 |
Claims  |
|
|
What is claimed is:
1. A hologram color filter, comprising:
a hologram, wherein incident light is spectrally diffracted by said
hologram into spectral components of different wavelength, wherein one of
said spectral components is emitted to a desired position at a
predetermined spatial period, and wherein said hologram has an efficiency
of diffraction independent, or less dependent, on wavelength.
2. A hologram color filter as claimed in claim 1, wherein said hologram is
produced by disposing converging unit holograms in an array wherein said
converging unit holograms have an efficiency of diffraction independent,
or less dependent, on wavelength.
3. A hologram color filter as claimed in claim 2, wherein said hologram
color filter is located on a light-incident side of an imaging device made
up of a periodic arrangement of photodetection elements.
4. A hologram color filter as claimed in claim 2, wherein said hologram
color filter is located on a side of a liquid crystal display element onto
which backlight is incident and wherein said liquid crystal display
element comprises a periodic arrangement of liquid crystal cells.
5. A hologram color filter as claimed in claim 4, wherein said hologram
color filter is located on said side of said liquid crystal display
element onto which backlight is incident and wherein said liquid crystal
display element comprises means for projecting an image displayed by said
liquid crystal display.
6. A hologram color filter as claimed in claim 4, wherein said liquid
crystal display element comprises a light-blocking means at a position
corresponding to a region between said liquid crystal cells.
7. A hologram color filter as claimed in claim 6, wherein said hologram
color filter is located on said side of said liquid crystal display
element onto which backlight is incident and wherein said liquid crystal
display element comprises means for projecting an image displayed by said
liquid crystal display.
8. A hologram color filter as claimed in claim 6, wherein an additional
color filter is disposed between said liquid crystal display element and
said light-blocking means.
9. A hologram color filter as claimed in claim 4, wherein a light-diffusing
means is located at any position on said light-emerging side of said
hologram.
10. A hologram color filter as claimed in claim 9, wherein said hologram
color filter is located on said side of said liquid crystal display
element onto which backlight is incident and wherein said liquid crystal
display element comprises means for projecting an image displayed by said
liquid crystal display.
11. A hologram color filter as claimed in claim 9, wherein said liquid
crystal display element comprises a light-blocking means at a position
corresponding to a region between said liquid crystal cells.
12. A hologram color filter as claimed in claim 11, wherein said hologram
color filter is located on said side of said liquid crystal display
element onto which backlight is incident and wherein said liquid crystal
display element comprises means for projecting an image displayed by said
liquid crystal display.
13. A hologram color filter as claimed in claim 11, wherein an additional
color filter is disposed between said liquid crystal display element and
said light-blocking means.
14. A hologram color filter as claimed in claim 1, wherein said hologram
comprises uniform interference fringes with an efficiency of diffraction
independent, or less dependent, on wavelength and wherein an array of
converging elements is arranged on a light-striking or emerging side of
said hologram.
15. A hologram color filter as claimed in claim 14, wherein said hologram
color filter is located on a light-incident side of an imaging device made
up of a periodic arrangement of photodetection elements.
16. A hologram color filter as claimed in claim 14, wherein said hologram
color filter is located on a side of a liquid crystal display element onto
which backlight is incident and wherein said liquid crystal display
element comprises a periodic arrangement of liquid crystal cells.
17. A hologram color filter as claimed in claim 16, wherein said hologram
color filter is located on said side of said liquid crystal display
element onto which backlight is incident and wherein said liquid crystal
display element is used for projecting an image displayed by said liquid
crystal display.
18. A hologram color filter as claimed in claim 16, wherein said liquid
crystal display element comprises a light-blocking means at a position
corresponding to a region between said liquid crystal cells.
19. A hologram color filter as claimed in claim 18, wherein said hologram
color filter is located on said side of said liquid crystal display
element onto which backlight is incident and wherein said liquid crystal
display element is used for projecting an image displayed by said liquid
crystal display.
20. A hologram color filter as claimed in claim 18, wherein an additional
color filter is disposed between said liquid crystal display element and
said light-blocking means.
21. A hologram color filter as claimed in claim 16, wherein a
light-diffusing means is located at any position on said light-emerging
side of said hologram.
22. A hologram color filter as claimed in claim 21, wherein said hologram
color filter is located on said side of said liquid crystal display
element onto which backlight is incident and wherein said liquid crystal
display element is used for projecting an image displayed by said liquid
crystal display.
