U.S. patent application number 10/615399 was filed with the patent office on 2004-06-24 for volume hologram medium.
This patent application is currently assigned to DAI NIPPON PRINTING CO., LTD.. Invention is credited to Kodama, Daijiro.
Application Number | 20040121241 10/615399 |
Document ID | / |
Family ID | 32588030 |
Filed Date | 2004-06-24 |
United States Patent
Application |
20040121241 |
Kind Code |
A1 |
Kodama, Daijiro |
June 24, 2004 |
Volume hologram medium
Abstract
The invention is concerned with a volume hologram medium
obtained by multiple recording of holograms, which is improved in
terms of just only security for forgery prevention but also
aesthetics. A volume hologram medium 29' comprises a reflection
hologram in which a stereoscopic image of a three-dimensional
object and an image of a plane pattern of a mask plate are recorded
by interference of the same reference light beams having the same
angle of incidence and the same wavelength with object light beams
having mutually different angles of incidence. The stereoscopic
image of the three-dimensional object is reconstructed in the form
of diffracted light 31 in a single color and in angle relations
close to recording conditions, and the image of a plane pattern of
the mask plate is reconstructed as diffracted light 32b, 32'b at
various angles of incidence of white illumination light 30 and in
different colors depending on those angles of incidence. Thus, more
improved aesthetics are achievable, and more enhanced security is
ensured by determination of whether or not the volume hologram
medium has such aesthetic properties.
Inventors: |
Kodama, Daijiro; (Tokyo,
JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
DAI NIPPON PRINTING CO.,
LTD.
|
Family ID: |
32588030 |
Appl. No.: |
10/615399 |
Filed: |
July 9, 2003 |
Current U.S.
Class: |
430/1 ; 359/2;
359/24; 430/2 |
Current CPC
Class: |
G03H 2210/32 20130101;
G03H 2210/55 20130101; G03H 2001/2268 20130101; G03H 1/0248
20130101; G03H 2223/19 20130101; G03H 2001/2231 20130101; G03H
1/181 20130101; G03H 2001/0417 20130101; G03H 1/0011 20130101; G03H
2001/187 20130101; G03H 2210/562 20130101; G03H 2001/2263 20130101;
G03H 2223/12 20130101 |
Class at
Publication: |
430/001 ;
430/002; 359/024; 359/002 |
International
Class: |
G03H 001/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 9, 2002 |
JP |
2002-199832 |
Claims
What we claim is:
1. A volume hologram medium, wherein an image of a
three-dimensional object and an image of a plane pattern are
multi-recorded in a reflection hologram form by interference of the
same reference light beams having the same angle of incidence and
the same wavelength with object light beams having mutually
different angles of incidence.
2. The volume hologram medium according to claim 1, wherein a
hologram of said image of a plane pattern is selectively recorded
in only an area corresponding to said plane pattern and as a
hologram comprising parallel interference fringes in one section at
an angle with respect to at least a recording plane.
3. The volume hologram medium according to claim 2, wherein said
section includes a normal to said recording plane, said hologram of
said image of a plane pattern is recorded in such an angle relation
that object light and reference light are incident on said
recording plane at substantially identical angles of incidence on
the same side with respect to said normal to said recording plane
and from mutually opposite directions between said recording plane
is interposed, and a hologram of said image of a three-dimensional
object is recorded in such an angle relation that a center light
ray of said object light is substantially vertically incident on
said recording plane.
4. The volume hologram medium according to claim 2 or 3, wherein
said hologram of said image of a plane pattern is recorded by
interference of object light and reference light that diffuse in
only a direction crossing at right angles with said section.
5. The volume hologram medium according to any one of claims 1 to
4, wherein said image of a plane pattern is an image of a painted
design or micro-characters.
6. The volume hologram medium according to any one of claims 1 to
4, wherein said image of a plane pattern is an image of an array of
lines or dots.
7. The volume hologram medium according to any one of claims 1 to
6, wherein at least one of said image of a three-dimensional object
and said image of a plane pattern is multi-recorded at two or more
different wavelengths.
8. The volume hologram medium according to any one of claims 1 to
7, wherein a hologram photosensitive material comprises a
photopolymer.
9. A volume hologram medium, wherein a plurality of plane pattern
images are multi-recorded as a reflection hologram by interference
of the same reference light beams having the same angle of
incidence and the same wavelength with object light beams having
mutually different angles of incidence.
10. The volume hologram medium according to claim 9, wherein an
image of a three-dimensional object is multi-recorded by
interference of reference light having the same angle of incidence
and wavelength as those of said reference light used for recording
said plurality of plane pattern images with object light having an
angle of incidence different from that of said object light used
for recording to said plurality of plane pattern images.
11. The volume hologram medium according to claim 9 or 10, wherein
each hologram of said plurality of plane pattern images is
selectively recorded in only an area corresponding to each plane
pattern, and as a hologram comprising parallel interference fringes
in one section at an angle with respect to at least a recording
plane.
12. The volume hologram medium according to any one of claims 9 to
11, wherein said plurality of plane pattern images comprise an
image of the same plane pattern.
