Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02680255 2015-01-26
WO 2007/109626
PCT/US2007/064325
HYBRID REFLECTION HOLOGRAM
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of the filing of U.S. Provisional Patent
Application Serial No.
60/783,502, entitled "Method and Apparatus for Mass Production of Volume
Holograms from Plane
Holograms", filed on March 17, 2006. This application is also related to U.S.
Patent Application Serial No.
11/459,821, entitled "Method and Apparatus for Mass Production of Holograms",
filed on July 25, 2006, which
application claims the benefit of the filing of U.S. Provisional Paient
Application Serial No. 60/702,785, entitled
"Method and Apparatus for Mass Production of Reflection Holograms and Volume
Holographic Optical
Elements", filed on July 26, 2005.
BACKGROUND OF THE INVENTION
Field of the Invention (Technical Field):
The present invention is a method and apparatus for making a reflection
hologram (or volume
hologram) that is made using a transmission hologram (or plane hologram) as
the object. This invention
obtains the benefits of the transmission hologram's diffraction spectral color
playback and color separation of
a white light or other multi-wavelength source by directly converting the
transmission hologram to a reflection
hologram for security and forgery prevention. The present invention preferably
utilizes a single color laser, or
optionally a tunable laser or other coherence light source, to record the
hologram by scanning the plane
hologram with a profiled narrow beam. The resulting hybrid reflection
hologram, when illuminated by white
light, can replay in a single color or in the multiplicity of colors of the
original transmission hologram while
adding the unique optical characteristics of the reflection hologram.
Background Art:
Note that the following discussion refers to a number of publications and
references.
Discussion of such publications herein is given for more complete background
of the scientific
CA 02680255 2009-09-04
WO 2007/109626 PCT/US2007/064325
principles and is not to be construed as an admission that such publications
are prior art for
patentability determination purposes.
Differentiation of Transmission and Reflection holograms
When constructing a hologram, as the angle difference between the object beam
(or the
wavefronts bouncing off the object) and the reference beam changes, so does
the spacing of the
patterns in the emulsion. As long as the angle difference remains less than
about 90 degrees the
hologram is typically called a transmission hologram, where "plane" typically
means that the
holographic information is primarily contained in the two-dimensional plane of
the emulsion. Although
the emulsion does have a thickness, typically around seven microns, the
spacing between fringes is
large enough, when the angle is less than about 90 degrees, so that the depth
of the emulsion isn't
being utilized in the recording of the hologram. At about 90 degrees, which is
really a convenient but
arbitrary point, the angle is great enough, and fringe spacing has become
small enough, so that the
recording process is taking place throughout the volume of the thickness of
the emulsion, thus
producing a reflection hologram. Thus the same emulsion can be used to make
both transmission
and reflection holograms depending on the angle difference between the
reference and object beams.
(However, some emulsions or other photosensitive materials are better for
either transmission
holograms or reflection holograms.) Thus, as the incidence angle of the
reference beam is rotated,
either a transmission or reflection hologram is constructed, as shown in Fig.
1.
A very important point for differentiation occurs as the reference beam swings
around its arc
of possible positions. In a plane (transmission) hologram the reference beam
is hitting the film from
the same side as the object beam. In a volume (reflection) hologram the
reference beam hits the film
from the side opposite to the modulated object beam. When a difference of 180
degrees is reached,
an in-line, volume reflection hologram is constructed.
A transmission type hologram means that the reference beam must be transmitted
through
the hologram, in order to decode the interference patterns and render the
reconstructed image. The
light which is used for playback of a transmission hologram must be coherent
or semi-coherent or the
image will not be sharp. If a non-coherent source is used, such as the light
from a common, unfiltered
slide projector, then the hologram will diffract all the different
wavelengths. The interference pattern or
grating etched in the emulsion is not particular as to which wavelengths it
bends or focuses; therefore,
the result is an unclear overlapping spectrum of colors which somewhat
resemble the object. A
hologram will playback just as well with laser light of a different color or
wavelength than the light with
2
CA 02680255 2009-09-04
WO 2007/109626 PCT/US2007/064325
which it was made. However, the object will appear to be of a different size
and/or distance from the
plate. For example, a hologram of an object made with red light will playback
that object smaller or
seemingly further away if a blue colored laser is used to view it. This is
because the grating will bend
the blue or shorter light less severely than the red with which it was made
and with which it is intended
to be decoded.
