contrast, it is preferable that the waveguide in
the peripheral area of the screen is designed to have a height
within 50 mm. Thus, if this consideration is reflected upon the
design of a waveguide, the screen becomes higher in its central
area and lower in its outer peripheral area, and thus the screen
cannot have a uniform height. Consequently, overall, the screen has
an even surface, which is not preferable in terms of the viewing
angle and the resolution thereof, and which also leads to a
complicated manufacturing process.
[0056] In addition, FIGS. 3 and 4 are schematic diagrams showing
the reflection of imaging light rays inside a waveguide, the length
of whose bottom face is 40 mm and the gradient of whose sidewall is
7.degree. More specifically, FIG. 3 shows the relationship between
the imaging light rays and the waveguide structure in the case
where the incident angle is zero degrees (0.degree.), and FIG. 4 is
a case where the incident angle is ten degrees) (10.degree.).
[0057] The refraction index, the critical angle for total
reflection, and the length of the bottom face are the same as in
both FIGS. 1 and 2, and the gradient of the sidewall (7.degree.) is
different from the previous illustration of FIGS. 1 and 2. In the
case where the incident angle q.sub.3 is 0.degree. as shown in FIG.
3, the incident imaging light rays L.sub.3 are totally reflected on
the sidewall S.sub.2 until the third reflection. At this time,
total reflection occurs within the height of 137 mm.
[0058] On the other hand, when the incident angle q.sub.4 is 10
degrees) (.degree.), the imaging light rays L4 perform a total
reflection until second reflection, as shown in FIG. 4. The maximum
height of the waveguide, within which total reflection occurs, is
96 mm, and thus the height of the waveguide needs to be determined
to be no more than 96 mm in order to obtain a high luminance.
[0059] In view of the above explanation in conjunction with FIGS. 3
and 4, if the height of the waveguide is designed so as to be
suitable for the peripheral waveguides where the incident angle is
7 degrees (.degree.), the central waveguides in the screen
experience only one total reflection, thus failing to achieve an
effective viewing angle. Generally, it is preferable that the
screen is configured such that its central area has a wider viewing
angle. Therefore, it is preferable that the central waveguides are
designed so as to cause at least two times of total
reflections.
[0060] Considering the above two cases where the gradient of
sidewall is 10.52.degree. (FIGS. 1 and 2) and 7.degree. (FIGS. 3
and 4), an optimum condition for total reflection can be determined
over the entire area of a screen. For example, the height of the
waveguide is established to be 80 mm, which is within a common
height range where a total reflection can occur in both the central
and the peripheral area of the screen. Simultaneously, the gradient
of the waveguide is determined to be 10.52.degree. for the central
area of the screen and 7.degree. for the peripheral area of the
screen. More specifically, the central waveguides of the screen are
configured such that the sidewall thereof has a gradient of
10.52.degree. as illustrated in FIGS. 1 and 2. The peripheral
waveguides of the screen are structured so as to have a gradient of
7.degree. as illustrated in FIGS. 3 and 4. In this way, one or two
times of total reflections can occur in all the waveguides arranged
over the whole screen, and thus a wide viewing angle can be
achieved in the central area thereof and a high luminance can be
obtained in the peripheral area thereof. Here, the sidewall
gradients of the waveguides are designed so as to decrease
gradually towards the peripheral waveguides from the central ones
in the screen. That is, the sidewall gradient is decreased
gradually by a certain increment of angle towards the outer
waveguides within the range of 10.52.about.7.degree. over the
entire screen. Thus, the sidewall gradient may decrease towards the
outer peripheral waveguides in a symmetrical pattern about the
screen center or in a non-symmetrical fashion. As one exemplary
approach, the sidewall gradient may be gradually decreased in a
concentric pattern in such a way that the same magnitude of
gradient is provided to the waveguides placed at the same distance
from the central waveguide. In this case, the sidewall gradient
decreases gradually in radial direction towards the outer periphery
of the screen from the center thereof, thus achieving a uniform
luminance in vertical and horizontal directions, i.e., along the
radial directions. An exemplary screen according to this embodiment
is illustrated in FIGS. 6 to 8.
[0061] As an alternative, the sidewall gradient may be decreased
gradually towards the peripheral area of the screen along the
horizontal or vertical direction from the horizontal center of the
screen or from the vertical center thereof. In this case, the
gradual decrease of the gradient is applied to either one of the
horizontal and vertical directions, and thus the luminance can be
improved along any one direction only. However, even if the
luminance is improved along any one direction so as to be suitable
to its use, a common screen or monitor is enabled to provide a
distinct and clear image. This will be hereinafter explained in
detail, in conjunction with FIGS. 9 to 11.
