Computer-generated hologram and its fabrication process, reflector using a computer-generated hologram, and reflective liquid crystal display Number:7,054,044 from the United States Patent and Trademark Office (PTO) owispatent The invention provides a 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. The computer-generated hologram H is designed to diffuse light having a given reference wavelength .lamda..sub.STD and incident thereon at a given angle of incidence .theta. in a specific angle range. In a range of wavelengths .lamda..sub.MIN to .lamda..sub.MAX including the reference wavelength .lamda..sub.STD wherein zero-order transmission light or zero-order reflection light of incident light on the computer-generated hologram at a given angle of incidence is seen in white by additive color mixing, the maximum diffraction angle .beta..sub.2MIN of incident light of the minimum wavelength .lamda..sub.MIN in the wavelength range and incident at the angle of incidence .theta. is larger than the minimum diffraction angle .beta..sub.1MAX of incident light of the maximum wavelength .lamda..sub.MAX in the wavelength range and incident at said angle of incidence .theta..<H fabrication, reflective, Computer, genera, 7054044.html, Patent, pto, 7054044

Title: Computer-generated hologram and its fabrication process, reflector using a computer-generated hologram, and reflective liquid crystal display

Abstract: The invention provides a 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. The computer-generated hologram H is designed to diffuse light having a given reference wavelength .lamda..sub.STD and incident thereon at a given angle of incidence .theta. in a specific angle range. In a range of wavelengths .lamda..sub.MIN to .lamda..sub.MAX including the reference wavelength .lamda..sub.STD wherein zero-order transmission light or zero-order reflection light of incident light on the computer-generated hologram at a given angle of incidence is seen in white by additive color mixing, the maximum diffraction angle .beta..sub.2MIN of incident light of the minimum wavelength .lamda..sub.MIN in the wavelength range and incident at the angle of incidence .theta. is larger than the minimum diffraction angle .beta..sub.1MAX of incident light of the maximum wavelength .lamda..sub.MAX in the wavelength range and incident at said angle of incidence .theta..

Patent Number: 7,054,044 Issued on 05/30/2006 to Hamano, et al.

Inventors: Hamano; Tomohisa (Tokyo, JP); Kitamura; Mitsuru (Tokyo, JP); Kodama; Daijiro (Tokyo, JP); Fujita; Hiroshi (Tokyo, JP); Yabuhara, legal representative; Manami (Saitama, JP); Yabuhara, deceased; Hideo (Tokyo, JP)
Assignee: Dai Nippon Printing Co., Ltd. (Tokyo, JP)

Appl. No.: 808469

Filed: March 25, 2004

Related U.S. Patent Documents


Application Number	Filing Date	Patent Number	Issue Date
09866605	May., 2001	6747769

Foreign Application Priority Data


May 30, 2000 [JP]			2000-159914
Jun 09, 2000 [JP]			2000-173935
Jul 19, 2000 [JP]			2000-219582

Current U.S. Class: 359/9 ; 430/2

Current International Class: G03H 1/08 (20060101)

Field of Search: 359/9,15,35 430/1,2

References Cited [Referenced By]

U.S. Patent Documents


4846552	July 1989	Veldkamp et al.
5153751	October 1992	Ishikawa et al.
5543228	August 1996	Taniguchi et al.
5936751	August 1999	Wenyon
6043910	March 2000	Slinger
6120950	September 2000	Unno
6166833	December 2000	Mendlovic et al.
6285503	September 2001	Chao et al.
6417940	July 2002	Sekine
6421148	July 2002	Steiner

Primary Examiner: Robinson; Mark A.
Assistant Examiner: Amari; Alessandro
Attorney, Agent or Firm: Sughrue Mion, PLLC

Parent Case Text

This is a divisional of application Ser. No. 09/866,605, filed May 30, 2001 now U.S. Pat. No. 6,747,769; the disclosure of which is incorporated herein by reference.

Claims

We claim:

1. A process for fabricating a computer-generated hologram by defining a range which diffraction light obtained by diffraction of incident light leaves, determining a hologram phase distribution for allowing said diffraction light to leave the defined range, quantizing a determined phase distribution to find a quantized depth of a hologram relief, forming a relief on a substrate by photoetching on the basis of a found quantized depth to obtain a relief pattern, and patterning a resin layer using said relief pattern to form a hologram relief on a surface of said resin layer; wherein said phase distribution is determined per minute elemental hologram piece forming the hologram, and said relief is formed on the basis of a phase distribution obtained by repeatedly arranging a phase distribution of said elemental hologram piece across said substrate.

2. The computer-generated hologram fabrication process according to claim 1, wherein an optical reflective layer is laminated on and along a relief side or other side of said resin layer.

3. The computer-generated hologram fabrication process according to claim 2, further comprising quantizing the determined phase distribution to find the number of steps of said quantized depth, and repeating photoetching given times corresponding to the obtained depth and the number of steps to form the relief pattern on the substrate, wherein the number of steps L having the depth of said relief is the N-th power of 2 where N is the number of photoetching cycles.

4. The computer-generated hologram fabrication process according to claim 1, wherein an optical reflective layer is laminated on and along a relief side or other side of said resin layer.

5. The computer-generated hologram fabrication process according to claim 1, further comprising quantizing the determined phase distribution to find the number of steps of said quantized depth, and repeating photoetching given times corresponding to the obtained depth and the number of steps to form the relief pattern on the substrate, wherein the number of steps L of the depth of said relief is the N-th power of 2 where N is the number of photoetching cycles.

