U.S. patent number RE39,864 [Application Number 10/857,803] was granted by the patent office on 2007-10-02 for controlled diffraction efficiency far field viewing devices.
This patent grant is currently assigned to HoloSpex, Inc.. Invention is credited to Ravindra A. Athale, Joseph van der Gracht.
United States Patent |
RE39,864 |
Athale , et al. |
October 2, 2007 |
Controlled diffraction efficiency far field viewing devices
Abstract
This invention pertains to the design of optimized far field
viewing devices that simultaneously produce bright far field
holographic light patterns and achieve good see-through performance
to present a well focused scene. A far field transmission hologram
recorded on a transparent substrate has regions having high
diffraction efficiency juxtaposed with regions having low
diffraction efficiency. The high diffraction efficiency regions
contribute to production of bright far field holographic light
patterns, whereas the low diffraction efficiency regions contribute
to see-through performance.
Inventors: |
Athale; Ravindra A. (Burke,
VA), van der Gracht; Joseph (Columbia, MD) |
Assignee: |
HoloSpex, Inc. (Columbia,
MD)
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Family
ID: |
22559441 |
Appl.
No.: |
10/857,803 |
Filed: |
May 28, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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60156406 |
Sep 28, 1999 |
|
|
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Reissue of: |
09671092 |
Sep 27, 2000 |
06452699 |
Sep 17, 2002 |
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Current U.S.
Class: |
359/13; 359/9;
351/51 |
Current CPC
Class: |
G02B
30/34 (20200101); G02C 7/00 (20130101); G03H
1/22 (20130101); G03H 1/18 (20130101); G03H
1/24 (20130101); G03H 2001/303 (20130101); G03H
2001/2234 (20130101); G03H 1/2249 (20130101); G03H
2210/20 (20130101); G03H 1/182 (20130101); G03H
1/265 (20130101); G03H 2001/2284 (20130101); G03H
1/0236 (20130101); G03H 2001/2273 (20130101); G03H
1/0248 (20130101); G03H 2270/55 (20130101); G03H
1/0244 (20130101); G03H 2001/306 (20130101); G03H
1/0841 (20130101) |
Current International
Class: |
G03H
1/00 (20060101) |
Field of
Search: |
;359/1,9,13,22,29,32,33
;351/51,52,158 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Isreal Government Coins and Medals Corporation "And There Was Ligh"
Isreal State Medal Designed by Yaacov Agam (undated). cited by
examiner .
Saxby, "Practical Holography" Prentice Hall, 1998, pp. 209,211.
cited by examiner.
|
Primary Examiner: Boutsikaris; Leonidas
Attorney, Agent or Firm: Roberts, Mardula & Wertheim,
LLC
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims priority under 35 U.S.C. .sctn.119(e) from
U.S. provisional application No. 60/156,406, filed Sep. 28, 1999.
The Ser. No. 60/156,406 application is incorporated herein by
reference in its entirety for all purposes.
Claims
What is claimed is:
1. A viewing device for viewing by a user, the device comprising: a
support structure; and a far field transmission hologram supported
by the support structure, the far field transmission hologram
having a graphic image encoded therein; wherein, when the support
structure is disposed in a viewing position of the user, the
graphic image is superimposed, with substantially no reversed
diffracted copy of the graphic image, on a natural scene as viewed
by the user through the hologram, and wherein the superimposed
graphic image and the natural scene are viewable by the user in
combination with substantial clarity.
2. The viewing device of claim 1, wherein the far field
transmission hologram is a spatially varying diffraction efficiency
far field hologram.
3. The viewing device of claim 2, wherein the far field
transmission hologram is a fill factor modulated far field
hologram.
4. The viewing device of claim 3, wherein the support structure is
formed as a spectacle frame.
5. The viewing device of claim 3, wherein the support structure is
formed as a hand-held viewer.
6. The viewing device of claim 3, wherein the support structure is
formed as a bookmark.
7. The viewing device of claim 3, wherein the support structure is
formed as an article of jewelry.
8. The viewing device of claim 2, wherein the far field
transmission hologram has a high diffraction efficiency region with
plural low diffraction efficiency regions distributed irregularly
across the high diffraction efficiency region.
9. The viewing device of claim 8, wherein the percentage of area of
the far field transmission hologram occupied by the plural low
diffraction efficiency regions is selected so as to obtain a
balance of un-diffracted light seen by the user and light
diffracted into the graphic image.
10. The viewing device of claim 8, wherein the size of each of the
plural low diffraction efficiency regions is selected to be
sufficiently large so as to prevent any diffraction patterns caused
by the low diffraction efficiency regions from distracting from the
graphic image.
11. The viewing device of claim 8, wherein the size of each of the
plural low diffraction efficiency regions is selected to be
sufficiently small so as to prevent a need to maintain precise
position with respect to an eye of the user in order to view the
graphic image.
12. The viewing device of claim 1, wherein the far field
transmission hologram is a computer-generated multilevel phase far
field transmission hologram.
13. A viewing device for viewing by a user, the device comprising:
a spectacle frame having lens apertures; and a far field
transmission hologram disposed in one or more of the lens apertures
of the frame, the far field transmission hologram having a graphic
image encoded therein; wherein, when the spectacle frame is
disposed in a viewing position of the user, the graphic image is
superimposed, with substantially no reversed diffracted copy of the
graphic image, on a natural scene as viewed by the user through the
hologram, and wherein the superimposed graphic image and the
natural scene are viewable by the user in combination with
substantial clarity.
14. The viewing device of claim 13, wherein the far field
transmission hologram is a fill factor modulated far field
hologram.
15. The viewing device of claim 13, wherein the far field
transmission hologram is a spatially varying diffraction efficiency
far field hologram.
16. The viewing device of claim 13, wherein the far field
transmission hologram includes an interferometrically recorded
pattern of optical phase variation.
17. The viewing device of claim 13, wherein the far field
transmission hologram is a computer-generated multilevel phase far
field transmission hologram.
18. A filter for use with a camera having a light gathering path
and an image sensor, the filter comprising: a far field
transmission hologram, the far field transmission hologram having a
graphic image encoded therein and being adapted for mounting in the
light gathering path; wherein, when the far field transmission
hologram is mounted in the light gathering path, the graphic image
is superimposed, with substantially no reversed diffracted copy of
the graphic image, on a natural scene as viewed by the image sensor
through the hologram, and wherein the superimposed graphic image
and the natural scene are viewable by the image sensor in
combination with substantial clarity.
