Protein-based volumetric memories

This paper will explore the use of the protein, bacteriorhodopsin, as the photoactive recording medium in an optical three-dimensional memory. Although this protein has been used previously as the photoactive medium in a number of three-dimensional architectures (e.g., holographic and two- photon), a sequential one-photon volumetric architecture employing a photochemical branching reaction characteristic of the protein is currently showing the most promise. This unique branching reaction allows for long-term data storage by the protein, and rigorously excludes unwanted photochemistry. During the past two years, two prototypes have been constructed, and the preliminary results look promising. The use of chemical modification and genetic engineering of the protein has improved data reliability by roughly five-fold, but reliability remains an issue. Some of the key problems will be discussed. In addition, the use of gray-scale and polarization multiplexing to increase the storage capacity will be examined.