Photorefractive Volume Holographic High Density Optical Storage And Its Applications

With the development of the computer science and the internet technologies, the amount of information to be obtained, processed, transferred, stored and to be displayed keeps exponential increasing. Holographic storage has the potential to provide high storage densities, data transfer rates and access times, therefore it will become the main storage of the next generation. Because doped lithium niobate crystals have the advantages of easy growth, low cost, stable performance and etc., these crystals have been widely studied. The fixing technologies of the grating and the nonvolatile retrieval technologies are in practice, so the storage mediums used mostly in photorefractive volume holographic storage are doped lithium niobate. The photorefractive storages are in the ascendant in parallel computing, optical fiber communications, military targets fast recognition and satellite-borne data storage. Many research institutes and companies are designing their own prototype of photorefractive volume holographic storage.In this dissertation, we focus on solving some difficulties in the practical process. First, we address the issue of optimization of the lithium niobate crystals. We study the fanning noise and its intensity threshold effect experimentally, and testify the multi-wave mixing mechanism of the light-induced scattering, which was put forward by our research group. Based on this, we propose the optimization methods through double-doping engineering and choosing optimal working intensity and realize high recording speed, low noise storage in lithium niobate co-doped with iron, magnesium and co-doped with iron, indium.We discovered the enhancement of ultraviolet photorefraction in highly magnesiumdoped lithium niobate crystals, which provide the foundation for optimizing the crystals in order to record holograms with UV lights.We propose the polaron effect to explain the mechanism of the two-color gated storage and get the experimental confirmation. Then we focus on the dual-wavelength method, another nonvolatile storage technique. We make use of different wavelengths for recording and readout to reduce the grating decay while retrieving data. Image field losses are analyzed on the basis of the Bragg-mismatch and solved by utilizing one cylindrical lens. We theoretically and experimentally study the factors, which affect the resolution of the image retrieved in detail.In the process of digital data storage, we develop a dynamic-differential coding anddesign the detection and the coding algorithms in software. The dynamic-differential coding can realize the capture of the effective information and reduce the bit-error caused by the large-scale noise.In the end of this thesis, we introduce two special kinds of photorefractive storage:color-pattern recognizer and self-pumped phase conjugator.Based on the results of our research group and of this thesis, we have performed the photorefractive volume holographic high-density optical storage, and have successfully designed the principle prototype. We store plenty of holograms in lithium niobate co-doped with iron and magnesium by single-color method and by dual-wavelength method. The nonvolatile readout is realized through dual-wavelength method.