[0062] FIG. 5 is a sectional view of an optical display device
producing a uniform light distribution according to a first
embodiment of the invention, where the invention is applied to a
projection screen. In FIG. 5, the projection screen of the
invention is generally denoted at 1. FIGS. 6 to 8 show one example
for the configuration of the waveguides in the optical display
device in FIG. 5. FIG. 6 is a perspective view of the waveguide
array, FIG. 7 is a sectional view taken along the line A-A in FIG.
6, and FIG. 8 is a sectional view taken along the line B-B in FIG.
6.
[0063] As illustrated in FIG. 5, the projection screen 1 of this
embodiment includes a front transparent plate 10, a rear
transparent substrate 20, and a waveguide array 30 interposed
in-between. A unit waveguide 32 (hereinafter, referred to as a
"waveguide") is structured to have a smaller bottom face to a light
source 40 side and a larger top face contacted with the front
transparent plate 10. That is, the waveguide 32 is structured such
that its cross-section is gradually narrowed towards the front side
of the screen, to which imaging light rays L are projected. Thus,
the waveguides 32 have an inclined sidewall, and consequently may
have the shape of a conical frustum or a polypyramidal frustum. In
this embodiment, the waveguide is illustrated to have a pyramidal
frustum. Between the waveguides 32 is formed a space, in which a
light-absorbing material 34 is filled. The light-absorbing material
34 absorbs light rays incident from the outside of the screen so
that the imaging light projected from the inside can be viewed more
clearly and distinctly. The light absorbing material 34 is formed
of a mixture of a monarch-carbon black, a baysilone-platinum
catalyst, and a vinyl silicone material.
[0064] As depicted in FIG. 6, in the waveguide array 30, a
horizontal centerline C.sub.H and a vertical centerline C.sub.V
intersect at the center point C.sub.P. The waveguides at the same
distance from the center point C.sub.P have the same sidewall
gradient A.sub.S. At the same time, the sidewall gradient A.sub.S
of the waveguide 32 is decreased gradually towards the outer
peripheral area of the screen 1 from the center point C.sub.P
thereof. Thus, the sidewall gradient A.sub.S of the waveguide 32
gradually decreases in a concentric pattern toward the outer part
of the screen 1 from the center thereof. When sectioned along an
arbitrary line passing through the center point C.sub.P, the screen
1 has a left-right symmetrical structure, in particular, in terms
of the sidewall gradient of the waveguides. At this time, the
concentric pattern may include a circular concentric pattern and an
oval-concentric pattern. A circular concentric pattern is more
efficient. For example, in the cross-section of the waveguide array
30 taken along the horizontal centerline as shown in FIG. 7, the
sidewall gradient A.sub.S1 of the waveguides is formed in a
left-right symmetrical fashion about the center point C.sub.P. As
shown in FIG. 8, in the cross-section of the waveguide array 30
taken along the vertical centerline of the screen 1, the sidewall
gradient A.sub.S2 of the waveguides 32 is formed in a up-down
symmetrical fashion about the center point C.sub.P.
[0065] The sidewall gradient A.sub.S of the waveguide 32 is defined
with respect to the normal line to the light input surface of the
waveguide as follows.
A.sub.S=tan.sup.-1((h-t)/X), h=H/2, t=T/2.
[0066] Here, H denotes the length of the bottom side, T denotes the
length of the topside, and X is the height of the waveguide in the
vertical cross-section of the waveguide.
[0067] The waveguides placed in the central area of the screen are
preferred to have a sidewall gradient of 10.about.12.degree. and
the waveguides placed in the outermost area thereof are preferred
to have a sidewall gradient of 6.about.8.degree. In addition,
preferably, the pitch, which is the spacing between the bottom
sides of the waveguides, is determined to be less than 3 mm.
[0068] In addition, the refraction index of the waveguide 32 is
1.4.about.1.6, the refraction index of the light projection surface
is 1.0.about.1.2, and the refraction index of the light-absorbing
material 34 is 1.2.about.1.3. When a diffusion plate is applied to
the front face of the waveguide 32, the reflection index of the
waveguide 32, the light projection surface, and the light-absorbing
material 34 are preferred to be 1.6, 1.0, and 1.2 respectively. If
the diffusion plate is not employed, the refraction index of the
waveguide 32, the light projection surface, and the light-absorbing
material 34 are preferred to be 1.6, 1.1, and 1.2 respectively.
