Demonstration Of Digital Holographic Storage And Retrieval

Volume holographic storage (VHS) is an intriguing approach for next generation data storage, owing to its attractive combination of density and speed. The potential applications of VHS include a variety of fields such as information processing, aviation and spaceflight, multimedia and large database. Although VHS has been progressing rapidly in recent years, high density holographic storage with high image/data fidelity is still a key in making the technique practical. This paper briefly introduces the fundamental of VHS in photorefractive crystals. The effects of various noises on the quality of images andlor fidelity of data retrieved from multiple holograms are discussed in detail. Then the assessment methods suitable for quality analyses of holographic images are illustrated. We have proposed a method to investigate quantitatively how the scattering noise in photorefractive crystals influences the quality of an input data page in holographic storage. By exposing the crystal under investigation to an intense coherent light beam, and measuring the signal- to-noise ratio(SNR) of an image formed through the crystal before and after the exposure, the loss of SNR, LSNR, provides a good assessment for the suitability of the crystal for data storage. Using the proposed quantity, LSNR, a variety of doped and co-doped lithium niobate crystals have been investigated. The results show that the intensity of fanning light and the scattering factor depends on the dopants doping concentration, treatment after crystal growth, and the recording configuration. However, a deterministic relation between the fanning strength and the fidelity degradation has not been found by the experiments. Owing to the low noise and hence the high data fidelity, iron-and-zinc co-doped lithium niobate crystal can be a promising material for high-density holographic data storage. We have conducted a preliminary experiment to demonstrate the full course of digital holographic storage. We optimized the system by selecting the suitable optics, materials and recording geometry, achieved pixel match between the spatial light modulator (SLM) and the detector array (CCD). A small multimedia data file was composed into 25 pages of binary data and stored in a 450-cut Fe: LiNbO3 cube. The average raw bit- error rate of the reconstructed data file is the order of 1 O~. The successful replay of the data file shows that VHS can be potentially used for the multimedia data storage if the system is further improved.