Optical: systems and elements – Holographic system or element – For producing or reconstructing images from multiple holograms
Reexamination Certificate
2001-07-18
2003-10-07
Juba, John (Department: 2872)
Optical: systems and elements
Holographic system or element
For producing or reconstructing images from multiple holograms
C359S022000, C359S032000, C359S008000
Reexamination Certificate
active
06631016
ABSTRACT:
FIELD OF THE INVENTION
Background of the Invention
One-step hologram (including holographic stereogram) production technology has been used to satisfactorily record holograms in holographic recording materials without the traditional step of creating preliminary holograms. Both computer image holograms and non-computer image holograms may be produced by such one-step technology. In some one-step systems, computer processed images of objects or computer models of objects allow the respective system to build a hologram from a number of contiguous, small, elemental pieces known as elemental holograms or hogels. To record each hogel on holographic recording material, an object beam is passed through the rendered image (e.g., as displayed on a spatial light modulator (SLM)) and used with a reference beam to create an interference pattern on the holographic recording material. Examples of techniques for one-step hologram production can be found in the U.S. Patent Application entitled “Method and Apparatus for Recording One-Step, Full-Color, Full-Parallax, Holographic Stereograms,” Ser. No. 09/098,581 (hereafter “the '581 application”), naming Michael A. Klug, Mark E. Holzbach, and Alejandro J. Ferdman as inventors, and filed on Jun. 17, 1998, which is hereby incorporated by reference herein in its entirety.
There is great interest in holograms with very wide viewing angles of 180°-360°. In many cases, “wrapping” the hologram image on a curved substrate during the hologram recording produces images with a broad angle of view when the images are mounted on the curved substrate. Such holograms enable viewing by a much larger audience than standard flat-format holograms. Additionally, curved format holograms can potentially improve the illusion of a suspended image, since the image is no longer anchored to a planar surface. In some cases, the image can be made to appear at the radial center of the mounting substrate, either as a virtual (behind the hologram plane) or aerial (in front of the hologram plane) image.
The difficulty in mounting, recording and illuminating curved-format holograms, however, has limited the usefulness and practice of this technique. It is particularly difficult to record holograms on substrates curved in two dimensions, since such holograms require the holographic recording material (e.g., photopolymerizable compositions, dichromated gelatin, and silver halide emulsions) to be directly coated onto such a substrate. Cylindrically-curved substrates are generally easier to accommodate, since they are curved in only one dimension and can be flattened temporarily, thereby simplifying recording and film processing.
There is wide and varied prior art for cylindrical-format holograms, beginning with the “Multiplex” hologram developed by Lloyd Cross in the early 1970's, proceeding most recently to Benton's “Alcove” hologram of t he late 1980's. U.S. Pat. No. 4,4834,476, entitled “Real Image Holographic Stereograms,” and naming Stephen A. Benton as inventor, which is hereby incorporated by reference herein in its entirety, discloses a hemi-cylindrical format holographic stereogram (the “alcove hologram”) comprised of 900 slit holograms that are 1 millimeter wide by 300 millimeters high. An example of a reflection alcove hologram
100
is shown in FIG.
1
A. The image volume can occupy any portion of the solid angle subtended by the intersection of the viewer's eyes and the hemi-cylinder
102
. The image(s)
104
incorporated in the reflection alcove hologram
100
are typically computer-generated and processed graphics, and the hologram itself can be reconstructed with a standard white light source
106
placed above and centered relative to the hemi-cylinder
102
.
Although the reflection alcove hologram can produce imagery with a wide (up to 180°) viewing angle, a number of limitations are notable. Referring to
FIGS. 1B and 1C
, which show side and top views, respectively, of reflection alcove hologram
100
, the reference illumination angle from light source
108
for the reflection alcove hologram
100
is fixed by the recording geometry, e.g., the angle of incidence of the reference beam with respect to the holographic recording material. Reflection alcove hologram
100
is horizontal parallax-only, and each of the component strip holograms has a horizontal viewing angle of about 53°, as shown in FIG.
1
C. So, for example, a projected image about 275 mm across can be seen over an angle of approximately 90°-100° before cut off of the edges of the image is noticeable. Reflection alcove hologram
100
displays parallax in only the horizontal direction, and there is no apparent change in the position of an object with variations in the vertical viewpoint. Moreover, the same vertical image information is distributed across the entire 30° viewing angle (e.g., vertical viewing zones) for each of the hologram points
110
,
120
, and
130
. Thus, viewability and image information are severely limited by the recording geometry and techniques.
The reflection alcove display is also particularly sensitive to defects in the mounting substrate. The lack of vertical parallax between the image and the hologram surface places the image vertical focus at the hologram surface, and this impression is heightened by any cosmetic defects in the hologram or its substrate.
Additionally, Benton describes the possibility of producing multi-color imagery in the reflection alcove as a process requiring exposure in a single wavelength with tedious multiple emulsion swelling steps between, and carefully calibrated image processing for each step. This is due primarily to the existence of optical elements in the recording system that only function properly with the monochromatic laser light, including holographic optical elements (HOEs) and non-achromatic refractive optics.
The use of specialized HOEs and cylindrical optics also make it difficult to scale the reflection alcove hologram, since doing so would likely involve incorporating optics with at least one dimension measuring the same size as the hologram itself. Thus, cylinder heights much larger than 300 millimeters would be very difficult to demonstrate in a nearly seamless fashion. Finally, the horizontal parallax-only characteristic of the reflection alcove necessitates a significant amount of astigmatism in the imaging system, thus limiting the maximum depth tolerable for comfortable viewing.
Given these, and other limitations of the prior art, it is therefore desirable to provide wide field of view, full-parallax, full-color holograms that are adaptable to substrates that are curved in one, two, or three dimensions, including cylindrical, conical, and spherical surfaces. It is also desirable to provide holograms on curved substrates that are scalable to unlimited size.
SUMMARY OF THE INVENTION
The current invention comprises the recording of full parallax, one-step, full color holographic stereograms that can be mounted on a curved substrate after recording. It also comprises mounting the hologram on a substrate that is curved in on a substrate that can be curved in one or two dimensions, thereby producing any arbitrary shape. The hologram is comprised of one or more tiles, and thus curved holograms of unlimited size can be generated. The hologram is adaptable to a variety of curved substrates including hemi-cylindrical substrates with opaque backing to allow up to 180° of horizontal view zone, and full cylinders with transparent backing to allow viewing through 360° horizontally.
In one embodiment, the present invention is a system for generating a holographic display on a curved substrate. The holographic display includes an image recorded on one or more tiles, and each tile is comprised of one or more holographic elements (hogels). The one or more tiles are mounted on the curved substrate. An image generation module is operable to allow a designer to specify a reference beam angle for each hogel and at least one of a radius of curvature for the substrate, a hogel orientation with respect to an image volume,
Holzbach Mark E.
Klug Michael A.
Ascolese Marc R.
Assaf Fayez
Campbell Stephenson Ascolese LLP
Juba John
Zebra Imaging, Inc.
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