6. The computer-generated hologram process of claim 1, wherein the step of patterning a resin layer using said relief pattern to form a hologram relief on a surface of said resin layer includes pressing the relief pattern against the resin layer, and then curing the resin layer.

7. A process for fabricating a computer-generated hologram by defining a range which diffraction light obtained by diffraction of incident light leaves, determining a hologram phase distribution for allowing said diffraction light to leave the defined range, quantizing a determined phase distribution to find a quantized depth of a hologram relief and the number of steps of said depth, repeating photoetching given times corresponding to an obtained depth and the number of steps to form a relief pattern on an etching substrate, and patterning a resin layer using said relief pattern to form a hologram relief on a surface of said resin layer; wherein said phase distribution is determined per minute elemental hologram piece forming the hologram, and said relief is formed on the basis of a phase distribution obtained by repeatedly arranging a phase distribution of said elemental hologram piece across said substrate.

8. The computer-generated hologram fabrication process according to claim 7, wherein an optical reflective layer is laminated on and along a relief side or other side of said resin layer.

9. The computer-generated hologram fabrication process according to claim 7, wherein the number of steps L having the depth of said relief is the N-th power of 2 where N is the number of photoetching cycles.

10. The computer-generated hologram process of claim 7, wherein the step of patterning a resin layer using said relief pattern to form a hologram relief on a surface of said resin layer includes pressing the relief pattern against the resin layer, and then curing the resin layer.

11. A process for fabricating a computer-generated hologram by defining a range which diffraction light obtained by diffraction of incident light leaves, determining a hologram phase distribution for allowing said diffraction light to leave the defined range, quantizing a determined phase distribution to find a quantized depth of a hologram relief and the number of steps of said depth, repeating photoetching given times corresponding to an obtained depth and the number of steps to form a relief pattern on an etching substrate, and patterning a resin layer using said relief pattern to form a hologram relief on a surface of said resin layer; wherein the number of steps L having the depth of said relief is the N-th power of 2 where N is the number of photoetching cycles.

12. A process for fabricating a computer-generated hologram by defining a range which diffraction light obtained by diffraction of incident light leaves, determining a hologram phase distribution for allowing said diffraction light to leave the defined range, quantizing a determined phase distribution to find a quantized depth of a hologram relief and a number of steps of said depth, forming a relief on a substrate by photoetching on the basis of a found quantized depth to obtain a relief pattern, and patterning a resin layer using said relief pattern to form a hologram relief on a surface of said resin layer; wherein said relief is formed on the basis of a phase distribution obtained by repeatedly arranging a phase distribution of an elemental hologram piece across said substrate.

13. The process for fabricating a computer-generated hologram according to claim 12, wherein the number of steps L having the depth of said relief is the N-th power of 2 where N is a number of photoetching cycles performed.

14. The process for fabricating a computer-generated hologram according to claim 12, further comprising: quantizing the determined phase distribution to find the number of steps of said quantized depth, and repeating photoetching given times corresponding to the obtained depth and the number of steps to form the relief pattern on the substrate.

15. The computer-generated hologram process of claim 12, wherein patterning a resin layer using said relief pattern to form a hologram relief on a surface of said resin layer includes pressing the relief pattern against the resin layer, and then curing the resin layer.

16. A process for fabricating a computer-generated hologram by defining a range which diffraction light obtained by diffraction of incident light leaves, determining a hologram phase distribution for allowing said diffraction light to leave the defined range, quantizing a determined phase distribution to find a quantized depth of a hologram relief and a number of steps of said depth, forming a relief on a substrate by photoetching on the basis of a found quantized depth to obtain a relief pattern, and patterning a resin layer using said relief pattern to form a hologram relief on a surface of said resin layer; wherein the number of steps L having the depth of said relief is the N-th power of 2 where N is a number of photoetching cycles.

17. The process for fabricating a computer-generated hologram according to claim 16, further comprising: quantizing the determined phase distribution to find the number of steps of said quantized depth, and repeating photoetching given times corresponding to the obtained depth and the number of steps to form the relief pattern on the substrate.

18. The computer-generated hologram fabrication process according to claim 16, wherein an optical reflective layer is laminated on and along a relief side or other side of said resin layer.

19. The computer-generated hologram process of claim 16, wherein the step of patterning a resin layer using said relief pattern to form a hologram relief on a surface of said resin layer includes pressing the relief pattern against the resin layer, and then curing the resin layer.

Description

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. A 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: .lamda..sub.MIN/.lamda..sub.MAX.gtoreq.(sin .beta..sub.1STD-sin .theta.)/(sin .beta..sub.2STD-sin .theta.) (11) where .theta. is the angle of incidence of illumination light, .lamda..sub.MIN is the minimum wavelength, .lamda..sub.MAX is the maximum wavelength, .beta..sub.1STD is the minimum diffraction angle at a given reference wavelength .lamda..sub.STD and .beta..sub.2STD is the maximum diffraction angle at the given reference wavelength .lamda..sub.STD.