23. A hologram color filter as claimed in claim 21, wherein said liquid
crystal display element comprises a light-blocking means at a position
corresponding to a region between said liquid crystal cells.
24. A hologram color filter as claimed in claim 23, wherein said hologram
color filter is located on said side of said liquid crystal display
element onto which backlight is incident and wherein said liquid crystal
display element comprises means for projecting an image displayed by said
liquid crystal display.
25. A hologram color filter as claimed in claim 23, wherein an additional
color filter is disposed between said liquid crystal display element and
said light-blocking means.
26. A hologram color filter as claimed in claim 1, wherein said hologram
color filter is located on a side of a liquid crystal display element onto
which backlight is incident and wherein said liquid crystal display
element comprises a periodic arrangement of liquid crystal cells.
27. A hologram color filter as claimed in claim 26, wherein a
light-diffusing means is located at any position on a light-emerging side
of said hologram.
28. A hologram color filter as claimed in claim 27, wherein said hologram
color filter is located on said side of said liquid crystal display
element onto which backlight is incident and wherein said liquid crystal
display element is used for projecting an image displayed by said liquid
crystal display.
29. A hologram color filter as claimed in claim 27, wherein said liquid
crystal display element comprises a light-blocking means at a position
corresponding to a region between said liquid crystal cells.
30. A hologram color filter as claimed in claim 29, wherein said hologram
color filter is located on said side of said liquid crystal display
element onto which backlight is incident and wherein said liquid crystal
display element is used for projecting an image displayed by said liquid
crystal display.
31. A hologram color filter as claimed in claim 29, wherein an additional
color filter is disposed between said liquid crystal display element and
said light-blocking means.
32. A hologram color filter as claimed in claim 26, wherein said liquid
crystal display element comprises a light-blocking means at a position
corresponding to a region between said liquid crystal cells.
33. A hologram color filter as claimed in claim 32, wherein said hologram
color filter is located on said side of said liquid crystal display
element onto which backlight is incident and wherein said liquid crystal
display element is used for projecting an image displayed by said liquid
crystal display.
34. A hologram color filter as claimed in claim 32, wherein an additional
color filter is disposed between said liquid crystal display element and
said light-blocking means.
35. A hologram color filter as claimed in claim 26, wherein said hologram
color filter is located on said side of said liquid crystal display
element onto which backlight is incident and wherein said liquid crystal
display element is used for projecting an image displayed by said liquid
crystal display.
36. A hologram color filter as claimed in claim 1, wherein said hologram
color filter is located on a light-incident side of an imaging device made
up of a periodic arrangement of photodetection elements.
37. A liquid crystal display device, comprising:
a hologram color filter, which is illuminated by backlight from behind to
provide a color display, wherein said hologram filter comprises a hologram
which has an efficiency of diffraction independent, or less dependent, on
wavelength is located on a side of said liquid crystal display device onto
which said backlight is incident and
liquid crystal cells, wherein wavelength components of said backlight which
are spectrally diffracted by said hologram are allowed to strike onto said
liquid crystal cells for creating corresponding colors of said color
display.
38. A liquid crystal display device as claimed in claim 37, wherein a
light-blocking means is located at a position corresponding to a region
between said liquid crystal cells.
39. A liquid crystal display device as claimed in claim 38, wherein a
photopolymer is used as a material for recording said hologram.
40. A liquid crystal display device as claimed in claim 38, wherein a
converging element corresponding to each of said liquid crystal cells is
located between said hologram and each of said liquid crystal cells.
41. A liquid crystal display device as claimed in claim 38, wherein said
hologram comprises uniform interference fringes with said efficiency of
diffraction independent, or less dependent, on wavelength, and wherein
converging elements are arranged on a side of said hologram on which said
backlight strikes or from which said backlight is emitted, and wherein
each of said converging elements corresponds to three liquid crystal cells
which are adjacent to each other.
42. A liquid crystal display device as claimed in claim 38, wherein said
hologram comprises an array of converging unit holograms, wherein each of
said converging unit holograms corresponds to three liquid crystal cells
which are adjacent to each other, and wherein each converging unit
hologram spectrally diffracts said backlight, which substantially
obliquely strikes a hologram plane, onto a set of liquid crystal cells in
in-line configuration.
