Investigation On Transverse Effects Of Two-wave Mixing And Separate Soliton Pairs In Photorefractive Crystal

The photorefractive (PR) effect is a phenomenon in which the local index of refraction of a medium is changed by the illumination of a beam of light with spatial variation of the intensity. The PR two-wave mixing is the most fundamental and important kind of nonlinear wave mixing effects and it is a basic phenomena to study PR effect. The theory of the PR two-wave mixing is the base of optical amplification and holographic data storage in PR crystal, therefore, the research on two-wave mixing can help us to understand a lot of PR properties and to achieve the applications of the corresponding functions. The photorefractive spatial optical soliton is a non-diffracting optical-beam, which still maintaining its shape and amplitude when evolved forward inside the photorefractive material. Potential applicated in many fields such as optical-information, integrat-optics and optical communications, they have attracted more and more attention of experts. Judged by whether to consider the absorption or amplification in crystals or systems or not during the forming of the PR solitons, the PR solitons can be divided into Hamiltonian spatial solitons and dissipative holographic spatial solitons. This dissertation investigates theoretically the transverse effects of two-wave mixing in PR crystals. We also investigate the dynamical evolution and self-deflection of the Hamiltonian spatial solitons and dissipative holographic spatial solitons theoretically. At last, we investigate the separate spatial Holographic-Hamiltonian soliton pairs, separate spatial holographic soliton pairs and solitons interaction in a series photorefractive crystal circuit.Based on the theory of PR two-wave mixing, we analyze the process of two Gaussian wave mixing in PR crystals and photovoltaic PR crystals, and under different system parameters, we investigate the dynamical evolutions of the peak intensities and intensitis FWHM of the signal and pump beams after two-wave mixing. In PR crystals, we can control the signal beam to be absorbed or amplified by adjusting the biased field, the intensity and beam width of pump beam. In unbiased photovoltaic PR crystals, the self-focusing effect of signal beam becomes more obvious as the intensity of pump beam and the angle between the two beams increase. By use of top-and side-view method, we investigate the transverse effects of two-wave mixing in photovoltaic PR crystals and verify the numerical results. Based on the physical process of the PR effect and Kukhtarev-Vinestskii model, the theoretical model of Hamiltonian spatial optical solitons is given and the numerical integral solutions of the screening-photovoltaic bright and dark solitons are derived. Based on the theory of PR two-wave mixing and holographic focusing, the theoretical model of dissipative holographic spatial solitons is provided and the analytical study of holographic both bright and dark solitons under the small signal approximation are given. We also discuss the properties of Hamiltonian spatial solitons and dissipative holographic solitons and the differences between them. The dynamical evolutions and self-deflection properties of Hamiltonian solitons and dissipative holographic solitons are investigated using a numerical method. Our results indicate that Hamiltonian solitons and dissipative holographic solitons can stably propagate in the crystal with unchanged profile. Both Hamiltonian solitons and dissipative holographic solitons will move under a parabolic way named the self-deflecting process when the diffusion effect of the crystal is considered. The results indicate that bright and dark solitons have different self-deflection properties, and the spatial shift of beam center of Hamiltonian solitons depends on the biased field and the incident beam, whereas the spatial shift of beam center of dissipative holographic solitons depends on the biased field and the angle between the signal and pump beam.The separate spatial Holographic-Hamiltonian soliton pair is studied firstly. Conducting wires are used to connect two photorefractive crystals (with or without a power source). Four sorts of separate spatial Holographic-Hamiltonian soliton pair form the experiment circuits, namely bright-bright, bright-dark (holographic bright-Hamiltonian dark), dark-bright (holographic dark-Hamiltonian bright), dark-dark. In the limit of the width of the crystal which is much bigger than the spatial extent of the optical wave, the Hamiltonian dark soliton can affect the other one whereas the Hamiltonian bright soliton and holographic soliton not. Based on the asymmetric property of the soliton pair, the influence of the optical amplitude of the Hamiltonian dark soliton on the properties of dynamic evolution and self-deflection of the holographic dark soliton in a dark-dark soliton pair is investigated in detail.At last, we investigate separate holographic soliton pairs and solitons interaction in the biased serial PR crystals circuit. There are three types of separate holographic soliton pair: bright-bright bright-dark and dark-dark. When changing the input intensity of pump beam of a crystal, not only will the characters the soliton formed in that crystal change, but also the characters of the other soliton formed in the other crystal will change. That is, the two solitons in a separate holographic soliton pair can interact or affect each other by the light-induced current.