It is also preferable that the computer-generated hologram satisfies: sin .theta..gtoreq.(.lamda..sub.MAX sin .beta..sub.1STD-.lamda..sub.MIN sin .beta..sub.2STD)/(.lamda..sub.MAX-.lamda..sub.MIN) (12) where .theta. is the angle of incidence of illumination light, .lamda..sub.MIN is the minimum wavelength, .lamda..sub.MAX is the maximum wavelength, .beta..sub.1STD is the minimum diffraction angle at a given reference wavelength .lamda..sub.STD and .beta..sub.2STD is the maximum diffraction angle at the given reference wavelength .lamda..sub.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 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. Thus, the computer-generated hologram can be seen in white in the angle range defined between the maximum diffraction angle of the minimum wavelength and the minimum diffraction angle of the maximum wavelength, and there is no change in the color seen even when the viewer moves his eyes within that range. This computer-generated hologram is suitable for reflector in reflective LCDs.

In one typical process for the fabrication of computer-generated holograms used so far in the art, phase distributions are calculated all over the region of the hologram to be fabricated. Then, a large amount of data are entered into an aligner on the basis of the results of calculations for exposure processing. According to the invention provided to achieve the aforesaid second object, a computer-generated hologram is constructed of an array of minute elemental hologram pieces arranged in columns and rows. Then, the calculation of the phase distribution is performed only for the minute elemental hologram piece by far smaller than the entire computer-generated hologram. When exposure is carried out for photoetching, too, a much smaller amount of data on the minute elemental hologram piece than before are used, so that loads on the data processing on the aligner can be alleviated to reduce the overall exposure time. Thus, the twelfth invention provided to achieve the second object has been accomplished.

That is, the twelfth invention provided to achieve the second object relates to a computer-generated hologram comprising minute elemental hologram pieces closely arranged on a plane, characterized in that each elemental hologram piece has an optical path length enough to impart an identical phase distribution to reflection light or transmission light.

The thirteenth invention provided to achieve the second object and according to the twelfth invention relates to 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.

The fourteenth invention provided to achieve the second object and according to the twelfth or thirteenth invention relates to a computer-generated hologram, characterized in that each elemental hologram piece has 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 elemental hologram piece vertically.

The fifteenth invention provided to achieve the second object and according to the twelfth or thirteenth invention relates to a computer-generated hologram, characterized in that each elemental hologram piece 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.

The sixteenth invention provided to achieve the second object is characterized in that the computer-generated hologram according to any one of the aforesaid twelfth to fifteenth inventions comprises a resin layer including a hologram.

The seventeenth invention provided to achieve the second object is characterized in that the computer-generated hologram according to the aforesaid sixteenth invention further comprises a transparent substrate for supporting the resin layer including a hologram.

The eighteenth invention provided to achieve the second object is characterized in that the computer-generated hologram according to any one of the aforesaid twelfth to seventeenth inventions is defined by a relief pattern on the surface of a hologram-forming layer.

The nineteenth invention provided to achieve the second object is characterized in that the computer-generated hologram according to the aforesaid eighteenth invention further comprises an optical reflective layer laminated on and along said relief pattern.

The 20th invention provided to achieve the second object is characterized in that in the aforesaid 18th invention, said optical reflective layer is laminated on the other bare surface of said hologram-forming layer which is free from said relief pattern.

The 21th invention provided to achieve the second object relates to a reflector characterized by using the computer-generated hologram according to any one of the aforesaid 12th to 20th inventions.

The 22nd invention provided to achieve the second object relates to a reflective liquid crystal display characterized in that the computer-generated hologram according to claim 10 is disposed on a back surface thereof.

The 23rd invention provided to achieve the second object relates to a reflective liquid crystal display characterized in that the computer-generated hologram according to the aforesaid 21st invention is interposed between a liquid crystal layer and a back substrate in said liquid crystal display.

The 24th invention provided to achieve the second object relates to a computer-generated hologram fabrication process characterized by defining a range which diffraction light obtained by diffraction of incident light leaves, determining a hologram phase distribution for allowing said diffraction light to leave the defined range, quantizing the determined phase distribution to find a quantized depth of a hologram relief, forming a relief on a substrate by photoetching on the basis of the found quantized depth to obtain a relief pattern, and patterning a resin layer using said relief pattern to form a hologram relief on the surface of said resin layer.

The 25th invention provided to achieve the second object relates to a computer-generated hologram fabrication process characterized by defining a range which diffraction light obtained by diffraction of incident light leaves, determining a hologram phase distribution for allowing said diffraction light to leave the defined range, quantizing the determined phase distribution to find a quantized depth of a hologram relief and the number of steps of said depth, repeating photoetching given times corresponding to the obtained depth and the number of steps to form a relief pattern on an etching substrate, and patterning a resin layer using said relief pattern to form a hologram relief on the surface of said resin layer.

The 26th invention provided to achieve the second object relates to the computer-generated hologram fabrication process according to the aforesaid 24th or 25th invention, characterized in that said phase distribution is determined per minute elemental hologram piece forming the hologram, and said relief is formed on the basis of a phase distribution obtained by repeatedly arranging a phase distribution of said elemental hologram piece in a longitudinal direction of said substrate.

The 27th invention provided to achieve the second object relates to the computer-generated hologram fabrication process according to any one of the aforesaid 24 to 26th inventions, characterized in that an optical reflective layer is laminated on and along a relief side or other side of said resin layer.

The 28th invention provided to achieve the second object relates to the computer-generated hologram fabrication process according to any one of the aforesaid 24th to 26th inventions, characterized in that the number of steps L having the depth of said relief is the N-th power of 2 where N is the number of photoetching cycles.

