Holographic Media Research Articles

Polarization Multiplexing, Angle Multiplexing and Circumrotation Multiplexing Holographic Recording Experiments with 3-Indoly-Benzylfulgimide/PMMA Film

Fulgide is well-known as a thermally irreversible organic photochromic compound. The fulgide films can be applied as recording materials in ordinary holography and polarization holography, which were respectively based on the photochromic and photoinduced anisotropy properties. In this report, different kinds of multiplexing holographic storage, like angle multiplexing, circumrotation multiplexing and polarization multiplexing are realized in a 3-indoly-benzylfulgimide/ PMMA film for the first time, where 5 images, 18 images and 2 images are stored at the same position of the film, and diffracted without crosstalk with each other. It is proved that 3-indoly-benzylfulgimide film has spatial resolution of 6300lines/mm, sensitivity of 2.89 × 10-3cm2/mJ at 632.8nm on the polarization direction of the exciting beam, fatigue resistance of 70 times, thermal stability of 14 months and has advantages like low cost, easy to used, rewritable, long life time at room temperature for both states, and high signal to noise ratio. Overall, 3-indoly-benzylfulgimide is a better rewritable holographic storage medium, but the fatigue resistance and thermal stability should be improved.

Efficient Synthesis, Photochromism and Holographic Optical Recording of a Photochromic Diarylethene with a Isoxazole Unit

A new unsymmetrical photochromic diarylethene 1-(2,5-dimethylisoxazolyl)-2-[(2-n-butyl-5-formylthiophenyl)] perfluoroncyclopentene (1a), was synthesized and its optoelectronic properties, such as photochromism in solution as well as in poly-methylmethacrylate (PMMA) amorphous films, and the fluorescence spectra of diarylethene 1a was investigated. The photochromic reaction kinetics indicated that the cyclization process of 1a belongs to the zeroth order reaction and the cycloreversion process belongs to the first order reaction.Using diarylethene 1/PMMA film as recording medium and a linearly polarized 633 nm laser diode for recording and readout, polarization multiplexed image recording can be carried out in this film, which illustrated that the diarylethene can be potentially used as holographic optical recording medium.

Half-data-page insertion method for increasing recording density in angular multiplexing holographic memory

We have developed a method to use a half-size data page between two full-size data pages to increase the recording density in angular multiplexing holographic memory up to 1.5× as much as the conventional angular multiplexing sequence. In our recording sequence, the full- and half-size data pages are alternately multiplexed. This is because each plane wave from various points in a data page has different angular selectivity. A half-size data page has higher angular selectivity than a full-size data page. The required angular intervals were estimated by numerical simulation taking holographic medium tilt into account. Also, an angular multiplexing experiment using the half-data-page insertion method resulted in a low bit error rate of the order of 10(-3), which is sufficient for practical use.

Angle-multiplexed holographic data storage with minimum cross talk noise

The cross talk noise-to-signal ratio (NSR) of an angle-multiplexed holographic data storage system is studied, and we propose a method to determine the optimized multiplexing spacing with which the cross talk noise can be less than the conventional method. In our method, the optimization location at the image plane can be chosen arbitrarily, so the multiplexing of asymmetrical image patterns can be optimized. In particular, we investigate the 90° scheme and the transmission scheme angle multiplexing. For the 90° scheme, a holographic medium with a higher refractive index is recommended for cross talk-limited multiplexing. For the transmission scheme, a holographic medium with a lower refractive index is recommended for angular range-limited multiplexing. In addition, for the transmission scheme, a larger angle between the object arm and the reference arm results in less cross talk noise, whereas the highest storage density is achieved at a 45° angle.

Factors determining optical absorption of variously doped single crystals of Bi12SiO20

Bi12SiO20 are widely used in optical devices, spatial-time light modulators and as holographic media depending on their properties in a wide spectral range. This work deals with the optical absorption coefficient of pure and doped Bi12SiO20 (BSO) crystals measured in the energy region 1.5 – 3.2 eV and generalise our already published and new experimental data on crystals doped with Al, P, Cr, Mn, Fe, Co, Ni, Cu, Se, Ru. It is shown that such doping affects differently the optical absorption in both the near-fundamental-edge shoulder (3.2 – 2.2 eV) and on impurity levels in the band gap (2.2 – 1.5 eV). The main factors determining the absorption are concentration and segregation coefficient, electro-negativity of the doping ion and its difference from that of oxygen (DEN), the oxidation states, possible coordination and corresponding ionic radius. The role of some of these factors to the spectral dependence of the optical absorption of BSO is discussed from the view point of a suitable doping of BSO to obtain and modify the optical transparency.

