Theoretical Investigation Of Holographic Performances In Doubly Doped LiNbO₃ Crystals

The promise of a next-generation optical storage technology that offers both high-density volumetric storage and fast page-oriented output has driven recent research in holographic data storage. Dopant lithium niobate (LiNbO₃) is one of promising holographic recording materials. However,the information recorded in doped LiNbO₃ crystals can be erased during readout process because of the dynamic nature of photorefractive medium. The volatility of stored data in photorefractive materials can be overcome by using a storage scheme of two-center holographic recording.In this thesis, we mainly investigate the optimization of holographic performances for two-center holographic storage with different crystal conditions (including the dopant concentration of the deeper and shallower traps, oxidization-reduction state) and the recording conditions (the intensity ratio of recording light to gate light), by using the Runge - Kutta method .We explain the mechanism and procedure of two-center holographic storage, and describe the dynamic equations of two-center holographic recording——extended Kukhtarev equations in detail. All the theoretical investigations in this paper are based on those equations.We study the holographic performances of sensitivity and dynamic range in the doubly doped LiNbO₃:Fe:Mn crystal. After having found out the photo-excitation coefficient, electron recombination coefficient and bulk photovoltaic coefficient of Cu in doubly doped LiNbO₃:Fe:Cu crystals, its holographic performances are investigated. In doubly doped LiNbO₃:Fe:Cu crystals, we study the variation of sensitivity and dynamic range with different dopant concentration ratio ,oxidization-reduction states and intensity ratio.We investigate the oscillation in the initial phase of grating formation. The oscillation can be attributed to the decay of electrons in the shallower trap centers. By considering both features of the electron decay in shallower trap centers in recording phase and optical erasure in multiplexing holograms, we analyze the feasibility of multiplexing holograms with equal diffraction efficiency by using the recording schedule of equal-time exposure. The theoretical result is in consistent with the experimental result of 15 gratings multiplexing with 100s-equal-time exposure. The recording time constant and erasure time constant of two-center holographic recording are also preliminary studied in this thesis.