19. The filter of claim 18, wherein the far field transmission
hologram is a fill factor modulated far field hologram.
20. The filter of claim 18, wherein the far field transmission
hologram is a computer-generated multilevel phase far field
transmission hologram.
21. The filter of claim 18, further comprising: a filter frame, the
far field transmission hologram being mounted in the frame.
.Iadd.22. A viewing device for viewing by a user, the device
comprising: a support structure; and a far field transmission
hologram supported by the support structure, the far field
transmission hologram having a graphic image encoded therein;
wherein, when the support structure is disposed in a viewing
position of the user, the graphic image is superimposed on a
natural scene as viewed by the user through the hologram, wherein
the superimposed graphic image and the natural scene are viewable
by the user in combination with substantial clarity, and wherein
the far field transmission hologram is a spatially varying
diffraction efficiency far field hologram..Iaddend.
.Iadd.23. The viewing device of claim 22, wherein the far field
transmission hologram is a fill factor modulated far field
hologram..Iaddend.
.Iadd.24. The viewing device of claim 23, wherein the support
structure is formed as a spectacle frame..Iaddend.
.Iadd.25. The viewing device of claim 23, wherein the support
structure is formed as a hand-held viewer..Iaddend.
.Iadd.26. The viewing device of claim 23, wherein the support
structure is formed as a bookmark..Iaddend.
.Iadd.27. The viewing device of claim 23, wherein the support
structure is formed as an article of jewelry..Iaddend.
.Iadd.28. The viewing device of claim 22, wherein the far field
transmission hologram has a high diffraction efficiency region with
plural low diffraction efficiency regions distributed irregularly
across the high diffraction efficiency region..Iaddend.
.Iadd.29. The viewing device of claim 28, wherein the percentage of
area of the far field transmission hologram occupied by the plural
low diffraction efficiency regions is selected so as to obtain a
balance of un-diffracted light seen by the user and light
diffracted into the graphic image..Iaddend.
.Iadd.30. The viewing device of claim 28, wherein the size of each
of the plural low diffraction efficiency regions is selected to be
sufficiently large so as to prevent any diffraction patterns caused
by the low diffraction efficiency regions from distracting from the
graphic image..Iaddend.
.Iadd.31. The viewing device of claim 28, wherein the size of each
of the plural low diffraction efficiency regions is selected to be
sufficiently small so as to prevent a need to maintain precise
position with respect to an eye of the user in order to view the
graphic image..Iaddend.
.Iadd.32. A viewing device for viewing by a user, the device
comprising: a spectacle frame having lens apertures; and a far
field transmission hologram disposed in one or more of the lens
apertures of the frame, the far field transmission hologram having
a graphic image encoded therein; wherein, when the spectacle frame
is disposed in a viewing position of the user, the graphic image is
superimposed on a natural scene as viewed by the user through the
hologram, wherein the superimposed graphic image and the natural
scene are viewable by the user in combination with substantial
clarity, and wherein the far field transmission hologram is a fill
factor modulated far field hologram..Iaddend.
.Iadd.33. A viewing device for viewing by a user, the device
comprising: a spectacle frame having lens apertures; and a far
field transmission hologram disposed in one or more of the lens
apertures of the frame, the far field transmission hologram having
a graphic image encoded therein; wherein, when the spectacle frame
is disposed in a viewing position of the user, the graphic image is
superimposed on a natural scene as viewed by the user through the
hologram, wherein the superimposed graphic image and the natural
scene are viewable by the user in combination with substantial
clarity, and wherein the far field transmission hologram is a
spatially varying diffraction efficiency far field
hologram..Iaddend.
.Iadd.34. A filter for use with a camera having a light gathering
path and an image sensor, the filter comprising: a far field
transmission hologram, the far field transmission hologram having a
graphic image encoded therein and being adapted for mounting in the
light gathering path; wherein, when the far field transmission
hologram is mounted in the light gathering path, the graphic image
is superimposed on a natural scene as viewed by the image sensor
through the hologram, wherein the superimposed graphic image and
the natural scene are viewable by the image sensor in combination
with substantial clarity, and wherein the far field transmission
hologram is a fill factor modulated far field transmission
hologram..Iaddend.
.Iadd.35. The filter of claim 34, further comprising: a filter
frame, the far field transmission hologram being mounted in the
frame..Iaddend.
.Iadd.36. A filter for use with a camera having a light gathering
path and an image sensor, the filter comprising: a far field
transmission hologram, the far field transmission hologram having a
graphic image encoded therein and being adapted for mounting in the
light gathering path; wherein, when the far field transmission
hologram is mounted in the light gathering path, the graphic image
is superimposed on a natural scene as viewed by the image sensor
through the hologram, wherein the superimposed graphic image and
the natural scene are viewable by the image sensor in combination
with substantial clarity, and wherein the far field transmission
hologram is a spatially varying diffraction efficiency
hologram..Iaddend.
.Iadd.37. The filter of claim 36, further comprising: a filter
frame, the far field transmission hologram being mounted in the
frame..Iaddend.
.Iadd.38. A viewing device for viewing by a user, the device
comprising: a support structure; and a far field transmission
hologram supported by the support structure, the far field
transmission hologram having a graphic image encoded therein;
wherein, when the support structure is disposed in a viewing
position of the user, the graphic image is superimposed on a
natural scene as viewed by the user through the hologram, wherein
the superimposed graphic image and the natural scene are viewable
by the user in combination with substantial clarity, wherein the
far field transmission hologram is a spatially varying diffraction
efficiency far field hologram, and wherein the far field
transmission hologram has plural high diffraction efficiency
regions and plural low diffraction efficiency regions distributed
among the high diffraction efficiency regions..Iaddend.
.Iadd.39. A viewing device of claim 38, wherein at least a portion
of the plural high diffraction efficiency regions are contiguous
with one another..Iaddend.
.Iadd.40. A viewing device of claim 38, wherein at least a portion
of the plural low diffraction efficiency regions are contiguous
with one another..Iaddend.
.Iadd.41. A viewing device of claim 38, wherein the plural low
diffraction efficiency regions are distributed irregularly among
the high diffraction efficiency regions..Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to controlling the brightness of light
patterns created by a hologram. More specifically, this invention
balances the brightness of a far field holographic light pattern
and the clarity of a scene when viewed through a far field viewing
device.
2. Background Information
Holograms of many different types have become commonplace in modern
society. They are used as ornaments and as novelty items, as well
as security devices on credit cards. A hologram is a pattern
recorded on a substrate that provides a predetermined light
diffraction effect.
