Recording media that exhibit high dynamic range for digital holographic data storage

A general strategy for fabricating thick, optically flat photopolymer recording media with high dynamic range (M/#) that exhibit low levels of recording-induced Bragg detuning for holographic data storage is presented. In particular, media with M/# values as high as 42 in 1-mm-thick formats are obtained. We believe that these results are the first demonstration of a holographic storage medium with a dynamic range of this magnitude. In addition, we report the holographic recording and recovery of high-capacity (480-kbit) digital data pages in these media, further illustrating their data-storage capabilities.     

Holographic storage of three-dimensional image and data using photopolymer and polymer dispersed liquid crystal films

We present holographic storage of three-dimensional(3D) images and data in a photopolymer film without any applied electric field.Its absorption and diffraction efficiency are measured,and reflective analog hologram of real object and image of digital information are recorded in the films.The photopolymer is compared with polymer dispersed liquid crystals as holographic materials.Besides holographic diffraction efficiency of the former is little lower than that of the latter,this work demonstrates that the photopolymer is more suitable for analog hologram and big data permanent storage because of its high definition and no need of high voltage electric field.Therefore,our study proposes a potential holographic storage material to apply in large size static 3D holographic displays,including analog hologram displays,digital hologram prints,and holographic disks.     

Optimization of a holographic memory setup using an LCD and a PVA-based photopolymer

Holographic data pages were stored in a polyvinyl alcohol (PVA)/acrylamide (AA) photopolymer. This material is formed of AA photopolymers which are considered interesting materials for recording holographic memories. A liquid crystal device was used to modify the object beam and store the data pages in the material. During the storage process, some parameters like exposure time, beam ratio and reading beam intensity were controlled to obtain high image quality after the reconstruction process. The bit error rate (BER) was calculated fitting the histograms of the images to determine what parameters improve the quality of the images.     

Shift-multiplexed holographic digital data page storage in a nanoparticle-(thiol-ene) polymer composite film

We demonstrate shift-multiplexed holographic storage of 180 digital data pages with low symbol-error rates in a thick (250 μm) SiO2 nanoparticle-polymer composite film using step-growth thiol-ene photopolymerization. A two-dimensional 2:4 modulation code was employed for formatting digital data pages in order to reduce the average intensity of code block without decreasing the coding efficiency. This study clearly shows the feasibility of the thiol-ene based nanoparticle-polymer composite system as a holographic data storage medium.     

A wideband sensitive holographic photopolymer

A novel wideband sensitive dry holographic photopolymer sensitized by rose bengal (RB) and methylene blue (MB) is fabricated, the holographic storage characteristics of which are investigated under different exposure wavelengths. The result shows that the sensitive spectral band exceeds 200 nm in visible light range, the maximum diffraction efficiency under different exposure wavelengths is more than 40% and decreases with the decrease of exposure wavelength, the exposure sensitivity is not change with the exposure wavelength.This photopolymer is appropriate for wavelength multiplexing or multi-wavelength recording in digital holographic storage.     

Evaluation of polycarbonate substrate hologram recording medium regarding implication of birefringence and thermal expansion

In this paper, we evaluate photopolymer media using a polycarbonate (PC) substrate. In holographic data storage medium, substrates that sandwich the photopolymer material are needed to protect the photopolymer material against exogenous shock and open air. An optical glass such as BK-7 is normally used as a substrate, but a PC substrate has a cost advantage and is easy to fabricate compared with optical glass. For holographic recording and reading, however, the high birefringence and high thermal expansion of a PC substrate are significant problems. First, we analyze the degree of degradation of output power by the polarization change and estimate the threshold value of birefringence to record hologram normally. Next, we estimate the temperature tolerance of hologram readout with polycarbonate substrate hologram medium. These analyses results indicate the possible usage of the PC substrate as holographic recording media.     

吖啶橙敏化的光致聚合物及其数字全息存储研究

制备了一种吖啶橙敏化的光致聚合物材料,并研究了材料的全息特性.用Ar+激光器三种波长的光对材料进行记录.结果表明,该材料具有较高的衍射效率、较高的曝光灵敏度和较大的折射率调制度,最大衍射效率均大于40%.将计算机二进制文件经过编码生成的二值图像存入样品,其再现图像较为清晰,译码后能够准确地还原出原文,表明该光致聚合物适合数字全息存储.     