43. A liquid crystal display device as claimed in claim 38, wherein said
hologram comprises an array of converging unit holograms, wherein each of
said converging unit holograms corresponds to three liquid crystal cells
which are adjacent to each other, and wherein each converging unit
hologram spectrally diffracts said backlight, which substantially
vertically strikes a hologram plane of said hologram, onto a set of liquid
crystal cells in offset configuration.
44. A liquid crystal display device as claimed in claim 38, wherein another
color filter of a different color is periodically located with respect to
an adjacent liquid crystal cell.
45. A liquid crystal display device as claimed in claim 44, wherein a
photopolymer is used as a material for recording said hologram.
46. A liquid crystal display device as claimed in claim 44, wherein a
converging element corresponding to each of said liquid crystal cells is
located between said hologram and each of said liquid crystal cells.
47. A liquid crystal display device as claimed in claim 44, wherein said
hologram comprises uniform interference fringes with said efficiency of
diffraction independent, or less dependent, on wavelength, and wherein
converging elements are arranged on a side of said hologram on which said
backlight strikes or from which said backlight is emitted, and wherein
each of said converging elements corresponds to three liquid crystal cells
which are adjacent to each other.
48. A liquid crystal display device as claimed in claim 44, wherein said
hologram comprises an array of converging unit holograms, wherein each of
said converging unit holograms corresponds to three liquid crystal cells
which are adjacent to each other, and wherein each converging unit
hologram spectrally diffracts said backlight, which substantially
obliquely strikes a hologram plane, onto a set of liquid crystal cells in
in-line configuration.
49. A liquid crystal display device as claimed in claim 44, wherein said
hologram comprises an array of converging unit holograms, wherein each of
said converging unit holograms corresponds to three liquid crystal cells
which are adjacent to each other, and wherein each converging unit
hologram spectrally diffracts said backlight, which substantially
vertically strikes a hologram plane of said hologram, onto a set of liquid
crystal cells in offset configuration.
50. A liquid crystal display device as claimed in claim 37, wherein another
color filter of a different color is periodically located with respect to
an adjacent liquid crystal cell.
51. A liquid crystal display device as claimed in claim 50, wherein a
photopolymer is used as a material for recording said hologram.
52. A liquid crystal display device as claimed in claim 50, wherein a
converging element corresponding to each of said liquid crystal cells is
located between said hologram and each of said liquid crystal cells.
53. A liquid crystal display device as claimed in claim 50, wherein said
hologram comprises uniform interference fringes with said efficiency of
diffraction independent, or less dependent, on wavelength, and wherein
converging elements are arranged on a side of said hologram on which said
backlight strikes or from which said backlight is emitted, and wherein
each of said converging elements corresponds to three liquid crystal cells
which are adjacent to each other.
54. A liquid crystal display device as claimed in claim 50, wherein said
hologram comprises an array of converging unit holograms, wherein each of
said converging unit holograms corresponds to three liquid crystal cells
which are adjacent to each other, and wherein each converging unit
hologram spectrally diffracts said backlight, which substantially
obliquely strikes a hologram plane, onto a set of liquid crystal cells in
in-line configuration.
55. A liquid crystal display device as claimed in claim 50, wherein said
hologram comprises an array of converging unit holograms, wherein each of
said converging unit holograms corresponds to three liquid crystal cells
which are adjacent to each other, and wherein each converging unit
hologram spectrally diffracts said backlight, which substantially
vertically strikes a hologram plane of said hologram, onto a set of liquid
crystal cells in offset configuration.
56. A liquid crystal display device as claimed in claim 37, wherein said
hologram comprises an array of converging unit holograms, wherein each of
said converging unit holograms corresponds to three liquid crystal cells
which are adjacent to each other, and wherein each converging unit
hologram spectrally diffracts said backlight, which substantially
vertically strikes a hologram plane of said hologram, onto a set of liquid
crystal cells in offset configuration.
57. A liquid crystal display device as claimed in claim 37, wherein said
hologram comprises an array of converging unit holograms, wherein each of
said converging unit holograms corresponds to three liquid crystal cells
which are adjacent to each other, and wherein each converging unit
hologram spectrally diffracts said backlight, which substantially
obliquely strikes a hologram plane, onto a set of liquid crystal cells in
in-line configuration.
