Holographic Data Storage Applications Research Articles

Reduction of spatio-temporal phase fluctuation in a spatial light modulator using linear phase superimposition

Spatio-temporal phase modulation with a phase-only liquid-crystal spatial light modulator (SLM) plays an important role in the optics and photonics community. SLMs are generally affected by either or both spatial and temporal phase fluctuations, depending on driver electronics, thereby reducing the quality of a generated beam. In this study, to reduce phase fluctuations, we present an optical-based linear phase superimposition method with spatial bandpass filtering. We experimentally investigate the method’s effectiveness, particularly for holographic data storage applications. Experimental results show that the presented method is useful in robustly generating phase distributions against fluctuations, regardless of the SLM driving scheme.

A Review of Hologram Storage and Self-Written Waveguides Formation in Photopolymer Media.

Photopolymer materials have received a great deal of attention because they are inexpensive, self-processing materials that are extremely versatile, offering many advantages over more traditional materials. To achieve their full potential, there is significant value in understanding the photophysical and photochemical processes taking place within such materials. This paper includes a brief review of recent attempts to more fully understand what is needed to optimize the performance of photopolymer materials for Holographic Data Storage (HDS) and Self-Written Waveguides (SWWs) applications. Specifically, we aim to discuss the evolution of our understanding of what takes place inside these materials and what happens during photopolymerization process, with the objective of further improving the performance of such materials. Starting with a review of the photosensitizer absorptivity, a dye model combining the associated electromagnetics and photochemical kinetics is presented. Thereafter, the optimization of photopolymer materials for HDS and SWWs applications is reviewed. It is clear that many promising materials are being developed for the next generation optical applications media.

Multiplexing recording in nickel-ion-doped photopolymer material for holographic data storage applications.

In the present study, a series of holographic gratings were recorded in a single location of nickel-ion-doped photopolymer film using different methods of multiplexing. The uniformity of their diffraction efficiency was shown to improve by using an exposure time scheduling method for holographic recording. Thirty-five gratings were recorded in the 130 μm thick photopolymer material with M#=6.18 and an average diffraction efficiency of 3.24% using peristrophic multiplexing. In the next step, a combination of peristrophic and angular multiplexing was used for storing 50 gratings in the material with a dynamic range of 7 and a mean diffraction efficiency of 2.15%.

High efficiency panchromatic photopolymer recording material for holographic data storage systems

Studies carried out to gauge the potential of a metal-ion doped panchromatic photopolymer recording material for application in real-time holographic data storage is presented. The photopolymer films are spin coated on glass plates to ensure better surface uniformity. Volume holographic transmission gratings with peak diffraction efficiency of 80% could be stored in the photopolymer films of 100μm thickness. An efficiency of 70% is achievable even for gratings recorded with exposure energy as low as 10mJ/cm2. A checkerboard pattern data page recorded in the photopolymer film using a defocused 4-f recording geometry could be reconstructed with good image quality. The experimental results illustrate the competency of the developed photopolymer for holographic data storage applications.

Holographic Data Storage and Display by PANDA Ring Resonator Technique <sup></sup>

In this paper, a novel method of holographic data storage and display was demonstrated. The use of nonlinear optical device called PANDA ring resonator is realized by Whispering Gallery Mode (WGM) and manipulated by Phase Conjugate Mirror (PCM) techniques. The result shown that the proposed model was performed a 3x3 optical waveguide holographic matrix which manipulated with a various wavelength and can be well applied to dynamic holographic optical data storage, holographic display, and other applications by compact nonlinear optical device.

Spatial cross modulation method using a random diffuser and phase-only spatial light modulator for constructing arbitrary complex fields

We propose a spatial cross modulation method using a random diffuser and a phase-only spatial light modulator (SLM), by which arbitrary complex-amplitude fields can be generated with higher spatial resolution and diffraction efficiency than off-axis and double-phase computer-generated holograms. Our method encodes the original complex object as a phase-only diffusion image by scattering the complex object using a random diffuser. In addition, all incoming light to the SLM is consumed for a single diffraction order, making a diffraction efficiency of more than 90% possible. This method can be applied for holographic data storage, three-dimensional displays, and other such applications.

A Review of the Optimisation of Photopolymer Materials for Holographic Data Storage

Photopolymers are very interesting as optically sensitive recording media due to the fact that they are inexpensive, self-processing materials with the ability to capture low-loss, high-fidelity volume recordings of 3D illuminating patterns. We have prepared this paper in part in order to enable the recognition of outstanding issues, which limit in particular the data storage capacity in holographic data storage media. In an attempt to further develop the data storage capacity and quality of the information stored, that is, the material sensitivity and resolution, a deeper understanding of such materials in order to improve them has become ever more crucial. In this paper a brief review of the optimisation of photopolymer materials for holographic data storage (HDS) applications is described. The key contributions of each work examined and many of the suggestions made for the improvement of the different photopolymer material discussed are presented.

Biophotopol: A Sustainable Photopolymer for Holographic Data Storage Applications.