There are many different types of holograms that are differentiated
from one another by their optical properties and behavior. Most of
the commonly seen holograms depend upon reflection of light from
the hologram to the observer's eye. Less commonly seen are
transmission type holograms wherein light passes through the
hologram.
When an observer looks through a far field hologram at a scene that
contains compact bright points of light, the observer sees
holographic diffracted light patterns associated with each bright
point location. We define this unique form of display holography as
a far field viewing application. Far field viewing devices are made
up of physical apertures (or frames) and far field holograms
combined in a way designed for viewing a scene and superimposing
holographic light patterns around each compact bright point of
light in the scene.
Referring to FIG. 1, a far field viewing device containing of a far
field hologram 10 mounted in a frame 12 is illustrated. The far
field viewing device is placed in front of an observer's eye 14.
The observer's eye 14 looks through far field hologram 10 mounted
in frame 12 at a scene containing at least one bright compact
source of light 16. Each point in the scene is viewed through a
utilized hologram area 18. Schematic depictions of a tree and a
star represent scene elements 20 that the observer wants to see in
sharp focus.
Examples of far field viewing devices include the eyeglass device
containing far field holograms as described in U.S. Pat. No.
5,546,198, as well as far field holograms mounted in windows.
Ordinarily, a human observer looks through a far field device.
Additionally, far field devices can also be incorporated into
film-based or electronic image capture devices, such as still or
motion cameras.
An example of an algorithm for calculating computer generated
holograms is described by Gallagher and Liu. See N. C. Gallagher
and B. Liu, "Method for Computing Kinoforms That Reduces Image
Reconstruction Error" Applied Optics, v. 12, pp.2328-2335 (1973).
The output of the algorithm is a set of numerical values. Each
value corresponds to the desired complex transmittance at a
different spatial location on the physical hologram. The resultant
data set is used to drive any of a variety of fabrication methods
which impose the desired transmittance values onto a physical
substrate. There are a number of methods for producing a physical
computer generated hologram from a set of date. These are
summarized in the textbook MICROOPTICS [editor Hans P. Herzig,
published by Taylor and Francis, London 1997] in chapters 4 and 5.
An original hologram can be used as a master and copied or
replicated using a variety of techniques as discussed in chapter of
7 of Herzig's MICROOPTICS.
Referring to FIG. 2, an idealized view of the overall scene as seen
through an ideal far field viewing device is illustrated. The ideal
view contains a well-focused representation of scene elements 220
in addition to a desired diffracted light pattern 222 produced by
light diffracted by the far field hologram adjacent a bright
compact source of light 216. In the example, the hologram has been
tailored to diffract the light pattern in the form of letters
spelling the word "NOEL". FIG. 2 shows only one bright compact
point of light to keep the illustration simple. In the case where
many such sources of light are present, the desired diffraction
pattern will surround each bright compact source of light.
A salient aspect of far field viewing applications that is
different from most display hologram applications is that the
observer is encouraged not to focus all of the attention on the
holographic diffracted light pattern. Instead, the observer focuses
on an overall scene in a unique combination with the holographic
diffracted light patterns at each bright point source of light
present in the scene. Accordingly, it is important for the viewing
device to present a clear image of the scene while also presenting
bright holographic light patterns.
It is also desirable for a far field viewing device to have a loose
tolerance for the distance between the observer's eye and the
hologram so that the viewer is not forced to maintain a particular
position relative to the far field viewing device.
Additionally, it is desirable for the hologram in a far field
viewing application to be capable of producing relatively large
diffracted light patterns containing fine spatial detail.
The problem of balancing the clarity of the scene and the
brightness of the holographic light patterns is not common in
display holography. In most applications of display holography, the
hologram is designed to diffract as much of the light as possible
to create the brightest possible holographic reconstruction. Such a
hologram is said to have high diffraction efficiency. The push in
the industry is directed to design methods and fabrication
processes that maximize the diffraction efficiency of display
holograms since most applications of display holography call for
maximum brightness in the holographic reconstruction.
Referring to FIG. 3, a view through a high diffraction efficiency
far field hologram is illustrated. The scene elements appear as
blurred images 324 when viewed through a far field transmission
hologram having a high diffraction efficiency. FIG. 3 also shows
that such a far field hologram also produces an undesired
diffracted light pattern 326, symmetrically disposed about a bright
compact light source 316 in the form of a mirror image of desired
diffracted light pattern 322.
In contrast, our goal for far field viewing applications is to
attain a diffraction efficiency that is often considerably less
than the diffraction efficiency produced by standard methods for
designing and fabricating holograms. When a highly efficient far
field hologram is used in a far field viewing application, the
diffracted light patterns are bright but the scene appears blurred.
This effect on the view of the scene is much like looking through a
light diffusing piece of shower glass, and it is undesirable since
viewing, not obscuration, is desired. On the other hand, when the
hologram has low diffraction efficiency the scene observed through
the hologram appears well focused, but the holographic light
patterns surrounding the point sources of light in the scene are
not sufficiently bright.
Whereas the prior art provides no way to simultaneously maximize
the scene clarity and the brightness of the holographic light
patterns, we recognize that the diffraction efficiency of the
hologram should be chosen to strike an optimum balance between the
un-diffracted energy and the energy in the desired diffracted light
pattern. The optimum diffraction efficiency can depend on the
nature of the desired holographic pattern as well as the expected
scene characteristics. Thus, flexible and simple control in
achieving the desired diffraction efficiency of the hologram is
needed.
One broad approach to the problem of reducing diffraction
efficiency would be to start with an established method that
produces high diffraction efficiency and to modify the approach to
obtain reduced diffraction efficiency. The need for intentionally
reducing diffraction efficiency of a far field hologram in a
controlled manner has not been recognized in the prior art. In
contract, we have made it a goal to increase the amount of
un-diffracted light by reducing the amount of energy in the desired
diffracted light pattern. Preferably, the modified process should
not substantially increase the energy into undesired diffracted
distributions that would distract from the desired diffracted
pattern.
An unsatisfactory solution would be to modify standard hologram
fabrication processes by adjusting process parameters to achieve
the desired diffraction efficiency. In an amplitude hologram, it is
possible to reduce the diffraction efficiency by reducing the
transmittance contrast of the hologram. The transmittance contrast
is a measure of the ratio of the highest transmittance to the
lowest transmittance. Lowering the transmission contrast would in
fact make the diffracted pattern weaker and improve the see-through
performance of the hologram as desired. A significant drawback is
that nonstandard processes would have to be developed to accomplish
this. The use of nonstandard processes leads to increased costs and
increased process variations.