Reference is then made to a computer-generated hologram constructed to achieve the aforesaid third object of the present invention. This computer-generated hologram comprises a transparent plate material having a light refractive index higher than that of air and a blaze pattern of sawtoothed shape in section, which blaze pattern is disposed on the back surface of the transparent plate, and is designed in such a way that the depth d of the blaze is equivalent to a half wavelength or d=.lamda./2 n wherein .lamda. is the wavelength of reference light and n is the light refractive index of the transparent plate. This computer-generated hologram can provide solutions to prior art problems in conjunction with diffraction efficiency, master pattern fabrication and replication and applications. Thus, the present invention provides such a computer-generated hologram as well as a reflector and a reflective LCD constructed using the same.

The 29th invention provided to achieve the third object relates to a computer-generated hologram characterized in that a blaze pattern of sawtoothed shape in section is formed on a back side of a transparent substrate and the depth d of said blaze pattern is d=.lamda./2 n where .lamda. is the wavelength of reference light and n is the light refractive index of a material forming said transparent plate.

The 30th invention provided to achieve the third object relates to a computer-generated hologram characterized in that a blaze pattern of sawtoothed shape in section is formed on a back side of a transparent substrate with N steps having differences in level and the depth d of said blaze pattern is d=.lamda./2 n where .lamda. is the wavelength of reference light and n is the light refractive index of a material forming said transparent plate.

The 31st invention provided to achieve the third object relates to the computer-generated hologram according to the aforesaid 29th or 30th invention, characterized in that an optical reflective layer is laminated on and along said blaze pattern formed on the back surface of said transparent plate.

The 32nd invention provided to achieve the third object relates to the computer-generated hologram according to any one of the aforesaid 29th to 31st inventions, characterized in that the front surface of said transparent plate has been subject to antireflection treatment.

The 33rd invention provided to achieve the third object relates to a reflector characterized by using the computer-generated hologram according to any one of the aforesaid 29th to 32nd inventions.

The 34th invention provided to achieve the third object relate to the reflector according to the aforesaid 33rd invention, characterized in that a transparent adhesive layer is laminated on the front surface of said transparent plate.

The 35th invention provided to achieve the third object relates to a reflective liquid crystal display characterized in that said front surface of the reflector according to the aforesaid 33rd invention is in close contact with the back surface of said liquid crystal display.

The 36th invention provided to achieve the third object relates to a reflective liquid crystal display characterized in that said front surface of the reflector according to the aforesaid 34th invention is laminated on the back surface of said liquid crystal display with said transparent adhesive layer interposed therebetween.

The 37th invention provided to achieve the third object relates to the reflective liquid crystal display according to the aforesaid 35th or 36th invention, characterized in that a liquid crystal display device and said transparent plate in said reflector have a substantially identical light refractive index, or said liquid crystal display device, said transparent adhesive layer and said transparent plate in said reflector have a substantially identical light refractive index.

The 38th invention provided to achieve the third object relates to a reflective liquid crystal display characterized in that the computer-generated hologram according to the aforesaid 33rd invention is interposed between the liquid crystal layer and the back substrate in said liquid crystal display with the front surface of said computer-generated hologram opposite to said liquid crystal layer.

The 39th invention provided to achieve the third object relates to a reflective liquid crystal display characterized in that said front surface of the reflector according to the aforesaid 33rd invention is in close contact with the back surface of a light transmission display.

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

FIGS. 1(a), 1(b) and 1(c) are illustrative of a computer-generated hologram comprising an array of elemental hologram pieces.

FIGS. 2(a), 2(b) and 2(c) are illustrative of some combinations of elemental hologram pieces.

FIGS. 3(a), 3(b) and 3(c) are representations illustrative of some examples of phase distributions for computer-generated holograms.

FIGS. 4(a) and 4(b) are illustrative of how a viewing position is shifted.

FIG. 5 is a flowchart illustrative of calculation steps for a computer-generated hologram.

FIG. 6 is illustrative of the range of emergent light with respect to incident light.

FIGS. 7(a), 7(b) and 7(c) are illustrative of diffraction for each wavelength in a narrow viewing range.

FIG. 8 is illustrative of diffraction of each wavelength in a narrow viewing range.

FIGS. 9(a), 9(b) and 9(c) are illustrative of diffraction for each wavelength in a wide viewing range.

FIG. 10 is illustrative of diffraction of each wavelength in a wide viewing range.

FIG. 11 is illustrative of a phase distribution on the hologram surface of one embodiment of the computer-generated hologram according to the invention.

FIG. 12 is illustrative of an amplitude distribution on a reconstruction plane when the computer-generated hologram of the FIG. 11 embodiment is vertically illuminated at the design wavelength.

FIG. 13 is illustrative of an amplitude distribution on a reconstruction plane when the computer-generated hologram of the FIG. 11 embodiment is obliquely illuminated at the reference wavelength.

FIG. 14 is illustrative of an amplitude distribution on a reconstruction plane when the computer-generated hologram of the FIG. 11 embodiment is obliquely illuminated at the minimum wavelength.

FIG. 15 is illustrative of an amplitude distribution on a reconstruction plane when the computer-generated hologram of the FIG. 11 embodiment is obliquely illuminated at the maximum wavelength.

FIG. 16 is illustrative in schematic form of the superposition of visible regions that are the distribution range of diffraction light in FIGS. 13 to 15.

