Orthogonal-reference-pattern-modulated shift multiplexing for collinear holographic data storage

A novel hybrid shift multiplexing method for collinear holographic data storage (CHDS) by using orthogonal reference patterns (RPs) is proposed, analyzed, and demonstrated. For this method, holograms are multiplexed by not only shifting the media but also using different RPs. Compared with the traditional method, the shift pitch for the hybrid method is substantially reduced because of the selectivity introduced by different RPs. The interpage cross talk due to Bragg mismatch and degeneracy for multiplexing holograms in the same volume by using orthogonal RPs is also attenuated by utilizing the shift selectivity of the hologram. A 1.5 μm shift pitch is experimentally achieved by using three amplitude RPs in a system that would be 4.5 μm with only one RP. This new method offers an alternative to significantly increase the data density and transfer rate of the CHDS system given that the media has ideal properties.     

Two-dimensional shift-orthogonal random-interleaving phase-code multiplexing for holographic data storage

A novel phase encoding technology for phase-code multiplexing in holographic data storage (HDS) system called two-dimensional shift-orthogonal random-interleaving (2-D SORI) phase encoding is proposed. Compared with the traditional one-dimensional orthogonal phase-code multiplexing methods, the 2-D method is less sensitive to the variations of the diffraction amplitude and to the phase error of the phase mask. Phase masks for the 2-D SORI phase-code multiplexing can be generated by shifting an elaborately designed phase plate at a certain step, which can avoid the use of a high-cost phase spatial light modulator for the generation of multiple orthogonal phase masks. The cross-talk arising from the systematic phase defects of the static phase modulator is eliminated by the shift operation of the phase plate. Phase codes are interleaved under a predetermined random mapping rule to prevent unauthorized users from accessing the data and eliminate the Bragg degeneration cross-talk. A 2-D SORI phase plate with the size of 5.12 mm × 10.24 mm is designed and fabricated, from which 128 orthogonal phase patterns are generated. The feasibility of the 2-D SORI phase-code multiplexing method for HDS is experimentally demonstrated.     

A simple technique for holographic multiplexing

A technique for holographic multiplexing is proposed which utilizes a combination of theta modulation and carrier frequency multiplexing. Twenty two binary transparent object were multiplexed with this technique and a resolution of 10 lines/mm with good diffraction efficiency was obtained. The technique can be used for studying the sequential events at discrete time intervals.     

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.     

Gray-scale data pages for digital holographic data storage

The prospects for gray-scale (or multilevel) digital holographic data storage are theoretically and experimentally investigated. A simple signal-to-noise ratio (SNR) partitioning argument shows that when SNR scales as 1 over the number of holograms squared, five gray levels (log(2) 5bits/pixel) would be expected to result in a 15% capacity increase over binary data pages. However, the additional signal-dependent noise sources present in practical systems create a baseline SNR that reduces both the optimal number of gray levels and the resulting gain in capacity. To implement gray-scale recording experimentally, we adapt the predistortion technique previously developed for binary page-oriented memories [Opt. Lett. 23, 289 (1998)]. Several new block-based modulation codes for decoding gray-scale data pages are introduced. User capacity is evaluated by an experimental technique using LiNbO(3) :Fe in the 90 degrees geometry. Experimental results show that a balanced modulation code with three gray levels provides a 30% increase in capacity (as well as a 30% increase in readout rate) over local binary thresholding.     

Numerical simulations on optoelectronic deep neural network hardware based on self-referential holography

Optical Review - We propose a novel optoelectronic deep neural network (OE-DNN) hardware called the self-referential holographic deep neural network (SR-HDNN). The SR-HDNN features a combination of...     

Experimental implementation of multiplexing/demultiplexing in digital images using virtual phase conjugation for holographic data storage

We experimentally implemented and proved the concept of multiplexing and demultiplexing in digital images using virtual phase conjugation, which was proposed in our previous study. In the experiment, we concluded that two digital images multiplexed in a single signal beam are recorded in a holographic medium, and these images are independently and successfully reproduced. In this method, the digital images are multiplexed by superimposing them on a complex amplitude, and not using volume hologram’s multiplexing. Thus, the exposure amount in the holographic medium is constant regardless of the number of multiplexing of digital images, and the method has great potential for achieving high recording density.     

Modulation coding for pixel-matched holographic data storage

We describe a digital holographic storage system for the study of noise sources and the evaluation of modulation and error-correction codes. A precision zoom lens and Fourier transform optics provide pixel-to-pixel matching between any input spatial light modulator and output CCD array over magnifications from 0.8 to 3. Holograms are angle multiplexed in LiNbO(3):Fe by use of the 90 degrees geometry, and reconstructions are detected with a 60-frame/s CCD camera. Modulation codes developed on this platform permit image transmission down to signal levels of ~2000 photons per ON camera pixel, at raw bit-error rates (BER's) of better than 10(-5). Using an 8-12-pixel modulation code, we have stored and retrieved 1200 holograms (each with 45,600 user bits) without error, for a raw BER of <2x10(-8).     

Associative recall in a volume holographic storage system based on phase-code multiplexing

We present two different techniques on how to realize a content-addressed holographic memory when using phase-code multiplexing, relying on simple intensity measurements rather than phase distributions. Theoretical and experimental results of associative recall in a phase-coded system designed for digital data storage will be presented and compared to the corresponding method when using angular multiplexing. Received: 2 August 2001 / Revised version: 20 September 2001 / Published online: 23 November 2001     

Optical data storage on protein using angular multiplexing

Diffractive data recording was investigated during recent years mainly by using holography, on a large range of materials. Every material that can be light modulated has advantages and disadvantages. But none of the advantages identified for using these investigated materials allows an effective optimal use for standard high-capacity data storing.We propose a new data recording method and process for data storage relying on the performances of doped protein material. We describe this material, its preparation and the storage process that we have validated experimentally. We demonstrated that data storage capacity can be effective on protein, opening stimulating perspectives. In this paper, we describe a way to operate analogic diffractive storage and retrieval.     