Unlike a transmission hologram, also called a thin, transmission, laser-
illuminated, or phase
hologram, which requires a coherent or highly filtered playback source, a
reflection hologram, also
called a volume or thick hologram, can be viewed very satisfactorily in white
light or light which
contains many different wavelengths. For best results, the light preferably
should be from a point
source and have limited divergence, such as light from a slide projector light
or penlight, or the sun on
a clear day. Any ambient light may alternatively be used, but this will
typically produce lesser quality
of the playback image. This ability to use white light occurs because, in a
way, a reflection hologram
acts as its own filter. In a reflection hologram the fringes are packed so
closely together that they
constitute layers throughout the thickness of the emulsion. The spacing
between fringes remains
constant. If the distance between fringes is two microns, for example, then
the distance between the
remaining layers of fringes will also be two microns. This distance is a
function of the wavelength of
light used in constructing the hologram and also the angle difference between
reference and object
beam. This layered structure allows the reflection hologram to absorb, i.e.
not reflect, any of the colors
of light which do not have the correct wavelength. The wavelength which
matches the fringe spacing
will be reflected: the crests of the wavelengths which are too short or too
long will eventually miss one
of the planes and be absorbed into the darkness of the emulsion.
In a reflection type hologram the playback light or reconstruction beam comes
from the same
side of the hologram as the viewer. Some parts of the incident light are
reflected, some are not,
depending on the interference pattern. If the hologram was made correctly the
result should be a
visible three dimensional image. In contrast, for transmission holograms the
reconstruction beam
must pass through the hologram and come towards the viewer from the opposite
side of the
hologram. Just as very few transmission holograms are made in-line (or at 0
degrees), very few
reflection holograms are made inline; otherwise the viewer would have to hold
the playback light
source close to his or her eyes. Most reflection holograms are made at a less
severe angle, perhaps
160 degrees, so that the light can come in at an angle without being blocked
by the person who is
trying to see the hologram.
3
CA 02680255 2009-09-04
WO 2007/109626 PCT/US2007/064325
Real and Virtual Images
The image produced by the hologram can either appear to be in front of the
holographic plate
or film, or behind the film (or any position in between). As shown in Fig. 2,
in the former case it is
called a real image (projection); the latter is called a virtual image. In
general it is easier to view a
virtual image because you can see through the hologram as if it were a window.
Note that the size of
the window does not affect the apparent size of the image; a smaller window
would simply allow a
more confined view, or fewer possible angles of view, of the image. To view a
virtual image the
viewer looks through the hologram to perceive the object floating in the space
behind it. In contrast, a
real image appears in free space in front of the hologram. It is a little more
difficult to view a real
image because the viewer must find the image and focus his or her eyes in
front of the hologram; the
hologram itself is typically less capable to act as a guide for the viewer's
eyes.
The real image is very exciting but there are a number of drawbacks. The
object holographed
should be quite a bit smaller than the size of the film you are using, or the
viewer will not be able to
see the complete real image of the object all at once. Also, without special
precautions taken when
constructing the hologram, the real image will be pseudoscopic. This means
that everything that was
closer to the film when the hologram was made will now be further away, and
vice versa. This
includes both individual objects in a shot or the different planes of space of
an individual object. The
pseudoscopic image is made by reversing the direction of the reference beam,
or by turning the
completed hologram around until seeing the image in front of the plate.
For example, referring to Fig. 3, if in making a hologram a salt shaker is
placed closer to the
film than a pepper shaker (the salt shaker may even cast a shadow from the
object beam onto the
pepper shaker), then in a pseudoscopic playback as a real image the pepper
shaker will appear to be
closer to the viewer than the salt shaker, which may no longer appear.
