Optical: systems and elements – Holographic system or element – Using a hologram as an optical element
Reexamination Certificate
2001-05-15
2003-12-23
Chang, Audrey (Department: 2872)
Optical: systems and elements
Holographic system or element
Using a hologram as an optical element
C359S022000, C359S024000, C359S019000, C349S104000, C349S105000, C349S106000
Reexamination Certificate
active
06667819
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a reflection type diffuse hologram that can be used for display devices such as liquid crystal display devices, a hologram for reflection hologram color filters, etc., and a reflection type display device using such holograms.
Backlight used with a liquid crystal display device should have some scattering characteristics, so that the display device can have a wide viewing angle. So far, scattering characteristics have been imparted to backlight by use of beads or the like, but a problem with this is that too large an angle of diffusion results in wasteful illumination light loss.
This is also true of an automotive brake lamp or direction indicator. That is, although too large a diffusion angle is not required in view of the positional relation to succeeding cars, light from these lamps is not only wastefully consumed but also becomes dark because lenses positioned in front of the lamps cause the light to be diffused at an angle larger than required.
The present applicant has filed Japanese Patent Application No. 12170/1993 to come up with a color filter in which a hologram is used to achieve a remarkable increase in the efficiency of backlight used for liquid crystal display purposes, etc., and a liquid crystal display device that makes use of such a color filter.
A typical liquid crystal display device that makes use of this hologram color filter will now be briefly described with reference to a sectional view attached hereto as FIG.
43
. As illustrated, a hologram array
55
forming the color filter is spaced away from the side of a liquid crystal display element
56
upon which backlight
53
is to strike, said element being regularly divided into liquid crystal cells
56
′ (pixels). On the back side of the liquid crystal display element
56
and between the liquid crystal cells
56
′ there are located black matrices
54
. Although not illustrated, polarizing plates are arranged on the incident side of the hologram array
55
, and the exit side of the liquid crystal display element
56
. As is the case with a conventional color liquid crystal display device, between the black matrices
54
there may additionally be located an absorption type of color filters which transmit light rays of colors corresponding to pixels R, G, and B.
The hologram array
55
comprises micro-holograms
55
′ which are arranged in an array form at the same pitch as that of R, G, and B spectral pixels, corresponding to the period of repetition of R, G, and B spectral pixels, i.e., sets of liquid crystal cells
56
′, each including three adjoining liquid crystal cells
56
′ of the liquid crystal display element
6
as viewed in a plane direction of the drawing sheet. One micro-hologram
55
′ is located in line with each set of three adjoining liquid crystal cells
56
′ of the liquid crystal display element
6
as viewed in the plane direction of the drawing sheet. The micro-holograms
55
′ are then arranged in a Fresnel zone plate form such that a green component ray of the backlight
3
incident on the hologram array
55
at an angle &thgr; with respect to its normal line is collected at a middle liquid crystal cell G of the three R, G, and B spectral pixels corresponding to each micro-hologram
55
′. Each or the micro-hologram
55
′ in this case is constructed from a relief, phase, amplitude or other transmission type of hologram which has little, if any, dependence of diffraction efficiency 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 now the incidence of the white backlight
3
from the side of the hologram array
55
, which does not face the liquid crystal display element
56
at the angle &thgr; with respect to its normal line. The angle of diffraction of the light by the micro-hologram
55
′ varies depending on wavelength, so that light collection positions for wavelengths are dispersed in a direction substantially parallel with the surface of the hologram array
55
. If the hologram array
55
is constructed and arranged such that the red wavelength component is diffractively collected 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 pass through the corresponding liquid crystal cells
56
′ with no or little attenuation through the black matrices
4
, so that color displays can be presented depending on the state of the liquid crystal cells
56
′ at the corresponding positions. It is here noted that the angle of incidence &thgr; of backlight
53
on the hologram array
55
is determined by various conditions including hologram-recording conditions, the thickness of hologram array
55
, and the distance between the hologram array
55
and the liquid crystal display element
6
.
By using the hologram array
55
as a color filter in this way, the wavelength components of backlight used with a conventional color filter are allowed to strike on the liquid crystal cells
56
′ without extravagant absorption, so that the efficiency of utilization thereof can be greatly improved.
The aforesaid hologram color filter proposed by the present applicant is applicable to only a color liquid crystal display device making use of backlight. However, when surrounding ambient light alone is used as illumination light, this hologram color filter cannot diffract, and collect its wavelength components into desired positions. In other words, this hologram color filter can never be applied to a direct-view type of liquid crystal display device or other like device in which surrounding ambient light is used as illumination light, or any particular backlight source is not required.
Moreover, the applicant has filed Japanese Patent Application No. 120016/1993 to come up with a method for using a swelling film to make from a volume hologram having uniform interference fringes recorded therein a color pattern that varies in reconstructed color depending on position. The principles are similar to those applied to a photopolymer. First, a swelling film is prepared by mixing a monomer or oligomer, a photopolymerization initiator, etc. with a binder polymer. Then, the swelling film is irradiated with a given quantity of light before or after its close contact with a photopolymer or other photosensitive material having interference fringes recorded therein, so that a given proportion of the monomer or oligomer contained in the swelling film, on the one hand, is polymerized for deactivation and the amount of the remaining active monomer or oligomer, on the other hand, is controlled. The thus controlled amount of the monomer or oligomer is diffused, and swollen into the photosensitive material with interference fringes recorded therein, whereby fringe spacings are precisely controlled to any desired quantity to control reconstruction wavelengths to given ones. After this swelling treatment, the photosensitive material with the interference fringe recorded therein is irradiated with light or otherwise heated to fix the diffused monomer or oligomer in the interference fringes, so that there can be obtained a hologram excelling in the storage stability of reconstructed colors. In addition, a color pattern can be formed on the hologram by allowing the illumination light to have a spatial distribution.
This method will now be explained in a little more detail with reference to
FIGS. 44
Hotta Tsuyoshi
Kuwabara Yuko
Nishikawa Shingo
Segawa Toshikazu
Ueda Kenji
Chang Audrey
Dai Nippon Printing Co. Ltd.
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