【作者】 展凯云；

【导师】 侯春风；

【作者基本信息】 哈尔滨工业大学 ， 光学， 2011， 博士

【摘要】 由于光折变空间孤子在很低的入射光强下即可产生,以及潜在的应用价值,从最初理论预言和实验报道以来一直是非线性光学领域的一个研究热点。目前,对光折变空间光孤子的研究主要集中在非中心对称光折变晶体中,人们已经在该种晶体中相继理论预测和实验报道了多种不同类型的空间孤子。本文将对中心对称光折变晶体中空间孤子现象进行全面系统的研究。分别用数值模拟方法和微扰法研究了单光子中心对称光折变晶体中扩散场对亮空间孤子传播的影响。在扩散效应的作用下,亮空间孤子沿着外加电场的反方向发生了自偏转效应,孤子的中心轨迹是一条抛物线,偏转量与外加电场的三次方成正比。讨论了晶体的温度对中心对称光折变晶体中亮孤子的形状及由扩散效应引起的自偏转效应的影响。温度影响因素有三个,分别是扩散效应、暗辐射强度和相对介电常数,其中相对介电常数的影响处于主导地位。理论研究了中心对称光折变晶体中空间光孤子的时间行为,给出了中心对称光折变晶体中随时间变化的空间光孤子演化方程,讨论了亮暗空间孤子的时间行为。对于高入射能量饱和值,亮孤子的演化过程存在准稳态孤子和稳态孤子两种状态,当入射光强较低时,不存在准稳态。对于任意的入射光强,暗空间孤子的宽度均随时间单调的减小至最小值,直至稳态暗孤子的形成。对在中心对称光折变晶体中两束偏振方向和波长都相同的非相干高斯光束的传播行为进行了研究。理论证明了二次电光系数为正值的中心对称光折变晶体可以支持稳定的高斯型亮-亮非相干孤子对,讨论了这些孤子对的性质。研究了中心对称光折变哈密顿系统和耗散系统中全息孤子形成的条件及其特征。在中心对称光折变哈密顿系统中,两束光可以同时演化为暗或亮空间孤子。理论预言了,信号光可以在同一种中心对称光折变耗散系统中,形成暗或亮全息孤子。由Castro–Camus双光子模型出发,推导出了基于双光子光折变效应的外加电场作用下的中心对称光折变晶体中一维稳态屏蔽空间光孤子的演化方程,理论预言了亮暗屏蔽孤子态,用微扰法研究了扩散场引起的亮孤子的自偏转效应。此外,理论预言了双光子中心对称光折变晶体中可以形成非相干亮、暗孤子族以及亮暗混合孤子族;对于只含有两束非相干光束耦合的情况,当两束光的总能量远低于暗辐射强度时,双光子中心对称光折变晶体中可以形成暗–暗,亮–亮和亮–暗Manakov孤子对。理论研究了中心对称光折变晶体中宽光束的调制不稳定性。给出单光子中心对称光折变晶体中宽光束的全局调制不稳定增长率和局域调制不稳定增长率,以及双光子中心对称光折变晶体中宽光束的局域调制不稳定增长率。更多还原

【Abstract】 Since their existence was first predicted and observed, photorefractive optical spatial solitons have been the subject of very intense experimental and theoretical studies for their feature of formation at low laser power and potential important applications. Thus far, several different kinds of photorefractive spatial solitons have been investigated in non-centrosymmetric photorefractive crystals. In this dissertation, the spatial optical solitons in centrosymmetric photorefractive crystals are investigate systematically.The effects of diffusion on self-deflection of steady-state bright spatial optical soliton are studied systematically by both numerical and perturbation methods. The center of the soliton moves on a parabolic trajectory, and the deflection effects vary cubically with applied external field. Moreover, a theoretical investigation of temperature effects on bright solitons in centrosymmetric photorefractive crystals is provided. Three physical factors related to the temperature, i.e., the dielectric constant, diffusion process and dark irradiance, are considered. It is shown that the dielectric constant temperature dependence dominates the process.A one-dimensional time-dependent wave propagation equation wihich in centrosymmetric photorefractive crystals is derived. The equation exhibits the bright and dark soliton solutions whose evolutions against time are investigated. It is shown that the screening bright soliton exists in both quasi-steady-state and steady-state regimes for high intensity saturation values. When the intensity ratio is smaller than unity, only steady-state regime is shown. Moreover, the wave equation exhibits only steady-state screening dark spatial optical solitons.The coupling between two mutually incoherent Gaussian beams that propagate collinearly in centrosymmetric photorefractive crystals is investigated. The centrosymmetric photorefractive crystals with a positive effective quadratic electro-optic coefficient can support bright-bright Gaussian spatial soliton pairs. The physical properties of these soliton pairs are also discussed in detail.A comprehensive theoretical study on holographic solitons is provided in centrosymmetric photorefractive crystals. It is predicted that both dark and bright spatial soliton states can exist in centrosymmetric photorefractive Hamiltonian systems and that the signal beam alone can evolve into steady-state bright and dark holographic solitons in a centrosymmetric photorefractive dissipative system.Based on Castro-Camus model, the evolution equation of one-dimensional steady-state spatial solitons is presented in two-photon centrosymmetric photorefractive crystals, which predicts not only bright but also dark solitons. By using a perturbation method, the effect of diffusion on the self-deflection of bright solitons is also investigated. Furthermore, it is shown that incoherently coupled dark, bright and bright-dark soliton families are possible in two-photon centrosymmetric photorefractive crystals and that Manakov soliton pairs can be established provided that the total intensity of two mutually incoherent optical beams is much lower than the dark irradiance.By global and locally treating the space-charge field, one-dimensional modulation instability of broad optical beams in biased centrosymmetric photorefractive crystals is studied under steady-state conditions. The expressions of global and locally modulation instability gains in single-photon centrosymmetric photorefractive crystals and locally modulation instability gain in two-photon centrosymmetric photorefractive crystals are provided.更多还原