Optical: systems and elements – Holographic system or element – Having multiple object beam or diffuse object illumination
Reexamination Certificate
1999-11-02
2001-04-03
Nguyen, Thong (Department: 2872)
Optical: systems and elements
Holographic system or element
Having multiple object beam or diffuse object illumination
C359S015000
Reexamination Certificate
active
06211977
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The invention relates generally to an application technique using holography, and more particularly, to a method of producing a projection holographic screen for displaying a three-dimensional color images.
2. Description of the Related Art
A projection holographic screen is a kind of holographic optical element that serves as a general image display screen where an image, being projected on the screen, can be observed if an eye is disposed within a limited viewing zone. In order to observe a stereoscopic or multiview image, the viewing zones should be narrow enough to deliver to the left and right eyes of the viewer the left and right images correspondingly. For projection of the stereoscopic image the viewing zone centers should be spaced apart from each other by an eye-to-eye distance (about 6.5 cm).
There are two types of the projection holographic screens known in the art, i.e., a reflection type and a transmission type. The holographic screen of the reflection type selectively displays only an image projected through a projector on the screen, while serving as a reflection mirror having a focusing capacity which allows an image of the exit pupil of a projection lens to be focused to form the viewing zone. However, as this type of holographic screen has a high angular and spectral selectivity, only a monochromatic image with a limited viewing zone can be displayed on the screen. Further, three holographic screens of the reflection type formed by red, blue and green lasers should be stacked to display a color image.
The transmission type holographic screen is formed as a hologram of the diffusive light scatterer. When the screen is illuminated by the projected image the light scattered by the screen surface is directed to the predefined domain or viewing zone. The properly produced holographic screen as seen from the viewing zone should have the uniform illumination of all its surface and true color reproduction. These peculiarities depend of the screen recording method.
In the conventional setup for the holographic screen recording as disclosed, for example, in U.S. Pat. No. 4,799,739 and PCT International Publication WO 93/02372, a converging reference wave is made to interfere on a holographic photoplate with an object wave incident upon the photoplate via a diffuser. Being illuminated by the projector, the holographic screen is forming the real image of the diffuser in front of the screen, the viewing zone coincides with this image. The most serious drawback of the described setup is the necessity to use big size optics for the screen recording: at least one lens should be bigger than the screen itself.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method of producing a holographic screen for displaying a stereoscopic or multiview color image without big size optical elements in the screen recording setup, which is optimized by mathematically analyzing the image reproduction process via the produced holographic screen. For the optimized holographic screen recording, an elongate and narrow diffusing slit is used as an object and the diffuser position relative to the photoplate is mathematically set to make the light, being diffracted into viewing zone, to possess all spectral components within a visible range. The diffuser should be in the form of the narrow slit to provide the sharp separation of the viewing zones for the left and right eyes, the slit should be inclined to the photoplate surface to provide appropriate focusing of all spectral component in the viewing zone, and the lengths of the slit should be big enough to provide overlapping in the viewing zone all spectral components of the visible spectrum. If these conditions are satisfied, the viewer can see a 3D color image, projected on the screen.
A method of producing a holographic screen for displaying a stereoscopic or multi-view color image in accordance with the present invention comprises the steps of placing a photoplate on the x-y plane of a three-dimensional space, center of the photoplate being disposed in the origin of a three-dimensional space; forming a point light source from the laser beam for radiating a reference beam at position on the z-axis spaced apart by the distance R
1
from the origin of a three-dimensional space; and placing a elongated narrow slit diffuser illuminated by the same laser as used for forming the reference beam in front of the photoplate; R
2
is a distance between the origin of the three-dimensional space and a point of the diffuser, &agr; is the angle between the positive z-axis and a straight line connecting the origin to the same point of the diffuser. The reference wave is interfering on the photoplate with an object wave from diffuser, wherein the diffuser is placed such that the distance R
2
and angle &agr; satisfy the following equations:
k
2
r
3
+k
1
(
r
1
−r
2
)=−
k
2
r
4
+const (1)
α
=
sin
-
1
[
k
2
k
1
sin
β
]
=
sin
-
1
[
λ
1
λ
2
sin
β
]
(
2
)
R
2
=
R
1
1
+
2
λ
1
R
1
λ
2
R
4
(
3
)
where r
1
is the distance between an arbitrary point (x,y) on the photoplate and the point source of the reference beam; r
2
is the distance between the point (x,y) and the point on the diffuser; R
3
is the distance between the origin and the exit pupil of the projector; r
3
is the distance between the point (x,y) and the exit pupil; r
4
is the distance between the origin and the center of the viewing zone; &bgr; is the angle between the negative z-axis and the straight line connecting the origin to the center of the viewing zone; &lgr;
1
and &lgr;
2
represent wavelengths of the recording and projecting waves, respectively; and k
1
and k
2
are wave numbers of the recording and projecting waves, respectively.
Preferably the diffuser is a narrow and elongate slit-shaped ground glass as derived from equations (2) and (3); the reference wave is diverging from the point distant by R
1
from photoplate.
An additional advantage of the presented screen is the possibility to use all wavelengths of the visible spectrum for the image projection contrary to the reflection type screen, which can use only selected wavelengths.
Furthermore, a reflection mirror can be attached to the holographic screen so that the combination of the holographic screen and the mirror can be used as a reflection-type holographic screen and small angular displacements of the screen, together with the mirror can be used to make the viewing zone follow the viewer's eye movements.
REFERENCES:
patent: 4427265 (1984-01-01), Suzuki et al.
patent: 4799739 (1989-01-01), Newswanger
patent: 5046793 (1991-09-01), Hockley et al.
patent: WO 93/02372 (1993-02-01), None
Hillaire et al., Real-time Holographic Display, Practical Holography, pp. 254-261, Feb. 1991.
Bobrinev Vladimir I.
Son Jung Young
Korea Institute of Science and Technology
Nguyen Thong
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Treas Jared
LandOfFree
Method of producing a holographic projection screen for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of producing a holographic projection screen for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of producing a holographic projection screen for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2503620