Holographic Read-Only Memory Fabricated by Deposition of Reflector after Writing Process with Aromatic Photopolymer Recording Layer

The deposition of reflector after writing (DRAW) process has been proposed for the fabrication of reflective-type holographic read-only memories. In the DRAW process, a reflector is deposited on a recording medium after signal writing, resulting in the reduction of noise holograms written by reflected beams from a reflector in the write process. Significant improvements are experimentally confirmed in read and write (R/W) performances in DRAW-processed holographic media. The combination of the DRAW process and an aromatic photopolymer recording material realizes low noise, high signal-to-noise ratio, and low symbol error rate characteristics at large multiplexing numbers up to 1020. In conventional reflective-type holographic media, ghost noise is superimposed on the readout signal, causing deterioration in R/W characteristics. The wave vector analyses clarify the mechanism by which the noise holograms are written and ghost noise is superimposed on the signal beam in the conventional media.

The future of PACS in healthcare enterprises

Picture Archiving and Communication System (PACS), which was originally designed as a tool for facilitating radiologists in interpreting images more efficiently, is evolving into a hospital-integrated system storing diagnostic imaging information that often reaches far beyond Radiology. The continuous evolution of PACS technology has led to a gradual broadening of its applications, ranging from teleradiology to CAD (Computer-Assisted Diagnosis) and multidimensional imaging, and is moving into the direction of providing access to image data outside the Radiology department, so to reach all the branches of the healthcare enterprise. New perspectives have been created thanks to new technologies (such as holographic media and GRID computing) that are likely due to expand PACS-based applications even further, improving patient care and enhancing overall productivity.

Positioning and localization of two-wavelength interferograms for wavefront reconstruction with volume holographic media

This work studies both theoretically and experimentally the formation of the contour interference patterns generated by a two-wavelength real-time holographic interferometer. The resulting contour interference fringes are due to the intersection of the measured surface with parallel, equally spaced planes of constant elevation. The theoretical analysis describes how the spatial frequency of the elevation planes, their angular position, and the localization of the fringes depend on parameters of the optical setup. A theoretical model for fringe localization is developed and confirmed by the experiments, showing a strong dependence of the interferogram position on the slope of the studied surface. Due to the thick Bi(12)TiO(20) crystal employed as the storage medium the Bragg selectivity of the holographic readout is also considered.

Photosemiconducting properties of holographic media based on ferrocenyl-containing cooligomers of glycidyl carbazole with these oligomers sensitized by organic dye

Spectral, photosemiconducting, and information properties of holographic recording media with films of glycidyl carbazole-butyl glycidyl ether cooligomer, methylated ferrocenyl oligoglycidyl carbazole, and o-carboxybenzoyl ferrocene glycidyl ether cooligomer with squaryl dye additives were studied. An increase in the holographic sensitivity and photoconductivity of recording media with ferrocenyl-containing cooligomer films in comparison with media based on a glycidyl carbazole cooligomer was found. This phenomenon was attributed to the effect of iron ions on the singlet-triplet conversion rate in photogenerated charge pairs, which was validated by analyzing the dependence of the photocurrent on the external magnetic field. A phenomenological model of the effect of ferrocene on the photoconductivity of studied films was proposed.

2-9 ホログラム記録媒体における収縮の温度依存性とその光学的補償(第2部門 コンシューマエレクトロニクス&マルチメディアストレージ)

2-9 ホログラム記録媒体における収縮の温度依存性とその光学的補償(第2部門 コンシューマエレクトロニクス&マルチメディアストレージ)

Holographic Recordings Using Bistable SmC* Structures

Numerous methods of re-writable optical recordings using nematic mixtures for holographic media have been presented. A new approach to this problem is possible by using surface stabilized ferroelectric liquid crystal structures (SSFLC). This is very promising from the theoretical point of view because the surface stabilized the structure of ferroelectric smectic SmC* material inherently consists of a memory effect while driving by external electric field. Moreover, due to the layered structure of the surface stabilized ferroelectric liquid crystal there is a possibility of obtaining high resolution of the written gratings. In the paper, some theoretical basis regarding possibility of optical addressing of SSFCL cells are discussed. Methods of preparation of the optically addressed SSFLC cells in room temperature bistable SmC* structure are presented. Experiments with these cells in simple holographic two-beam set-up (DWTM) are described.

Investigation of a Reflective Counter-Propagating Holographic Setup

A reflective counter-propagating holographic setup for optical data storage is presented. The system makes efficient use of the laser light by using the reference beam to generate the signal beam. After passing through the holographic medium, the reference beam is sent onto a spatial light modulator that directs the modified reference beam back into the holographic medium, where it interferes with the original reference beam. Thus 100% of the available laser power can be used for the reference beam. Furthermore, a special random phase mask and a corresponding data page format are introduced. The phase mask has an improved alignment tolerance of ±0.5 pixels in contrast to a conventional binary phase mask that has a tolerance of only ±0.1 pixels. Moreover, the mask still improves the shift-selectivity and eliminates the strong intensity peak in the Fourier plane. We investigate the shift selectivity and compare experimental and simulated results that were obtained with a two-dimensional fast-Fourier-transform (2D-FFT) volume integral method.

