Optical: systems and elements – Optical modulator – Light wave directional modulation
Reexamination Certificate
2001-08-17
2003-09-09
Schwartz, Jordan M. (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave directional modulation
C359S259000, C359S298000
Reexamination Certificate
active
06618190
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optical element and a manufacturing method thereof and, more particularly, relates to an optical element capable of recording a stereoscopic image as a hologram and reconstructing the image, and a manufacturing method thereof.
A holographic technique is conventionally known as a method for recording a stereoscopic image on a medium and reconstructing this image. A hologram produced by this method is used in various fields, such as ornamental art or anti-counterfeit seals. In order to optically produce the hologram, it is common to record the interference fringe between object light reflected from an object and reference light on a photosensitive medium. A laser beam superior in coherence is usually used as a light source for the object light and the reference light. Generally, the motion of electromagnetic radiation, such as light, can be regarded as the propagation of a wave front provided with amplitude and a phase, and it can be said that the hologram is an optical element that functions to reconstruct such a wave front. Therefore, it is necessary to record information for accurately reconstructing the amplitude and phase of the object light at each position in space on the recording medium of the hologram. If interference fringes generated by the object light and the reference light are recorded on the photosensitive medium, information that includes both the phase and the amplitude of the object light can be recorded, and, by projecting illumination reconstructing light equivalent to the reference light onto the medium, a part of the illumination reconstructing light can be observed as light provided with a wave front equivalent to the object light.
If the hologram is produced by an optical method using a laser beam or the like in this way, the phase and amplitude of the object light can be recorded only as interference fringes resulting from interference between the object light and the reference light. The reason is that the photosensitive medium has a property of being photosensitized in accordance with light intensity. On the other hand, a technique of producing a hologram by computations with use of a computer has recently been put to practical use. This technique is called a “CGH” (Computer-Generated Hologram) method, in which the wave front of object light is calculated by use of a computer, and its phase and its amplitude are recorded on a physical medium according to a certain method so as to produce a hologram. The employment of this computational holography, of course, enables the recording of an image as interference fringes between object light and reference light, and, in addition, enables the recording of information for the phase and amplitude of the object light directly onto a recording surface without using the reference light. For example, a recording method has been proposed in which an amplitude is represented by the size of an opening formed in a recording medium whereas a phase is represented by the position of the opening or in which a medium is made up of two recording layers on one of which an amplitude is recorded and on the other one of which a phase is recorded.
The method for recording an image as interference fringes that has been widely used as an optical hologram producing method is at an advantage in that productivity is high because, in general, a reconstructed image with high resolution can be obtained and because an optical method is used, but it is at a disadvantage in that an image darkens because diffraction efficiency by interference fringes is poor when reconstructed. By contrast, the method for recording the phase and amplitude of object light directly onto a medium that has been proposed as one of the computer-generated hologram methods is at an advantage in that high diffraction efficiency can be obtained, but it is at a disadvantage in that, practically, productivity decreases because the recording of the phase and the amplitude onto the medium is technically difficult.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an optical element that can obtain high diffraction efficiency when reconstructed and that is excellent in productivity.
(1) The first feature of the present invention resides in an optical element consisting of a set of a plurality of three-dimensional cells, wherein:
a specific amplitude and a specific phase are defined in each individual cell,
and the individual cell has a specific optical property so that, when incident light is provided to the cell, emission light is obtained by changing an amplitude and a phase of the incident light in accordance with the specific amplitude and the specific phase defined in the cell.
(2) The second feature of the present invention resides in the optical element according to the first feature, wherein each cell has an amplitude-modulating part provided with transmittance corresponding to a specific amplitude.
(3) The third feature of the present invention resides in the optical element according to the first feature, wherein each cell has an amplitude-modulating part provided with reflectivity corresponding to a specific amplitude.
(4) The fourth feature of the present invention resides in the optical element according to the first feature, wherein each cell has an amplitude-modulating part provided with an effective area corresponding to a specific amplitude.
(5) The fifth feature of the present invention resides in the optical element according to the first to the fourth features, wherein each cell has a phase-modulating part provided with a refractive index corresponding to a specific phase.
(6) The sixth feature of the present invention resides in the optical element according to the first to the fourth features, wherein each cell has a phase-modulating part provided with an optical path length corresponding to a specific phase.
(7) The seventh feature of the present invention resides in the optical element according to the first feature, wherein each cell has a concave part formed by hollowing a part provided with an area corresponding to a specific amplitude by a depth corresponding to a specific phase.
(8) The eighth feature of the present invention resides in the optical element according to the first feature, wherein each cell has a convex part formed by protruding a part provided with an area corresponding to a specific amplitude by a height corresponding to a specific phase.
(9) The ninth feature of the present invention resides in the optical element according to the seventh or eighth feature, wherein a surface where the concave part or the convex part of each cell is formed serves as a reflecting surface, and incident light provided to the cell is reflected by the reflecting surface and thereby turns into emission light.
(10) The tenth feature of the present invention resides in the optical element according to the seventh or eighth feature, wherein each cell includes a main body layer having a concave part or a convex part and a protective layer with which a surface where the concave part or the convex part of the main body layer is formed is covered, and the main body layer and the protective layer are made of materials different from each other.
(11) The eleventh feature of the present invention resides in the optical element according to the tenth feature, wherein the main body layer and the protective layer are made of transparent materials different in a refractive index from each other, and incident light provided to the cell passes through the main body layer and the protective layer and thereby turns into emission light.
(12) The twelfth feature of the present invention resides in the optical element according to the tenth feature, wherein a boundary between the main body layer and the protective layer forms a reflecting surface, and incident light provided to the cell is reflected by the reflecting surface and thereby turns into emission light.
(13) The thirteenth feature of the present invention resides in the optical element according to the first
Hamano Tomohisa
Kitamura Mitsuru
Dai Nippon Printing Co. Ltd.
Ladas & Parry
Schwartz Jordan M.
Stultz Jessica
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