58. A liquid crystal display device as claimed in claim 37, wherein said
hologram comprises uniform interference fringes with said efficiency of
diffraction independent, or less dependent, on wavelength, wherein
converging elements are arranged on a side of said hologram on which said
backlight strikes or from which said backlight is emitted, and wherein
each of said converging elements corresponds to three liquid crystal cells
which are adjacent to each other.
59. A liquid crystal display device as claimed in claim 37, wherein a
converging element corresponding to each of said liquid crystal cells is
located between said hologram and each of said liquid crystal cells.
60. A liquid crystal display device as claimed in claim 37, wherein a
photopolymer is used as a material for recording said hologram.
61. A liquid crystal display device as claimed in claim 37, wherein said
hologram comprises a relief hologram.
62. A liquid crystal display device as claimed in claim 37, wherein said
hologram comprises a computer-generated hologram.
63. A fabrication process of a hologram color filter comprising the steps
of:
disposing converging unit holograms in an array wherein said converging
unit holograms have an efficiency of diffraction independent, or less
dependent, on wavelength and spectrally diffract light incident thereon
into spectral components of different wavelength in order to emit said
spectral components to a desired position at a predetermined spatial
period;
producing a computer-generated hologram having properties of said
converging unit holograms;
bringing said computer-generated hologram in contact with a photosensitive
material or superposing said computer-generated hologram and said
photosensitive material together with a gap therebetween; and
illuminating said computer-generated hologram with coherent light such that
light diffracted by said computer-generated hologram and undiffracted
light propagated rectilinearly through said computer-generated hologram
interfere with each other in said photosensitive material for reproducing
a copied hologram from said computer-generated hologram.
64. A fabrication process of a hologram color filter as claimed in claim
63, wherein said copied hologram is used as an original for further
copying.
65. A fabrication process of a hologram color filter comprising the steps
of:
disposing converging unit holograms in an array, wherein said converging
unit holograms have an efficiency of diffraction independent, or less
dependent, on wavelength and spectrally diffract light incident thereon
into spectral components of different wavelength in order to emit said
spectral components to a desired position at a predetermined spatial
period;
producing a relief computer-generated hologram having properties of said
converging unit holograms;
coating a photosetting resin on a relief surface of said relief
computer-generated hologram; and
irradiating said photosetting resin with light for copying said relief
computer-generated hologram in the form of a relief hologram onto said
photosensitive resin. |
|
 |
|
 |
Claims |
|
|
|
Description |
|
|
BACKGROUND OF THE INVENTION
The present invention relates generally to a color filter making use of a
hologram and, more particularly, to a hologram color filter designed to
improve the efficiency of utilization of backlight, etc., by using a
hologram as well as a liquid crystal display device with a built-in
hologram color filter and a fabrication process of such a hologram color
filter.
So far, backlight for displaying purposes has been indispensable for a
color liquid crystal display device with a built-in color filter. When the
color liquid crystal display device is immediately illuminated by white
light from behind, however, the efficiency of utilization of the white
light is very low for the following major reasons:
1. The area occupied by black matrixes except the cell of each color is
large, and thus light striking on them will be wasted.
2. Of the white light incident onto each pixel, the color components
passing through the color filters R (red), G (green) and B (blue) is
limited to one color. Thus, other complementary color components will
again be wasted.
3. Each color filter has light loss due to absorption.
To solve such problems, it has been known in the art to locate a microlens
array 2 in front of a color filter 1, as shown in FIG. 17 as an example,
to converge white backlight 3 onto color filter cells R, G and B, thereby
improving the efficiency of utilization of the backlight 3. In connection
with FIG. 17, it is understood that reference numeral 4 represents black
matrixes located between the color filters R and G, and G and B.
Even with this technique, however, the problem 2 mentioned above remains
unsolved, because it is impossible to separate the white light 3 into its
spectral components for the illumination of the color filter cells R, G
and B. Moreover, the problem 3 mentioned above remains unsolved, because
reliance is still on the color filter 1.
There is another plausible process in which a hologram is located in front
of each pixel such that the red, green and blue components are selectively
converged onto the red, green and blue color filters, respectively.
According to this process, it is possible to improve the efficiency of
utilization of backlight because each pixel is illuminated by the white
light while it is separated into its spectral components.
