Study On Optimization Of Holographic Storage Properties And Application Of Lithium Niobate Crystals

Volume holographic memories have attracted intense interest because of theirpotential in high capacity storage, fast parallel process and content addressability. Toa large extent, the system performances depend on the properties of storage media.Photorefractive lithium niobate (LiNbO₃) crystal has been widely investigatedfor applications in holographic data storage. Improvement and optimization ofholographic storage properties of LiNbO₃ crystals are still one of the most importanttasks for volume holographic storage. In this thesis a comprehensive study is madeon the optimization of holographic storage properties and application of LiNbO₃crystals, based on the influences of dopants on holographic storage properties ofLiNbO₃ crystals.Important parameters for the performances of photorefractive crystals, such asabsorption coefficient, dynamic range, sensitivity and scattering noise, areanalysized and evaluated. Moreover, experimental platforms of testing theseperformances of photorefractive materials have been setup.As for doubly doped LiNbO₃ crystals with damage-resistant dopants, theinherent mechanisms are studied. A two-center model is built to discuss the relationsbetween holographic storage properties and iron doping concentration,damage-resistant ions doping concentration and oxidization state. Based onanalyzing and synthesizing the relations, an efficient way to improve the wholeholographic storage properties of LiNbO₃ crystals is proposed.In order to further optimize LiNbO₃ crystals, Indium (In) dopant is doped intoLiNbO₃:Fe crystals and the effect of In doping on holographic storage properties isfirstly studied. It is found that slight In doping (such as 0.5mol%) in LiNbO₃:Fe, Incrystal could be a good way to improve the sensitivity with small M/# changing.Based on the optimization method and experimental results, LiNbO₃:Fe, In crystal isoptimized. According to the proposed way, a sample of LiNbO₃:Fe, In andLiNbO₃:Mn, In crystals have been grown and achieved larger dynamic range, highersensitivity and better signal-to-noise ratio than LiNbO3:Fe (Fe:0.03wt.%) crystal thatis generally considered as a preferable storage medium for high-density holographicdata storage.An appropriate exposure time schedule must be designed in high capacityholographic storage according to the characteristics of the crystal and the system. Anew restrictedly gradually-reduced exposure time schedule is proposed to adjust thedynamic changes of time constants during the process of large holographic storage.Furthermore, combining with the new restricted degressive exposure schedule toequilibrate diffraction efficiency, electrolytic solution to minish the influence of thephotovoltaic field, and speckle modulation to suppress correlation sidelobe noise, ina coherent volume 0.074cm3 of optimized LiNbO3:Fe, In crystals, 21Gbits/cm3storage density and 98.4% recognition correlation accuracy in a compact volumeholographic data storage and correlation recognition system, of which the number ofcorrelation channels is improved to 2030.