干法在线处理全息存储材料

综述了干法在线处理全息存储材料在高密度数字全息存储中的应用。详细介绍了光折变材料、光致聚合物和光寻址聚合物的基本组成、全息存储性能及其优缺点等。最后,对干法在线处理全息存储材料的发展现状和前景进行了简要介绍。     

光致聚合物中单体及粘结剂对全息性能的影响

研究了单体及粘结剂等成份对全息光致聚合物薄膜光存储性能的影响。在相同引发条件下．以丙烯酰胺作为单体时，光聚物的衍射效率明显高于以丙烯酸和N羟甲基丙烯酰胺作为单体时光聚物的衍射效率。向丙烯酰胺中加入少量N-羟甲基丙烯酰胺，可以改善膜表面的光学质量．降低散射光强度，并提高膜的保存时间。在聚乙烯醇膜中单体聚合程度明显优于在聚乙烯吡咯烷酮中的程度，在大分子量的聚乙烯醇中的衍射效率及感光灵敏度高于在小分子量中的衍射效率和感光灵敏度，而且大分子量的聚乙烯醇能够制备厚膜，这是实现全息海量存储的一个重要因素。     

Fabrication and characterization of poly(methyl methacrylate) photopolymer doped with 9,10-phenanthrenequinone (PQ) based derivatives for volume holographic data storage

We present our studies on the photopolymer of poly(methyl methacrylate) (PMMA) doped with 9,10-phenanthrenequinone based derivatives for volume holographic storage. By introducing different functional groups on the side-chain of 9,10-phenanthrenequinone molecule, the holographic characteristics of the material can be modified. The photoreaction involved with the holographic recording in the samples was investigated by measuring UV-Vis absorption spectrum and mass spectrum. The experimental results show that the similar behaviors were exhibited in these photopolymers. It is found that phase hologram recording in our PQ derivatives doped PMMA photopolymer involves a structure change of the quinone based molecule, which induces a strong change of the refractive index. Experimental characterizations on holographic data storage, including material sensitivity, dynamic range (M#) and bit-error-rate have been performed. We found that, by selecting appropriate functional groups, an improvement in sensitivity and M# for holographic data storage can be achieved.     

Distortions in pixel-matched holographic data storage due to lateral dimensional change of photopolymer storage media

Dimensional changes in polymerizable storage materials during exposure are a source of pixel misregistration in digital holographic storage. Lateral shrinkage or expansion of photopolymer recording materials can be deduced from quantitative measurement of the shift and the magnification errors of reconstructed holograms.     

Dynamic analysis of holographic gratings in amulti-wavelength visible light sensitive photopolymer

A dynamic theoretical model of photochemistry and hologram formation in holographic photopolymer is established, and the dynamic development process of holographic gratings in the photopolymer is discussed with the model. A novel multi-wavelength visible light sensitive photopolymer for holographic storage is prepared. The influence of exposure wavelength on holographic storage characteristics is analysed. By fitting the experimental data of transmittance and diffraction efficiency to a function of time with different exposure intensities and wavelengths, the variations of dynamic parameters of photochemistry and photopolymerization diffusion are presented.     

Phase modulated gray-scale data pages for digital holographic data storage

We propose a method for gray level holographic digital data storage by using three-gray levels in the phase mode. Gray level data pages are displayed on a SLM operating in the phase mode to obtain a homogenized Fourier spectrum by suppressing the extremely high intensity DC component in the Fourier spectrum of conventional amplitude based binary/gray level data pages. Holographic interferometry has been used to recover the gray level amplitude data page from phase data page. Numerical simulation results are presented for three-gray level data pages. Fourier plane homogeneity, bit-error-rate, storage density, phase modulation error of the SLM, and misalignment tolerances are investigated through computer modeling. A comparison of the present method with the amplitude-modulated gray level case with and without using a phase mask in conjunction with the data page is carried out. An experimental demonstration of the proposed three-gray level phase data page method is also presented.     