13. The volume hologram medium according to claim 11 or 12, wherein
each hologram of said plurality of plane pattern images is recorded
by interference of object light and reference light that diffuse in
only a direction crossing at right angles with said section.
14. The volume hologram medium according to any one of claims 9 to
13, wherein said plurality of plane pattern images are
multi-recorded at two or more different wavelengths.
15. A method for authentication of a volume hologram medium having
an image of a three-dimensional object and an image of a plane
pattern multi-recorded in a reflection hologram form by
interference of the same reference light beams having the same
angle of incidence and the same wavelength with object light beams
having mutually different angles of incidence, wherein: an image of
an array of lines or dots is recorded as said image of a plane
pattern, and a pattern film on which an array of lines or dots is
drawn at the same pitch as that of said plane pattern comprising an
array of lines or dots is brought in alignment with said volume
hologram medium, so that said volume hologram medium can be
authenticated with moir fringes created between said image of a
plane pattern and a plane pattern comprising an array of lines or
dots on said pattern film.
16. The method for authentication of a volume hologram medium
according to claim 15, wherein said image of a plane pattern is
recorded in such a way as to be re-constructible near to a hologram
plane of said volume hologram medium.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates generally to a volume hologram
medium, and more particularly to a volume hologram medium improved
in terms of aesthetics and security.
[0002] Patent Publication 1 proposes a hologram medium in which a
stereoscopic image and a pupil image comprising a repetition of
usually invisible fine patterns are recorded in a volume hologram
to determine whether the hologram is genuine or fake through a
pattern reconstructed pattern from that pupil image.
[0003] Patent Publication 2 proposes a hologram medium in which a
volume hologram medium is deactivated in a fine repetitive pattern
using ultraviolet radiation to record an object image in the
remaining photosensitive area, so that whether the hologram is
genuine or fake is judged by the deactivated pattern.
[0004] Patent Publication 1
[0005] JP-A 11-24538
[0006] Patent Publication 2
[0007] JP-A 11-277958
[0008] Both the hologram media proposed in the above patent
publications 1 and 2 are satisfactory in terms of security, but
they are not always satisfactory in terms of aesthetics because the
fine patterns used for authentication are invisible.
SUMMARY OF THE INVENTION
[0009] In view of such problems with the prior art as described
above, the primary object of the present invention to provide a
volume hologram medium obtained by multiple recording of holograms,
in which just only security for forgery but also aesthetics are
improved.
[0010] According to one aspect of the invention, there is provided
a volume hologram medium, characterized in that an image of a
three-dimensional object and an image of a plane pattern are
multi-recorded in a reflection hologram form by interference of the
same reference light beams having the same angle of incidence and
the same wavelength with object light beams having mutually
different angles of incidence.
[0011] Preferably in this aspect, the hologram of said image of a
plane pattern is selectively recorded in only an area corresponding
to said plane pattern and as a hologram comprising parallel
interference fringes in one section at an angle with respect to at
least a recording plane.
[0012] In one specific embodiment of the invention, the hologram of
the image of a plane pattern is recorded in such an angle relation
that object light and reference light are incident on the recording
plane at substantially identical angles of incidence on the same
side with respect to the normal to said recording plane and from
mutually opposite directions between the recording plane is
interposed, and the hologram of the image of a three-dimensional
object is recorded in such an angle relation that the center light
ray of said object light is substantially vertically incident on
the recording plane.
[0013] Preferably, the hologram of the image of a plane pattern is
recorded by interference of object light and reference light that
diffuse in only a direction crossing at right angles with that
section.
[0014] The image of a plane pattern could be recorded in the form
of an image of a painted design or micro-characters.
[0015] Alternatively, the image of a plane pattern could be
recorded in the form of an image of an array of lines or dots.
[0016] Still alternatively, at least one of the image of a
three-dimensional object and the image of a plane pattern could be
multi-recorded at two or more different wavelengths.
[0017] Throughout the above embodiments of the invention, the
hologram photosensitive material used comprises a photopolymer.
[0018] According to another aspect of the invention, there is
provided a volume hologram medium, characterized in that a
plurality of plane pattern images are multi-recorded as a
reflection hologram by interference of the same reference light
beams having the same angle of incidence and the same wavelength
with object light beams having mutually different angles of
incidence.
[0019] In this aspect of the invention, the image of a
three-dimensional object is multi-recorded by interference of
reference light having the same angle of incidence and wavelength
as those of the reference light used for recording the plurality of
plane pattern images with object light having an angle of incidence
different from that of the object light used for recording to the
plurality of plane pattern images.
[0020] Preferably, each hologram of the plurality of plane pattern
images is selectively recorded in only an area corresponding to
each plane pattern and as a hologram comprising parallel
interference fringes in one section at an angle with respect to at
least a recording plane.
[0021] The plurality of plane pattern images could comprise an
image of the same plane pattern.
[0022] Preferably, each hologram of the plurality of plane pattern
images is recorded by interference of object light and reference
light that diffuse in only a direction crossing at right angles
with the section.
[0023] The plurality of plane pattern images could be
multi-recorded at two or more different wavelengths.
