We present an overview of our research effort on volume holographic digital data storage. Innovations, developments, and new insights gained in the design and operation of working storage platforms, novel optical components and techniques, data coding and signal processing algorithms, systems tradeoffs, materials testing and tradeoffs, and photon-gated storage materials are summarized.

Holographic data storage

The polarized optical spectra of the ions Ti3+, V3+, Cr3+, Mn3+, Co3+, and Ni3+ in corundum single crystals have been studied at temperatures from 4.2° to 1200°K. A theory of the band strength based on the point‐charge model and p‐d mixing has been developed and applied to the data with results in fair agreement with experiment. The effects of temperature show that the vibrational‐electronic contribution to band strength is quite small at low temperature but may be appreciable at high temperatures. The crystal‐field parameters have been calculated as convergent lattice sums. The observed trigonal‐field parameter has the opposite sign from that calculated by the point‐charge model if the impurity ion is assumed to occupy an Al3+ ion position in the lattice, but has the same sign as calculated for an ion 0.1 A displaced along the c3 axis toward the empty octahedral site. Details of the spectra have been interpreted as showing that the surroundings of an ion are distorted in some electronic states.

Optical spectra of transition-metal ions in corundum

Wave front shaping, the ability to manipulate light fields both spatially and temporally, in complex media is an emerging field with many applications. This review summarizes how insights from mesoscopic scattering theory have direct relevance for optical wave control experiments and vice versa. The results are expected to have an impact on a number of fields ranging from biomedical imaging to nanophotonics, quantum information, and communication technology.

Light fields in complex media: Mesoscopic scattering meets wave control

We demonstrate for the first time to our knowledge a digital phase conjugation technique for generating a sharp focus point at the end of a multimode optical fiber. A sharp focus with a contrast of 1800 is experimentally obtained at the tip of a 105μm core multimode fiber. Scanning of the focal point is also demonstrated by digital means. Effects from illumination and fiber bending are addressed.

Focusing and scanning light through a multimode optical fiber using digital phase conjugation

Research into and the development of data storage devices is a race to keep up with the continuing demand for more capacity, more density, and faster readout rates. Improvements in conventional memory technologies-magnetic hard disk drives, optical disks, and semiconductor memories-have managed to keep pace with the demand for bigger, faster memories. However, there is strong evidence that these two-dimensional surface storage technologies are approaching fundamental limits. An alternative approach for next-generation memories is to store data in three dimensions. This article describes developments in holographic 3D memories, in which high density is achieved by superimposing many holograms within the same volume of recording material. Holographic storage is a promising candidate for next-generation storage. Research has demonstrated that holographic storage systems with desirable properties can be engineered. The next step is to build these systems at costs competitive with those of existing technologies and to optimize the storage media.

/pdf/holographic-data-storage-i6ionpw23n.pdf

Although the concept of using multiplexed holography for data storage has been considered for some time, recent advances in several critical device technologies along with developments in storage materials have greatly enhanced the likelihood of successful implementations. We review several basic architectural concepts along with various multiplexing options and associated techniques for holographic data storage.

Volume holographic memory systems: techniques and architectures

We consider the storage density limited by the cross talk between stored pages during readout. We review some earlier work done in this area and present new theoretical work that characterizes the storage capacity limitations due to the cross talk. The results show that because of the presence of degeneracy noise, storage capacity does not benefit from expanding the reference points from one dimension to two dimensions. An optimum configuration that fully utilizes storage capacity and completely eliminates degeneracy noise is given for an angularly multiplexed volume holographic memory system.

Cross-talk-limited storage capacity of volume holographic memory

We demonstrate energy exchange by nondegenerate two-wave mixing in ruby. Our results are in agreement with the theory of nondegenerate two-wave mixing when the theory is generalized to take into account a complex nonlinear index. Two-wave mixing gain exceeding the absorption and reflection losses is demonstrated, and we show that these experiments provide a simple and accurate method for determining the complex nonlinear index, response time, and saturation intensity of the medium.

Nondegenerate two-wave mixing in ruby.

We demonstrate energy exchange by nondegenerate two-wave mixing (NDTWM) in ruby. Our results are in agreement with the theory ot NDTWM in Kerr media,1 when the theory is generalized to take into account a complex nonlinear index. NDTWM provides a method for determining the complex nonlinear index and the response time of the medium. NDTWM gain exceeding the absorption and reflection losses is demonstrated.

Nondegenerate two-wave mixing in ruby

Interpixel cross talk that is due to diffraction and aberrations is, to some extent, unavoidable because of trade-offs in the design of holographic storage systems. Phase masks have been proposed to avoid problems encountered in Fourier-transform holographic recording, but they have other effects on pixel cross talk. We investigate the effect of using phase masks in the data-bearing object beam on the output interpixel cross talk in a holographic memory system.

Ian McMichael

Papers

Volume holographic memory systems: techniques and architectures

Cross-talk-limited storage capacity of volume holographic memory

Nondegenerate two-wave mixing in ruby.

Nondegenerate two-wave mixing in ruby

Influence of phase masks on cross talk in holographic memory.