A hybrid glass

For high-density, holographic data storage has been developed. Holographicstorage techniques, which record data using interfering beams of light, can potentially sequester information at tens to hundreds of times the density of digital versatile disks (DVDs). Unfortunately, holographic recording media generally fail to meet the practical requirements—stability, cost, and processing simplicity—that would make them competitive with conventional technologies. Now, Pavel Cheben of Optenia Inc in Canada and María Luisa Calvo of Complutense University of Madrid believe they have developed a practical holographic medium that meets the most critical requirements for commercial data storage. Using a sol-gel process at room temperature, the researchers suspended thermally sensitive photoactive compounds in a porous silica glass to form a hybrid organic-inorganic glass. The resulting medium is rigid, stable, and can be cast in virtually any thickness, allowing the production of slablike structures. On moderate exposure to a pattern of green light, the glass undergoes chemical reactions that alter its index of refraction in only those regions that are bright. Once recorded, data are permanently inscribed in the new material, but future developments may lead to rewritable media as well as other applications, including optical interconnects, neural networks, and image-processing devices. (P. Cheben, M. L. Calvo, Appl. Phys. Lett. 78, 1490, 2001 http://dx.doi.org/10.1063/1.1354665 .)