The growth in demand for digital storage capacity exceeds 60% per annum. Facilities such as storage area networks, data warehouses, supercomputers and e-commerce related data mining, require ever-greater capacity in order to handle the volume of data to be processed. In addition, with the advent of high bandwidth Internet and data intensive applications such as High Definition TV (HDTV) and Video & Music On Demand, even smaller devices such as Personal VCRs, PDAs, mobile phones, etc. Will in the next couple of years demand multi-gigabyte and terabyte capacities. Not less important, is the growing demand for faster data access and reading. For instance High Definition TV and Video & Music on Demand applications require over terabit/sec reading speed. Such and higher speed in conjunction with huge capacity can be implemented only by means of parallel access to any part of information on the carrier.
In the year 2000, one (1) ExaByte (ID^18 Bytes) of information will be stored, growing to more than two (2) ExaBytes by the year 2002. Approximately 10% of the information will be stored on magnetic disk drives (HDD), with the remainder on tapes, optical discs and paper. This increasing capacity demand has thus far, been met through steady increases in the areal density of the magnetic and optical recording media.
While the limits of magnetic recording are still being debated-recently 35 Gbit/sqi has been demonstrated-the limits of conventional optical storage are well understood. Current optical storage technology is working close to the diffractionlimits (5 Gbit/sqi).
Future increases in density are possible by taking advantage of shorter wavelength lasers, higher lens numerical aperture (NA), or by employing Near Field techniques. Finally, optical data storage capacities have been increased by creating double-sided media. Another approach to increasing the effective storage capacity is quite unique for optical memory technologies. This is three-dimensional storage.
True three-dimensional optical storage opens up another dimensional in which to increase the capacity of a given volume of media, with the objective of achieving a cubic storage element having the dimensions of the writing/reading laser wavelength. Even with current wavelengths of 650um, this should surface to store up to a Terabit per cubic centimeter.
Holographic memory is developing technology that has promised to revolutionaries the storage systems. It can store data upto 1 Tb in a sugar cube sized crystal. Data from more than 1000 CDs can fit into a holographic memory System. Most of the computer hard drives available today can hold only 10 to 40 GB of data, a small fraction of what holographic memory system can hold. Conventional memories use only the surface to store the data. But holographic data storage systems use the volume to store data. It has more advantages than conventional storage systems. It is based on the principle of holography.
Scientist Pieter J. van Heerden first proposed the idea of holographic (three-dimensional) storage in the early 1960s. A decade later, scientists at RCA Laboratories demonstrated the technology by recording 500 holograms in an iron-doped lithium-niobate crystal and 550 holograms of high-resolution images in a light-sensitive polymer material. The lack of cheap parts and the advancement of magnetic and semiconductor memories placed the development of holographic data storage on hold.
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