[0069] In this case, the critical angle for total reflection inside
the waveguide is 45.about.50.degree. and the critical angle for
total reflection on the light projection surface is
35.about.60.degree. For example, if a diffusion plate is employed,
the critical angle for total reflection inside the waveguide is
preferred to be 45.about.50.degree. and the critical angle for
total reflection on the light projection surface is preferred to be
40.about.45.degree. In addition, when the diffusion plate is not
employed, the critical angle for total reflection inside the
waveguide is preferred to be 45.about.50.degree. and the critical
angle for total reflection on the light projection surface is
preferred to be 35.about.40.degree.
[0070] Consequently, over the entire screen 1, each waveguide 32
has the same length H of the bottom side and the same height X. Due
to the variation in the sidewall gradient A.sub.S, the length T of
the topside varies with the waveguides. Here, it is preferable that
the sidewall gradient A.sub.S between the adjacent waveguides is
varied within 2%, the topside between the adjacent waveguides is
varied within 5%.
[0071] The waveguides placed in the central area of the screen 1
have the highest sidewall gradient A.sub.S and thus the incident
image light rays are outputted after being totally reflected
several times, at least two or more times, thereby resulting in a
wider viewing angle. In contrast, the sidewall gradient A.sub.S of
the waveguide 32 is gradually decreased towards the peripheral area
of the screen. Accordingly, for the waveguides placed in the outer
peripheral area, the total reflection of imaging light is less
frequent. Therefore, the peripheral area of the screen 1 has a
relatively narrower viewing angle due to less frequent total
reflections, but remains within the allowed frequency of total
reflection, thereby minimizing the light loss and thus preventing
degradation in luminance.
MODE FOR THE INVENTION
[0072] FIGS. 9 to 11 illustrate another embodiment of the waveguide
structure in the optical display device in FIG. 5. FIG. 9 is a
perspective view of the waveguide array, which is denoted by
reference numeral 60, FIG. 10 is a sectional view taken along the
line C-C in FIG. 9, and FIG. 11 is a sectional view taken along the
line D-D in FIG. 9.
[0073] As illustrated in FIGS. 9 and 10, the waveguide array 60 of
this embodiment is designed such that the sidewall gradient A.sub.S
of the waveguide 62 is gradually decreased towards the peripheral
area of the screen in a horizontal direction from the vertical
centerline C.sub.V. That is, the sidewall gradient A.sub.S varies
in a left-right symmetrical fashion about the vertical centerline
C.sub.V. For example, the sidewall gradient of the waveguide 62
placed in the center is 10.52.degree. the outermost waveguide has a
sidewall gradient of 7.degree. and the sidewall gradients of the
waveguides in-between are gradually decreased within the range of
10.52.about.7.degree. On the other hand, all the waveguides along
the vertical direction have the same sidewall gradient. In this
embodiment, the sidewall gradient of waveguide is decreased
gradually along the horizontal direction from the vertical
centerline, but remains constant along the vertical direction.
However, the opposite case, i.e., the case where the waveguide
array 60 is rotated by 90 degrees) (.degree.), is included in the
embodiments of the invention. Therefore, in this embodiment, the
sidewall gradient decreases in a symmetrical pattern with respect
to either the horizontal centerline or the vertical centerline,
thus enhancing the luminance of the peripheral area of the
screen.
[0074] FIG. 12 is a process diagram explaining a method of
fabricating the optical display device illustrated in FIGS. 9 to
11, FIG. 13 is a schematic diagram showing the variation of the
sidewall gradient with the light-exposing time.
[0075] The method of fabricating a screen 3, in which the sidewall
gradient of the waveguides is decreased gradually along one
direction, will be described, referring to FIG. 12. First, a grid
72 is placed on the photomask 70 and a transparent substrate 80 is
attached on top of the grid 72 (step S.sub.1, S.sub.3). Then, due
to the grid 72, a gap is formed between the photomask 70 and the
transparent substrate 80. In order to remove the gap, a filling
material 82 is filled in the gap. The filling material may employ a
high-purity isopropanol alcohol (IPA). The transparent substrate 80
may be formed of a transparent resin such as polyethylene
terephthalate (PET), polymethyl methacrylate (PMMA), or methyl
methacrylate styrene (MS) copolymer.
