Optical: systems and elements – Holographic system or element – Using modulated or plural reference beams
Reexamination Certificate
2003-03-20
2004-07-06
Dunn, Drew A. (Department: 2872)
Optical: systems and elements
Holographic system or element
Using modulated or plural reference beams
C359S022000, C359S009000, C356S457000
Reexamination Certificate
active
06760134
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
Three-dimensional (3D) imaging, 3D-image projection, holography, color holography, electronic holography, digital holography, optical scanning holography, multicolor electronic holography, true-color 3D imaging and spatial light modulators.
2. Description of Prior Art
For many years holography has been investigated as a way to project three-dimensional (3D) information. Realistic 3D image projection has many applications both in the commercial and military sectors, such as entertainment, advertising, computer gaming for commercial markets, simulation, immersive training and 3D displays for military applications. For instance, army researcher have recently been investigating the use of photo-refractive crystals for holographic 3D displays. For example see “Three-dimensional image reconstruction using strontium-barium-niobate” by Brian P. Ketchel, Gary L. Wood, Richard J. Anderson and Gregory J. Salamo published in
Applied Physics Letters
, Vol. 71, p. 7-9, (1997) or “Three-dimensional holographic display using a photo-refractive crystal” by Christy A. Heid, Brian P. Ketchel, Gary L. Wood, Richard J. Anderson and Gregory J. Salamo, published in
SPIE
Vol. 3358
, Proceedings of the Sixth International Symposium on Display Holography
, p. 357-366, (1997). To date, there has been only limited success in applying holography techniques to the projection of realistic images, due largely to the single color nature of most hologram-reconstructed images. True-color holography (recording and reconstruction) has been investigated in detail and demonstrated using traditional photographic techniques, see for example,
Practical Holography
by Graham Saxby, published by Prentice Hall, New York, (1994) or “Color-reflection holography: theory and experiment,” by Paul M. Hubel and Laszlo Solymar published in
Applied Optics
, Vol. 30, No. 29, p. 4190-4203. (1991). In recent years, researchers have proposed electronic (or digital) holography techniques, by which the time consuming chemical processing involved in traditional holography is eliminated, see for example “Optical Scanning Holography,” by T. C. Poon, M. Wu, K. Shinoda, and Y. Suzuki, published in
Proceedings of the IEEE
, Vol. 84, p. 753-764 (1996). In electronic holography, holograms are recorded directly by photosensitive devices such as photodiodes or a CCD camera and usually stored as digital images, for example see “Digital Recording and numerical reconstruction of holograms: reduction of the spatial frequency spectrum,” by Ulf Schnars, Thomas M. Kreis, and Werner P. O. Juptner published in
Optical Engineering
, Vol. 35 No.4, p. 977-982, (1996) or “Three-dimensional microscopy with phase-shifting digital holography,” by Tong Zhang and lchirou Yamaguchi published in
Optics Letters
, Vol. 23, p. 1221-1223, (1998). These techniques have opened the way for such things as 3D holographic imaging in real-time, as indicated in “Real-time Optical Holography Using a Spatial Light Modulator” by T. C. Poon, B. D. Duncan, M. H. Wu, K. Shinoda and Y. Suzuki published in the
Japanese Journal of Applied Physics
, Vol. 29, pp. Ll840-Ll842, (1990) and also in “Real-Time Two-Dimensional Holographic Imaging Using an Electron-Beam-Addressed Spatial Light Modulator,” by T. C. Poon, B. W. Schilling, M. H. Wu, K. Shinoda and Y. Suzuki published in
Optics Letters
, Vol. 18, pp. 63-65, (1993).