However, in a virtual image of
the same hologram the shakers would resume their original positions.
Image Plane holograms
Image plane holograms are transmission holograms which are viewable in white
light and
made using a first, master hologram as the object for making a final, second
transmission hologram.
However, although the master hologram is reproduced using an open aperture,
the image is
achromatic (black and white), and this method can only produce extremely
shallow holograms without
substantial blurriness. Rainbow or Benton holograms are modified image plane
holograms in which
the final transmission hologram is produced using a limited aperture. This
reduces blurring of deeper
4
CA 02680255 2016-03-22
WO 2007/109626 PCT/US2007/064325
holograms. However, Benton holograms may only be viewed from a small angular
range due to the
limited aperture; the entire hologram cannot be viewed from, for example,
above or below. Because a
Benton hologram is a transmission hologram, color control is limited. That is,
all of the colors in a Benton
hologram will shift throughout the color spectrum of the viewing light source,
for example white light,
when the viewing angle changes.
15
5
CA 02680255 2016-03-22
WO 2007/109626
PCT/US2007/064325
SUMMARY OF THE INVENTIONIDISCLOSURE OF THE INVENTION)
According to the invention, there is provided a method for producing a
reflection hologram, the
method comprising the steps of: providing a holographic object, the
holographic object selected from the
group consisting of a transmission hologram, a diffraction grating, and a
grating structure; material,
disposing the holographic object in contact with a photosensitive scanning the
holographic object with a
light beam from a coherent light source, the light beam passing through the
photosensitive material; and
reflecting the light beam back through the photosensitive material, thereby
forming a reflection hologram
viewable in white light; modifying the size or angle of the apertures when
making the holographic object;
characterized in that in the scanning step a thickness of the light beam is
narrower than a length of the
holographic object, and a width of said light beam is at least as wide as the
holographic object's width so
as to provide said reflection hologram to behave in different aspects like a
transmission hologram or as a
reflection hologram.
6
CA 02 680255 2014-04-24
WO 2007/109626
PCT/US2007/064325
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated into and form a part of the
specification, illustrate
several embodiments of the present invention and, together with the
description, serve to explain the
principles of the invention. The drawings are only for the purpose of
illustrating a preferred embodiment of the
invention and are not to be construed as limiting the invention. In the
drawings:
Fig. 1 shows possible reference beam angles when constructing a hologram;
Fig. 2 shows the difference between a real image and a virtual image;
1 0 Fig. 3 illustrates a pseudoscopic image;
Fig. 4 depicts a method of making the white-light holograms of the present
invention wherein the angle
of incidence is less than ninety degrees;
Fig. 5 depicts a method of making the white-light holograms of the present
invention wherein the angle
of incidence is approximately ninety degrees; and
Fig. 6 depicts a method of making the white-light holograms of the present
invention wherein the angle
of incidence is approximately zero degrees, thereby producing an edge lit
reflection hologram.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
(BEST MODES FOR CARRYING OUT THE INVENTION)
2 0 The present invention preferably uses a transmission hologram or other
holographic object, for
example, as the object for making a reflection hologram. Single beam scanning
reflection techniques are
preferred but other techniques may be used. The mass production methods
disclosed in U.S. Patent
Application Serial No. 11/459,821 , entitled "Method and Apparatus for Mass
Production of Holograms", may
be used in producing the holograms of the present invention.
2 5 As used throughout the specification and claims, "reflection hologram"
means a volume hologram,
reflection hologram, or thick hologram, and the like. As used throughout the
specification and claims, "object
hologram" means a transmission hologram, plane hologram, thin hologram, laser-
illuminated or laser-lit
hologram, phase hologram, holographic optical element (HOE), Benton hologram,
rainbow hologram, image
plane hologram, limited aperture hologram, transmission type optical relief
hologram, image planed
30 transmission hologram, holographic stereogram, diffractive hologram,
diffraction grating, grating structure,
multiplex hologram, dot matrix, rainbow, phase, or relief diffraction grating,
electron beam hologram,
Kineogram, or anything derived from a master
7
CA 02680255 2009-09-04
WO 2007/109626 PCT/US2007/064325
hologram, whether comprising an image or designed for information storage and
playback, and the
like, including but not limited to any hologram that would be better, or more
effectively made, as a
transmission hologram, but that would be improved if it could be functionally
converted to a reflection
hologram.