[0076] Thereafter, a photopolymerizable material 90 is coated on
the transparent substrate 80 (step S.sub.S). The photopolymerizable
material 90 may be formed by mixing two or more materials selected
from etyoxylated (3) bisphenol A diacrylate, trimethylolpropane
triacrylate, irgacure, irganox, and the like. Preferably, the
photopolymerizable material 90 may be formed by mixing all the
above four materials, more specifically, 40.about.80 wt % of
diacrylate, 0.5.about.10 wt % of triacrylate, 0.5.about.12 wt % of
irgacure, and 0.5.about.12 wt % of irganox. Here, diacrylate is an
ultraviolet polymerizable monomer, triacrylate is a monomer for
adjusting viscosity, irgacure is an ultraviolet polymerization
initiator, and irganox is an inhibitor against oxide formation.
[0077] Next, ultraviolet rays are radiated to form a waveguide 62
shape in the photopolymerizable material 90 (step S.sub.7). When
radiating the ultraviolet rays, a line scanning method is used to
control the exposing time for each section and thus forms a
waveguide 62 having different sidewall gradients for different
sections. As shown in FIG. 13, as the light exposure time is
extended, the sidewall gradient A.sub.S of the waveguide 62 is
decreased. On the contrary, as the light exposure time is
shortened, the sidewall gradient A.sub.S of the waveguide 62 is
increased. Thus, according to this principle, when performing the
line scanning, the exposure time is decreased gradually towards the
central area from one horizontal end of the substrate such that the
center point thereof has the minimum exposure time. After passing
the center point, the exposure time is gradually increased towards
the other horizontal end of the substrate. Thus, the sidewall
gradients of the waveguides are distributed in a left-right
symmetrical pattern in such a way as to be decreased towards both
the left and right ends of the substrate from the center point.
[0078] Excepting the waveguide 62 shape formed through the UV
exposure, the unexposed portion is developed and removed (step
S.sub.9). Then, a space is formed between the waveguides. A
light-absorbing material 64 is filled in the space 63 and a front
transparent plate 100 is then attached, thus completing the
projection screen 3 of the invention (step S.sub.11). The front
transparent plate 100 may be made of the same material as the
transparent substrate 80.
[0079] The operation and effects of the invention will be described
in greater detail, referring to FIG. 5.
[0080] The light rays emitted from the light source 40 are
converted into imaging light rays containing images. Then, the
imaging light rays are converted into substantially parallel light
rays through a Fresnel lens 42 and incident on the screen 1. Thus,
the imaging light rays pass through the rear transparent substrate
20 and are inputted into the waveguide 32. While passing through
the waveguide, the light rays are reflected on the sidewall and
projected towards the front of the screen so as be seen by a
viewer. At this time, since the waveguides in the central area of
the screen 1 have a larger sidewall gradient, the light reflection
occurs relatively frequently. The incident angle in the central
area is zero degree (0.degree.), and thus the imaging light rays
are outputted after two or three times of total reflections inside
the waveguide to thereby widen the viewing angle thereof. In
contrast, in the peripheral area of the screen, the waveguides 32
have a relatively smaller sidewall gradient, the incident imaging
light rays are less frequently reflected inside the waveguide
before being outputted. Therefore, in the outer peripheral area of
the screen, the light loss caused through reflection can be
maximally suppressed such that the peripheral luminance is almost
the same as it is in the central area. In this way, according to
the present invention, the sidewall gradient of the waveguides 32
is adjusted to a suitable value for every section of the screen to
thereby achieve quality images in terms of the viewing angle and
luminance thereof.
[0081] FIG. 5 illustrates only the central and peripheral
waveguides 32, but the screen contains numerous waveguides
in-between. The areas between the waveguides are filled with a
light-absorbing material 34 for absorbing external lights incident
into the screen 1, thereby improving the distinctiveness and
clarity of the imaging light rays projected from the inside. A
diffuser may be applied to the front transparent plate 10.
[0082] FIGS. 14 and 15 are a front and rear perspective view of an
optical display device producing a uniform light distribution
according to a second embodiment of the invention. FIG. 16 is a
sectional view taken along the line E-E in FIG. 14, and FIG. 17 is
a partial sectional view of a modified example of FIG. 16. In this
embodiment, the waveguides have a uniform height. In addition, the
optical device according to the invention may or may not be
provided with a transparent protection plate attached to the front
face or the rear face thereof. The following embodiments illustrate
cases having no transparent protection plate attached thereto, and
are referred to as an "optical device."
[0083] In the optical display device 110 of this embodiment, the
waveguide 112 has a truncated conical shape whose cross-sectional
area gradually decreases towards the light output surface thereof.