[0024] Further, the invention provides a method for authentication
of a volume hologram medium having an image of a three-dimensional
object and an image of a plane pattern multi-recorded in a
reflection hologram form by interference of the same reference
light beams having the same angle of incidence and the same
wavelength with object light beams having mutually different angles
of incidence, characterized in that:
[0025] an image of an array of lines or dots is recorded as said
image of a plane pattern, and a pattern film on which an array of
lines or dots is drawn at the same pitch as that of said plane
pattern comprising an array of lines or dots is brought in
alignment with said volume hologram medium, so that said volume
hologram medium can be authenticated with moir fringes created
between said image of a plane pattern and a plane pattern
comprising an array of lines or dots on said pattern film.
[0026] Preferably in this case, the image of a plane pattern is
recorded in such a way as to be re-constructible near to the
hologram plane of the volume hologram medium.
[0027] In one volume hologram medium of the invention described
herein, the image of a three-dimensional object and the image of a
plane pattern are multi-recorded in a reflection hologram form by
interference of the same reference light beams having the same
angle of incidence and the same wavelength with object light beams
having mutually different angles of incidence, so that the
stereoscopic image of the three-dimensional object can be
reconstructed in angle relations close to the recording conditions
and in a single color, and the image of the plane pattern can be
reconstructed at various angles of incidence of white illumination
light and in colors varying depending on those angles of incidence.
It is thus possible to provide a volume hologram medium having
improved aesthetics, wherein much more enhanced security is ensured
by determination of whether or not the volume hologram medium has
such aesthetic properties.
[0028] In another volume hologram medium of the invention, a
plurality of plane pattern images are multi-recorded as a
reflection hologram by interference of the same reference light
beams having the same angle of incidence and the same wavelength
with object light beams having mutually different angles of
incidence, so that the plurality of plane pattern images can be
reconstructed in the form of an image whose color changes
successively at successively varying viewing positions relative to
the volume hologram medium. It is thus possible to provide a volume
hologram medium having improved aesthetics, wherein much more
enhanced security is ensured by determination of whether or not the
volume hologram medium has such aesthetic properties.
[0029] Still other objects and advantages of the invention will in
part be obvious and will in part be apparent from the
specification.
[0030] 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
[0031] FIGS. 1(a) and 1(b) are illustrative of how to make a first
input hologram used to prepare a volume hologram medium according
to one embodiment of the invention by recording.
[0032] FIGS. 2(a) and 2(b) are illustrative of how to make a second
input hologram used to make a second input hologram used to prepare
a volume hologram according to one embodiment of the invention by
recording.
[0033] FIG. 3 is illustrative of how to fabricate a volume hologram
medium according to one embodiment of the invention from the first
and second input holograms.
[0034] FIGS. 4(a) and 4(b) are illustrative of the characteristics
upon reconstruction of the volume hologram medium prepared as shown
in FIG. 3.
[0035] FIGS. 5(a), 5(b) and 5(c) are again illustrative of the
characteristics upon reconstruction of the volume hologram medium
prepared as shown in FIG. 3.
[0036] FIGS. 6(a), 6(b), 6(c) and 6(d) are illustrative of the
dependence of diffraction efficiency on wavelength and the
angle-of-diffraction characteristics of diffraction light for
reconstructing a three-dimensional object image and diffraction
light for reconstructing a plane pattern image when the volume
hologram medium according to one embodiment of the invention is in
one reconstruction state.
[0037] FIGS. 7(a), 7(b), 7(c) and 7(d) are illustrative of the
volume hologram medium in another reconstruction state, similar to
FIGS. 6(a), 6(b), 6(c) and 6(d).
[0038] FIGS. 8(a), 8(b), 8(c) and 8(d) are illustrative of the
volume hologram medium in yet another reconstruction state, similar
to FIGS. 6(a), 6(b), 6(c) and 6(d).
[0039] FIG. 9 is illustrative of how to fabricate a volume hologram
medium according to another embodiment of the invention from one
first input hologram and three second input holograms.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0040] The volume hologram medium of the invention is now explained
with reference to embodiments of how to record and the
characteristics upon reconstruction of the resultant hologram
media.
[0041] FIGS. 1(a) and 1(b) are illustrative of how to make a first
input hologram 11' (FIG. 3) used to fabricate the volume hologram
medium of the invention by recording. A three-dimensional object O
is provided for recording a stereoscopic image in the end volume
hologram medium. As shown in FIG. 1(a), the object O is located in
front of a volume hologram photosensitive material 1 that comprises
a photopolymer as an example. The object O is illuminated by
coherent reference light 3 of a given wavelength .lambda. to make
scattered (object) light 2 from the object 0 incident almost
vertically on the hologram photosensitive material 1. On the other
hand, coherent reference light 3 coming from the same light source
as that for the illumination light and having the same wavelength
.lambda. is obliquely directed onto the photosensitive material 1
from the same side as that for the object light 2, so that the
object light 2 interferes with the reference light 3 in the
hologram photosensitive material 1 to record therein a transmission
hologram 1' as shown in FIG. 1(b).