For this holographic process, however, it is required that one hologram be
subjected to trichromatic multiple exposure, or that three holograms, each
for one color, be superposed together at the same position. The
disadvantages of this process are that the trichromatic multiple exposure
gives rise to a lowering of the efficiency of diffraction of the hologram
for each color, and the superposition of three holograms incurs difficulty
in alignment, and is very troublesome to do as well.
SUMMARY OF THE INVENTION
In view of the prior art problems mentioned above, an object of the present
invention is to spectrally diffract white light by a hologram for the
illumination of a given position, thereby achieving some considerable
improvement in the efficiency of utilization of backlight for liquid
crystal display, etc.
To achieve the above object, the present invention provides a color filter
using a hologram, characterized in that incident light is spectrally
diffracted by the hologram into light of different wavelength and the
light is emitted to a desired position at a predetermined spatial period.
Preferably, the hologram is produced by setting in array converging unit
holograms with the efficiency of diffraction independent, or less
dependent, on wavelength.
In another preferable embodiment, the hologram is made up of uniform
interference fringes with the efficiency of diffraction independent, or
less dependent, on wavelength, and an array form of converging elements is
arranged on the light-striking or emerging side of said hologram.
In still another preferable embodiment, the hologram is made up of doubly
recorded or superposed, two uniform interference fringes that are
selective in terms of the wavelength to be diffracted and the angle of
diffraction, and an array form of converging elements is arranged on the
light-striking or emerging side of said hologram.
Preferably, the hologram color filter is located on the side of a liquid
crystal display element onto which backlight is incident, said liquid
crystal display element being made up of a periodic arrangement of liquid
crystal cells. When the hologram color filter is built in a direct-view
liquid crystal display device, it is desired that a light-diffusing means
be located at any position on the light-emerging side of said hologram.
Preferably, the liquid crystal display panel (or element) is provided with
a light-blocking means at a position corresponding to a region between
liquid crystal cells, and between the liquid crystal display element and
the light-blocking means there is an additional color filter.
Preferably, the hologram color filter is located on the side of the liquid
crystal display panel (or element) onto which backlight is incident, said
liquid crystal display device including means for projecting the image
displayed.
Alternatively, the hologram color filter located on the entrance side of an
imaging device made up of a periodic arrangement of photodetection
elements.
According to another aspect of the invention, there is provided a liquid
crystal display device using a hologram color filter, which is illuminated
by backlight from behind to provide a color display, characterized in that
a hologram with the efficiency of diffraction independent, or less
dependent, on wavelength is located on the side of said device onto which
backlight is incident, and wavelength components spectrally diffracted by
said hologram are allowed to strike onto liquid crystal cells for
providing the corresponding colors.
Preferably, a light-blocking means is located at a position corresponding
to a region between said liquid crystal cells, and another color filter of
different color is periodically located with respect to the adjacent
liquid crystal cell.
Preferably, the hologram is made up of converging unit holograms set in
array at a period corresponding to said period, and each unit hologram
spectrally diffracts backlight striking almost vertically on the hologram
plane into a position of a set of liquid crystal cells in offset
configuration.
Alternatively, the hologram may be made up of converging unit holograms set
in array at a period corresponding to said period, and each unit hologram
spectrally diffracts backlight striking obliquely on the hologram plane
into a position of a set of liquid crystal cells in in-line configuration.
Preferably, the hologram is made up of uniform interference fringes with
the efficiency of diffraction independent, or less dependent, on
wavelength, and converging elements are arranged on the side of said
hologram on or from which backlight strikes or is emitted at a period
corresponding to said period.
Preferably, a converging element is located at a position corresponding to
each cell between said hologram and liquid crystal cells.
According to still another aspect of the invention, there is provided a
liquid crystal display device using a hologram color filter, which is
illuminated by backlight from behind to provide a color display,
characterized in that said hologram color filter is made up of doubly
recorded or superposed, two uniform holograms that are selective in terms
of the wavelength to be diffracted and the angle of diffraction and an
array of converging elements located on the light-striking or emerging
side of said hologram, and is located on the side of the display device
onto which backlight is incident, whereby wavelength components spectrally
diffracted by said hologram are allowed to strike on liquid crystal cells
for representing the corresponding colors.
Preferably, a photopolymer is used as the material for recording said
hologram.
Preferably, the hologram comprises a relief hologram or a
computer-generated hologram.
