Optical: systems and elements – Holographic system or element – Using modulated or plural reference beams
Reexamination Certificate
1998-03-27
2001-06-12
Spyrou, Cassandra (Department: 2872)
Optical: systems and elements
Holographic system or element
Using modulated or plural reference beams
C359S001000, C359S009000, C356S340000, C356S340000, C356S329000, C365S125000
Reexamination Certificate
active
06246495
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a phase-shift digital holographic apparatus and a phase-shift digital hologram producing method. More particularly, the present invention relates to a phase-shift digital holographic apparatus in which an object wave and a reference wave fall simultaneously on an image forming surface of a photoelectric imaging device, such as a CCD image sensor, to produce holographic image data, and a phase-shift digital hologram producing method.
2. Description of the Related Art
Digital holography, in contrast to compute holography, records an interference pattern produced by interference between an object wave and a reference wave by a photoelectric imaging device, and the interference pattern is processed by a computer to reproduce an image. A known digital holographic apparatus projects an object beam and a reference beam on an image forming surface so that a very large angle &agr; is formed between the object beam and the reference beam as shown in
FIG. 2
to produce a hologram by the so-called off-axis system. A reproduced image includes a zero-order and ± first-order images in a lateral arrangement. Therefore, ghost images appear near the reproduced image and only a true reproduced image cannot be obtained. The object beam and the reference beam must be projected on the image forming surface so that a sufficiently large angle is formed between the object beam and the reference beam, and the degree of off-axis is large. An object which produces the object beam must be a small one and hence the conventional digital holographic apparatus is capable of forming holograms of only objects of limited sizes. Furthermore, the number of effective image pickup elements available for producing a hologram among those arranged in the image forming surface is reduced, and all the image pickup elements in the image forming surface cannot be effectively use for producing a hologram.
The conventional off-axis system projects the object beam and the reference beam on the image forming surface so that a large angle &agr; is formed between the object beam and the reference beam. Therefore, intervals between fringes forming a hologram is small, and the resolution of the image forming surface must be smaller than the intervals between the fringes forming the hologram. Consequently, it has been difficult to reproduce an image satisfactorily by the image pickup device having a resolution lower than that of photographic films.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to solve the foregoing problems in the prior art and to provide a phase-shift digital holographic apparatus and a phase-shift digital hologram producing method capable of forming a reproduced image without forming any ghost image near the reproduced image and without requiring off-axis adjustment.
According to a first aspect of the present invention, a phase-shift digital holographic apparatus comprises, a phase shifting means for shifting the phase of a reference wave, a holographic image pickup means for producing holographic image data, having an image forming surface on which an object wave and the reference wave fall simultaneously, an object wave calculating means for processing a plurality of holographic image data produced by the object wave and a plurality of reference waves of different phases determined by shifting the phase of the reference wave by the phase shifting means to calculate phase data on the phase of the object wave and amplitude data on the amplitude of the object wave, and a reproduced image calculating means for constituting object wave data of the phase data on the phase of the object wave and the amplitude data on the amplitude of the object wave calculated by the object wave calculating means, and subjecting the object wave data to a predetermined transformation process to calculate a reproduced image.
The object wave and the reference wave fall on the image forming surface at substantially the same incidence angle.
The object wave and the reference wave fall on the image forming surface so that a small angle, that may cause a ghost image to appear near the reproduced image if the reproduced image is formed by transforming the holographic image data without constituting the object wave data, is formed between the object wave and the reference wave.
The phase shifting means may be provided with a piezoelectric device.
The number of the plurality of phases may be three, and the number of the plurality of holographic image data may be three.
The phase shifting means may shift the reference wave so that steps of the phases of the reference waves having different phases are 90°.
The predetermined transformation process may be a Fresnel transformation process.
According to a second aspect of the present invention, a phase-shift digital hologram producing method comprises the steps of shifting the phase of a reference wave by a phase shifting means to provide a plurality of reference waves of different phases, producing a plurality of holographic image data by making the object wave and each of the plurality of reference waves fall simultaneously on an image forming surface of a holographic image pickup means, calculating phase data on the phase of the object wave and amplitude data on the amplitude of the object wave by using the plurality of holographic image data by an object wave calculating means, constituting object wave data of the phase data on the phase of the object wave and the amplitude data on the amplitude of the object wave calculated by the object wave calculating means, and subjecting the object wave data to a predetermined transformation process to calculate a reproduced image by a reproduced image calculating means.
The amplitude data on the amplitude of the object wave may be calculated on the basis of holographic image data obtained by blocking the reference wave and making only the object wave fall on the image forming surface of the holographic image pickup means.
The phase of the reference wave may be shifted in a step of, for example, &pgr;/2 to produce, for example, three reference waves of different phases, each of the reference waves of different phases and the object wave are made to fall on the image forming surface to produce, for example, three holographic image data. Each of the plurality of holographic image data includes a mixture of data on the object wave and data on the reference wave. Simultaneous equations are solved by using the plurality of holographic image data to calculate the phase data on the phase of the object wave and the amplitude data on the amplitude of the object wave. The object wave data containing all the information necessary for forming a reproduced image is produced from the phase data on the phase of the object wave and the amplitude data on the amplitude of the object wave. The object wave data thus produced is subjected to the predetermined transformation process, such as a Fresnel transformation process to calculate the reproduced image.
REFERENCES:
patent: 5656932 (1997-08-01), Kitayoshi
patent: 5777742 (1998-07-01), Marron
Curtis Craig
Jacobson Price Holman & Stern PLLC
Spyrou Cassandra
The Institute of Physical and Chemical Research
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