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.     

Spatiotemporal multiplexing and streaming of hologram data for full-color holographic video display

We propose a new approach to spatiotemporally multiplex sub-holograms and stream hologram data in parallel by using multiple spatial light modulators (SLMs) to increase the spatiotemporal resolution of holographic display system. With the proposed approach, we have achieved a spatiotemporal resolution of 4.5 × 10¹⁰ pixel/s, as compared with 1.89 × 10⁹ pixel/s of a single SLM. Each frame of computer-generated hologram video has a pixel count of 378 Mpixels and is divided into 288 sub-holograms, each of 1.31 Mpixels. During the playback of holographic video, these sub-holograms are spatiotemporally multiplexed and streamed in parallel to form the integrated hologram within 16.67 ms, which enables full-color holographic video display with a 10-in. diagonal at a hologram data frame rate of 60 frames per second (fps). New SLM devices with higher spatiotemporal resolution need to be developed in order to meet the data bandwidth requirement of about 10¹²–10¹⁴ pixel/s for future 3D holographic displays.     

Multifrequency acousto-optic page composers for holographic data storage

A new concept for one- and two-dimensional acousto-optic page composers to be used in holographic memories is proposed and experimentally demonstrated. The concept is based on multifrequency operation and compensation of the Doppler shift of the optical frequencies. Acousto-optic page composers without the usual exposure time limitation are in this way realized.     

White light micrograting multiplexing for high density data storage

Recording of multiplexed microholographic gratings with improved recording volume for high density optical data storage is proposed and demonstrated. By using a hybrid diffractive-refractive objective lens with extended depth of focus, we have achieved a recording beam size of approximately 1 microm and a focal depth of 20 microm. Multiple gratings corresponding to spectral lines within the 400-650 nm spectral band have been successfully multiplexed in a single recording spot or pit of size 1.25 microm on a DuPont photopolymer film using a white light source along with narrowband filters or dispersion elements, thus demonstrating the storage of multiple bits in a single pit. Simultaneous readout of multiple bits in a single storage pit is accomplished with a microspectrometer-type readout head using a white light source.     

Compensation for pixel-mismatch errors in shift-multiplexed holographic data storage

To read out correct data from shift-multiplexed holographic data storage, we propose a novel method of pixel matching by use of a tiny plane-parallel refraction plate placed in the path of converging readout beams. Tilting the refraction plate produces a shift in the lateral position of the readout beam incident upon the holographic storage disk, leading to compensation for pixel-mismatch errors by an improvement in bit-error rate of 3 orders of magnitude.     

Compensation for pixel misregistration in volume holographic data storage

We describe what we believe to be a novel postprocessing algorithm for compensating for misregistrations between a detector array and the coherent image of a pixelated two-dimensional data page. A lookup table of baseline local offsets is combined with the dynamically measured global offset of the received data page, producing an estimate of the total lateral shift of each small block of pixels. A serial algorithm then reallocates the appropriate portion of the signal detected by each pixel to its neighbors, accounting for both the linear and the quadratic contributions introduced by coherent illumination of square-law detectors. This procedure can relax the tight constraints on page registration, optical distortion, and material shrinkage that currently hamper page-oriented holographic storage systems. Experimental results from a pixel-matched 1-Mpixel volume holographic system are presented, showing an increase in position tolerance (for a raw bit-error rate <10(-3)) from +/-16% to +/-40% of the pixel pitch.     

Optical noise reduction for dc-removed coaxial holographic data storage

A method of reconstructing positive and negative images from Fourier holograms recorded without the dc components is demonstrated by use of a coaxial holographic storage system. Reconstructed images are obtained by adding a phase-modulated dc component of the signal beam on reading. Contrast reversal of the reconstructed images can be achieved by reversing the readout reference pattern. This method can realize not only optical noise reduction but also less consumption of the dynamic range of the recording medium, potentially contributing to increasing the number of multiplexed holograms.     

Non-interferometric phase retrieval for collinear phase-modulated holographic data storage

Optical Review - Because of its simple optical system setup and robust noise tolerance, non-interferometric phase retrieval is an important technique for phase-modulated holographic data storage....     

二芳烯材料在重复擦写体全息存储中的应用研究

二芳烯材料是一种性能优异的光致色变材料,具有很好的抗疲劳性能,一般能重复擦写上万次,而不损失其性能。通过体全息光栅记录实验、角度复用体全息存储实验、重复擦写及强光记弱光读等实验,对二芳烯材料在重复擦写体全息存储中的应用进行了系统研究。由于二芳烯材料具有很高的折射率调制度(Δn=1.15×10-3)、可多次重复擦写、强光记弱光读的准非易失等性能,在可重复擦写的体全息存储中具有广阔的应用前景。     

Pixel-matched holographic data storage with megabit pages

Digital data-page holograms consisting of 1024 x 1024 arrays of binary pixels have been stored and subsequently retrieved with an optical exposure consistent with a data rate 1 Gbit /s. Each input pixel was precisely registered with a single detector pixel, and a raw bit-error rate as low as 2.4 x 10(-6) was demonstrated with global-threshold detection. To our knowledge, this is the first demonstration of the often-cited goal of holographic data storage of megabit data pages and a gigabit-per-second data rate.