Photopolymers have proved to be useful for different holographic applications such as holographic data storage or holographic optical elements. However, most photopolymers have certain undesirable features, such as the toxicity of some of their components or their low environmental compatibility. For this reason, the Holography and Optical Processing Group at the University of Alicante developed a new dry photopolymer with low toxicity and high thickness called biophotopol, which is very adequate for holographic data storage applications. In this paper we describe our recent studies on biophotopol and the main characteristics of this material.

Photonic applications with photoanisotropic nanomaterials

Linearly polarized light beam can rotate the trans-azobenzene molecules into cis-form resulting in inducing photoanisotropy. This property is used to control the transmission of nanosecond and picosecond laser pulses and also for holographic data storage applications. Studies were performed using four commercially available azobenzene dyes in different solvents and also in custom prepared nanoporous azobenzene Dendron films. Nanopores are created in a silica matrix and azobenzene molecules are attached to the inner walls of these pores to mimic solution like environment for the azobenzene molecules such that they can undergo photoinduced trans-cis-trans isomerization process at a faster rate.

Crystalline perfection, EPR, prism coupler and UV-VIS-NIR studies on Cz-grown Fe-doped LiNbO3: A photorefractive nonlinear optical crystal

The Fe-doped (0.05 mol%) lithium niobate (LiNbO3) bulk single crystal was gown by the Czochralski (Cz) method using a co-axial two zone low thermal gradient furnace. The crystalline perfection of the grown crystal was evaluated by high resolution X-ray diffractometry which showed that it does not contain any structural grain boundaries, and the dopants predominantly occupied vacancy sites of Li+ in the lattice. Electron paramagnetic resonance studies revealed the incorporation of Fe3+ ions at Li sites. The Z-cut optically polished 450 μm thick wafer was used for birefringence measurements on a prism coupler spectrometer with 632.8 nm wavelength and it was found that the difference in refractive index (Δn) for ordinary and extraordinary rays is 0.0833. The optical transmission/absorption spectra were studied by UV-VIS-NIR spectroscopy and this showed that the grown crystal has good optical sensitivity for 482 nm wavelength radiation. The present studies reveal that the crystal grown with a two zone low thermal gradient furnace has very good device properties which are needed for holographic data storage applications.

Silver-doped photopolymer media for holographic recording

Incorporation of silver ions into a dye-sensitized poly(vinyl alcohol)/acrylamide photopolymer is observed to give better performance compared to other metal-ion-doped photopolymer holographic recording media. Plane-wave transmission gratings were recorded in the photopolymer films using a He-Ne laser, and various holographic parameters were optimized so as to explore maximum potential of the material for various holographic applications. Silver-doped films showed good energy sensitivity, and gratings recorded in optimized film exhibited a diffraction efficiency of more than 75%. The potential of the material for holographic data storage applications is also studied using peristrophic multiplexing.

Light-induced redistribution of Si-MFI zeolite nanoparticles in acrylamide-based photopolymer holographic gratings

Results of studies of the redistribution of Si-MFI zeolite nanoparticles within a photopolymer layer during hologram recording are presented. Light-induced mass transfer studies provide valuable information leading to ways of controlling the spatial distribution of nanoparticles. Nanoparticle-doped photopolymers are very promising materials for development of new holographic-based sensing techniques and for holographic data storage applications. In our studies, diffraction gratings were recorded with a spatial frequency of 200 lines mm−1 at different recording intensities in an acrylamide-based photopolymer system containing 4 wt.% MFI zeolite nanoparticles. Maps of Si-MFI nanoparticle concentration as a function of position in the samples after recording were prepared by Raman spectroscopy and AFM. It has been proven that mass transfer of MFI zeolite nanoparticles takes place during the recording of holographic gratings.

Optical Response of Photopolymer Materials for Holographic Data Storage Applications

We briefly review the application of photopolymer recording materials in the area of holographic data storage. In particular we discuss the recent development of the Non-local Polymerisation Driven Diffusion model. Applying this model we develop simple first-order analytic expressions describing the spatial frequency response of photopolymer materials. The assumptions made in the derivation of these formulae are described and their ranges of validity are examined. The effects of particular physical parameters of a photopolymer on the material response are discussed.

Investigation on effect of methylene spacer in holographic grating formation in eosin containing polymethacrylates

A new series of eosin dye based poly(alkyloxymethacrylate)s was synthesized with an even number of side-chain methylene spacers by a free radical addition polymerization method for holographic optical data storage applications. These polymers were characterized by UV, IR and 1H NMR spectroscopy. The glass transition temperature and thermal stability of the polymers were investigated by DSC and TGA, respectively. As the spacer length increases in the side-chain, Tg, Tm and thermal stability of the polymers decrease, while a reverse trend was observed with film forming ability of the polymers. The optical characterization of the polymers was investigated by forming holographic grating using an Argon ion laser. The grating diffraction efficiency was found to depend not only on the concentration of polymeric film but also on the spacer length of the polymers.