[0042] Then, as shown in FIG. 1(b), reconstruction illumination
light 3' that travels oppositely to the travel direction of the
reference light 3 is entered into the transmission hologram 1' from
the side opposite to the side on which the reference light 3 is
incident upon recording, whereupon diffraction light 2' for
reconstructing the stereoscopic image O' of the object O is
diffracted to the position of the object O at which the
transmission hologram 1' has been recorded. Then, another volume
hologram photosensitive material 1 that comprises a photopolymer as
an example is located near to the reconstructed stereoscopic image
O'. Diffraction light 2' from the transmission hologram 1' is
entered into the volume hologram photosensitive material 1, and
coherent reference light 4 comprising substantially parallel light
4 coming from the same light source for the reconstruction
illumination light 3' and having the same wavelength .lambda. is
directed onto the opposite side of the photosensitive material 1 at
an angle of incidence .theta., so that the diffracted (object)
light 2' interferes with the reference light 4 to record therein a
first input hologram 11' as shown in FIG. 3.
[0043] FIGS. 2(a) and 2(b) are illustrative of how to make a second
input hologram 21" (FIG. 3) used to fabricate the volume hologram
medium of the invention by recording. A mask plate 22 is provided
for recording a plane pattern in the end volume hologram medium.
This mask plate 22 has a given masked pattern that is to define the
finally reconstructed plane pattern. As shown in FIG. 2(a), the
mask plate 22 is located in close contact with or slightly away
from a volume hologram photosensitive material 21 that comprises a
photopolymer as an example. Light 23 for deactivation of the
hologram photosensitive material 21 such as ultraviolet radiation
is directed thereto through the mask plate 22 to deactivate
portions thereof in association with openings in the mask plate 22
(or deprive them of photosensitivity).
[0044] Then, as shown in FIG. 2(b), a one-dimensional diffuser 24
providing diffusion in a one-dimensional direction alone is placed
in close contact with the front surface of the partly deactivated
hologram photosensitive material 21'. For such a one-dimensional
diffuser 24 providing diffusion in the one-dimensional direction
alone, a lenticular lens plate a diffusing plate having ground
slits in a one direction alone, etc. may be used, with the
one-dimensional diffusing direction being perpendicular to the
surface of the paper. With the hologram photosensitive material 21'
in close contact with the one-dimensional diffuser 24,
substantially parallel coherent reference light 26 having the same
wavelength .lambda. as that of reference light 4 used to make the
first input hologram 11' of FIG. 1(b) is entered in the hologram
photosensitive material 21' at the same angle of incidence .theta.
as that of reference light 4, and coherent illumination light 25
from the same light source as that for reference light 26 is
entered therein through the one-dimensional diffuser 24 at an angle
of incidence .theta.' included within the plane of the paper. Upon
passing through the one-dimensional diffuser 24, the illumination
light 25 incident on the one-dimensional diffuser 24 at that angle
of incidence .theta. is converted into light that, when projected
within the plane of the paper, diffuses at the same angle .theta.
in the vertical direction to the plane of the paper. Then, the
diffuse light is entered in the hologram photosensitive material
21', so that it interferes with reference light 26 incident thereon
from the opposite side at the angle of incidence .theta., thereby
recording the second input hologram 21" of FIG. 3 therein.
[0045] In one sectional plane of the thus recorded second input
hologram 21" inclusive of reference light 26 and illumination light
25 (the plane of FIG. 2(b)), mutually parallel, uniform
interference fringes are recorded at a slant angle parallel with a
vector directing to the middles of the direction vectors of
reference light 26 and illumination light 25 in the medium of the
hologram photosensitive material 21'. While the illumination light
25 is here described as being entered in the plane of FIG. 2(b), it
could be entered in the plane of the paper at any desired angle
from its front or back surface. In a sectional plane of the
resultant input hologram including reference light 26 and
illumination light 25 (not the plane of FIG. 2(b)), too, mutually
parallel, uniform interference fringes are recorded at a slant
angle parallel with a vector directing to the middles of the
direction vectors of reference light 26 and illumination light 25
in the medium of the hologram photosensitive material 21'.
[0046] Then, the first input hologram 11' prepared in the steps of
FIGS. 1(a) and 1(b) is put on the second input hologram 21"
prepared in the steps of FIGS. 2(a) and 2(b), as shown in FIG. 3.
While a volume hologram photosensitive material 29 comprising
another photopolymer is brought in close contact with the second
input hologram 21", illumination light 27 that travels oppositely
to reference light 4 used to make the first input hologram 11' and
reference light 26 used to make the second input hologram 21" and
having the same wavelength .lambda. as do they is entered in the
hologram assembly through the hologram photosensitive material 29.
Illumination light 27 passing through the hologram photosensitive
material 29 is entered in the first input hologram 11' to generate
diffraction light 2" for reconstructing an image O" of the
stereoscopic reconstructed image O'. This diffraction light 2" is
then almost vertically incident on the back surface of the hologram
photosensitive material 29, interfering with illumination light 27
first received at the hologram photosensitive material 29, so that
reflection hologram interference fringes for reconstructing the
image of the stereoscopic reconstructed image O" are copied and
recorded in the hologram photosensitive material 29. The same
illumination light 27 passing through the hologram photosensitive
material 29 is also entered in the second input hologram 21",
generating from portions thereof not deactivated by light 23
(masked portions of the mask plate 22) diffraction light 25' that
travels oppositely to illumination light 25 passing through the
one-dimensional diffuser 24 at the time of making the second input
hologram 21", i.e., diffraction light 25' that, as projected within
the plane of the paper, diffuses at an angle of diffraction .theta.