Overloaded phase-code multiplexing for volume holographic storage

Overloaded phase codes for volume holographic data storage are introduced. In contrast to any previous phase-code design, overloaded phase codes enable multiplexing of a number of data pages that exceeds the number of utilized reference beams. In this way the achievable data capacity can be augmented. Overloaded codes are generated by extending multilevel phase codes based on the discrete Fourier transform. We demonstrate multiplexing of 70 analog pages by means of 64 reference beams. The analysis of reconstructed digital data pages suggests that a capacity gain of up to 15% is reasonable.     

红敏聚乙烯醇/丙烯酰胺体系光致聚合物全息记录材料的空间分辨力增强研究

针对目前聚乙烯醇/丙烯酰胺体系光致聚合物材料的空间分辨力不高的问题,提出了一种采用低相对分子质量的聚乙烯醇作为成膜剂来改进光致聚合物分辨力的新方法.采用不同相对分子质量(72000,15000,9000)的聚乙烯醇成膜剂制成光致聚合物,对其衍射效率和空间分辨力等指标进行了对比实验.实验表明选用低相对分子质量(9000)的成膜剂可将该体系光致聚合物的分辨力提高到3000 line/mm以上,实验中仅需40 mJ/cm2左右的曝光量即可获得85%的衍射效率.另外,还对该材料的全息存储特性及其在角度复用全息存储方面的初步应用结果进行了报道.     

光致聚合物的高密度数字全息存储特性综述

文章综述了光致聚合物的高密度数字全息存储特性,可以看到光致聚合物将是高密度数字全息存储最有希望最先获得突破的材料。     

Content-addressable Holographic Digital Data Storage Based on Hybrid Ternary Modulation with a Twisted-Nematic Liquid-Crystal Spatial Light Modulator

We propose and demonstrate the use of hybrid ternary modulated digital pages for content-addressable holographic data storage. Display of binary data pages with equal number of ZEROs and ONEs by modulating both amplitude and phase of beams using twisted-nematic liquid crystal spatial light modulator, reduces strong de component and produces a more homogeneous spectral distribution at the recording plane. This technique facilitates better recording of all spatial frequencies, thus improving the discrimination capability of a content-addressable memory. Hence we get better results in associative recall in a holographic memory system, with very low number of false hits. An important advantage of the hybrid ternary modulation over pure phase data pages is that it offers a dark state for coding the undesired portion of the SLM while the search argument is small. The unique orientation of quarter wave plate and the analyzer blocks the light transmitted from OFF pixels leading to near total removal of dark signals. This in turn improves the system performance and reduces the number of false hits when the size of the search argument is small. Our experimental results show good discrimination capability and signal-to-noise ratio for a hybrid ternary modulation based content addressable memory.     

Two-stage feedforward tracking control system with error-based disturbance observer for optical discs

Recently, the scaling up of the storage capacity and data transfer rate of digital storage media has been required. However, increasing in the storage capacity and transfer rate makes optical head control more difficult. Thus, a tracking control system for optical discs must exhibit a high degree of precision control. Consequently, a new two-stage feedforward control (TSFFC) system for high-precision control is proposed in this paper. The proposed system is constructed using two zero phase error tracking (ZPET) control systems based on error prediction and an error-based disturbance observer (EDOB) that uses a notch filter to suppress non periodic disturbances. The proposed control system is designed for DDU-1000 for digital versatile discs (DVDs). The experimental results demonstrate that the proposed system effectively suppresses tracking errors.     

Optical data storage in microfibers

Tests of optical data storage in arrays of microfibers confirm its applicability and potential for higher storage densities than those achievable with conventional holographic data storage. Arrays of single-mode microfibers, spaced 0.78 microm apart and 60 microm long, were generated in a photopolymer film with four laser beams and simultaneously inscribed with Lippmann-Bragg fringes by use of a counterpropagating beam. Following the curing steps, spectra of white light retroreflected from a single fiber exhibit the reconstructed spectral lines of the multiwavelength laser used in the recording step; 10(11) bits/cm(2), or 10(13) bits on a compact disk, appear to be recordable.     

Holographic data storage in a DX-center material

We report on the optical storage of digital data in a semiconductor sample containing DX centers. The diffraction efficiency and the bit-error-rate performance of multiplexed data images are shown to agree well with a simple model of the material. Uniform storage without an exposure schedule is demonstrated. The volume sensitivity is found to be ~10(3) times that of LiNBO(3):Fe. The importance of coherent addition of scattered light with diffracted light in holographic data storage is discussed.