FIG. 17 is a sectioned representation showing the construction of one reflective LCD according to the invention.

FIG. 18 a sectioned representation showing the construction of another reflective LCD to which the computer-generated hologram reflector of the invention is applied.

FIG. 19(a) to 19(d) are illustrative of the photosteps for fabricating a hologram relief pattern substrate.

FIGS. 20(a), 20(b) and 20(c) are illustrative of the number of photoetching cycles and the number of steps in the relief.

FIG. 21(a) to 21(e) are illustrative of relief patterns and replicated holograms.

FIGS. 22(a) and 22(b) are illustrative of liquid crystal display devices to which the computer-generated holograms of the invention are applied.

FIGS. 23(a) and 23(b) are illustrative in section of another computer-generated hologram of the invention.

FIG. 24(a) to 24(e) are illustrative of blaze patterns and replicated holograms.

FIGS. 25(a) and 25(b) are illustrative of liquid crystal display devices to which the computer-generated holograms of the invention are applied.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The computer-generated hologram 1 according to the present invention is a composite or compound-eye array wherein computer-generated hologram pieces or minute elemental hologram pieces 2 are closely arranged on a plane.

The computer-generated hologram 1 of FIG. 1(a) is designed as a grid array of square elemental hologram pieces 2 arranged in columns and rows. As shown in FIG. 1(b), the square elemental hologram pieces 2 in an even row (e.g., the second or fourth row) may be shifted transversely with respect to those in an odd row by a half pitch. Alternatively, elemental holograms 2 of rectangular slim shape may be closely arranged side by side, as shown in FIG. 1(c).

In any of the aforesaid computer-generated holograms 1, all adjacent elemental hologram pieces 2 are the same. In other words, each hologram piece 2 has an optical path length enough to impart the same phase to reflection light or transmission light.

Such computer-generated holograms 1 have a structure well suitable for reducing loads on a fabrication system; that is, the process of fabricating the elemental hologram pieces 2 under the necessary conditions is repeatedly carried out while a material forming the hologram 1 or a relief pattern for giving the hologram 1 is displaced, as will be described later.

FIGS. 2(a), 2(b) and 2(c) show a composite or compound-eye computer-generated hologram 1 comprising at least two types of minute elemental hologram pieces 2.

Referring first to FIG. 2(a), two kinds of minute elemental hologram pieces 2a and 2b having different optical path lengths for imparting different phases to reflection light or transmission light. As shown, one elemental hologram pieces 2a are arranged every other in a row while the other elemental hologram pieces 2b are arranged between adjacent pieces 2a. Thus, the elemental hologram pieces 2 used herein may be defined by such different sets of elemental hologram pieces.

It is here noted that the elemental hologram pieces 2a and 2b may be arranged in columns rather than in rows.

As shown in FIG. 2(b), three kinds of elemental hologram pieces 2a, 2b and 2c may be used in a group, and as shown in FIG. 2(c), one elemental hologram piece 2a may be surrounded with the other elemental hologram pieces 2b.

Thus, if the computer-generated hologram 1 comprises a plurality of groups of different elemental hologram pieces, then the hologram 1 can possess the respective properties of a plurality of elemental hologram pieces 2a, 2b, . . . .

As in the computer-generated holograms 1 of FIG. 1(a) to 1(b), the computer-generated holograms 1 of FIG. 2(a) to 2(b), too, have a structure well suitable for reducing loads on a fabrication system; that is, the process of fabricating the elemental hologram pieces 2 under the necessary conditions is repeatedly carried out while a material forming the hologram 1 or a relief pattern for giving the hologram 1 is displaced, as will be described later.

The shape of each elemental hologram piece 2 used herein is not necessarily limited to a quadrilateral such as a square or rectangle. In other words, other polygonal elemental hologram pieces may be used. For instance, triangular elemental hologram pieces 2 can be closely arranged in a row if one of adjacent hologram pieces is located inversely with respect to the other and hexagonal elemental hologram pieces can be closely arranged if pieces in one row are displaced by a half pitch with respect to those in a row just below it, as shown in FIG. 1(b).

Alternatively, if octagonal elemental hologram pieces 2 are combined with square elemental hologram pieces 2 with their sides having the same length as one side of the octagon, groups of two kinds of different elemental hologram pieces can then be arranged.

Although not critical, the computer-generated hologram 1 of the present invention has usually a size of about 1 cm to about a few tens of cm. Each elemental hologram piece 2, of whatever type, has a size of about a few tens of .mu.m to about 1 mm as an example. For instance, an elemental hologram piece 2 of 250 .mu.m.times.250 .mu.m in size accounts for 1/40,000 of a computer-generated hologram 2 of 5 cm.times.5 cm in size.

In context of the computer-generated hologram 1 of the present invention, the "closely arranged elemental hologram pieces 2" is understood to mean an array of elemental hologram pieces 2 slightly spaced away from one another, to say nothing of an array of elemental hologram pieces 2 brought in perfect contact with one another.

For the elemental hologram 2 in the computer-generated hologram 1 of the present invention, use is made of (1) the computer-generated hologram obtained on the basis of JP-A 11-187316, (2) the computer-generated hologram obtained on the basis of JP-A 11-296054, and (3) the novel computer-generated hologram which can be viewed in white at the desired viewing region and proposed by the present invention on the premise of the computer-generated hologram (1) or (2). In this regard, it is appreciated that this computer-generated hologram (3) may not only be used as the elemental holograms 2 and 2a to 1c of FIGS. 1 and 2 but may also be used by themselves as a reflector having similar properties.

