Multiplex Hologram Research Articles

Holographic memory with correlator based readout

The investigation of an inverted hybrid digital/optical VanderLugt type correlator based on a holographic memory is reported in this paper. A set of reference templates is stored in a photorefractive crystal (PRC) by angular hologram multiplexing. In the filter plane, a phase-modulating liquid crystal television (LCTV) serves as a phase-only input device. During the recognition process, which is based on the pure phase correlation, the reference templates are correlated sequentially with the input object. This correlator shows high sensitivity to object rotation, sharp correlation peaks, high light efficiency, and is fully shift-invariant in spite of the PRC thickness. The influences of the LCTV on the performance of the system are discussed and experimental results are shown.

Pure phase correlator with photorefractive filter memory

We report on the investigation of a new compact configuration of an inverted VanderLugt-type correlator system. The phase of the Fourier transform of the image to be recognized is displayed on a phase-modulating electrically addressed spatial light modulator. This phase display is compared with the phase of the Fourier transforms of a reference library recorded in a photorefractive LiNbO(3) crystal. Angular hologram multiplexing permits fast data access, and the use of the conjugated replica of the stored templates leads to an elimination of phase distortions introduced by the optical system. With such a configuration, the correlator is fully shift invariant in spite of the photorefractive crystal thickness and has good discrimination with sharp correlation peaks.

Making Holograms from Archive Footage: Converting Temporal Parallax to Stereoscopic Parallax

Useful temporal parallax can be found in films, video and television sequences in great abundance, and with the advent of modern computers it is possible for the first time to manipulate a sequence of film frames to eliminate flat or pseudoscopic features. This paper outlines the distinction between temporal and stereoscopic parallax and shows by example how appropriated subject motion may be used to create 3D images as multiplex holograms.

Random phase-coded multiplexing of hologram volumes using ground glass

We apply an encoding method, random phase-coded multiplexing, to volume hologram multiplexing and demonstrate the recording of 100 holograms in LiNbO3: 0.01% Fe. A theory is developed to interpret the noise generated by this method, and a computer simulation is provided for direct comparison.

Optical pattern recognition system based on a winner-take-all model of a neural network

A three-layer neural network implemented by optical and electronic techniques for pattern recognition is described. The principle, the architecture, and the experimental results of the hardware system for pattern recognition are presented. A multiplex hologram is used as the interconnections between neurons of the input layer and the middle layer. The winner-take-all (WTA) operation of the intermediate layer is performed by an electronic circuit. The interconnection between neurons of the middle layer and the output layer is simply implemented with an optical transparency. By changing the patterns on the transparency, this system can be used for both auto- or heteroassociative memories. In addition to noise and partial hindrance tolerances, it also has illuminance invariance because of the WTA layer of the system.

Image Processing of Automatic Hologram Synthesizer for Medical Use.

An image processing system for providing original images for synthesizing multiplex holograms is developed. This system reconstructs 3D (three dimensional) surface rendering images, two surfaces rendering images and/or band selected Computed Tomography values’ projection images of internal organs and/or bones of a patient from a series of tomograms such as CT (Computed Tomography). Image processing includes interpolation, enhancement, extraction of diseased parts, selection of axis of projection, and compensation of distortions. This research note presents the features of this system, and the results of new type images with conventional images.

Potentialities and limitations of hologram multiplexing by using the phase-encoding technique

The advantages and limitations of data storage in holographic materials by implementing a pure phase-encoding method of the reference beam are studied. We show that if deterministic orthogonal binary phase addresses are used, such a system is theoretically able to store as many images as the usual angular multiplexing method. However, we demonstrate that imperfections of available optical components generate optical noise and limit the storage capacity. We propose an improved recording technique to overcome some of these limitations.

Incremental recording for photorefractive hologram multiplexing: reply to comment

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text Yoshinao Taketomi, Joseph E. Ford, Hironori Sasaki, Jian Ma, Yeshaiahu Fainman, and Sing H. Lee, "Incremental recording for photorefractive hologram multiplexing: reply to comment," Opt. Lett. 17, 962-962 (1992) Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

Incremental recording for photorefractive hologram multiplexing: comment

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text Eric S. Maniloff and Kristina M. Johnson, "Incremental recording for photorefractive hologram multiplexing: comment," Opt. Lett. 17, 961-961 (1992) Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

Holographic Optical Beam Splitters in Dichromated Gelatin

Abstract Holographic beam splitters can split an incoming beam into several partial beams travelling at different angles with arbitrary intensities, thus offering high design flexibility. In this paper the fabrication of beam splitters as multiplex holograms in dichromated gelatin is reported. Shrinking or swelling of the gelatin was avoided by careful process control, reciprocity law failure (as expected from silver halide holograms) was not observed, and, for example, a 1 : 2 beam splitter diffracting 47·4% and 47·0% of the incoming light into two higher orders was realized.

