Two color hologram storage using stoichiometric lithium niobate

Digital holographic memory using photorefractive material is one of the most promising candidates for the next-generation of data storage, which simultaneously provides high capacity, fast transfer rate and short access time. This comes from a three-dimensional volume holographic multiplexing scheme based on two dimensional page oriented read-write mechanisms. However there are numerous hurdles on the road to success. The development of a really satisfactory recording material for holographic data storage applications remains perhaps most important barrier to practical implementation of the technology. The ideal material must simultaneously possess many properties such as good sensitivity, large dynamic range, long data retention times and excellent optical quality. In addition, it must be able to be mass produced. From the above points of view, lithium niobate (LiNbO₃; abbreviated as LN) is the most promising candidate among all the inorganic photorefractive materials. High quality crystals of up to 3 inches (recently 4 inches) diameter of LN are commercially produced by the Czochralski method as substrate material of SAW devices. Because the growth method has been established, LiNbO₃ single crystals doped with hundred wt. ppm of Fe have been investigated as photorefractive data storage material. However, the photorefractive properties are not sufficient for applications and further improvements, especially in writing speed is required as a high priority.