Multiplexed Holographic Storage In Doubly Doped LiNbO₃ Crystals

The volume holographic storage is one of the most promising optical storage techniques for its high storage density and high data transfer rates. Photorefractive materials have been considered as one kind of the most important materials for volume holographic storage with their advantages of wider dynamic range and commercial availability in large size. It is well known that the holographic information stored in a photorefractive crystal is gradually erased during readout due to the dynamic nature of photorefractive effect. The volatility of the stored data in Photorefractive crystals has become serious obstacle to the practical realization of Photorefractive holographic memories.By using doubly doped LiNbO3 crystals with deep-doped and shallow-doped centers, nonvolatile holographic storage can be achieved in a completely optical way, which is known as two-center or two-color holographic storage.Although multiplexing holograms have been realized in doubly doped LiNbO3 crystals, there are still a lot of problems such as the erasure of recorded holograms by UV light and the recording schedule for equal diffraction efficiency.In the thesis, angle-multiplexed holographic storage in doubly doped LiNbO3 crystals is studied experimentally. We performed a series of experiments to find out the proper crystals, the optimized experiment parameters, and exposure recording scheme for multiplexed holographic storage. The method of achieving equal diffraction efficiency and better hologram fidelity in doubly doped LiNbO3 crystals is investigated.The media is one of the most important influencing factors on the holographic storage properties. The effects of different dopants and annealing on two-center holographic recording in LiNbO3 crystals are investigated. The experimental results demonstrate that, the LiNbO3:Fe:Cu crystals and LiNO3:Ce:Cu crystals are fit for holographic recording due to their high fixed diffraction efficiencies. Based on this, the adaptive crystals are selected for the following experiments.The effects of the various design parameters on the holographic recording characteristics are considered, an optimization scheme is presented and the two-color holographic storage is performed in LiNbO3:Fe:Cu crystal. The erasure characteristics of two-center storage are analyzed, and the recording schedule for multiplexing many persistent holograms is designed. 50 holographic gratings with equal diffraction efficiencies are angle-multiplexed in LiNbO3:Fe:Cu crystal .The behavior of multiplexing holograms under exposure is analytically discussed in LiNbO3:Fe:Cu crystal. The multiplexing recording of holograms with equal diffraction efficiencies is implemented by using pre-exposure recording scheme and the recording schedule of an equal time exposure.We conduct holographic storage of images in LiNbO3:Ce:Cu crystal by using pre-exposure recording scheme. Two-center holographic storage of images are performed experimentally in LiNbO3:Ce:Cu crystal, and the characteristics of the holograms noise are analyzed. The effects of the various experimental factors on the noise of holograms are presented. Angle-multiplexed holographic storage of 50 images with almost equal diffraction efficiencies are multiplexed in a LiNbO3:Ce:Cu crystal with equivalent exposure schedule. The average diffraction efficiency of 50 holograms is 7.64×10-6.