(in the vertical direction to the plane of the paper). This
diffraction light 25', too, enters the back surface of the hologram
photosensitive material 29, interfering with illumination light 27
first received at the hologram photosensitive material 29, so that
reflection hologram interference fringes for reconstructing a plane
pattern consistent with the masked portions of the mask plate 22
are copied and recorded in the hologram photosensitive material 29.
The reflection hologram interference fringes for reconstructing the
image of the plane pattern consistent with the masked portions of
the mask plate 22 are similar to those in the second input hologram
21", and are uniform and parallel as viewed in one section
(corresponding to a plane including reference light 26 and
illumination light 25 used to make the input hologram 21").
[0047] While FIG. 3 shows that the second input hologram 21" is put
on the hologram photosensitive material 29, the first and second
input holograms 11' and 21' could be positioned the other way
around.
[0048] The characteristics upon reconstruction of the thus
fabricated volume hologram medium according to one embodiment of
the invention are now explained. Only for the sake of clarity,
consider three cases, i.e., case (a) wherein the angles .theta. and
.theta.' in FIGS. 1-3 are 45.degree. (plus) and 35.degree. (minus),
case (b) where the angles .theta. and .theta.' are 45.degree.
(plus) and 45.degree. (minus), and case (c) where the angles
.theta. and .theta.' are 45.degree. plus) and 55.degree. (minus)
with the proviso that the refractive index of the volume hologram
medium 29' is 1.52 with a refractive index modulation of 0.05 and a
thickness of 15 .mu.m, and the recording wavelength .lambda. is 532
nm.
[0049] As shown in FIG. 4(a), white illumination light 30 for the
reconstruction of this volume hologram medium 29' is entered in the
volume hologram medium 29' at an angle of incidence of 45.degree.
(plus), whereupon diffraction light 31 for reconstructing the image
of a stereoscopic reconstructed image O" is diffracted in the
frontal direction of the volume hologram medium 29', so that the
image of the stereoscopic reconstructed image O", i.e., the image
of a three-dimensional object O is visible to an eyeball E of a
viewer positioned in that direction. The then center wavelength of
diffraction light 31 is nearly 532 nm, and so the stereoscopic
image is seen in green. FIG. 6(a) is illustrative of the dependence
of diffraction efficiency on wavelength and the
angle-of-diffraction characteristics of diffraction light 31 in
this state.
[0050] Referring here to the angule relation of white illumination
light 30 to the volume hologram medium 29' of FIG. 4(a), the
diffraction light for reconstructing a plane pattern image of the
masked portion of a mask plate 22 is diffracted as diffraction
light 32a in a direction having an angle of diffraction of
35.degree. (minus) in case (a); as diffraction light 32b in a
direction having an angle of diffraction of 45.degree. (minus) in
case (b); and as diffraction light 32c in a direction having an
angle of diffraction of 55.degree. (minus) in case (c). The plane
pattern image, as viewed in each case in each direction, is seen in
green at the center wavelength of nearly 532 nm. FIGS. 6(b), 6(c)
and 6(d) are illustrative of the dependence of diffraction
efficiency on wavelength and the angle-of-diffraction
characteristics of diffraction light 32a, 32b and 32c in this
state, respectively.
[0051] Thus, as the white illumination light 30 is entered in the
volume hologram medium 29' at the angle of incidence of
+45.degree., the image of the three-dimensional object O is seen in
the same green as the recording wavelength in the frontal
direction. Likewise, the plane pattern image is seen in the same
green as the recording wavelength in the direction of -35.degree.
(case (a)), -45.degree. (case (b)), and -55.degree. (case (c)).
However, ordinarily, only the stereoscopic image of the
three-dimensional object O reconstructed in the frontal direction
can be seen, because there is little or no case where the volume
hologram medium 29' is viewed at an angle of view of, e.g.,
-35.degree. to -55.degree..
[0052] Next, consider the case where, while both the position of a
light source for the white illumination light 30 and the position
of the viewer's eyeball E are fixed, the volume hologram medium 29'
is positioned at an angle, as shown in FIG. 4(b). As the normal to
the volume hologram medium 29' is positioned at an angle of
22.5.degree. with respect to the white illumination light 30,
diffraction light 32'a, 32'b and 32'c for reconstructing the plane
pattern image of the masked portion of the mask plate 22 is
diffracted at an angle of -13.8.degree. (case (a)),-22.5.degree.