According to a further aspect of the invention, there is provided a
fabrication process of a hologram color filter which is produced by
setting in array converging unit holograms with the efficiency of
diffraction independent, or less dependent, on wavelength, and which
spectrally diffracts light incident thereon into light of different
wavelength, thereby emitting said light to a desired position at a
predetermined spatial period, characterized by producing a
computer-generated hologram having said properties by writing, bringing
the thus produced computer-generated hologram in contact with a
photosensitive material or superposing both together with a gap
therebetween, and illuminating CGH by coherent light such that light
diffracted by the computer-generated hologram and undiffracted light
propagated rectilinearly through the computer-generated hologram interfere
with each other in the photosensitive material for copying the
computer-generated hologram.
Preferably, the copied hologram is used as the original for further
copying.
According to a still-further aspect of the invention, there is provided a
fabrication process of a hologram color filter which is produced by
setting in array converging unit holograms with the efficiency of
diffraction independent, or less dependent, on wavelength, and which
spectrally diffracts light incident thereon into light of different
wavelength, thereby emitting said light to a desired position at a
predetermined spatial period, characterized by producing a relief
computer-generated hologram having said properties by writing, coating a
photosetting resin such as ultraviolet setting resin on the relief surface
of the thus produced relief computer-generated hologram, and irradiating
the resin with light such as ultraviolet rays for setting, thereby making
a copy in the form of a relief hologram.
By use of the hologram color filter according to the present invention is
it possible to provide a bright display or image, because incident light
is spectrally diffracted by the hologram into light of different
wavelength, which can in turn be emitted to a desired position at a
predetermined spatial period; that is, since there is no need of passing
the incident light through a color filter, there is a limited loss by
absorption. Moreover, since efficiently spectrally diffracted light can be
converged at a given positions, it is possible to make full use of the
wavelength components of backlight for color filters, etc., thereby
achieving some considerable improvement in the efficiency of utilization
of the backlight.
With the liquid crystal display device using the hologram color filter
according to the present invention, it is possible to make full use of the
wavelength components of the backlight for the color filter, thereby
achieving some considerable improvement in the efficiency of utilization
of the backlight. This is because the hologram that is not selective in
terms of the wavelength to be diffracted is located on the side of
incidence of the backlight such that the wavelength components spectrally
diffracted by the hologram are allowed to strike on the color filter cells
of the corresponding colors.
The fabrication process of a hologram color filter according to the present
invention is characterized by producing a computer-generated hologram
having given properties by writing, bringing the thus produced
computer-generated hologram in contact with a photosensitive material or
superposing both together with a gap therebetween, and illuminating CGH by
coherent light such that light diffracted by the computer-generated
hologram and undiffracted light propagated rectilinearly through the
computer-generated hologram interfere with each other in the
photosensitive material for copying the computer-generated hologram. Thus,
it is possible to easily fabricate a microhologram array which can
separate backlight into its spectral wavelength components so that they
can be allowed to strike on the color filter of a liquid crystal display
panel (or element) without being wasted and in which each microhologram is
small enough to be commensurate to a color filter pixel. Also, similar
holograms can be easily produced by using this as the original.
Still other objects and advantages of the invention will in part be obvious
and will in part be apparent from the specification.
The invention accordingly comprises the features of construction,
combinations of elements, and arrangement of parts which will be
exemplified in the construction hereinafter set forth, and the scope of
the invention will be indicated in the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic of the principle of the hologram color filter
according to the invention.
FIG. 2 illustrates a modification of the hologram color filter shown in
FIG. 1.
FIG. 3 is a schematic of one embodiment of the invention wherein a
converging hologram is located between a hologram filter and a liquid
crystal display element.
FIG. 4 illustrates another modification of the arrangement shown in FIG. 1.
FIG. 5 is a schematic of a color filter made up of two uniform holograms
that are selective in terms of the wavelength to be diffracted and the
angle of diffraction.
FIG. 6 is a schematic of a liquid crystal display panel (or element) in
which the color filter according to the invention is incorporated.
FIG. 7 is a schematic of an optical system for recording the hologram shown
in FIG. 2.
FIG. 8 is a schematic of another optical system for recording the hologram
shown in FIG. 2.
FIG. 9 is a schematic of another hologram fabrication process according to
the invention.