These waveguides are arranged in vertical and horizontal
directions. In particular, the height of the waveguide 112 is
uniform over the whole region of the optical device 110, but the
size thereof varies over the entire area of the device. That is, as
shown in FIG. 16, the size of the waveguides 112a to 112f increases
gradually towards the peripheral area of the optical device 110
from the central area thereof, more precisely, towards the
peripheral area along the radial direction from the central area
having a large amount of incident light rays. More specifically,
from the central area of the optical device towards the peripheral
area thereof, the topside and the bottom side of the waveguides
112a to 112f are gradually increased, and the sidewall gradient
thereof is gradually decreased. Thus, in FIG. 16, the rightmost
waveguide 112a corresponding to the center of the optical device
has the smallest size, and the leftmost waveguide 11f corresponding
to the outermost area of the optical device has the largest
size.
[0084] Furthermore, the spacing between the waveguides 112 may vary
to adjust light distribution. Between the waveguides 112 is formed
a valley-like space, in which a resin 114 having a low refraction
index is filled. The low index resin 114 may include vinyl
silicone, hydride containing silicone, or the like. The refraction
index of the waveguide 112 is larger than that of the low index
resin 114, but the smaller the difference in their refraction
indices the better. For example, it is preferable that the
refraction index of the waveguide 112 is 1.3.about.2.0, and that of
the resin 114 is no more than 1.3. Of course, if the waveguide has
a higher refraction index beyond the above range, the refraction
index of the resin 114 becomes higher by as much. As illustrated in
FIG. 17, the low index resin 114 may contain a light diffuser 116
for generating light diffusion. That is, in the case where a large
amount of light rays are incident through the gap between the
bottom sides of the waveguides 112a to 112f, preferably a light
diffuser 116 is added to the low index resin 114 to allow the light
to be diffused thereinside. In this way, the light diffuser 116 is
used so that the light introduced outside the waveguide can be
prevented from being lost and a more uniform light distribution can
be achieved. The light diffuser 116 may be comprised of light
transmissive fine spherical particles.
[0085] On the other hand, instead of the light diffuser, the low
index resin 114 may be mixed with a light-absorbing material (not
shown) as in the previous embodiment. The light-absorbing material
may be added, in the case where the amount of light introduced
between the bottom sides of the waveguides is small to the extant
that it does not affect the entire light quantity, or whenever
required for other purposes. The light-absorbing material absorbs
light rays incident from the outside of the optical device so that
the imaging light projected from the inside can be viewed more
clearly and distinctly. The light absorbing material is formed of a
mixture of a monarch-carbon black, a baysilone-platinum catalyst,
and a vinyl silicone material. Optical devices such as projection
TVs and rear projector screens employ the light-absorbing
material.
[0086] FIG. 18 is a process diagram explaining a method of
fabricating the optical device according to the second embodiment
of the invention, which is illustrated in FIGS. 14 to 16. FIG. 19
is a plan view showing the grid structure of a photomask used in
the manufacturing process of FIG. 18.
[0087] As illustrated in FIG. 19, a photopolymer 140 is coated on a
photomask 130 having a grid structure, in which the line spacing is
not uniform (I). As the photopolymer 140, an acrylic synthetic
resin is preferred, which can be obtained, for example, by mixing
ethoxylated (3) bisphenol A diacrylate, trimethyloloptopane
triacrylate, methyl metacrylate, n-butyl acrylate, 2-ethylhexyl
acrylate, isodecyl acrylate, 2-hydroxyethyl acrylate with, as an
additive, benzidimethyl ketal, alpha.,.alpha.-diethyloxy
acetophenone, or the like.
[0088] Thereafter, ultraviolet rays are radiated on the
photopolymer 140 from below the photomask 130. At this time, the
ultraviolet rays are made to reach the front face of the
photopolymer 140. For this purpose, of course, the thickness of the
photopolymer 140 coated on the photomask 130 should be
appropriately controlled. According to the light exposure, the
photopolymer 140 is formed with waveguides 112 having non-uniform
size, due to the photomask 130 having a non-uniform grid structure
(II). In this embodiment, the waveguides 112 formed above have a
uniform height, but have different sizes, i.e., different bottom
and top faces and different sidewall gradients. In particular, the
size of the waveguide 112 is gradually increased, but the sidewall
gradient is gradually decreased towards the peripheral area of the
optical device from the central area thereof. In FIG. 18, the
right-hand side represents the central area of the optical device,
and the left-hand side corresponds to the peripheral area of the
optical device. In addition, the waveguides placed at the same
distance from the central area have the same size and the same
sidewall gradient.