(case (b)) and -30.5.degree. (case (c)), respectively. The light
source for the white illumination light 30 and the viewer's eyeball
E are fixedly positioned and at mutual angles of 45.degree. with
respect to the volume hologram medium 29' (FIG. 4(a)), and so in
case (b), the viewer's eyeball E is positioned in the direction of
the diffraction light 32'b so that the diffraction light 32'b is
incident on the viewer's eyeball E to allow the viewer to see that
plane pattern image. In case (a), the viewer's eyeball E is
positioned in the direction of the diffraction light 32'a if the
eyeball E is close to the white illumination light 30, and in case
(c) the viewer's eyeball E is positioned is the direction of the
diffraction light 32'c if the eyeball E is far away from the white
illumination light 30. In both the cases, therefore, the viewer can
see the plane pattern image of the masked portion of the mask plate
22. However, it is noted that in these angular arrangements the
angle of the white illumination light 30 with respect to the volume
hologram medium 29' is different from the angle of incidence of the
illumination (reference) light 27 used for recording, and so the
center wavelength of the diffraction light 32'a, 32'b and 32'c is
shifted from the recording wavelength 532 nm to nearly 575 nm,
nearly 580 nm and nearly 590 nm, forming a yellow green image, a
yellow green-close-to-yellow image, and a yellow image,
respectively. However, it is then understood that the diffraction
light 31' for reconstructing the image of the three-dimensional
object O is diffracted in a direction of nearly +20.degree.; it is
difficult to view that image clearly because of low diffraction
efficiency in that direction. FIGS. 7(a), 7(b), 7(c) and 7(d) are
illustrative of the dependence of diffraction efficiency on
wavelength and the angle-of-diffraction characteristics of
diffraction light 31', 32'a, 32'b and 32'c in this state.
[0053] As the white illumination light 30 is entered in the volume
hologram medium 29' from the frontal direction, diffraction light
32"a, 32"b, and 32"c for reconstructing a plane pattern image of
the masked portion of the mask plate 22 is diffracted at an angle
of +8.4.degree. (case (a)), 0.degree. (frontal direction; case
(b)), and -7.5.degree. (case (c)), respectively, so that the plane
pattern image becomes visible to the eyeball E of a viewer
positioned in the direction corresponding to each case. The center
wavelength of the diffraction light 32"a, 32"b, and 32"c is then
found at nearly 585 nm (yellow), nearly 600 nm (orange close to
yellow), and nearly 615 nm (orange), respectively. It is noted that
the diffraction light 31" for reconstructing the image of the
three-dimensional object O is diffracted in a direction of nearly
+45.degree. near to the center wavelength of 530 nm; however, it is
difficult to view that image clearly because of low diffraction
efficiency in that direction. FIGS. 8(a), 8(b), 8(c) and 8(d) are
illustrative of the dependence of diffraction efficiency on
wavelength and the angle-of-diffraction characteristics of
diffraction light 31", 32"a, 32"b and 32"c in this state.
[0054] As exemplified-above, when the white illumination light 30
and viewer's eyeball E are positioned in the same angule relation
as is the case with the reference light 27 and object light 2" used
to record the image of the three-dimensional object O, the image of
the three-dimensional object O can be seen in the same color as
recorded, but it is less visible in other angule relations and
colors. On the other hand, the plane pattern image of the masked
portion of the mask plate 22 is clearly seen even when the white
illumination light 30 and viewer's eyeball E are positioned in
different angule relations than that of the reference light 27 and
object light 25' as they are recorded; however, the color of that
image appears to vary depending on the viewing direction, and so
the plane pattern image can be seen by color switching.
[0055] From FIGS. 6-8, it is seen that the peak value of
diffraction efficiency of the hologram with the plane pattern image
of the masked portion of the mask plate 22 recorded therein is 100%
even with deviations from the hologram recording conditions (FIGS.
7(b)-(d) and FIGS. 8(b)-(d)), because uniform, parallel hologram
interference fringes exist in one section. It is also seen that the
peak value of diffraction efficiency of the hologram with the image
of the three-dimensional object O recorded therein decreases with
deviations from the hologram recording conditions, probably because
of the presence of many hologram interference fringes at angles
with the surface of the photosensitive material. Referring here to
FIGS. 6, 7 and 8, the dependence of diffraction efficiency on
wavelength is found from Logelnik's coupled-wave theory, and the
angle-of-diffraction characteristics are determined from the
diffraction equation.
[0056] As described above, the plane pattern of the masked portion
of the mask plate 22 is recorded in a hologram form using the
one-dimensional diffuser 24. In the hologram in which the image of
the plane pattern of the masked portion of the mask plate 22 is
recorded, diffraction light 32'a, 32'b, 32'c, 32"a, 32"b, and 32"c
also diffuses in the direction vertical to the plane of the paper
(when the second input hologram 21" is recorded in the arrangement
of FIG. 2(b)), unlike in a simple hologram mirror, as shown in FIG.
5(b), so that the field of view having an angle .alpha. is assured
in the transverse direction. In addition, when the white
illumination light 30 is incident on the hologram within the range
having an angle .alpha. and at an angle in the transverse direction
as shown in FIG. 5(c), too, only the image of the plane pattern of
the masked portion of the mask plate 22 is reproduced for
observation, because of the presence of some components incident in
the direction of the viewer's eyeball E.
[0057] In the volume hologram medium 29' of the invention, the
stereoscopic image of the three-dimensional object O and the image
of the plane pattern of the mask plate 22 are thus recorded in a
reflection form by interference of the same reference light beams
having the same angle of incidence and wavelength and the object
light beams having mutually different angles of incidence.