First of all, the computer-generated hologram (1) or (2) is explained.

The computer-generated hologram obtained on the basis of JP-A 11-187316 comprises an array of two-dimensionally arranged minute cells. Each cell has an optical path length enough to impart a unique phase to reflection light or transmission light, and a phase distribution obtained by adding the 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 the second phase distribution that allows an obliquely incident light beam at a given angle of incidence to leave the cell vertically.

Here, the first phase distribution is a phase distribution for the computer-generated hologram which, when the hologram plane is vertically illuminated with parallel light, diffracts the light to the given viewing region alone. For instance, the first phase distribution may be such a phase distribution .phi..sub.HOLO as illustrated in FIG. 3(a).

The second phase distribution is provided for a phase diffraction grating which diffracts light incident from behind at an angle of incidence .theta. in the forward direction. In other words, this is a phase distribution .phi..sub.GRAT obtained by approximating such a phase distribution as indicated by broken lines in FIG. 3(b) in the form of a digital step-formed function.

The phase distribution obtained by the addition of two such phase distributions .phi..sub.HOLO and .phi..sub.GRAT provides the phase distribution .phi. of the computer-generated hologram set forth in JP-A 11-183716 and shown in FIG. 3(c), and the computer-generated hologram having this phase distribution .phi. acts to diffract the light obliquely incident from behind at the angle of incidence .theta. toward the given viewing region in the forward direction.

Generally, a computer-generated hologram is found as follows.

Now consider a certain hologram. When the hologram plane is vertically illuminated with parallel light at a reconstruction distance much larger than the size of the hologram, the diffraction light obtained at the reconstruction plane is represented in terms of an amplitude distribution at the hologram plane and the Fourier transform of a phase distribution (Fraunhofer diffraction).

To impart given diffraction light to the reconstruction plane, a computer-generated hologram positioned at the hologram plane has so far been found by a method wherein the Fourier transform and inverse Fourier transform are alternately repeated between the hologram plane and the reconstruction plane with the application of constraints. This method is known as the Gerchberg-Saxton iterative algorithm method.

Here let h(x, y) represent the distribution of light at the hologram plane and f(u, v) indicate the distribution of light at the reconstruction plane. Then, these distributions of light are written as: h(x, y)=A.sub.HOLO(x, y) exp(i.phi..sub.HOLO(x, y)) (1) f(u, v)=A.sub.IMG(u, v) exp(i.phi..sub.IMG(u, v)) (2) where A.sub.HOLO(x, y) is an amplitude distribution at the hologram plane, .phi..sub.HOLO(x, y) is a phase distribution at the hologram plane, A.sub.IMG(u, v) is an amplitude distribution at the reconstruction plane and .phi..sub.IMG(u, v) is a phase distribution at the reconstruction plane.

Then, the aforesaid Fourier transform and inverse Fourier transform are given by

.function..intg..intg..infin..infin..times..function..times..times..times.- I.function..times.d.times.d.function..intg..intg..infin..infin..times..fun- ction..times..times..times.I.function..times.d.times.d ##EQU00001##

Consider the case where using this Gerchberg-Saxton iterative algorithm method, a computer-generated hologram is obtained, which hologram diffracts parallel light toward the given viewing region alone when the hologram plane is vertically illuminated with the parallel light.

For a better understanding of the following discussions, the amplitude distribution A.sub.HOLO(x, y) at the hologram plane is represented by A.sub.HOLO, the phase distribution .phi..sub.HOLO(x, y) at the hologram plane by .phi..sub.HOLO, the amplitude distribution A.sub.IMG(u, v) at the reconstruction plane by A.sub.IMG, and the phase distribution .phi..sub.IMG(u, v) at the reconstruction plane by .phi..sub.IMG.

FIG. 5 is a flowchart to this end. At step (1), the hologram amplitude A.sub.HOLO and hologram phase .phi..sub.HOLO are initialized to 1 and a random value, respectively, at hologram plane regions x.sub.0.ltoreq.x.ltoreq.x.sub.1 and y.sub.0.ltoreq.y.ltoreq.y.sub.1 in FIG. 6, and at step (2), the thus initialized values are subject to the aforesaid Fourier transform (3). If, at step (3), the amplitude A.sub.IMG at the reconstruction plane, obtained by the Fourier transform, has a substantially constant value within the given regions, e.g., u.sub.0.ltoreq.u.ltoreq.u.sub.1 and v.sub.0.ltoreq.v.ltoreq.v.sub.1, and becomes substantially zero within other regions, then the amplitude and phase initialized at step (1) provide a desired computer-generated hologram.

If, at step (3), such conditions are not satisfied, then constraints are applied at step (4). For instance, a value of 1 is imparted to the amplitude A.sub.IMG at the reconstruction plane within the aforesaid given regions and a value of 0 is applied within other regions, while the phase .phi..sub.IMG at the reconstruction plane is kept intact. After such constraints are applied, the aforesaid inverse Fourier transform (4) is applied at step (5). At step (6), constraints are applied to the value at the hologram plane, obtained by the inverse Fourier transform, to take the amplitude A.sub.HOLO as 1 and allow the phase .phi..sub.HOLO to have many values (bring the original function approximate to a digital step-formed function (quantization)). It is noted that when the phase .phi..sub.HOLO is allowed to have a continuous value, such a multi-valued phase is not always needed.