As used throughout the specification and claims, "hologram area" means an area
of a
hologram or an image or part of an image that is reproduced in a hologram. As
used throughout the
specification and claims, "white light" means white light or any light which
comprises multiple
wavelengths.
Referring to Fig. 4, the object hologram is placed in the position to be
converted with its
exposed emulsion either up or down in relation to the film; preferably the
emulsion is up and contacts
the medium, which is preferably disposed emulsion side down. Any
photosensitive, photoprofilable,
or ablatable recording medium may be used in place of the film. If the object
hologram's exposed
emulsion does not contact the film, it is preferable to use a larger scanning
length, or "thickness", of
the scanned beam. The recording medium can be disposed on any suitable
substrate or carrier
medium, including but not limited to glass or film. Thus the photosensitive
material is preferably
sandwiched between the transmission hologram and the glass or film substrate.
A cover plate which
is clear, or substantially transparent to the laser's wavelength, may
optionally be used. The entire
"sandwich" is preferably disposed on a base plate, or optionally a roller or
other curved support, the
surface of which may optionally be mirrored to enhance reflectivity. The
object hologram may also (or
alternatively) comprise a highly reflective metal, typically vacuum-deposited,
for example on the
grating surface, or otherwise metallized surface for enhanced reflectivity.
Any highly reflective
material, such as aluminum, may be used. The hologram or support may
alternatively be
electroformed, as is normally done to produce a nickel shim. Any method that
will maximize the
reflective qualities of the hologram or support may be used. The "sandwich" is
then scanned or
exposed with a beam from a source of coherent electromagnetic radiation, for
example a laser or
other light, to a proper exposure time for the photosensitive material being
used. The beam passes
through the optional cover plate and unexposed recording medium and reflects
off the base plate or
object hologram and back through the recording medium to form a reflection
hologram. The thickness
or scanning length of the scanning beam is preferably as narrow as possible,
and should be narrower
than the length of the object hologram being scanned. As is shown in the
figures, the width of the
scanning beam preferably is at least as wide as the width of the object
hologram to be scanned. After
the exposure of the copy plate, a reflection hologram is developed. The
resulting hologram will be a
8
CA 02680255 2009-09-04
WO 2007/109626 PCT/US2007/064325
reflection hologram but will behave like a transmission hologram in certain
aspects and as a reflection
hologram in others.
The laser may be scanned at an angle of incidence approximately equal to the
original angle
used in the manufacture of the object hologram in order to produce a
pseudoscopic image. Or the
angle of incidence may be the chosen to be the appropriate angle to provide an
orthoscopic (i.e. right
reading) image, which may enhance the playback diffraction efficiency,
preferably in white light, of the
finished reflection hologram. However, it is possible to use any reference
angle, or angle between the
laser beam and the surface of the plate, for the exposure. Some applications
may require a different
incident angle, for example when reading a predetermined position to obtain
selected information that
is stored in the hologram. If the scan is made at an angle of incidence
different than the reference
angle of the master hologram, the optimal playback viewing angle is typically
shifted. For example,
Brewster's angle may be used as the scanning angle of incidence, which
substantially eliminates any
internal reflections of the scanning beam. This substantially eliminates
Newton rings which are
typically formed when the master is made at a different reference angle
without having to rely on
nonreflective coatings.