Accordingly, the stereoscopic image of the three-dimensional object
O is reconstructed in a single color and in an angular relation
close to that for the recording conditions, and the image of the
plane pattern of the mask plate 22 is reproduced at various angles
of incidence of white illumination light 30 and in different colors
depending on those angles of incidence, resulting in improvements
in aesthetics as well as security that is ensured by judgment of
whether or not such characteristics are obtained.
[0058] In the arrangement of FIG. 3, the volume hologram medium 29'
is copied and recorded while the first input hologram 11' prepared
in the process of FIGS. 1(a) and 1(b) is put on one second input
hologram 21" prepared using the illumination light 25 at one
specific angle of incidence .theta.' (-35.degree. (case (a)),
-45.degree. (case (b)), and -55.degree. (case (c)) in the step of
FIG. 2(b). In the state of FIG. 4(a), FIG. 4(b), and FIG. 5(a) of
this hologram recording medium 29', any one of the diffraction
light 32a, 32b and 32c, the diffraction light 32'a, 32'b and 32'c
and the diffraction light 32"a, 32"b and 32"c, that is, only the
diffraction light 32a, 32'a and 32"a, the diffraction light 32b,
32'b and 32"b or the diffraction light 32c, 32'c and 32"c is
diffracted and reconstructed; all these light beams are not
simultaneously diffracted. Another volume hologram medium 29'
capable of diffracting those diffraction light beams simultaneously
could be prepared as follows.
[0059] In the arrangement of FIG. 2(b), three hologram
photosensitive materials 21' deactivated using the same mask plate
22 are first provided. Then, three input holograms 21"a, 21"b and
21"c are each prepared by recording the plane pattern image of the
masked portion of the same mask plate 22 using illumination light
25 having the same wavelength .lambda. at a different angle of
incidence .theta.' (e.g., -35.degree., -45.degree., -55.degree. as
in the aforesaid embodiment) and the same reference light 25 at an
angle of incidence .theta. (e.g., 45.degree. as in the aforesaid
embodiment). Then, as shown in FIG. 9, three such input holograms
21"a, 21"b and 21"c are put on the first input hologram 11'
prepared at the steps of FIGS. 1(a) and 1(b). Subsequently, while a
volume hologram photosensitive material 29 comprising another
photopolymer is brought in close contact with the input hologram
21"a, the reference light 4 used to record the first input hologram
11' and illumination light 27 that propagates oppositely to the
reference light 26 used to record the input holograms 21"a, 21"b
and 21"c and has the same wavelength .lambda. as that of the
reference light 26 are entered in the assembly via the hologram
photosensitive material 29. This then allows diffraction light 2"
diffracted from the first input hologram 11' to reconstruct an
image O" of a stereoscopic reconstructed image O' to interfere with
the initially incident illumination light 27 to copy and record
reflection hologram interference fringes for reproducing an image
of the stereoscopic reconstructed image O", and the initially
incident illumination light 27 to interfere with diffraction light
25'a, 25'b and 25'c that, upon incidence on the input holograms
21"a, 21"b and 21"c, is diffracted from portions of the mask plate
22 (corresponding to the masked portions of the mask plate 22)
other then the portions deactivated by light 23, propagating
oppositely to the illumination light 25 passing through the
one-dimensional diffuser 24 used to record the input holograms
21"a, 21"b and 21"c, thereby providing multiple copying and
recording in the hologram photosensitive material 21 of reflection
hologram interference fringes for reconstructing the plane pattern
image of the masked portion of the mask plate 22. Three sets of
reflection hologram interference fringes for the reconstruction of
the plane pattern image of the masked portion of the mask plate 22
are similar to those in the input holograms 21"a, 21"b and 21"c,
providing uniform, parallel interference fringes in one section
(that corresponds to a plane including the reference light 26 and
illumination light 25 used to record the input holograms 21"a, 21"b
and 21"c).
[0060] In the thus copied and recorded volume hologram medium 29',
the diffraction light 32a, 32b and 32c, the diffraction light 32'a,
32'b and 32'c and the diffraction light 32"a, 32"b and 32"c are all
simultaneously diffracted in the states of FIGS. 4(a) and 4(b) and
FIG. 5(a). Accordingly, as the viewer's eyeball E is moved as
indicated by a double-headed arrow solid line in FIG. 4(b) upon
incidence of the white illumination light 30 on the volume hologram
medium 29' at an angle of, e.g., 22.5.degree. with respect to the
normal thereto as shown in FIG. 4(b), the diffraction light 32'a,
32'b and 32'c strikes successively upon the viewer's eyeball E, so
that the plane pattern image of the masked portion of the same mask
plate 22 is visible while the color changes successively from
yellow green (of around 575 nm) to yellow green close to yellow (of
around 580 nm) to yellow (of around 590 nm). Alternatively, as the
viewer's eyeball E is moved as indicated by an double-headed arrow
solid line in FIG. 5(a) upon incidence of the white illumination
light 30 on the volume hologram medium 29' from its frontal
direction as shown in FIG. 5(a), the diffraction light 32"a, 32"b
and 32"c strikes successively upon the viewer's eyeball E, so that
the plane pattern image of the masked portion of the same mask
plate 22 is visible while the color changes successively from
yellow (of around 585 nm) to orange close to yellow (of around 600
nm) to orange (of around 615 nm). When, in FIGS. 4(b) and 5(a), the
volume hologram medium 29' is moved as indicated by a double-headed
arrow broken line while the viewer's eyeball E is fixed, the plane
pattern image of the masked portion of the same mask plate 22 is
again visible while the color changes successively, provided that
there is some extent in the direction of incidence of the white
illumination light 30.