Material Consumption and Crosstalk Characteristics of Different Holographic Storage Concepts

Holographic data storage is considered to be one of the most promising technologies for high-capacity data storage. Several holographic concepts have been suggested and investigated in detail by many companies. The concepts differ in the method of superposing object and reference beams inside the holographic medium. At present, the most relevant concepts are the plane wave concept, the collinear concept, and a concept with counterpropagating beams. We compare all three concepts, with regard to their beam overlap, efficiency of material consumption, diffraction efficiency, and crosstalk characteristics. The investigation is performed by numerical simulations, which offer well-defined conditions in all setups and are independent of experimental uncertainties such as the nonlinear behavior of medium sensitivity and the effects of light scattering or reflection.

Third-harmonic generation and its applications in optical image processing

We review potential applications of third-harmonic generation (THG) in polymer composites to implement optical image processing applications at the eye-safe and technologically relevant telecommunication bands. We discuss two examples, time-gated imaging through scattering media, and image recognition using Fourier-based techniques, where THG in a polymer composite offers significant advantages over typical holographic media, in that it produces signals that are non-degenerate in optical frequency and space, and allows the development of applications that are compatible with low-cost Si-based electronic components.

Dynamic holographic joint fourier transform correlator based on a CdF2:Ga crystal

A joint Fourier transform correlator based on a bulk holographic medium—a CdF2:Ga crystal serving a dynamic matched spatial-frequency filter—is implemented. Specific features of the correlator design are discussed. Correlatorf’s possibilities for selective recognition of objects of different type are demonstrated. Experimental data, results of mathematical modeling, and their analysis are reported. Suggestions for modifying the correlator scheme in order to improve its characteristics (operating speed, stability with respect to orientational and scale changes in objects, signal-to-noise ratio, correlation peak sharpness) are formulated.

Erasure mechanisms of polarization holographic gratings in spirooxazine‐doped polymer films

AbstractDynamic holographic recording under linear polarized writing beams at 632.8 nm was performed on two different new spirooxazine doped PMMA matrices assisted by UV light. Thermal rate constants of the two holographic storage medium were determined. It was found that diffraction efficiency and erasure dynamics of the holographic gratings in the two polymer films were dependent on the thermal stability and aggregation of spirooxazine molecules in PMMA matrices. During erasure of the holographic gratings, only in the polymer film with a lower thermal rate constant, a nearly instantaneous increase of diffraction efficiency was observed, resulting from the formation of a transient orientation grating. A theoretical description of the transient orientation grating, competing with isomerization gratings, agrees well with experimental results. The interaction between the chromophores and matrices was also discussed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

On the possibility of using Fourier holography in the problem of modeling creative thought: Requirements on the transfer characteristics of reversible holographic media

This paper shows that Feigenbaum's scenario of transition to chaos can be implemented in a Fourier-holography layout with wave-front reversal in the correlation plane. Based on this, it is proposed to use the Fourier-holography layout with wave-front reversal as an approach to the task of implementing creative thought. The requirements on the transfer functions of reversible recording media are determined for implementing self-adjustment of the system to the type of dynamics needed to solve the encountered problem. The results of numerical modeling of the dynamics of the system are presented.

Light-induced lens analysis in photorefractive crystals employing phase-shifting real-time holographic interferometry

The purpose of this work is to study the potentialities of phase-shifting real-time holographic interferometry for the analysis of light-induced lens in photorefractive and nonlinear optical materials. We show that this technique can be used for quantitative evaluation of the phase distribution of a wavefront changed by a light-induced lens and, consequently, the refractive index changes in these materials. The basic principle of this technique combines real-time holographic interferometry with phase-shifting technique for interferogram analysis. This method is demonstrated with in situ visualization, monitoring and analysis in real-time and uses a Bi 12SiO 20 crystal as the holographic medium and a Bi 12TiO 20 as the test sample.

Light Diffraction in Anisotropic Reflection Gratings

The Bragg diffraction in thick anisotropic holographic media is studied. Solutions for the wave amplitudes, diffraction efficiencies, and angular mismatch sensitivities are given in reflection geometries for the case of dielectric modulation.

Technique for characterization of dimensional changes in slanted holographic gratings by monitoring the angular selectivity profile

A method has been developed for retrieving the complete angular selectivity profile of transmission holographic gratings in one step. The method is applied to study in real time the shrinkage and changes in the effective optical thickness of a slanted holographic grating recorded in an acrylamide-based photopolymer. It can form the basis of a holographic sensor of analytes that cause a thickness change in the holographic medium. It can also be useful for the study and optimization of holographic recording materials and for quality control during production of holographic optical elements.