It is possible to use a zero order, or approximately perpendicular, reference
beam, as shown
in Fig. 5, which produces particularly good results for certain object
holograms, for example a dot
matrix hologram or holographic image, HOE, or grating formed image. Use of
zero order scanning
preferably creates a color in the emulsion, related to the recording
wavelength, that shifts when
viewed in white light. This shift, similar to that of optical variable ink,
preferably occurs within certain
parameters that are related to the recording wavelength and thickness of the
recording medium.
As shown in Fig. 6, the angle of incidence of the scanning beam may be between
zero and
approximately five degrees. This configuration can be used to produce a
reflection edge lit hologram
of any size. Typical edge lit holograms are very large transmission holograms
for displays. Edge lit
reflection holograms made according to the present invention can be of any
size, including small
labels.
Because the beam is scanned relative to the object hologram, unlike
traditional holography
methods, the beam need not be stabilized relative to the object hologram. This
enables the use of a
much simpler manufacturing apparatus.
Unlike Benton holograms, the aperture used in the present invention may be
fully open. In
that case, the resulting hybrid reflection hologram, made from a full spectrum
transmission hologram
as the object hologram, will typically have a solid color when viewed in white
light (within a predefined
9
CA 02680255 2009-09-04
WO 2007/109626 PCT/US2007/064325
area and depth of the hologram). Alternatively, the aperture may be limited to
any desired value,
producing a master hologram having a range of playback colors (which range is
typically limited when
compared to the range of colors displayed by a transmission hologram). All
aperture widths are
preferably controlled when producing the master hologram as is known in the
art. Traditional
reflection hologram methods must select for color by varying the color of the
recording laser(s) or
swelling the emulsion between exposures. In addition to those methods, the
present invention
enables the user to choose which colors are displayed by modifying the size or
angle of the
aperture(s) when making the master hologram. And different apertures can be
used for exposing
different hologram areas according to the present invention, so that when the
final hybrid reflection
hologram is produced, certain hologram areas can have solid, nonshifting
colors (as is typical with a
reflection hologram) while other hologram areas exhibit color shifting when
the viewing angle is
varied.
The hybrid reflection holograms of the present invention have many unique
properties.
Typical reflection holograms can only play back in the same color it was
produced in, even when
illuminated with white light. In order to get multiple colors, the emulsion
must be swelled between
multiple exposures, or alternatively a mutable laser and multiple color-
sensitive emulsion must be
used (with appropriately colored object holograms). Also typical reflection
holograms do not exhibit
color shifting when the viewing angle is changed. In contrast, the present
holograms, when
illuminated with white light, copy (for example) the rainbow effect of a
rainbow hologram that was
used as the object hologram. The colors may optionally have been modulated by
the color of the
exposing laser or other known techniques. The holograms of the present
invention preferably have
some of the benefits and playback properties of reflection holograms; for
example, viewability in a
reflected white light source, image solidity and stability, color selection,
color stability (limited color
shifting), wider deeper colors, front reflection playback, and single area
image playback. They exhibit
some or all of the diffraction colors and visual effects of the original
transmission hologram while
retaining the color control of a reflection hologram. The multiple shifting
colors displayed by the hybrid
reflection holograms of the present invention are typically centered around
the reference angle and
can change as the viewing angle is shifted, although the range of colors is
typically far more limited
than the range exhibited by a transmission hologram, which, like a prism,
displays all of the colors
included in the viewing light source (e.g. a complete spectrum for white
light). Thus the range of color
shifting that the hybrid reflection hologram exhibits preferably comprises
only a subset of the colors
included in the light source.
CA 02680255 2009-09-04
WO 2007/109626 PCT/US2007/064325
Unlike transmission holograms (e.g. embossed security holograms or those made
from
diffraction gratings by, for example, dot matrix or e-beam methods),
reflection holograms typically can
only be viewed from approximately the direction and angle of the recording
source; they cannot be
viewed from the reverse angle. Thus, as a reflection hologram, the present
invention can produce
another image (which is the same as or different than the original image) that
is viewable only from
the reverse angle, or other images which are viewable from their own reference
angles. This
capability is advantageous for security applications. This also is difficult
to accomplish cleanly using
transmission holograms known in the art, since there can be interference or
"crosstalk" between the
multiple images. And, since reflection holograms are more sensitive to the
reference angle for image
playback than transmission holograms, the hybrid reflection holograms of the
present invention may
be used for applications where precise control of the viewing angle, or
location of stored information to
be transferred, is desired while still providing some of the advantages of
transmission holograms,
such as color control and color shifting.