FIG. 10 is a schematic of an arrangement for confirming the degree of an
improvement in the efficiency of utilization of backlight by the hologram
according to the invention.
FIG. 11 is a schematic of an arrangement in which the hologram according to
the invention is built in a liquid crystal projector.
FIG. 12 is a schematic of one construction of the device for illuminating a
liquid crystal display device.
FIG. 13 is a partly enlarged view of FIG. 12.
FIG. 14 is a sectional view of another construction of the device for
illuminating a liquid crystal display device.
FIG. 15 is a perspective view of main parts of the device shown in FIG. 14.
FIG. 16 is a perspective view of main parts in a modification of the
construction shown in FIG. 14.
FIG. 17 illustrates a conventional process for illuminating a liquid
crystal display device.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the following description, the principle and embodiments of the hologram
color filter according to the invention will be explained with reference
to the accompanying drawings.
The principle of the color filter according to the invention will first be
explained with reference to FIG. 1. As illustrated in FIG. 1, a
transmission hologram 5 is located on the side of a liquid crystal display
element 10 onto which backlight 3 strikes. The liquid crystal display
element 10 comprises a repetition of three adjacent liquid crystal cells 6
to represent trichromatic (red, green, and blue) components for each
pixel. On the back side of the liquid crystal display element 10 there is
arranged a color filter 1 made up of red, green and blue cells 1' that are
in alignment with each liquid crystal cell 6 and have black matrixes 4
located between them. In another arrangement, the black matrixes 4 alone
may be provided in the absence of the colored cells 1'. On both sides of
the liquid crystal display element 10 there are located polarizing plates,
although not illustrated.
The transmission hologram 5 is constructed in an array of unit holograms
having the same pitch as the pixels, corresponding to each set of the
three liquid crystal cells 6 representing one pixel of the liquid crystal
display element 10. Then, each unit hologram is constructed in a Fresnel
zone plate form, so that white backlight 3 striking almost vertically on
the surface of the hologram is converged by diffraction on the pixel of
the liquid crystal display element 10 that is located at a position offset
from the corresponding unit hologram. As the hologram 5 use may be made of
relief, phase, amplitude and other holograms with the efficiency of
diffraction independent, or less dependent, on wavelength. Here the
wording "the efficiency of diffraction independent, or less dependent, on
wavelength" should be understood to mean a type that allows every
wavelength to be diffracted by one diffraction grating, rather than a type
that allows only a specific wavelength not to be diffracted and other
wavelengths to be diffracted, as in the case of a Lippmann hologram (that
is selective in terms of the wavelength to be diffracted and the angle of
diffraction). Such a diffraction grating less dependent on wavelength
generally varies the angle of diffraction depending on wavelength.
Accordingly, the angle of diffraction by the unit hologram varies
depending on the wavelength of the incident light 3, so that the
converging position for each wavelength is dispersed in the direction
parallel with the plane of the hologram 5. For this reason, the red, green
and blue wavelength components of the incident white light 3 are
respectively converged by diffraction at the positions of the color filter
cell R or the liquid crystal cell 6 for representing red, the color filter
cell G or the liquid crystal cell 6 for representing green, and the color
filter B or the liquid crystal cell 6 for representing blue. Also, the
color components can pass through the liquid crystal cells 6 without being
substantially attenuated by the color filter cells R, G and B and the
black matrixes 4, thereby representing colors depending on the states of
the liquid crystal cells at the corresponding positions.
By making use of a difference in the angle of diffraction of the hologram
depending on wavelength, it is thus possible to diffract the wavelength
component of the color to be displayed and allow it to be incident on the
liquid crystal cell 6 of each color of the liquid crystal display element
10 located behind the hologram 5, thereby enabling the respective
wavelength components of the backlight to directly strike the each liquid
crystal cell without being wasted. Consequently, the efficiency of
utilization of the backlight is improved.
In the above arrangement explained with reference to FIG. 1, the backlight
3 is allowed to strike almost vertically on the surface of the hologram.
