Optical: systems and elements – Holographic system or element – For producing or reconstructing images from multiple holograms
Reexamination Certificate
1998-09-14
2002-07-30
Henry, Jon (Department: 2872)
Optical: systems and elements
Holographic system or element
For producing or reconstructing images from multiple holograms
C359S024000, C359S019000, C359S015000, C359S016000, C349S062000, C349S095000, C349S106000
Reexamination Certificate
active
06426812
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to a hologram color filter and its fabrication method, and more particularly to a hologram color filter for liquid crystal display devices which is much more reduced in terms of dependence of diffraction efficiency on wavelength and so is well corrected for a color balance among three colors R, G and B, and its fabrication method.
Moreover, the present invention relates generally to an alignment mark and method, and more specifically to an alignment mark for hologram color filters and a method of aligning a hologram color filter and a back matrix.
Applicant has already filed Japanese Patent Application No. 5-12170, etc., to propose a color filter for color liquid crystal display devices, which enables the respective wavelength components of backlight to be more efficiently incident on liquid crystal cells without wasteful absorption as compared with a conventional wavelength absorption type of color filter, whereby the efficiency of utilization of backlight can be greatly improved. This color filter is generally broken down into two types, one of which makes use of an array of an eccentric Fresnel zone plate form of microholograms. Another type utilizes an array of micro-lenses superposed on a hologram or diffraction grating having parallel and uniform interference fringes thereon. A brief account will now be given of these hologram color filters.
A liquid crystal display device making use of the first type of hologram color filter is explained with reference to
FIG. 11
that is a sectional schematic thereof. As shown, a hologram array
5
forming this hologram color filter is spaced away from the side of a liquid crystal display element
6
on which backlight
3
is to be incident, said element
6
being regularly divided into liquid crystal cells
6
′ (pixels). On the back side of the liquid crystal display element
6
and between the liquid crystal cells
6
′ there are located black matrices
4
. Although not illustrated, polarizing plates are arranged on both sides of the liquid crystal display element
6
. As is the case with a conventional color liquid crystal display device, between the black matrices
4
there may additionally be located an absorption type of color filters which transmit light rays of colors corresponding to red, green and blue pixels.
The hologram array
5
comprises microholograms
5
′ which are arranged in an array form at the same pitch as that of red, green and blue pixels, corresponding to the period of repetition of red, green and blue pixels, i.e., sets of liquid crystal cells
6
′, each including three adjoining liquid crystal cells
6
′ of the liquid crystal display element
6
as viewed in a longitudinal direction thereof. One microhologram
5
′ is located in line with each set of three adjoining liquid crystal cells
6
′ of the liquid crystal display element
6
as viewed in the longitudinal direction thereof. The microholograms
5
′ are then arranged in a Fresnel zone plate form such that a green component ray of the backlight
3
incident on the hologram array
5
at an angle &thgr; with respect to its normal line is converged at a middle liquid crystal cell G of the three red, green and blue pixels corresponding to each microhologram
5
′. Each or the microhologram
5
′ in this case is constructed from a relief, phase, amplitude or other transmission type of hologram which has little, if any, dependence of diffraction efficient on wavelength. The wording “little, if any, dependence of diffraction efficiency on wavelength” used herein is understood to refer specifically to a hologram of the type which diffracts all wavelengths by one diffraction grating, much unlike a Lippmann type hologram which diffracts a particular wavelength alone but does not substantially permit other wavelengths to be transmitted therethrough. The diffraction grating having little dependence of diffraction efficiency on wavelength diffracts different wavelengths at different angles of diffraction.
In such an arrangement, consider the incidence of the white backlight
3
from the side of the hologram array
5
, which does not face the liquid crystal display element
6
at the angle &thgr; with respect to its normal line. The angle of diffraction of the light by the microholograms
5
′ varies depending on wavelength, so that convergence positions for wavelengths are dispersed in a direction substantially parallel with the surface of the hologram array
5
. If the hologram array
5
is constructed and arranged such that the red wavelength component is diffractively converged at a red-representing liquid crystal cell R; the green wavelength component at a green-representing liquid crystal cell G; and the blue wavelength component at a blue-representing liquid crystal cell B, the color components transmit the corresponding liquid crystal cells without undergoing little or no attenuation through the black matrices
4
, so that color displays can be presented depending on the state of the liquid crystal cells
6
′ at the corresponding positions.
By using the hologram array
5
as a color filter in this way the wavelength components of backlight used with a conventional color filter are allowed to be incident on the liquid crystal cells' without extravagant absorption, so that the efficiency of utilization thereof can be greatly improved.
A liquid crystal display device with the second type of hologram color filter built in it is then explained with reference to
FIG. 12
that is a sectional schematic thereof. As illustrated, the second type of hologram color filter generally shown at
10
comprises a hologram
7
and a converging microlens array
8
. Microlenses
8
′ forming part of the microlens array
8
are arranged in an array form at the same pitch as that of red, green and blue pixels, corresponding to the period of repetition of red, green and blue pixels, i.e., sets of liquid crystal cells
6
′, each including three adjoining liquid crystal cells
6
′ of a liquid crystal display element
6
as viewed in a longitudinal direction thereof. The hologram
7
is made up of a relief, phase, amplitude or other transmission type of hologram which has thereon parallel and uniform interference fringes that act as a diffraction grating, and has little or no dependence of diffraction efficiency on wavelength. On the back surface of the liquid crystal display element
6
and between the liquid crystal cells
6
′ there are located black matrices
4
. Although not illustrated, polarizing plates are arranged on both sides of the liquid crystal display element
6
. As is the case with a conventional color liquid crystal display device, between the black matrices
4
there may additionally be located an absorption type of color filters which transmit light rays of colors corresponding to red, green and blue pixels.
In such an arrangement, consider the incidence of the white backlight
3
from the side of the hologram
7
that is not opposite to the liquid crystal display element
6
at an angle &thgr; with respect to its normal line. The incident light is diffracted at different angles depending on wavelength, and then emerges dispersively from the hologram
7
. The dispersed light is in turn separated for each wavelength by the microlenses
8
′ located on an incident or emergent side of the hologram
7
, so that it is converged at focal surfaces thereof. If the color filter
10
is constructed and arranged such that the red wavelength component is diffractively converged at a red-representing liquid crystal cell R; the green wavelength component at a green-representing liquid crystal cell G; and the blue wavelength component at a blue-representing liquid crystal cell B, the color components transmit the corresponding liquid crystal cells
6
′ without undergoing little or no attenuation through the black matrices
4
, so that color displays can be presented depending on the state of the liquid crystal
Hotta Tsuyoshi
Ichikawa Nobuhiko
Ueda Kenji
Dai Nippon Printing Co. Ltd.
Henry Jon
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