Then, the value is subjected to the Fourier transform at step (2). If, at step (3), the amplitude A.sub.IMG at the reconstruction plane, obtained by the Fourier transform, has a substantially constant value within the given regions, e.g., u.sub.0.ltoreq.u.ltoreq.u.sub.1 and v.sub.0.ltoreq.v.ltoreq.v.sub.1, and becomes substantially zero within other regions, then the amplitude and phase, to which the constraints are applied at step (1), provide a desired computer-generated hologram.

If, at step (3), such conditions are not satisfied, then the loop of steps (4).fwdarw.(5).fwdarw.(6).fwdarw.(2).fwdarw.(3) is repeated until the conditions for step (3) are satisfied (or converged), so that the final desired computer-generated hologram can be obtained.

For an estimating function for indicating that the amplitude A.sub.IMG at the reconstruction plane is converged to a substantial given value at step (3), for instance, the following expression (5) may be used.

However, the .SIGMA. (sum) with respect to u and v means the sum of the values at u.sub.0.ltoreq.u.ltoreq.u.sub.1 and v.sub.0.ltoreq.v.ltoreq.v.sub.1, for the cells in the hologram, and <A.sub.IMG(v, v)> represents an ideal amplitude in the cell. For instance, when this estimating function is 0.01 or less, the function is assumed to be converged.

Alternatively, the following expression (6) using a difference between the previous amplitude value and the present amplitude value in the repetition of the calculation loop may be used as the estimating function.

Here A.sub.IMG-1 is the previous amplitude value and A.sub.IMGi is the present amplitude value.

.times..times..times..times..function..function..times..times..times..time- s..function..function. ##EQU00002##

From the thus found phase distribution, the depth distribution of an actual hologram is found. Regarding how to find the depth distribution, there is a difference between a reflection hologram and a transmission hologram. When the hologram is of the reflection type, expression (7a) is used and when the hologram is of the transmission type, expression (7b) is used. In other words, .phi. of FIG. 3(c) (.phi.(x, y) in the following expressions) is transformed to the depth D of the computer-generated hologram (D(x, y) in the following expressions). D(x, y)=.lamda..phi.(x, y)/(4.pi.n) (7a) D(x, y)=.lamda..phi.(x, y)/{2.pi.(n.sub.1-n.sub.0)} (7b)

Here (x, y) is the coordinates indicative of a position on the hologram plane, .lamda. is the reference wavelength, n is the refractive index of the material forming the light incident side of the reflection surface in the reflection hologram, and n.sub.1 and n.sub.0 are the refractive indices of the two materials forming the transmission hologram provided that n.sub.1>n.sub.0.

As will also be explained later, a relief pattern having a depth D(x, y) found from the aforesaid expressions (7a) and (7a) for each minute cell having a lengthwise x breadthwise size .DELTA. is formed on the surface of a hologram-forming resin layer, with a given reflective layer laminated thereon. The resultant hologram can be used as a hologram with enhanced effects.

This .DELTA., for instance, is equivalent to the feed pitch of exposure light.

Reference is now made to the computer-generated hologram obtained on the basis of JP-A 11-296054. This computer-generated hologram comprises an array of two-dimensionally arranged minute cells. Each cell has an optical path length enough to impart a unique phase to reflection light or transmission light as well as a phase distribution that 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 a phase distribution that 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.

That is, a computer-generated hologram H is designed such that when the hologram plane is vertically illuminated with parallel light from behind, the region at which the amplitude distribution A.sub.IMG(u, v) at the reconstruction plane is kept substantially constant is designated as the range of u.sub.0'.ltoreq.u'.ltoreq.u.sub.1' and v.sub.0'.ltoreq.v'.ltoreq.v.sub.1' shifted from u.sub.0.ltoreq.u.ltoreq.u.sub.1 and v.sub.0.ltoreq.v.ltoreq.v.sub.1 and the amplitude distribution A.sub.IMG(u, v) becomes substantially zero at other region ((u, v) is the coordinates on the reconstruction plane).

As shown in FIG. 4(a), a computer-generated hologram H is designed such that when parallel illumination light 3' is vertically incident thereon, light is diffracted only to the range of u.sub.0'.ltoreq.u'.ltoreq.u.sub.1' and v.sub.0'.ltoreq.v'.ltoreq.v.sub.1' on a reconstruction plane 4.

When the phase distribution .phi..sub.HOLO(x, y) of the computer-generated hologram H is assumed to be a diffraction grating, diffraction by the computer-generated hologram H is represented by the following expression (8) that is a fundamental expression for the diffraction grating. sin .theta..sub.d-sin .theta..sub.i=m.lamda./d (8) where m is the order of diffraction, d is the pitch of the diffraction grating, .lamda. is a wavelength, .theta..sub.i is the angle of incidence and .theta..sub.d is a diffraction angle.

From design conditions, .theta..sub.i=0 and .alpha..sub.0'.ltoreq..theta..sub.d.ltoreq..alpha..sub.1'. Here .alpha..sub.0' is the angle of diffraction of light from the position of incidence to the position of u.sub.0' at the reconstruction plane 4, and .alpha..sub.1' is the angle of diffraction of light to the position of u.sub.1'.