As shown in FIG. 2, however, it is also possible to allow backlight 3 to
be incident on the plane of the hologram at a predetermined angle .theta.
with the normal line of that surface. In the arrangement shown, the
parallel backlight beams 3 are allowed to strike on the hologram at an
angle of 25 degrees with the normal line. Then, the blue (460 nm), green
(545 nm) and red (610 nm) wavelengths of the backlight 3 are converged by
diffraction on the pixels that are located at the relative positions shown
and are of the size shown. It should here be noted that the angle .theta.
of incidence of the backlight on the surface of the hologram is determined
by various conditions (e.g., the condition for recording the hologram 5,
the thickness of the hologram 5 and distance between the hologram 5 and
the liquid crystal display element 10).
Reference will now be made to the embodiment shown in FIG. 3, wherein
between such a hologram 5 as mentioned above and a liquid crystal display
element 10 there are located converging holograms 50 in alignment with
color filter cells R, G and B or red, green and blue liquid crystal cells
6 to achieve a more efficient convergence of the color components incident
on them. This enables each color component to strike on each cell more
efficiently and reduces the distance between the hologram 50 and the
liquid crystal display element 10. In this embodiment, even when the light
spectrally diffracted by the hologram 50 is cut off by the black matrix 4
and is wasted, such light can be further converged by the converging
hologram 50. It is possible to prevent the spectrally diffracted
components from striking on and being cut off by the black matrix 4. It is
understood that microlenses may be used in place of the converging
holograms 50.
In each of the arrangements explained with reference to FIGS. 1-3, an array
of microholograms for wavelength dispersion, each in a Fresnel zone plate
form, is provided corresponding to each set of red, green and blue liquid
crystal cells. However, some considerable improvement in the efficiency of
utilization of backlight is also achieved by using a uniform hologram
acting as a diffraction grating that disperses wavelength and is less
dependent on wavelength in combination with an array of microlenses,
thereby making use of the action of the hologram to disperse wavelength.
As shown in FIG. 4, an array g of microlenses 7, each having a diameter
corresponding to the pixel pitch of a liquid crystal display element 10
and being provided on a glass plate 8, is located in front of the liquid
crystal display element 10. A transmission hologram 5 made up of uniform
interference fringes and less dependent on wavelength is integrally
provided on the opposite side of the glass plate 8. In this arrangement,
white backlight 3 converged by the microlenses 7 is diffracted and
separated into its spectral components by the transmission hologram 5 at
different angles depending on wavelength. As in the case of the
arrangement shown in FIG. 1 or 3, the converging position for each
wavelength is dispersed in the direction parallel with the plane of the
hologram 5. The red, green and blue wavelength components of the incident
white light 3 are respectively converged at the positions of the color
filter cell R or the liquid crystal cell 6 for representing red, the color
filter cell G or the liquid crystal cell 6 for providing green, and the
color filter cell B or the liquid crystal cell 6 for representing blue,
thereby enabling each color component to be displayed depending on the
state of each liquid crystal cell 6. By using a transmission hologram 5
that has no property of converging light, comprises uniform interference
fringes, and so is less dependent on wavelength, this arrangement has the
major advantages of dispensing with alignment of the hologram 5 with the
liquid crystal display element 10. Also, since the pitch of the microlens
array 9 three times as large as the conventional arrangement shown in FIG.
17, it is easy to fabricate and align the microlens array 9.
It is here noted that even when use is made of holograms that are selective
in terms of the wavelength to be diffracted and the angle of diffraction,
for instance, Lippmann holograms that allow only a specific wavelength to
be diffracted and all other wavelengths not to be diffracted, a similar
hologram color filter may be constructed by superposing two uniform
transmission holograms capable of diffracting two wavelengths or recording
them twice in superimposed fashion, rather than by superposing three
transmission holograms selective in terms of wavelength and angle and
capable of diffracting three wavelengths or recording them three times in
superposed fashion. This arrangement is shown in FIG. 5. Here, too, some
considerable improvement in the efficiency of utilization of backlight is
achieved by using uniform holograms acting as diffraction gratings
selective in terms of wavelength and angle in combination with a microlens
array, thereby making use of the selectivity of wavelength and angle by
diffraction. As shown in FIG. 5, a microlens array 9 is located in front
of a liquid crystal display element 10. The array 9 is obtained by
arranging microlenses 7 with the diameters corresponding to the pixel
pitch of the element 10 on a glass substrate 8. 0n the opposite side of
the glass substrate 8 there is located a hologram assembly 5' made up of
blue and red holograms 52 and 51, each comprising uniform interference
fringes selective in terms of wavelength and angle. In this arrangement,
most o | | |