HoloStories: Reminiscences and a Prognostication on Holography

In this interview, Lloyd G. Cross and his wife Cecil Cross discuss the history of his involvement with holography. Matters touched upon include the founding of the San Francisco School of Holography, the development of the Multiplex hologram, and his recent work incorporating computers in the holographic process.

Incremental recording for photorefractive hologram multiplexing

We investigate an incremental recording technique for multiplexed hologram storage in photorefractive crystals, in which each hologram is recorded with multiple short exposures. The performance is theoretically compared with that of scheduled (single exposure per hologram) recording. Our analysis shows that this technique systematically controls the signal uniformity and can also decrease the total recording time. We present an experimental demonstration with LiNbO(3) using a binary orthogonal phase-code addressing technique.

High speed in-line holocinematography for dispersed-phase dynamics

A holocinematography system based on the copper vapor laser is described where a series of spatially multiplex holograms is recorded in rapid succession (up to 10 kHz).

Measurement of the diffraction efficiency of individual images in multiplexed holography

It is important in multiplex holography to measure the relative and absolute diffraction efficiencies of the individual images because of the phenomenon of holographic reciprocity law failure (HRLF). Existing techniques based on diffraction grating images cannot be used for realistic multiplex holograms. This paper describes a simple and rapid technique, based on a charge-coupled device (CCD) camera and digital oscilloscope, that can be applied to all multiplex holograms where the images are spatially separated. Both absolute and relative diffraction efficiencies can be measured, and by using an image area comparison technique some insensitivity to focusing errors is obtained.

Multiplexed permanent and real time holographic recording in photorefractive BSO

We report permanent hologram recording in crystals of photorefractive bismuth silicon oxide using reversible photochromic effects. At a recording wavelength of 488 nm, exposures of several minutes produce areas of faint discoloration in which the permanent hologram is stored. The normal photorefractive behavior is unaffected, however, permitting spatial multiplexing of both real time and permanent holograms. Experimental results and characteristics of this permanent recording in combination with the photorefractive process are presented.

Experimental use of a low cost liquid crystal TV in multiplex holography

We demonstrate experimentally the use of liquid crystal television to make a multiplex hologram.

Spatial filtering in multiplex holography

Multiplex holograms, resulting from incoherent overlay of planar images, can be used to create quasi-three-dimensional images. In the case of highly transparent objects, or many images, the dynamic range of the recording medium is used up rapidly. The authors describe a method whereby the quantity of light used at each exposure is reduced by a Fourier filtering technique that removes much of the 'zero-order' light which is relatively unimportant in recognising the features of the object. Several filtering regimes are discussed and their advantages compared.

Holography of 3D surface reconstructed CT images.

A multiplex hologram (cylindrical holographic stereogram) was successfully made from three-dimensional (3D) surface reconstruction CT images of a child with plagiocephaly. This method appears to be suitable as one of the projectional aids of 3D surface reconstruction CT images that are proving useful in plastic and reconstructive surgery. The principle of the method is described. Also discussed is the possibility of developing a computer-aided hologram synthesizing system that could be used for images obtained with U-arm X-ray equipment (by either cinefilm, or videotape, or digital subtraction angiography) or by CT as well as MR. For practical use, it is necessary for the hologram to be synthesized in a short time. One of the key problems in developing such a machine is the need for an incoherent-to-coherent image converter.

Multiplex holograms of a skull made of CT images

A multiplex hologram is sythesized from a series of CT (computer-aided tomogram) sectional images of the head of a patient taken with a small interval along the body axis. To show a skull shape in three dimensions through a synthesized hologram, images of the skull are first extracted by level slicing. Then, these images are transformed into a series of projected images and each view of different direction around the body axis is successively reconstructed and transformed into a hologram. The 3D shape of the skull is fairly well reconstructed by the synthesized hologram.

Image plane holography for holographic presentation of a three-dimensional data base

Holographic presentation of three-dimensional data from CT, NMR, PET or ultrasonic scan should greatly aid in diagnostic and therapeutic procedures. Originally a multiplex white light hologram was formed from many X-rays of a cadaver's hand. Many methods of computer generating a hologram have been explored. In this paper we examine a method of calculating an Image Plane Hologram by computer and show the white light characteristics of the Image Plane Hologram.