The case where parallel light 3 is obliquely incident on such a computer-generated hologram H at the angle of incidence .theta. is shown in FIG. 4(b).

From the aforesaid fundamental expression (2) for the diffraction grating, .theta..sub.i=.theta. in this case. Assuming that the embodiment shown is positive, the range of diffraction angle .theta..sub.d, .alpha..sub.0.ltoreq..theta..sub.d.ltoreq..alpha..sub.1, is shifted from .alpha..sub.0'.ltoreq..theta..sub.d.ltoreq..alpha..sub.1' to a smaller range, so that, as shown in FIG. 4(b), the diffraction range, u.sub.0.ltoreq.u.sub.d.ltoreq.u.sub.1 (where u.sub.0 is a position at which diffraction light is incident from the incidence position on the reconstruction plane 4 at a diffraction angel .alpha..sub.0, and u.sub.1 is a position at which diffraction light is incident thereon at a diffraction angle .alpha..sub.1), can be placed substantially in the forward direction with respect to the computer-generated hologram H.

The same also goes for the v direction.

Thus, the computer-generated hologram H obtained on the basis of JP-A 11-296054 is designed such that when parallel light is vertically incident on the hologram plane from behind, the light is diffracted to the forward, another region (u.sub.0'.ltoreq.u'.ltoreq.u.sub.1' and v.sub.0'.ltoreq.v'.ltoreq.v.sub.1') shifted from the forward given viewing region (u.sub.0.ltoreq.u.ltoreq.u.sub.1 and v.sub.0.ltoreq.v.ltoreq.v.sub.1), and when parallel light is obliquely incident on the hologram plane from behind, the light is diffracted to the forward given viewing region (u.sub.0.ltoreq.u.ltoreq.u.sub.1 and v.sub.0.ltoreq.v.ltoreq.v.sub.1).

From the thus found phase distribution .phi..sub.HOLO(x, y), the depth distribution of an actual hologram is found. When the hologram is of the reflection type, the aforesaid expression (7a) is used and when the hologram is of the transmission type, the aforesaid expression (7b) is used. A relief pattern having a depth D(x, y) found for each minute cell having a lengthwise x breadthwise size .DELTA. is formed on the surface of a hologram-forming resin layer, with a given reflective layer laminated thereon. The resultant hologram can be used as a hologram with enhanced effects, as is the case with the computer-generated hologram on the basis of JP-A 11-183716.

The phase distribution of the computer-generated hologram H may be calculated not only by the aforesaid methods themselves known so far in the art but also by other methods, e.g., one set forth in JP-A 47-6591.

If required, the found phase distribution may be optimized by suitable methods such as a hereditary algorithm or a simulated annealing method.

Reference is then made to the novel computer-generated hologram, herein referred to as (3), of the present invention, which can be seen in white at the desired viewing region.

The present invention provides a novel computer-generated hologram designed to diffuse light of a given reference wavelength incident thereon at a given angle of incidence in a specific angle range, wherein: 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 said 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.

For the sake of simplicity, an account is now given of a transmission computer-generated hologram. However, it is noted that the present invention can also be applied to a reflection computer-generated hologram.

FIGS. 7(a) and 7(b) are conceptual representations illustrative of how a narrow viewing region set for a computer-generated hologram H changes with wavelengths.

Here assume that the reference wavelength .lamda..sub.STD of illumination light is between the minimum wavelength .lamda..sub.MIN and the maximum wavelength .lamda..sub.MAX. The computer-generated hologram H is designed with respect to the reference wavelength .lamda..sub.STD.

As shown in FIG. 7(a), consider the case where illumination light 3 entering the computer-generated hologram H at the reference wavelength .lamda..sub.STD and a certain oblique angle .theta. (which is an angle from the normal to the hologram H with the proviso that the counterclockwise angle is positive) spreads as diffraction light 5.sub.STD in an angle range of .beta..sub.1STD to .beta..sub.2STD in the vicinity of the front. Numerical subscripts 1 and 2 indicate the minimum diffraction angle and the maximum diffraction angle, respectively. It is appreciated that the minimum diffraction angle is the diffraction angle of diffraction light that makes the minimum angle with zero-order transmission light and the maximum diffraction angle is the diffraction angle of diffraction light that makes the maximum angle with the zero-order transmission light. As illumination light 3 of the minimum wavelength .lamda..sub.MIN enters the hologram H at the same oblique angle .theta., a viewing region (the angle range of .beta..sub.MIN to .beta..sub.2MIN) to receive diffraction light 5.sub.MIN is shifted to a lower side (the zero-order transmission light side) as compared with the incidence of the reference wavelength .lamda..sub.STD, as shown in FIG. 7(a), because the computer-generated hologram H is taken as being a cluster of phase diffraction gratings. As illumination light 3 of the maximum wavelength .lamda..sub.MAX enters the hologram H at the same angle of incidence .theta., on the other hand, a viewing region (the angle range of .beta..sub.MAX to .beta..sub.2MAX) to receive diffraction light 5.sub.MAX is shifted to an upper side (the side opposite to the zero-order transmission light side) as compared with the incidence of the reference wavelength .lamda..sub.STD, as shown in FIG. 7(c).

It is here noted that such a distribution of diffraction light as mentioned above is found within a plane including the normal to the hologram H and the illumination light 3. Within a plane inclu