In a binary phase hologram, it is possible to reduce the
diffraction efficiency by changing the phase modulation depth. The
phase modulation depth is a measure of the maximum optical path
length difference between the two transmittance states in the
hologram. As in the amplitude case, implementation of this solution
would require processes that need tight control over transmittance
contrast or phase modulation depth. Such processes are difficult to
establish and maintain. These problems lead to increased costs and
questionable repeatability, since non-standard fabrication
procedures would be needed.
Additionally, a significant limitation of amplitude holograms and
binary phase holograms is their restriction to Hermitian symmetric
holographic light reconstruction patterns. Hermitian symmetry means
that the desired reconstruction pattern is always accompanied by a
copy of the pattern that is rotated by 180 degrees about the
un-diffracted component. This undesired symmetric diffraction
pattern in the form of a mirror image of the desired pattern is
distracting in many cases. Furthermore, the undesired diffraction
pattern takes up a large space that could otherwise be used to
create larger and more complicated desired diffracted light
patterns.
As discussed in our previous patent, U.S. Pat. No. 5,546,198,
multilevel phase computer generated holograms (CGH's) can diffract
light into asymmetric light patterns thus eliminating the
distracting reversed diffracted copy and enabling a larger area for
more complicated light patterns. In practice, such holograms are
highly efficient and have poor see-through performance resulting in
a severely blurred scene when used in a far field viewing device.
The idea of decreasing diffraction efficiency by modifing process
parameters is not an available option for multilevel phase CGH's.
Unlike the case of binary CGH's, intentionally reducing the phase
modulation to reduce diffraction efficiency of a multilevel CGH has
serious undesirable consequences. As the phase modulation depth
decreases, the diffraction efficiency does decrease but an
additional diffracted pattern appears in the form of a reversed
copy of the desired pattern. In practice, the strength of this
reversed copy eliminates the advantage of multilevel phase
holograms.
Referring to FIG. 4, a view of the scene through a multilevel phase
CGH far field transmission hologram is illustrated. In this view,
an undesired symmetric diffraction pattern has been eliminated so
that only a desired diffraction pattern 422 is seen adjacent a
bright compact light source 416. Elements of the natural scene are
blurred as represented by blurred images 424.
Thus, an alternative form of the multilevel phase CGH is needed to
balance see-through performance with the desired holographic
reconstruction without introducing additional undesired diffracted
light.
U.S. Pat. No. 5,210,625 and U.S. Pat. No. 5,278,008 disclose a
multi-step process for modifying the diffraction efficiency of
optically generated holograms without adjusting the contrast
transmittance or the phase modulation depth over the whole hologram
area. The disclosures of these patents are directed to beam
splitting and redirecting holograms. They are silent regarding far
field holograms, as well as information bearing holograms.
The process disclosed by the '625 and '008 Patents is not
applicable to far field viewing devices. The disclosed aspect of
introducing an unresolvable pattern of clear regions may be
workable for image plane and Fresnel holograms when attention is
focused at or near the plane of the hologram and may be useful for
some beam redirection applications for which it is taught. However,
the '625 and '008 disclosures do not recognize that the apertures
defining the clear regions contribute to undesired diffracted light
as well as un-diffracted light. The practical result is that the
teachings of the '625 and '008 Patents cannot be applied to far
field viewing applications because the small size of the
unresolvable regions produces undesirable diffraction artifacts
that compete with the desired reconstructions of far field
holograms when bright compact sources of light are present in the
scene.
Furthermore, the process of introducing unresolvable flat regions
as the '625 and '008 Patents can introduce undesirable degradation
in the see-through performance of holograms creating a blurred
scene. The prior art concept of resolving the flat regions really
loses meaning for holograms that are situated near the pupil of the
eye as in the case of many far field viewing devices. Thus,
different considerations are needed.
Moreover, the multi-step process disclosed by the '625 and '008
Patents is cumbersome and is not appropriate for computer generated
holography.
What would be useful would be far field viewing devices
incorporating holograms with diffraction efficiency adjusted to
provide robust control over the balance between the clarity of the
scene and the brightness of the holographic light pattern appearing
at each bright point of light while minimizing undesired diffracted
light patterns.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a far field
hologram viewing device.
It is another object of the present invention to provide a method
of manufacturing a far field hologram.
It is yet another object of the present invention to provide a far
field hologram viewing device through which a scene may be viewed
by an observer in combination with holographic diffracted light
patterns at each bright point source of light present in the
scene.
It is still another object of the present invention to provide a
far field hologram viewing device which produces a desired
reconstruction pattern that is not accompanied by a copy of the
pattern that is rotated by 180 degrees about an un-diffracted
component.
It is an object of the invention to provide a robust approach to
controlling diffraction efficiency of far field holograms in order
to achieve a balance between the clarity of the scene and the
brightness of the holographic light pattern appearing due to each
bright point of light while controlling undesired diffracted light
patterns.
It is another object of the invention to control the diffraction
efficiency for multilevel phase computer generated holograms that
are not limited to producing symmetrical holographic light
patterns, and therefore allow for larger and more detailed
diffracted light patterns than are possible with amplitude
holograms and binary phase holograms.
It is yet another object of the invention to establish a procedure
that is consistent with established cost-effective hologram
fabrication processes.
It is a further object of the invention to provide the balance
between the clarity of the scene and the brightness of the
holographic light patterns without requiring a tight tolerance on
the relative positions of the hologram and an observer's eye.
The present invention includes far field viewing devices employing
novel reduced diffraction efficiency far field holograms having
regions of spatially varying diffraction efficiency to provide
robust control over the balance between scene clarity and
holographic light pattern brightness.
This invention pertains to the design of optimized far field
viewing devices that simultaneously produce bright far field
holographic light patterns and achieve good see-through performance
to present a well focused scene. The implementation of the hologram
is critical to achieve the desired viewing conditions.
Some of the above objects are obtained by a viewing device for
viewing by a user. The device includes a support structure and a
far field transmission hologram. The far field transmission
hologram is supported by the support structure, and the far field
transmission hologram has a graphic image encoded therein. When the
support structure is disposed in a viewing position of the user,
the graphic image is superimposed, with substantially no reversed
diffracted copy of the graphic image, on a natural scene as viewed
by the user through the hologram. The superimposed graphic image
and the natural scene are viewable by the user in combination with
substantial clarity.