Hologram multiplexing in a highly photosensitive photopolymerizable material in a sol-gel matrix

In this paper, we present a photopolymerizable material in a sol-gel matrix suitable for recording a large number of multiplexed diffraction gratings with low total exposure energy. The matrix of this material is an inorganic porous silica glass, a material that does not shrink when radical photopolymerization is initiated. The photosensitive component is based on acrylamide, N,N′-methylenebisacrylamide, triethanolamine and yellow eosine as a photoinitiator. In the reported study, 50 holograms were angularly multiplexed with diffraction efficiencies between 0.1 and 1.9% resulting in a dynamic range of M/# = 3.9. The total exposure was 4.5 mJ/cm2 and the energy used in recording each hologram was 95 μJ/cm2. This indicates a very high sensitivity for this material in the range of 3.3 to 15.5 cm/mJ. Due to this good holographic performance, the material is suitable for holographic data storage applications.

Holographic data storage on azobenzene photopolymer film using nanosecond laser pulses

A new photopolymer has been developed as a material candidate for high-density holographic data storage applications. Holographic gratings have been recorded on the polymer film using nanosecond laser pulses at 532 nm wavelength with diffraction efficiency measured up to 20%. Further studies have shown 14 line pairs/mm as the material resolution of our photopolymer films at the current development stage. Combined with the erasability results published earlier, the results presented in this paper suggest the possibility of both types of recording (rewritable with low-power CW laser recording and read-only with high-energy pulse laser recording) on this new photopolymer film.

Ternary phase-amplitude modulation with twisted nematic liquid crystal displays for Fourier-plane light homogenization in holographic data storage

Summary Holographic data storage applications often use liquid crystal displays as spatial light-amplitude modulators for writing data images. The hologram created in the Fourier plane is usually applied to store the information, since this plane supplies optimal data density. A well known technique for homogenizing the light distribution in the Fourier plane is the application of external random phase modulating masks. The requirement for pixel by pixel matched positioning of the phase modulating mask and the pixels of the spatial light-amplitude modulator is hard to solve in the optical systems and any positioning error leads to significant signal degradations. The article analyses the possibilities of realizing the required simultaneous amplitude and phase modulation of light with the application of a single LCD. Twisted nematic LCDs with different maximal birefringence are numerically investigated using the Jones matrix method. Elliptical incident and exit polarizations are proposed, by which ternary phase-amplitude modulation (+1,–1,0) can be realized. Test measurements are also presented that demonstrate the validity of the calculated results.

Doubly doped stoichiometric and congruent lithium niobate for holographic data storage

Codoped lithium niobate of congruent and stoichiometric compositions had been successfully grown specifically for holographic data storage applications. The dopants we have selected are Mn and Ce and their role in the recording process is described. Growth methods, sample preparation, doping level measurements, holographic recording data as well as the results of optical characterization and photorefractive properties of the two-photon sensitivity are discussed. Compared to the previously grown crystals, the codoped LiNbO 3 shows a higher sensitivity and dynamic range for recording in red ( λ=632 nm ).

Improved Properties of Stoichiometric LiNbO3 for Electro-Optic Applications

High quality stoichiometric LiNbO3 single crystals, 40 mm in diameter and 80-100 mm in length, have been successfully grown by the double crucible Czochralski method equipped with automatic powder supply system using radio-frequency heating and automatic diameter control system. Although some difficulties still exist in growing 3 inch size single crystals from offcongruent composition melts, our results demonstrate that stoichiometric LiNbO3 crystals containing much less nonstoichiometric defects than congruent LiNbO3 exhibit some advantageous properties for holographic data storage applications. This was confirmed by the results of two-beam coupling experiment and digital hologram test. In digital holographic data storage, we have demonstrated that stoichiometric LiNbO3 shows more than 10 times larger photorefractive sensitivity than congruent LiNbO3 In order to interpret the high performance of stoichiometric LiNbO3, we compared several relevant parameters such as electro-optic constants, photoconductivity, and photogalvanic constants between stoichiometric and congruent LiNbO3 crystals. We report that material parameters are strongly dependent on the density of nonstoichiometric defects and control of these defects is of key importance in improving and tailoring those properties.

Growth of low-scattering single-domain photorefractive LiNbO/sub 3/ crystals

Low-scattering single-domain LiNbO/sub 3/ crystals can be from a 3 mol% LiVO/sub 3/-doped LiNbO/sub 3/ (50 mol% Li/sub 2/O-50 mol% Nb/sub 2/O/sub 5/) quasi-flux system. Approximately one order of magnitude less scattered light was detected in this crystal than in the commercially available congruent reference LiNbO/sub 3/ sample. For quantitative scattering measurements an integrating sphere technique developed at Lasergenics Corp. was utilized. Although no direct evidence can prove the improvement of the Li-Nb-O stoichiometry, the as grown single-domain character, the higher refractive index, and the significantly lower scattering are indirect evidences revealing unusual changes and improvements in the quality of the LiNbO/sub 3/ single crystals. These crystals may be promising for high-density holographic data storage applications.