[0089] After the light exposure, the remaining portions of the
photopolymer 140 other than the waveguides 112 are developed and
removed (III). Then, a valley-like space is formed between the
waveguides 112. In the subsequent process step, the space is filled
with a resin 114 having a low refraction index (IV). Of course, the
resin 114 has a refraction index lower than that of the
photopolymer. A light diffuser may be added to the low index resin
114.
[0090] As shown in FIGS. 1 and 5, in the optical display device 110
fabricated through the above process steps, the waveguides 112a to
112f have a uniform height. The size of the waveguides is gradually
increased radially towards the peripheral area of the optical
device 110 from the central area thereof. As described above, since
the size of the waveguides 112a to 112f increases gradually and the
sidewall gradient thereof decreases gradually toward the peripheral
area, the transmissivity in the peripheral area of the optical
device 110, which is far from the light source and thus has a
smaller light quantity and/or a smaller incident angle, is
improved, thus creating uniformity in the light distribution over
the optical device.
[0091] Hereafter, the operation and effect of the invention will be
explained in detail.
[0092] FIGS. 20 and 21 show the construction and characteristics of
a conventional display device contrasting with the present
invention. FIG. 20 shows a display panel such as an LCD or an LED,
and FIG. 21 is a graph showing the luminance for every section of
the display panel of FIG. 20. FIGS. 22 and 23 illustrate the
operational effects of the above second embodiment. FIG. 22
illustrates a display panel having an optical device of the
invention mounted thereon, and FIG. 23 is a graph showing the
luminance for every section of the display panel of FIG. 22.
[0093] In the conventional display panel 150 where the optical
device 10 of the invention is not mounted, as shown in FIG. 21, the
luminance distribution is not uniform, i.e., the luminance value is
highest in the central area of each pixel and decreases rapidly in
the boundary areas between the pixels. In such conventional display
devices, non-uniform lights are emitted from each section of the
device, thus degrading the homogeneity in the image quality.
[0094] In contrast, as depicted in FIG. 22, in the case where the
optical device 110 is mounted on the front face of the conventional
display device 150 of FIG. 20, since the optical device 110 of the
invention adjusts the light quantity over the whole area, the
central area of the pixels and the boundary area in-between have a
uniform luminance, as can be seen from FIG. 23. Thus, it can be
seen that the image generated through the optical device 110 of the
invention has a homogenized quality.
[0095] FIG. 24 shows a conventional optical device using a
plurality of unit light sources, and FIG. 25 shows an optical
device of the invention using a plurality of unit light
sources.
[0096] As shown in FIG. 24, the light rays emitted from the unit
light source 160 are very non-uniform, and the luminance thereof is
very weak in the boundary area between the unit light sources. In
contrast, in the optical device 110 of the invention, the light
rays emitted from the unit light source 160 exhibit a uniform
luminance over the entire device, as shown in FIG. 25.
[0097] In addition, FIG. 26 depicts a conventional display device
using a single diffusion light source, and FIG. 27 illustrates an
optical display device of the invention using a single light
source.
[0098] In FIG. 26, the light rays emitted from a diffusion light
source 170 pass through a Fresnel lens and are then projected
through a diffusion plate 174, which is formed of uniform-sized
waveguides. It can be seen from FIG. 26 that the luminance thereof
is significantly decreased further away from the light source.
[0099] In contrast, as can be seen from the graph of FIG. 27, when
the optical device 110 of the invention is employed, the luminance
thereof is almost the same over the entire device, regardless of
the distance from the light source 170. Thus, through the optical
device of the invention, a uniform luminance can be achieved, and
consequently the homogeneity of projected image can be
improved.
[0100] FIG. 28 is a graph contrasting the light characteristics of
the optical device of the invention in FIG. 21 with the
conventional one of FIG. 20. In the graph of FIG. 28, the solid
line represents the light characteristics of the invention, and the
dotted line represents the conventional case. According to the
invention, the display device can obtain great uniformity in
luminance over the entire section thereof, i.e., the non-uniform
light distribution (the dotted line) can be transformed into a
uniform state (the solid line).
[0101] FIGS. 29 and 30 are a front and rear perspective view of an
optical display device producing a uniform light distribution
according to a third embodiment of the invention. FIG. 31 is a
sectional view taken along the line F-F in FIG. 29. This embodiment
illustrates a case of waveguides having non-uniform heights.