Some of the above objects are also obtained by such a viewing
device where the support structure takes the form of a spectacle
frame having lens apertures. The far field transmission hologram is
disposed in one or both of the lens apertures of the frame.
Others of the above objects are obtained by an optical device
having a reflective far field hologram, where the hologram is a
fill factor modulated far field hologram.
Certain of the above objects are obtained by a method of generating
a far field transmission hologram. The method includes the step of
altering an optical property of a substrate to form a substantially
shift-invariant far field hologram that has a graphic image encoded
therein. The alteration of the optical property produces a high
diffraction efficiency. The method also includes the step of
substituting a low diffraction efficiency pattern for at least one
selected region of the far field hologram.
Some of the above objects are also obtained by a filter for use
with a camera that has a light gathering path and an image sensor.
The filter includes a far field transmission hologram that has a
graphic image encoded therein. The far field transmission hologram
is adapted for mounting in the light gathering path. When the far
field transmission hologram is mounted in the light gathering path,
the graphic image is superimposed, with substantially no reversed
diffracted copy of the graphic image, on a natural scene as viewed
by the image sensor through the hologram. The superimposed graphic
image and the natural scene are viewable by the image sensor in
combination with substantial clarity.
BRIEF DESCRIPTION OF THE DRAWINGS
Additional objects and advantages of the present invention will be
apparent in the following detailed description read in conjunction
with the accompanying drawing figures.
FIG. 1 illustrates schematically a human observer looking through a
far field viewing device.
FIG. 2 illustrates a view for an observer of a scene while looking
through an ideal far field viewing device.
FIG. 3 illustrates a view for an observer of a scene while looking
through a high diffraction efficiency far field hologram.
FIG. 4 illustrates a view for an observer of a scene while looking
through a conventional multilevel phase CGH.
FIG. 5 illustrates an SVDEFF hologram.
FIG. 6 illustrates a diffraction pattern produced by a square
aperture.
FIG. 7 illustrates a diffraction pattern produced by a multilevel
phase FFMFF hologram with small square low-diffraction regions.
FIG. 8 illustrates a view for an observer looking through a far
field viewing device employing FFMFF hologram with excessively
large low diffracting regions.
FIG. 9 illustrates a view of an FFMFF hologram according to a
preferred embodiment of the present invention.
FIG. 10 illustrates a controlled diffraction efficiency far field
viewing device wherein FFMFF holograms are incorporated into the
lens apertures of a spectacle frame according to a preferred
embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
A standard far field hologram is typically optimized to create
maximum brightness holographic light patterns and consists of
highly diffracting regions over the face of the entire hologram.
According to the present invention, a far field viewing device
includes a hologram with a diffraction efficiency chosen to balance
the clarity of the scene with the brightness of the holographic
light reconstructions.
The desired clarity of the scene is such that the natural scene can
be appreciated without undue effort. In other words, it is desired
that the observer still be able discern the aesthetic qualities of
the natural scene while looking through the far field transmission
hologram. Good tests for scene clarity (since aesthetic discernment
is too cumbersome to evaluate) assess how well an observer can read
while looking through the holograms. A near-reading test is to
determine whether the observer looking through the holograms can
still read text of a standard publishing font size at what would
ordinarily be a comfortable reading distance for that person. A
far-reading test is to determine whether the observer looking
through the holograms can make out street signs and road signs
without undue effort. Alternately, standard comparative visual
acuity tests would be useful in evaluating whether vision of
scenery through the far field transmission holograms is
substantially clear if it meets an objective standard, e.g., a
"20/40" standard.
According to one embodiment of the present invention, the local
diffraction efficiency of the far field hologram is modified in a
systematic way. Far field holograms intended for far field viewing
applications are typically designed to exhibit shift-invariance.
This means that as the far field hologram is translated laterally
with respect to an illuminating beam of light, the intensity
distribution of the diffracted light pattern does not change
substantially. This also means that the entire hologram need not be
illuminated to produce the desired diffracted pattern. In practice,
illuminating a very small portion of the hologram will still
reproduce the entire diffracted pattern. Note that if the portion
is made too small, the quality of the diffracted light pattern will
degrade excessively. We define a unit hologram region as the
smallest portion of the overall hologram that produces an
acceptable quality diffracted pattern. Preferably, far field
holograms used for far field viewing applications are composed of
spatially repeated copies of a unit hologram.
Similarly, for a fixed position hologram, the eye can make small
rapid movements without changing the diffracted light pattern. This
shift-inverted property is generally desirable so that the viewer
does not need to maintain a rigidly fixed position with respect to
the hologram.
In the case of a far field hologram illuminated by a beam of light,
shift-invariance means that as the far field hologram is translated
laterally with respect to an illuminating beam of light, the
intensity distribution of the diffracted light pattern does not
change substantially.
This also means that the entire hologram need not be illuminated to
produce the desired diffracted pattern. In practice, illuminating a
very small portion of the hologram will still reproduce the entire
diffracted pattern. As regions smaller than a unit hologram region
are illuminated, the quality of the diffracted pattern degrades,
but the strength of the diffracted light does not change except for
small random variations as the hologram is moved with respect to
the beam. In other words, the diffraction efficiency remains
constant even for illuminated regions smaller than the unit
hologram as the hologram is translated laterally with respect to
the illuminating beam. The constant diffraction efficiency property
holds as long as the illuminated region is sufficiently large. We
define the minimum probe area as the smallest allowable size that
maintains the constant diffraction efficiency property. The
diffraction efficiency of a typical hologram for far field viewing
devices remains constant except for some small random variations as
the hologram is moved with respect to a minimum probe diameter
illuminating beam. In practice, the minimum probe diameter is
typically less than ten pixels wide in a CGH, where a pixel is the
smallest addressable spatial region in the CGH.
The observer does not make use of the whole hologram when the
hologram subtends a larger angle than the angular field-of-view of
the human eye (or any other visual sensor, by analogy). We define
that each point in the scene is viewed through a utilized hologram
area 18 determined by the angular field-of-view of the eye and the
distance from the eye to the hologram.
Many minimum probe diameter regions fit within the utilized
hologram area 18 of a hologram designed for far field viewing
applications. The effective diffraction efficiency of the hologram
is the average of the diffraction efficiencies of all of the
minimum probe diameter regions that comprise the utilized hologram
area. In a conventional far field hologram, the individual
diffraction efficiencies of the minimum probe diameter regions are
identical except for small random variations.
