Optical: systems and elements – Holographic system or element – For synthetically generating a hologram
Reexamination Certificate
2001-05-30
2004-06-08
Dunn, Drew (Department: 2872)
Optical: systems and elements
Holographic system or element
For synthetically generating a hologram
C359S599000
Reexamination Certificate
active
06747769
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to a computer-generated hologram, and more particularly to a computer-generated hologram suitable for use as a reflector and its fabrication process as well as a reflective liquid crystal display using a computer-generated hologram.
Of a variety of display systems already put to practical use, liquid crystal display systems have now wide applications because they have some advantages of low power consumption, color display capability, low-profile size, and low weight.
Instead of LCDs, it is difficult to use other type of displays for terminal equipment having no other choice to rely on batteries or accumulators.
However, LCDs cannot emit light by themselves; in other words, extraneous light or illumination light is necessary for viewing images irrespective of whether they are of the reflection type or the transmission type.
However, the use of sufficiently bright illumination light goes against the valuable advantage of low power consumption. Accordingly, even when illumination light is used, it is unreasonable to make use of illumination having relatively high illuminance; whether the light used is extraneous light or illumination light, how limited light is effectively used is of vital importance.
The applicant has already filed patent applications (JP-A's 11-296054 and 11-183716) to come up with computer-generated holograms having a phase distribution capable of diffracting obliquely incident light in a predetermined viewing region. Of both, JP-A 11-296054 discloses a computer-generated hologram having a phase distribution for allowing light incident thereon at an oblique angle of incidence to be diffracted into the predetermined viewing region.
To fabricate these computer-generated holograms which are still found to have the desired effects, however, it is required to use a time-consuming, inefficient fabrication process comprising the steps of using a computer to find phase distributions all over the hologram region by computations, and making a relief pattern for the replication of computer-generated holograms on the basis of computation results.
For photoetching in particular, it is preferable to make use of a photomask fabrication system because precise exposure is needed. However, the photomask fabrication system has some disadvantages of high cost, severe fabrication conditions and extended fabrication time, in which the extended fabrication time in particular offers a grave problem.
SUMMARY OF THE INVENTION
One object of the present invention is to provide a novel computer-generated hologram which can be viewed in white at the desired viewing region, and a reflective liquid crystal display using the same as a reflector.
Another object of the present invention is to eliminate a problem in association with the fabrication of a relief pattern for computer-generated hologram fabrication, and especially a time problem in connection with data processing on aligners for photoetching.
Throughout the present disclosure, the term “photoetching” is understood to mean a photostep for providing the desired pattern to a photosensitive material by means of laser light, electron beams or the like and etching the pattern into a relief configuration.
Yet another object of the present invention is to provide a computer-generated hologram which has improved optical diffraction efficiency, allows a master pattern to be easily obtained for replication purposes, is easy to fabricate, and enables its relief surface to come into contact with the back surface of a light transmission display device as well as a reflective liquid crystal display using the same as a reflector.
According to the first invention to achieve the aforesaid first object, there is provided a computer-generated hologram designed to diffuse light having a given reference wavelength and incident thereon at a given angle of incidence in a specific angle range, characterized in that, in a range of wavelengths including said reference wavelength wherein zero-order transmission light or zero-order reflection light incident on said computer-generated hologram at a given angle of incidence is seen in white by additive color mixing, the maximum diffraction angle of incident light of the minimum wavelength in said range and incident at said angle of incidence is larger than the minimum diffraction angle of incident light of the maximum wavelength in said range and incident at said angle of incidence.
Preferably in this case, the computer-generated hologram comprises an array of two-dimensionally arranged minute cells, wherein each cell has an optical path length for imparting a unique phase to reflection light or transmission light, and a phase distribution obtained by adding a first phase distribution that substantially diffracts a vertically incident light beam within a given viewing region and does not substantially diffract the light beam toward other region to a second phase distribution that allows an obliquely incident light beam at a given angle of incidence to leave the cell vertically.
Alternatively, the computer-generated hologram may comprise an array of two-dimensionally arranged minute cells, wherein each cell has an optical path length for imparting a unique phase to reflection light or transmission light as well as a phase distribution which substantially diffracts an obliquely incident light beam at a given angle of incidence within a given viewing region and does not substantially diffract the light beam toward other region and which substantially diffracts a vertically incident light beam within another region shifted from said given viewing region and does not substantially diffract the light beam toward a region except for said another region.
Practically, the cells are arranged in columns and rows just like checkers.
Further, the computer-generated hologram may be a reflection computer-generated hologram wherein a reflective layer is provided on a relief pattern provided on the surface of the substrate.
Further, the computer-generated hologram may be constructed in such a way as to be adaptable to the minimum wavelength of 450 nm and the maximum wavelength of 650 nm.
Preferably, the computer-generated hologram should satisfy:
&lgr;
MIN
/&lgr;
MAX
≧(sin &bgr;
1STD
−sin &thgr;)/(sin &bgr;
2STD
−sin &thgr;) (11)
where &thgr; is the angle of incidence of illumination light, &lgr;
MIN
is the minimum wavelength, &lgr;
MAX
is the maximum wavelength, &bgr;
1STD
is the minimum diffraction angle at a given reference wavelength &lgr;
STD
and &bgr;
2STD
is the maximum diffraction angle at the given reference wavelength &lgr;
STD.
It is also preferable that the computer-generated hologram satisfies:
sin &thgr;≧(&lgr;
MAX
sin &bgr;
1STD
−&lgr;
MIN
sin &bgr;
2STD
)/(&lgr;
MAX
−&lgr;
MIN
) (12)
where &thgr; is the angle of incidence of illumination light, &lgr;
MIN
is the minimum wavelength, &lgr;
MAX
is the maximum wavelength, &bgr;
1STD
is the minimum diffraction angle at a given reference wavelength &lgr;
STD
and &bgr;
2STD
is the maximum diffraction angle at the given reference wavelength &lgr;
STD
.
A display system of the invention is characterized by using any one of the aforesaid computer-generated holograms as a reflector.
One reflective liquid crystal display system of the invention is characterized in that any one of the aforesaid computer-generated holograms is disposed as a reflector on the back surface thereof.
Another reflective liquid crystal display system of the invention is characterized in that any one of the aforesaid computer-generated holograms is interposed as a reflector between a liquid crystal layer thereof and a back surface substrate thereof.
According to the invention to achieve the aforesaid first object, the computer-generated hologram is constructed such that, in a range of wavelengths including the reference wavelength wherein zero-order transmission light or zero-order reflection light incident on the computer-generated hologram at a given angle of in
Fujita Hiroshi
Hamano Tomohisa
Kitamura Mitsuru
Kodama Daijiro
Yabuhara Hideo
Amari Alessandro
Dai Nippon Printing Co. Ltd.
Dunn Drew
Sughrue & Mion, PLLC
Yabuhara Manami
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