[0102] In this embodiment, the height of the waveguides 112' in the
optical device 110' is not uniform, but increases gradually towards
the peripheral area of the device from the central area thereof.
More specifically, as shown in FIG. 31, the height of the
peripheral waveguide 112f' in the optical device 110' is higher
than that of the central waveguide 112a', in such a manner that the
peripheral waveguides surround the central waveguides. The sidewall
gradient is almost the same in all the waveguides 112'. The bottom
side and the topside of the waveguides 112' are gradually increased
the farther away they are from the center of the optical device
110'. Consequently, the size of the waveguides 112' increases
gradually towards the peripheral area of the optical device
110'.
[0103] In addition, a resin 114' having a low refraction index is
filled in the spaces formed between the waveguides 112'. The low
index resin 114 has the same composition as in the previous
embodiment, and in this embodiment the lower height waveguides
112a' to 112e' are embedded in the low index resin 114, as shown in
FIG. 31. Therefore, in the central area of the device, the light
rays are projected through the low index resin 114' after passing
through the waveguides 112a' to 112e'. In the outermost waveguide
112f, its top surface is exposed so that the light rays are
projected directly outward from the waveguide 112f'. Accordingly,
since a relatively intense light is inputted into the central area
and a relatively weak light is inputted into the peripheral area,
the light intensity outputted from the optical device 110' of the
invention comes to have a uniform light intensity (luminance).
[0104] FIG. 32 is a partial sectional view of another embodiment
modified from that of FIG. 31. As shown in FIG. 32, a light
diffuser 116' may be added to the low index resin 114', which is
filled between the waveguides 112a' to 112f'. The light diffuser
116' is mixed with the low index resin 114' in a liquid state and
then the mixture of the light diffuser and the resin is filled
between the waveguides 112' to 112f'. The composition of the
mixture is preferred to be 70.about.80 wt % of the resin 114' and
20.about.30 wt % of the light diffuser 116'. The light diffuser
116' is formed of light transmissive fine spherical particles, the
material, particle size and content of which can be controlled to
adjust the light distribution. The light distribution is adjusted
mainly by controlling the size and height of the waveguides 112a'
to 112f', and the light diffuser 116' serves as an auxiliary means
for controlling the light distribution.
[0105] FIG. 33 is a process diagram explaining a method of
fabricating an optical device according to the third embodiment of
the invention and illustrated in FIGS. 29 to 31.
[0106] A photopolymer 140' is coated on a photomask 130' (i). The
coated photopolymer 140' layer has a higher thickness relative to
the second embodiment. At this time, the photomask 130' has a grid
structure whose line spacing is not uniform. Then, ultraviolet (UV)
rays are radiated on the photopolymer 140' from below the photomask
130'. At this time, the ultraviolet rays reach the front face of
the photopolymer 140' at the outermost area thereof, but do not
reach the front face of the photopolymer 140' at the remaining
area. Specifically, towards the central area of the optical device,
the reaching point is farther away from the front face of the
photopolymer 140'. Then, due to the grid 132' of non-uniform
spacing in the photomask 130', the waveguides 112' formed in the
photopolymer 140' have a non-uniform size (ii). That is, since the
grid 132' spacing increases towards the outer area from the central
area (from the right hand side to the left hand side in the
figure), the formed waveguides 112 have different bottom sides and
top sides, i.e., a gradually increasing height towards the
peripheral area. At this time, the sidewall gradient of the
waveguide may be formed to be the same or different.
[0107] After the light exposure, the remaining portion in the
photopolymer 140' except for the waveguides 112' is developed and
removed (iii). Then, a valley-like space is formed between the
waveguides 112'. In the subsequent process step, the space is
filled with a resin 114' having a low refraction index (iv). The
low index resin 114' covers the waveguides except the outermost
waveguide 112' in such a way that the surface of the low index
resin 114 is aligned with the light output surface of the outermost
waveguide. Of course, the resin 114' has a refraction index lower
than that of the photopolymer 140'. A light diffuser (not shown)
may be added to the low index resin 114'.
[0108] As depicted in FIGS. 29 to 31, the optical display device
110' fabricated as described above is structured in such a manner
that the height and size of the waveguides 112a' to 112f' is
increased gradually toward the radially peripheral area of the
optical device 110' from the central area thereof. In this way,
since the waveguides have an increasing height and size towards the
outer area, the transmissivity in the peripheral area of the
optical device 110', which is far from the light source and thus
has a smaller light quantity and/or a smaller incident angle, is
improved, thus providing uniformity in the distribution of light
over the optical device.