The present invention employs a novel form of a far field hologram
having systematically locally varying diffraction efficiency. This
locally varying diffraction efficiency is preferably manipulated to
create a particular desired effective diffraction efficiency when
averaged over an area corresponding to the utilized hologram area
18 (refer to FIG. 1). We call this novel hologram a Spatially
Varying Diffraction Efficiency Far Field (SVDEFF) hologram.
Referring to FIG. 5, an SVDEFF hologram is illustrated. The SVDEFF
hologram is made up of intentionally high diffraction efficiency
regions 528, which generate the desired diffracted light patterns,
and low diffraction efficiency regions 530, which possess low
diffraction efficiency and generate another set of weakly
diffracted light patterns. The size of the low efficiency regions
only needs to be small with respect to the utilized hologram area
18 and is much larger than the minimum probe diameter area of a
standard shift-invariant far field hologram. The size of the
intentionally low efficiency regions can even be much larger than
the unit hologram area provided that the unit hologram area is
small with respect to the utilized hologram area.
According to one embodiment of the present invention, a special
case of the SVDEFF hologram that we call a Fill Factor Modulated
Far Field (FFMFF) hologram is utilized. In such FFMFF holograms,
the low diffracting regions 530 are highly transmissive and nearly
optically flat regions with effectively zero diffraction
efficiency. The fill factor is the percentage of the holographic
surface that contains the intentionally high diffracting regions.
Introducing low diffracting regions 530 can be likened to punching
holes through the hologram. The size, shape and distribution of the
low diffracting regions 530 are important design parameters that
affect the usefulness of the resultant holograms in the context of
a far field viewing device.
When the size, shape and distribution of the low diffracting
regions 530 are chosen appropriately, the primary effect is to
lower the brightness of the holographic light patterns while
simultaneously increasing the scene clarity. Control over the
percentage fill of the diffracting region of the hologram over the
utilized hologram area 18 controls the effective diffraction
efficiency of the hologram and adjusts the balance between
holographic light pattern brightness and the scene clarity.
Increasing the fill factor increases the effective diffraction
efficiency and tends to brighten the diffracted light patterns at
the expense of scene clarity. Decreasing the fill factor decreases
the effective diffraction efficiency and tends to increase scene
clarity at the expense of reducing the brightness of the diffracted
light patterns.
In addition to the primary effect of increasing scene clarity, the
addition of low diffracting regions 530 creates a secondary effect
of introducing undesired diffracted light patterns that distract
from the desired holographic reconstructions. This can be
understood by considering diffraction by a mask that is clear in
the regions corresponding to the low diffracting regions 530 of an
FFMFF hologram and opaque in the regions corresponding to the high
diffracting regions 528. Such a mask will produce a unique far
field diffraction pattern corresponding to the shape of low
diffracting regions 530. This same diffraction pattern will be
produced by the corresponding FFMFF .[.hologrartad.].
.Iadd.hologram and .Iaddend.in many cases will distract from the
desired holographic reconstruction. In the example of FIG. 5, the
low diffraction efficiency regions 530 are regularly spaced square
regions.
Referring to FIG. 6, a far field diffraction pattern is
illustrated. A clear square aperture produces a far field
diffraction pattern and consists of a main central spot 632 and
multiple diffracted spots 634.
Referring to FIG. 7, a view of a single compact point of light as
seen through an FFMFF hologram with square low diffracting regions
with inappropriate sizes is illustrated. An undesired diffracted
pattern corresponding to the square low diffracting regions is
shown consisting of a main central spot 732 and unwanted diffracted
spots 734 as well as a desired diffracted light pattern 722
produced by high diffraction efficiency regions. The lack of an
unwanted mirror image of the desired diffracted pattern implies
that the high diffracting regions are in the form of a multilevel
phase CGH. The unwanted diffracted spots 734 can be very bright in
practice and distract from the appearance of desired diffracted
pattern 722.
One solution to the problem of the distracting undesired diffracted
pattern is to reduce the size of the square low diffracting regions
in order to increase the spacing between the undesired diffracted
spots so that the first unwanted diffracted spot is out beyond the
extent of desired diffracted light pattern 722. In the specific
case of the grid of square low diffracting regions, the designer
would then decrease the size of the individual squares while
attempting to maintain the same overall percentage fill factor by
appropriately reducing the spacing between regions. The choice of
very small regions can push unwanted diffracted spots 734 further
out beyond the extent of the desired diffracted light pattern 722.
However, the central spot 732 of the undesired diffraction pattern
broadens and corresponds to serious degradation in see-through
performance and is manifested as considerable blurring of the
scene.
We prefer to make the low diffracting regions 530 as large as
possible. The effect of sufficiently large low diffracting regions
530 is to make the overall undesired diffraction pattern small with
respect to the desired diffracted light pattern 722 thus minimizing
the distraction. Simultaneously, the central spot 732 of the
undesired diffraction pattern narrows and this results in practice
in improved see-through performance leading to a sharper focus of
scene elements.
Although we prefer making low diffracting regions as large as
possible, the size cannot be increased without limit. The upper
limit on the size is illustrated, referring to FIG. 8, where a
large low diffraction region size relative to the utilized hologram
area 818 has been chosen and the spacing has been chosen to
preserve a fifty percent fill factor. The utilized hologram area
818 is determined by a number of factors including the size of the
pupil of the eye 814 and the distance between the eye and the far
field viewing device (a hologram 810 mounted in a frame 812). When
the hologram 810 is situated within a few centimeters of the eye
814, the utilized hologram area 818 is relatively small and, as
shown in FIG. 8, the observer looks only through a low diffracting
region 830 when one of the apertures is co-centered with the center
of the pupil of the eye. In that case, the resultant effective fill
factor over the utilized hologram area is zero and the observer
will see no holographic light reconstructions. The other extreme
occurs when the hologram 810 is shifted laterally such that the
field-of-view of the eye only permits highly diffracting regions
828 of the hologram 810 to affect the view. In that case, the
resultant effective fill factor is 100 percent and the view of the
scene elements will be blurred. Other spatial shifts of the
hologram 810 of FIG. 8 relative to the eye 814 will produce
different effective fill factors.
It is desirable to have an effective fill factor that is
independent of the relative position of the eye and the hologram.
In order to achieve a position independent effective fill factor,
the size of the low diffracting regions and the repeat spacing
should be chosen such that several low diffracting regions are
contained within each utilized hologram area. According to the
preferred embodiment, the number of low diffracting regions
contained in the utilized hologram area is in the range of about
five or more.