They have also opened the way to numerical image reconstruction as discussed in “Real-time preprocessing of holographic information,” by B. W. Schilling and T. C. Poon published in
Optical Engineering
, Vol. 34, No. 11, pp. 3174-3180. Nov. (1995). Just as digital cameras will supplant photographic cameras in many situations. Advances in electro-optic devices such as CCD cameras and spatial light modulators (SLMs) are making electronic holography not only a reality, but also the preferred method for 3D holographic imaging for many applications. It is notable that electronic 3D color display of computer generated holograms (CGH) has also been investigated and demonstrated as indicated in “Color Images with the MIT Holographic Video Display,” by Pierre St-Hilaire, Stephen A. Benton, Mark Lucente, and Paul M. Hubel published in
SPIE Proc
, Vol. 1667
Practical Holography
Vl, p. 73-84, (1992) as well as in “Approach to the Multicolor Imaging From Computer Generated Hologram,” by Tadashi Nakamura, Hideya Takahashi, and Eiji Shimizu published in
SPIE Proc
, Vol. 2176
Practical Holography
VIII, p. 102-107, (1994). However, these techniques offer no means to record a hologram of a real object, as holograms are generated via computer.
It is easy to see the many advantages digital holography has over traditional, photographic holography, and there are even more such advantages when applied to the true-color holography problem. In the past, true color holography has meant the recording of three separate monochromatic holograms, each at a different laser wavelength, superimposed on the same photographic plate as can be seen in the article “Color-reflection holography: theory and experiment, mentioned above. Although the three separate holograms can be recorded simultaneously, often they are recorded in succession, sometimes using different emulsions and different exposure times. Saxby, above, cites a number of problematic practical considerations faced by true-color holographers, for instance the availability of truly panchromatic holographic emulsions, loss of fringe contrast, and cross talk. The lack of appropriate holographic emulsions forces the use of separate emulsions and therefore successive hologram recording for each color. For single emulsion holograms, fringe contrast can suffer due to very similar fringe patterns (from each color) occupying the same space in the photographic emulsion. Also, cross talk is a factor upon image reconstruction since the red laser will not only reconstruct the geometrically correct image from the “red” fringes, but also two smaller, displaced images from the fringes created by the green and blue lasers.
FIG. 1
shows a system used for Optical Scanning Holography (OSH). Holographic recording by OSH is a technique, described in U.S. Pat. No. 5,064,257 for an “Optical Heterodyne Scanning Type Holographic Device” which is based on scanning the object with a Fresnel Zone Pattern (FZP). The standard setup for mono-color holographic recording by OSH requires a two-beam laser light generator, which is a part of the system shown in FIG.
1
. The two beams originate from the same laser
1
operating at frequency &ohgr;
1
. The original laser beam is separated into first and second beams using a beam-splitter (BSI)
2
, that reflects nominally 50% of the original beam along an axis normal to the axis of the original laser beam. The first beam is passed through an Acousto-Optical Modulator
3
(AOM
1
) operating in the Bragg regime. Like other modulators this one produces sidebands of different orders of frequency, however, they are emitted at different angles. Here it is modulated with an electrically induced acoustic signal from an electrical signal generator
4
operating at cos (&OHgr;
1
t), e.g. &OHgr;
1
=40 MHz and the output angle is chosen to emit only the first order frequency (&ohgr;+&OHgr;
1
)t. The second beam is further redirected by a mirror
7
as a third beam parallel to the first direct beam. This third beam passes through a beam expander
8
(BE
2
) to collimate the beam and increase its diameter to a predetermined size. The third beam also passes through a correction lens
9
to form a spherical wave. The modulated first beam (&ohgr;
1
+&OHgr;
1
)t is also passed through a beam expander
5
(BE
1
), similar to BE
2
that collimates this first beam to have a plane wave-front and increases its diameter to match that of the third beam. The third and first beams define a co-dependent pair of output beams for one mono-color two-beam laser generator.
To create an FZP beam, the output beams of a co-dependent pair are redirected into a fourth or FZP beam, e.
Poon Ting-Chung
Schilling Bradley W.
Anderson William
Boutsikaris Leo
Dunn Drew A.
Samora Arthur
The United States of America as represented by the Secretary of
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