[0109] FIG. 34 is a partial sectional view of an optical display
device producing a uniform light distribution according to a fourth
embodiment of the invention. FIGS. 35 and 36 explain a method of
fabricating the optical display device of FIG. 34, more
specifically, FIGS. 35 and 36 are a perspective view and a plan
view showing a photopolymer coating method.
[0110] As shown in FIG. 34, the waveguides 112g to 112i of the
invention may have different refraction indices to adjust the light
distribution thereof. Specifically, photopolymer 140a, 140b and
140c having different refraction indices are coated on different
sections of the optical device, considering the light quantity
and/or the incident angle for each respective section. Then, as in
the previous embodiments, through light exposure and development,
the waveguides 112g, 112h, and 112i having different refraction
indices respectively are formed. For example, as illustrated in
FIG. 35, a multi-nozzle coating die 190 can be used to coat the
photopolymers 140a, 140b, and 140c of different indices on the
photomask 130a while moving the die 190 along the photomask. In
particular, as illustrated in FIG. 36, the photopolymers are coated
in such a manner that the refraction index thereof becomes
different towards both vertical end areas from the central
horizontal line (the highest intensity of light). At this time, it
is preferable that the refraction index is highest in the central
horizon area and becomes lower gradually towards both vertical end
portions. For example, the photopolymer 140a in the central
horizontal area has a refraction index of 1.60, the photopolymer
140h in the first adjacent horizontal areas has a refraction index
of 1.50, and the photopolymer 140c in the second adjacent
horizontal areas (the lowest intensity of light) has a refraction
index of 1.40. In this way, different photopolymers 140a, 140b, and
140c having different refraction indices can be coated on different
sections of the optical device, and, through subsequent light
exposure and development procedures, waveguides 112g, 112h and 112I
having different refraction indices can be obtained. In this
embodiment, the size and height of each waveguide may be made to be
the same as shown in FIG. 34, or different for every section as in
the previous embodiments. Of course, the low index resin 114a
filled between the waveguides 112g, 112h, 112i is preferred to be
no more than 1.35, i.e., lower than that of the photopolymers 140a,
140b and 140c.
[0111] FIGS. 37 and 38 illustrate modifications for the fourth
embodiment of the invention. FIG. 37 is a plan view of a
modification for the fourth embodiment. FIG. 38 is a side view for
another modification for the fourth embodiment.
[0112] As illustrated in FIG. 37, photopolymers 140d, 140e, 140f,
and 140g having different refraction indices are coated on a
photomask in concentric patterns about the center of the optical
device. That is, the photopolymer is coated in such a way that the
refraction index thereof is decreased gradually toward radially
peripheral areas of the device from the center thereof. Thus, the
formed waveguides through subsequent light exposure and development
have a gradually decreasing index toward the peripheral area in the
radial direction, and the waveguides at the same distance from the
center have the same refraction index. This concentric photopolymer
coating can be performed by rotating a multi-nozzle coating die
190a about the center of the optical device.
[0113] On the other hand, as illustrated in FIG. 38, the
photopolymer may be coated on a photomask 130b in multiple layers,
and the multi-layered photopolymer coating 140h, 140i and 140j can
be used for providing a special function to the optical device.
INDUSTRIAL APPLICABILITY
[0114] As described above, in the screen according to the
invention, the sidewall gradient of waveguides is made different
for each section, depending on the incident angle of imaging light
rays inputted into the waveguides. Thus, the imaging light can be
projected at desired angles, for example, in an advertisement board
where the viewing angle is of importance. In addition, the sidewall
gradient of waveguides can be controlled to adjust the viewing
angle, such that only a single viewer can see the screen, excluding
other neighboring people. Thus, great performance can be achieved,
for example, in a surveillance monitor where secrecy is of
importance.
[0115] Furthermore, according to the present invention, in a case
where plural unit light sources are used, the light intensity in
the boundary area between the light sources can be adjusted to be
uniform over all the sections of the display device. In addition,
in the case of a single diffusion light source, the light intensity
can be made almost uniform over the central and peripheral areas of
the device.
[0116] Thus, the optical display device or the invention can be
applied advantageously to a projection screen, a display for an
advertisement board, or a security screen in order to obtain a
distinct, clear and high-quality image.
[0117] Although the present invention has been described with
reference to several preferred embodiments, the description is
illustrative of the invention and not to be construed as limiting
the invention. Various modifications and variations may occur to
those skilled in the art without departing from the scope and
spirit of the invention, as defined by the appended claims.
* * * * *