• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.8
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• pp.656-661
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• 2013

In Guided Scrambling (GS) encoding for the holographic storage, after scrambling augmented source word into codeword, the best codeword satisfying modulation constraint is determined. Modulation constraints considered in this paper are strength which is the minimum number of transition between '0' and '1' in each row and column of codeword array and the symbol balancedness of codeword array. In this paper, we show that GS encoding procedure can be formulated as an integer programming model and develop a fast neighborhood search heuristic for fast computation of control bits. In the simulation, we compared the performance of heuristic algorithm with the integer programming model for various array and control bit size combinations.

• 정보저장시스템학회:학술대회논문집
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• 2005.10a
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• pp.139-144
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• 2005

Because of the photorefractive recording dynamics, each newly recorded hologram partially erases all previously stored image. Thus achieving the desired diffraction efficiency profile for the entire sequence after all images have been recorded requires exposure time schedule. The often cited classical exposure-schedule model predicts a rising-exponential build-up and an exponential decay in An with an exposure time. However because we cannot directly measure the An, it's difficult to establish the relation of both. In this paper, we deduce the relation of diffraction efficiency and exposure time from experiment data and suggest an algorithm to make time schedule profile in angle/fractal multiplexing of holographic data storage. After that, we present simulated result with equal hologram diffraction efficiency for a sequence of 250 holograms recorded by angle/fractal multiplexing.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.2C
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• pp.163-168
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• 2009

In this paper, a two-dimensional (2D) modulation code is introduced. The proposed code does not have any isolated pixel that is the most unwanted problem for holographic data storage. The proposed 2D modulation code is simpler than conventional 6/8 code and removes all the isolated 2D ISI patterns. As a result, when the grade of blur is 1.4, the proposed modulation code has better performance overall than conventional 6/8 modulation code. The proposed code has the optimal performance when 4bit quantization is applied.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39A no.10
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• pp.569-573
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• 2014

Holographic data storage is a strong contender to become the next-generation data storage method. Its major weaknesses are two-dimensional intersymbol interference between neighboring pixels and interpage interference caused by storing multiple pages in a single volume of hologram. In this paper, we present a trellis encoding scheme of 6/8 balanced modulation code, to address the two weaknesses. The proposed modulation coding scheme captures on characteristics of the balanced code: the scheme relaxes IPI and enables error correction by exploiting the trellis structure. The proposed method showed improved SNR over the conventional 6/8 modulation code.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39A no.10
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• pp.574-578
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• 2014

A holographic data storage (HDS) has some advantages of high storage capacity, fast transmission, and short access time. However, there are two major concerns with the system which are two-dimensional (2D) inter-symbol interference (ISI) and inter-page interference (IPI). Thus, this paper proposes a 4-level 6/9 modulation code which mitigate inter-symbol interference (ISI).

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39A no.10
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• pp.610-612
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• 2014

Mutilevel holographic data storage systems have a big advantage for capacity since it can store more than one bit per pixel. For instance, 2/3 modulation code stores 2/3(symbol/pixel) and 4/3(bit/pixel). Then it is about 1.3 bits per one pixel. In this paper, we propose two 4-level modulation codes, which have the minimum Euclidean distances of 3 and 4, respectively. The proposed codes perform better than random data. The performance of larger minimum distance code shows better than that of shorter one.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.12
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• pp.1070-1074
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• 2002

We have carried out two-beam interference experiments to form holographic gratings on As$_{40}$ Se$_{15}$ S$_{35}$Ge$_{10}$ single layer, Ag/As$_{40}$ Se$_{15}$ S$_{35}$Ge$_{10}$ multi-layer. In this study, holographic gratings have been formed using He-Ne laser(632.8nm) under different polarization combinations(intensity polarization holography, phase polarization holography). The diffraction efficiency was obtained by the +lst order intensity. The maximum diffraction efficiency of As$_{40}$ Se$_{15}$ S$_{35}$Ge$_{10}$ single layer, As$_{40}$ Se$_{15}$ S$_{35}$Ge$_{10}$ and MgF$_2$/As$_{40}$ Se$_{15}$ S$_{35}$Ge$_{10}$ multi-layer were 0.8%, 1.4% and 3.1% under intensity polarization holography, respectively.

• Macromolecular Research
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• v.13 no.6
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• pp.477-482
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• 2005

Photopolymers are attractive materials for holographic 3-D data storage because of their high photosensitivity and large refractive index modulation. We synthesized the six-armed dendrimer for fabricating the new photopolymer. It was prepared using the initiating mixture of hexaarylbiimidazole (HABI), mercapto-benzoxazole (MOBZ), and 2,6-bis(4-diethylaminobenzylidene)cyclopentanone (DEAW), which is sensitive to 514 nm wavelength. The holographic gratings were fabricated successfully in these photopolymer samples by conventional optical interference method. We investigated the effect of dendrimer, either as a binder or as a plasticizer in the cellulose acetate butyrate (CAB), on the diffraction behavior. The addition of only 1 wt$\%$ of dendrimer-I into the CAB significantly increased the diffraction efficiency. The sample doped with dendrimer showed around 80-83$\%$ of the diffraction efficiency.

• Korean Journal of Optics and Photonics
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• v.8 no.1
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• pp.14-18
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• 1997

Using holographic interferometry, strain distributions for a cantilever beam subjected to the eccentric force can be analysed. Holographic fringe pattern shows inclined straight lines for the composite deformation of bending and torsion. Using these inclinations of the fringe pattern, 3rd order polynomial of plane displacements can be determined without difficulty. As the result, both of axial and shear strain distribution can be obtained from the second partial derivatives of this polynomial. These results agree well with FEM.

• Korean Journal of Optics and Photonics
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• v.10 no.2
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• pp.120-127
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• 1999

We discussed two main types-conformal and non-conformal (powered) - of holographic combiner. A theoretical model based on the Kogelnik's coupled wave theory was used to illustrate bandwidth and efficiency properties. Also we showed numerical values for the aberrations that are induced by a wavelength shift from construction to reconstruction and found optimum coordinates to reduce the chrolatic aberation of construction beams using aberration balancing techniques. The holographic combiner manufactured in conformal type with 60$^{\circ}$ incidence angle at 514.5 nm had narrow angular bandwidth (FWHM) of 4.1" and spectral bandwidth of 11.4 nm, while non-conformal one with 50$^{\circ}$, 30$^{\circ}$ incidence angle at 514.5 nm showed spectral and angular bandwidth of 10.7 nm and 5.5$^{\circ}$, respectively.vely.