The present invention enables the use of object holograms or HOE's as
reflections which do
not comprise a reflective backing or metal surfacing (as is typically needed
when producing embossed
holograms) or the need for a back lighting source to playback the hologram in
white light conditions.
Thus the use of front mounted lighting is possible, with all its attendant
benefits. Unlike transmission
holograms, the information is stored throughout the emulsion layer of the
hybrid reflection hologram of
the present invention, as a true reflection hologram, and can not be
electroformed or copied as easily
as information in a transmission hologram, Benton or rainbow hologram, or the
like. Thus holograms
of the present invention are more secure than transmission holograms and thus
more suitable for use
as Optically Variable Devices, which are used, for example, as anti-
counterfeiting labels. In addition,
the quality and diffraction efficiency of the holograms produced according to
the present invention is
high enough to meet production standards for commercial use, using
commercially-available
recording media.
Multiple object holograms may be used to create a hybrid reflection hologram
according to the
present invention by multiply exposing the photosensitive medium. For example,
the photosensitive
medium may be exposed at different stations where different object holograms
are located.
The hybrid reflection hologram of the present invention may optionally be
affixed to a label,
such as an RFID tag. The information in the RFID tag may correspond to
information in the hologram.
It may also optionally comprise printing which may relate to the image or
other information contained
in the hologram, similar to printing on embossed holograms known in the art.
11
CA 02680255 2009-09-04
WO 2007/109626 PCT/US2007/064325
A reflection hologram according to the present invention may optionally be
made using
normal (non-holographic) object. In this case, there would be no color
shifting, but if a direct physical
developer, for example, were used, the hologram may exhibit chromatic
dispersion.
Example 1
A hybrid reflection hologram of the present invention was produced as follows:
1. A limited aperture white light transmission hologram of the size
required was
made.
2. The transmission hologram should be of high diffraction quality for best
results. For this example, certain areas of a transmission hologram were
exposed using a hinge point
method commonly known in the industry to enable the separation of colors in
the finished limited
aperture white light hologram. It may be advantageous to make the color slits
as narrow as possible
in order to maximize the diffractive color range of the finished white light
transmission hologram.
Additional areas of the hologram were exposed using an open aperture and then
were combined with
the areas previously exposed.
3. A photosensitive photoresist, commonly used in embossed holography, was
used as the recording medium. The hologram was developed in the normal manner.
4. When the hologram was finished it was metallized with aluminum, directly
onto the surface gratings.
5. The metallized object hologram was placed in the position to be scanned
and
converted to a hybrid reflection hologram.
6. In suitable conditions (e.g. under safe lighting if required) the
holographic
emulsion was placed in contact with the metallized surface of the transmission
hologram, forming a
"sandwich" structure. The grating structures were in contact with the
photosensitive material.
7. Relative to the angle that was used for the making of the original
limited
aperture transmission hologram, the object hologram was evenly scanned at an
appropriate angle of
incidence for playback with a single beam of a laser.
8. The photosensitive material was exposed at the correct exposure for the
photosensitive material being used.
9. GP8, a Russian developer commonly used to make reflection holograms,
was used to develop the hologram. A fixing agent was subsequently used. (Use
of a fixing agent is
optional.)
12
CA 02 680255 2014-04-24
WO 2007/109626
PCT/US2007/064325
10. After washing and
drying, the hologram was viewed in white light. Although the
invention has been described in detail with particular reference to these
preferred embodiments, other
embodiments can achieve the same results. Variations and modifications of the
present invention will be
obvious to those skilled in the art and it is intended to cover all such
modifications and equivalents.
15
25
13
