Sergei S. Orlov

Holographic Data Storage Systems

In this paper, we discuss fundamental issues underlying holographic data storage: grating formation, recording and readout of thick and thin holograms, multiplexing techniques, signal-to-noise ratio considerations, and readout techniques suitable for conventional, phase conjugate, and associative search data retrieval. Next, we consider holographic materials characteristics for digital data storage, followed by a discussion on photorefractive media, fixing techniques, and noise in photovoltaic and other media with a local response. Subsequently, we discuss photopolymer materials, followed by a discussion on system tradeoffs and a section on signal processing and en/decoding techniques, succeeded by a discussion on electronic implementations for control, signal encoding, and recovery. We proceed further by presenting significant demonstrations of digital holographic systems. We close by discussing the outlook for future holographic data storage systems and potential applications for which holographic data storage systems would be particularly suited.

High-transfer-rate high-capacity holographic disk data-storage system

We describe the design and implementation of a high-data-rate high-capacity digital holographic storage disk system. Various system design trade-offs that affect density and data-rate performance are described and analyzed. In the demonstration system that we describe, high-density holographic recording is achieved by use of high-resolution short-focal-length optics and correlation shift multiplexing in photopolymer disk media. Holographic channel decoding at a 1-Gbit/s data rate is performed by custom-built electronic hardware. A benchmark sustained optical data-transfer rate of 10 Gbits/s has been successfully demonstrated.

Digital holographic storage system incorporating optical fixing

Digital holograms have been written in stoichiometric Pr:LiNbO(3) in a two-color recording scheme, demonstrating what is to our knowledge the first all-optical nondestructive readout of digital data. Using writing light at 800nm and gating light at 476 nm, we stored and retrieved 256-kbit digital data pages with a raw bit-error rate BER of <10(-4) .

Coupled-mode analysis of fiber-optic add–drop filters for dense wavelength-division multiplexing

We present a coupled-mode theory of fiber-optic add-drop filters, which involve directional coupling between two fibers combined with fiber Bragg gratings defined inside the coupling region. The analysis self-consistently accounts for both the directional and the reflection coupling, and the propagation constants and structure of the supermodes of the combined structure are derived. We present a detailed analysis of a filter design based on identical fibers. The calculated device parameters satisfy the requirements for dense wavelength-division multiplexing applications.

Electrical fixing of photorefractive holograms in Sr0.75Ba0.25Nb2O6

Photorefractive holograms stored in Sr0.75Ba0.25Nb2O6 crystals are electrically fixed at room temperature. The fixed holograms can be read out directly or after a positive-voltage pulse is applied that can dramatically enhance the diffraction efficiency. Single gratings as well as images are recorded and fixed.

Holographic storage dynamics in lithium niobate: theory and experiment

We present a theoretical model that describes holographic ionic fixing and storage dynamics in photorefractive crystals. Holographic gratings that are based on charge redistribution inevitably decay because of ionic and electronic conduction. Relevant decay rates and transient hologram field expressions are derived. Ionic gratings are partially screened by trapped electrons on readout. The lifetimes of fixed ionic holograms are limited by the finite ionic conductivity at low (i.e., room) temperatures. Only under certain and restricted conditions can these decay times be acceptably long. A significant increase in fixed ionic hologram lifetime is realized in lithium niobate with a low hydrogen-impurity content. The residual ionic conductivity (decay-time constant) in these samples exhibits ~1.4-eV activation energy and is not due to protonic conduction. Fixed hologram lifetimes of ~2 years at room temperature in dehydrated lithium niobate crystals are projected.

Holographic fixing, readout, and storage dynamics in photorefractive materials

Holographic gratings in photorefractive crystals that are based on charge redistribution inevitably decay as a result of ionic and electronic conduction. Under certain and restricted conditions these decay times can be acceptably long. Relevant decay rates and transient hologram field expressions are derived with special reference to LiNbO(3). Some experimental data are presented.

Light-induced absorption in photorefractive strontium barium niobate.

Sr(0.59)Ba(0.41)Nb(2)O(6) and Sr(0.75)Ba(0.25)Nb(2)O(6) exhibit an intensity-dependent absorption in the visible spectral range. We perform pump (green)-probe (red) measurements and find variation as high as 0.45 cm(-1) in the absorption coefficient, which depends significantly on the polarization of the probe light beam. Our results indicate a nonexponential dark decay time of the induced absorption and suggest that the trapping potential of the shallow traps varies significantly from one trap to another (multiple isolated shallow traps).

Conjugation fidelity and reflectivity in photorefractive double phase-conjugate mirrors

We present an experimental study of the behavior of photorefractive double phase-conjugate mirrors that illustrates recent theoretical predictions. We observe a sharp fidelity threshold that significantly depends on the specific feature size in the input beams. Furthermore, we find that if the two input beams have unequal intensities the conjugation process is asymmetric and the steady-state fidelity is better on the side of the crystal on which the more-intense beam enters.

Doubly doped stoichiometric and congruent lithium niobate for holographic data storage

Abstract 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 ).