In addition to choosing an effective size, the shape of the low
diffracting regions should also be selected to further decrease the
distracting effect of undesired diffracted light. It is desirable
to use low diffracting region shapes that spread the diffracted
energy out over a larger area rather than producing concentrated
spots of undesired diffracted energy. As an example, circular low
diffracting region shapes spread the undesired diffracted energy
into rings of light surrounding the main central spot that have
lower energy values per area than do the spots diffracted by
comparable size square low diffracting regions.
Referring to FIG. 9, a preferred embodiment of an FFMFF hologram
910 with circularly shaped low diffracting regions 930 distributed
across a region of high diffraction efficiency 928 is illustrated.
In this illustrated embodiment, over sixteen low diffracting
regions 930 fall inside a utilized hologram area 918.
Alternatively, the shapes of the low diffracting regions may be
carefully chosen such that any diffracted light would fall on
bright regions of the desired holographic reconstruction and hence
create minimal distraction.
Referring to FIG. 10, a preferred embodiment of a controlled
diffraction efficiency far field viewing device 1000 is
illustrated, wherein FFMFF holograms 1010 are incorporated into the
lens apertures of a spectacle frame 1012. Each of the FFMFF
holograms 1010 has a distribution of both high diffraction
efficiency regions 1028 and low diffraction efficiency regions
1030. The combination of FFMFF holograms 1010 with spectacle frames
1012 provides a viewing device 1000 that very naturally prompts a
person to don the device so that the holograms are juxtaposed with
respect to the person's eyes for easy viewing of the natural scene
combined with the holographic images produced by the holograms.
The distribution of the low diffracting regions 1030 is preferably
tailored to optimize the far field viewing device 1000. A regular
grid of apertures produces a sampling effect in the diffraction
pattern that manifests itself as a fine grid structure superimposed
on the diffraction pattern. An irregular spacing of the apertures
(as shown in FIG. 10) reduces this sometimes distracting sampling
effect.
A practical design example is given below to illustrate the design
considerations given above. Consider a computer generated
multilevel phase far field hologram designed to produce an
asymmetric holographic reconstruction around each bright point of
light when incorporated into a far field viewing device. The device
may be embodied in many forms including an eyeglass worn or held
close to the eye or a window mounted device. In the case of the
window mounted device the observer might stand as close to the
window as possible, so a choice of approximately two centimeters
between the eye and the hologram is appropriate for the cases of
both the eyeglass and the window application. Such a design
approach for the window mounted hologram will also work when the
observer is far from the hologram. The choice of a small utilized
hologram area is a conservative one. In an application that
precludes the observer from standing very close to the window,
larger low diffracting regions can be used.
For multilevel phase holograms produced with known fabrication
methods, a fill factor ranging from about 50 to 80 percent is
preferred as producing a pleasing balance between scene clarity and
reconstruction brightness. Selection of a most preferred value from
within this general range depends on the ambient light level in the
scene, the nature of the holographic reconstruction and subjective
interpretation of the viewers.
According to a working example, we use the particular goal of 75
percent fill factor. According to our empirical data, for a screen
placed two centimeters from the eye, a typical human viewer looks
through a utilized hologram area 18 having a size of about 1 cm in
diameter. A reasonable design for SVDEFF holograms employs circular
low diffracting regions 30 having a diameter of 1 mm and a mean
center-to-center spacing of approximately 1.8 mm. A 1 cm diameter
utilized hologram area will allow approximately 25 such low
diffracting regions to contribute to the view of the scene. This
configuration produces an effective fill factor that remains close
to 75 percent even when the hologram is translated laterally with
respect to the eye. The diameter of the circularly shaped low
diffracting regions proves to be sufficiently large to concentrate
the undesired diffraction pattern such that it creates minimal
distraction from typical holographic reconstructions.
Physical fabrication of an SVDEFF CGH takes advantage of
established CGH fabrication methods without any need for
nonstandard modifications. Instead, the distribution of the low
diffracting regions can be incorporated directly into the computer
generated hologram data prior to fabrication. In general, computer
generated holograms are produced by using numerical algorithms to
calculate phase and amplitude transmittance values that will result
in a desired far field diffraction pattern.
Each value corresponds to the desired transmittance at a different
spatial location on the physical hologram. The resultant data set
is used to drive any of a variety of fabrication methods that
impose the desired transmittance values onto a physical substrate.
In order to create the special case of an FFMFF CGH, a standard far
field hologram algorithm is initially employed to generate a data
set to produce a standard shift-invariant and highly efficient far
field hologram. The designer then determines the necessary fill
factor to lower the effective diffraction efficiency by the desired
amount. Then the size, shape and distribution of the low
diffracting regions are determined. Finally, data values
corresponding to the low diffraction regions of the FFMFF CGH are
set to unity transmittance with a constant relative phase. The
modified data set is then used as the input to a standard CGH
physical fabrication procedure.
Optionally, in the event that the cost of manufacturing individual
holograms in this manner is excessive, the hologram is used as a
master and copied or replicated using a variety of techniques. As
an alternative, a standard far field hologram is used as a master
and the replication procedure is modified to introduce the low
diffracting regions at the replication stage.
The above-described procedure permits a hologram producer to choose
the size, shape and distribution of the low diffracting regions
according to the guidelines described. However, the present
invention is not limited to a production method that incorporates
so much human input. The present invention encompasses production
procedures where an automated algorithm incorporates the design of
the size, shape and distribution of the low diffracting regions
into the calculation of the hologram. Such an automated approach
would also provide the improvements in the effectiveness of SVDEFF
CGH's according to the various embodiments of the present
invention.
Similarly, a CGH designer can arrive at an SVDEFF hologram
approximating an FFMFF hologram in an indirect fashion without
directly incorporating the low diffracting regions into the
hologram characteristics. Such an indirect method is achieved by
specifying the overall hologram reconstruction as a combination of
the desired diffracted pattern and a weak diffraction pattern such
as might be expected from the circular low diffracting regions of
an FFMFF hologram. A well implemented algorithm would ultimately
converge to a subclass of an SVDEFF hologram having substantially
low diffracting regions distributed throughout the otherwise high
diffraction efficiency hologram. These indirectly designed
holograms would differ from an FFMFF hologram in that the
transitions from low diffraction efficiency regions to high
diffraction efficiency regions would tend to be less sharp than the
transitions of the simpler FFMFF special case.