[0061] Thus, in another volume hologram medium 29' of the
invention, a plurality of plane pattern images of the same mask
plate 22 are multi-recorded in the reflection form by interference
of the same reference light beams having the same wavelength and
the same angle of incidence with the object light beams having
mutually different angles of incidence, so that the plurality of
plane pattern images of the mask plate 22 can be reconstructed in
the form of an image whose color changes successively at
successively varying viewing positions relative to the volume
hologram medium 29'. Thus, this volume hologram medium 29' is
improved in terms of aesthetics, and ensures high security because
whether or not it has such aesthetic properties can be judged. A
stereoscopic image of the three-dimensional object O can also be
multi-recorded in the volume hologram medium 29' by interference of
the same reference light beams having the same angle of incidence
and the same wavelength with object light beams having different
angles of incidence, so that even much more improved aesthetics and
security can be achieved.
[0062] Whether the volume hologram medium 29' fabricated in the
arrangement of FIG. 3 or the volume hologram medium 29' fabricated
in the arrangement of FIG. 9 allows the images of the
three-dimensional object O and the plane pattern of the mask plate
22 to be triply recorded in R (red), G (green) and B (blue). In
that case, when the plane image pattern of the masked portion of
the mask plate 22 is viewed in the state of FIG. 4(b) or FIG. 5(a)
as an example, the image is seen as an image whose color changes
slightly depending on position. Thus, aesthetics are much more
improved.
[0063] It is noted that at the step of fabricating the second input
hologram 21" of FIG. 21(b), 21"a, 21"b or 21"c, the one-dimensional
diffuser 24 is not always required. In the absence of the
one-dimensional diffuser 24, however, such a transversely wide
viewing field as shown in FIG. 5(b) or FIG. 5(c) cannot be ensured,
and it is not possible to enter the white illumination light 30 in
the hologram photosensitive material at an angle in the transverse
direction, either.
[0064] As an alternative way of recording the first input hologram
11' of FIG. 1(b), use could be made of a reflection hologram
recording process that relies on a one-step or two-step Denisyuk's
arrangement.
[0065] As an alternative way of recording the second input hologram
21" of FIG. 2(b), 21"a, 21"b or 21"c, use could be made of a
reflection hologram recording process in the Denisyuk's arrangement
wherein a reflection type one-dimensional diffuser is used in place
of the transmission type one-dimensional diffuser 24.
[0066] To ensure much more enhanced security, a plane pattern
comprising micro-characters or painted designs used for securities,
etc. could be recorded as the plane pattern used when recording the
second input hologram 21", 21"a, 21"b or 21"c.
[0067] Further, a plane pattern comprising an array of lines or
dots could be recorded as the plane pattern used when recording the
second input hologram 21", 21"a, 21"b or 21"c.
[0068] In this case, a pattern film with lines or dots drawn
thereon at the same pitch as that of the lines or dots in the above
plane pattern is superposed on the volume hologram medium 29', as
set forth in Patent Publication 2, thereby observing moir fringes
created between the lines or dots in the plane pattern and the
lines or dots on the pattern film. In this way, whether the volume
hologram medium 29' is genuine or fake can be judged making use of
the shape and the presence or absence of the area where the moir
fringes are found.
[0069] In order to facilitate such authentication, it is desired to
record the plane pattern image in such a way that the reconstructed
image of the plane pattern is formed in the vicinity of the
hologram plane of the volume hologram medium 29'.
[0070] While the volume hologram medium of the invention has been
described with reference to some preferred embodiments, it is
understood that the invention is in no sense limited thereto, and
many modifications may be possible.
[0071] In one volume hologram medium of the invention described
herein, the image of a three-dimensional object and the image of a
plane pattern are multi-recorded in a reflection hologram form by
interference of the same reference light beams having the same
angle of incidence and the same wavelength with object light beams
having mutually different angles of incidence, so that the
stereoscopic image of the three-dimensional object can be
reconstructed in angle relations close to the recording conditions
and in a single color, and the image of the plane pattern can be
reconstructed at various angles of incidence of white illumination
light and in colors varying depending on those angles of incidence.
It is thus possible to provide a volume hologram medium having
improved aesthetics, wherein much more enhanced security is ensured
by determination of whether or not the volume hologram medium has
such aesthetic properties.
[0072] In another volume hologram medium of the invention, a
plurality of plane pattern images are multi-recorded as a
reflection hologram by interference of the same reference light
beams having the same angle of incidence and the same wavelength
with object light beams having mutually different angles of
incidence, so that the plurality of plane pattern images can be
reconstructed in the form of an image whose color changes
successively at successively varying viewing positions relative to
the volume hologram medium. It is thus possible to provide a volume
hologram medium having improved aesthetics, wherein much more
enhanced security is ensured by determination of whether or not the
volume hologram medium has such aesthetic properties.
* * * * *