Optical: systems and elements – Holographic system or element – For reconstructing image
Reexamination Certificate
1999-12-21
2001-08-28
Schuberg, Darren (Department: 2872)
Optical: systems and elements
Holographic system or element
For reconstructing image
C359S004000, C359S007000, C359S012000, C359S035000, C359S022000
Reexamination Certificate
active
06281994
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and an apparatus for three-dimensional holographic display suitable for video image display, using optical interference fringes recorded inside a photorefractive crystal which can display three-dimensional video images by irradiating a reference light thereon.
2. Description of the Background Art
The known methods for three-dimensional display of an object include a method based on stereography and a method based on holography. The former method based on stereography is a method in which images to be observed by left and right eyes are separately projected onto eyes, and only an observer can see a display target object three-dimensionally. The latter method based on holography is a method that faithfully reproduces wavefronts of lights reflected from an object.
The major factors that enable a human being to sense an object three-dimensionally include a binocular parallax and a focus adjustment. The method based on stereography is a method that reproduces only the binocular parallax, where the focus of the eyes is always set on a screen on which images are projected, so that there has been a problem that the eyestrain is inevitably caused by an observation over an extended period of time because the focal position is fixed despite of the object projection effect due to the binocular parallax.
On the other hand, the method based on holography is the most ideal method for three-dimensional display, in which both the binocular parallax and the focus adjustment can be realized exactly as in the real observation by the eyes. However, in order to record holograms, it is necessary to reproduce the light diffraction phenomenon, so that there is a need to record as many as several thousands of interference fringes per millimeter and reproduce a display from them. For this reason, the presently available holograms are all three-dimensional display of still pictures.
As a method for displaying moving objects by holography, there has been a proposition of a method using a liquid crystal panel, but the resolution (spatial frequency, pixel pitch) that can be displayed by the liquid crystal panel is insufficient for the holographic display. Namely, because of the low resolution (wide pixel pitch) and the limitation of the gray scale values that can be displayed, this method is still insufficient to display complicated fringes such as those of the actual holograms.
For this reason, in the holographic display using such electronic devices, it is only possible to display a few, small objects (point light sources). Moreover, because of the coarse resolution, there has been a problem that a separation of a light that is transmitted directly through the liquid crystal panel and the diffracted light is difficult, and the observation field is narrow.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method and an apparatus for three-dimensional holographic display capable of recording three-dimensional images efficiently into a photorefractive crystal that is to be used as a screen for projecting images.
It is another object of the present invention to provide a method and an apparatus for three-dimensional holographic display capable of reproducing a three-dimensional image in a wide view field by using an electronic device having a limited resolution.
It is another object of the present invention to provide a method and an apparatus for three-dimensional holographic display capable of displaying three-dimensional video images with less flickering, and displaying a plurality of frames of three-dimensional still images by switching frames at high speed.
It is another object of the present invention to provide a method and an apparatus for three-dimensional holographic display capable of displaying a three-dimensional image in a wide view field by using a compact configuration.
It is another object of the present invention to provide a method and an apparatus for three-dimensional holographic display using a spatial light modulator as an object light source for the hologram, capable of realizing finer three-dimensional image display.
It is another object of the present invention to provide a method and an apparatus for three-dimensional holographic display using a spatial light modulator as an object light source for the hologram, capable of improving the quality of the three-dimensional image display.
It is another object of the present invention to provide a method and an apparatus for three-dimensional holographic display using a spatial light modulator as an object light source for the hologram, capable of enlarging the spatial view field.
According to one aspect of the present invention there is provided a method of holographic display of a three-dimensional image, comprising the steps of: displaying at least one hologram of a display target object on a display device, and irradiating a non-scattered light onto the display device to produce a scattered light; irradiating the scattered light from the display device as an object light of the display target object and the non-scattered light as a reference light simultaneously at different incident angles onto a photorefractive medium having a photorefractive effect, and recording interference fringes generated by the object light and the reference light in the photorefractive medium; and displaying the three-dimensional image by irradiating only the non-scattered light onto the photorefractive medium so as to reproduce a holographic image corresponding to the interference fringes recorded in the photorefractive medium.
According to another aspect of the present invention there is provided a three-dimensional holographic display apparatus, comprising: a display device for displaying at least one hologram of a display target object; a photorefractive medium having a photorefractive effect for recording interference fringes generated by an object light and a reference light irradiated thereon; and an optical system for irradiating a non-scattered light onto the display device to produce a scattered light and then irradiating the scattered light from the display device as the object light of the display target object and the non-scattered light as the reference light simultaneously at different incident angles onto the photorefractive medium at a time of recording the interference fringes in the photorefractive medium, and irradiating only the non-scattered light onto the photorefractive medium at a time of reproducing a holographic image corresponding to the interference fringes recorded in the photorefractive medium as a three-dimensional image.
According to another aspect of the present invention there is provided a method of holographic recording of a three-dimensional image, comprising the steps of: irradiating first and second lights simultaneously at different incident angles onto a photorefractive medium having a photorefractive effect, the first light being irradiated directly onto the photorefractive medium and the second light being irradiated onto the photorefractive medium through a lens with an adjustable lens position which is adjusted such that a focal point position of the lens coincides with a point on a surface of the three-dimensional image to be displayed; recording interference fringes generated by the first light and the second light in the photorefractive medium; and repeating the irradiating step and the recording step while sequentially adjusting the adjustable lens position of the lens so as to set the focal point position of the lens on different points on the surface of the three-dimensional image to be displayed.
According to another aspect of the present invention there is provided a method of holographic recording of a three-dimensional image, comprising the steps of: displaying interference fringes on an electronic display device, the interference fringes being calculated for a case of irradiating first and second lights simultaneously at different incident angles onto a photorefractive
Akimoto Takaaki
Higuchi Kazuhito
Horikoshi Tsutomu
Imai Tadayuki
Kojima Haruhiko
Kilpatrick & Stockton LLP
Nippon Telegraph and Telephone Corporation
Schuberg Darren
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