There are numerous variations possible according to alternate
embodiments of the basic embodiments described above. These various
embodiments are grouped according to the aspect of the resultant
device that they pertain to. This list is meant to be illustrative
and not exhaustive. Furthermore, numerous combinations can be
constructed by taking different variations from each of the aspects
discussed below.
A first class of alternate embodiments is based on variations of
the high diffraction regions of the hologram.
Although the above description emphasizes multilevel phase CGH's in
the specification, the method also applies to binary and continuous
amplitude CGH's, binary phase CGH's and all optically recorded far
field holograms. Since the maximum diffraction efficiency obtained
with each of these different processes of producing holograms is
significantly different, the corresponding optimum fill-factors
will also be significantly different.
According to an alternate embodiment, the high diffraction regions
that contain the far field holograms for generating the desired
light patterns are themselves spatially varying. Thus, different
high diffraction efficiency regions of the hologram could produce
different light patterns. Such a configuration, as a natural
result, causes an observer to see different light patterns in
different parts of the scene.
Some alternate embodiments are based on various ways that the image
generation is conditioned upon the frequency of light of the light
source impinging the hologram. Multi-level phase far field
holograms can be made to respond in a color selective manner if the
phase modulation is chosen correctly. For example, a multi-level
far field hologram that has been designed to work with red light
will create a holographic image only when a point-like light source
of red color is viewed through it. For all other colors, the
hologram will not produce the encoded holographic image. Similarly
the optical phase modulation can be adjusted so that the hologram
responds to blue or green light. A single far field hologram can
then contain regions that are turned to lights of different colors
in producing different images. When a white light point source is
viewed through such a hologram, it will produce a multi-color image
that is a superposition of individual images encoded in far field
holograms tuned to different colors. The technique for describing
the design of a color-selective far field hologram by adjusting
optical phase modulation has been described by Barton, Blair and
Taghizadeh. See Ian M. Barton, Paul Blair, Mohammad R. Taghizadeh
"Dual-Wavelength Operation Diffractive Phase Elements for Pattern
Formation", OPTICS EXPRESS, vol. 1, no. 2 (July 1997)(published on
the Internet). Holograms incorporating these color selective
effects are not inconsistent with the present invention, and
alternate embodiments of the present invention include appropriate
phase modulation to effect such color selective effects.
The present invention may also be optionally embodied using
so-called "volume" hologram construction. Holograms can be recorded
in materials that are thicker than several hundred micrometers.
Such holograms have special properties and have been discussed for
display applications and optical storage applications for a number
of years. See J. W. Goodman, INTRODUCTION TO FOURIER OPTICS, McGraw
Hill (2d ed. 1996). Such holograms when reconstructed suppress the
conjugate image. In addition, these holograms can display color
selective and angle selective behavior. This means that volume
holograms recorded with certain angle between the object and the
reference wave will reconstruct only when illuminated with a
reconstruction wave impinging at an appropriate angle. This
property is utilized in a far field hologram viewing device
according to the present invention in the following way. Multiple
holograms of different images are recorded with reference beams
coming at different angles. When this composite hologram is used in
viewing point sources located at different positions, the
holographic image reconstructed will depend on the location of the
point source. This leads to an enhanced viewing experience by
generating several independently recorded images to appear for
light sources at different positions in the scene.
A second class of alternate embodiments is based on variations of
the low diffracting regions of the hologram.
The individual low diffraction regions need not all have the same
shape and size. Thus, according to one alternate embodiment,
circles are mixed with polygons of varying sizes in a single SVDEFF
hologram.
Moreover, the shapes need not be restricted to simple geometric
patterns. Thus, another alternate embodiment employs a mix of low
diffraction efficiency regions that are shaped like various
alphanumeric characters or graphic images. This results in an added
benefit of creating an esthetically pleasing appearance when
viewed.
Although the low diffracting regions are described above as being
optically flat, the low diffraction regions need not be perfectly
optically flat in order to practice the present invention.
Fabrication limitations arising in mass production cause the low
diffraction regions to vary from being perfectly optically
flat.
In addition to unintentional deviations from optical flatness, one
alternate embodiment calls for the low diffracting regions to have
intentionally imposed phase profiles in the form of weakly
diffracting patterns. For example, the weakly diffracting pattern
is embodied as high frequency gratings that produce attractive
light patterns beyond the extent of the desired diffracted light
pattern. Thus, the low diffraction efficiency region can be
utilized to augment and enhance the main light patterns without
introducing unacceptable loss in the see-through image quality of
the scene.
According to yet another alternate embodiment, the low diffracting
regions have a phase profile produced by an indirectly computed
SVDEFF.
According to a further alternate embodiment, the low diffracting
regions have a gradually varying amplitude transmittance as opposed
to a uniform transmittance.
One way to embody the low diffracting regions of the present
invention is to intentionally introduce gaps between small unit
holograms.
A third class of alternate embodiments is based on variations of
the design and construction of the far field viewing device.
The viewing device may be embodied as having two distinct eye
openings, one for each of a viewer's two eyes. In this case, the
high diffraction portions of the respective holograms for the left
and right eye are optionally embodied as a stereo pair. The use of
a stereo pair generates a depth effect on the light pattern.
It is permissible to embody the frame that holds the far field
device that places a hologram between the scene and the observer's
eye in a variety of forms. The frame is alternately embodied as
eyeglass frames, jewelry, bookmarks, greeting cards, and frames for
mounting in (or on) windows.
According to another alternate embodiment, the far field device is
incorporated into an imaging system. Examples of imaging systems
that will embody the present invention are binoculars and
telescopes. Use of far field devices according to the present
invention is not limited to any specific type of imaging system and
may be incorporated into any of a variety of possible
configurations that interpose a far field hologram between the
observer's eye and the scene.
According to one embodiment, the far field device is incorporated
in or near the pupil plane of an imaging system that has a
solid-state detector or film as the final detection plane rather
than a human eye. Some examples of such devices are film-based
still or movie cameras, as well as still or motion cameras
utilizing solid-state type detectors.
The far field holograms described above worked using transmitted
light. Holograms according to the present invention may also be
embodied so as to work with light reflected from them. An important
consideration for designing such reflective far field holograms is
to account for the double optical pass through the hologram.
According to an exemplary embodiment, reflective far field
holograms according to the present invention are incorporated into
stickers. When a sharp point-like light source is viewed after
being reflected by the far field hologram, the desired light
pattern will appear surrounding the light.
The present invention has been described in terms of preferred
embodiments, however, it will be appreciated that various
modifications and improvements may be made to the described
embodiments without departing from the scope of the invention.
* * * * *