光折变效应诱导的光子晶格中涡旋孤子缺陷局域态对光信号流的控制研究

All-optical networks provide a very promising platform to deal with the task, which is able to efficiently transmit and rapidly process huge amounts of data has become almost indispensable to our daily lives. Within such networks all-optical routing and switching, where light is directed by light, are a crucial building block for an effective operation. Optically induced photonic lattices, that has been successfully realized within the bulk of photorefractive crystals, give the effective means that light is controlled by light, Optical waves propagation in linear and nonlinear periodic photonic structures exhibit behanvior characteristic of that encountered in discrete systems, which in many cases has no counterparts in homogeneous systems. We have meet challenge which light beam is not deflected with the azimuthal angle by optical signals for constricted by the maximum deflection angle in photorefractive crystals. According to our results about properties of light beam propagating in photonic lattices and recent references of vortex beam, We predict there are the defect localized states in optically induced photonic lattices in photorefractive crystals, which combinations of vortex beam that carries phase singularity. The project will be doing：① We are going to investigate optical vortices propagation in 2D optically induced photonic lattices with photorefractive effect, the optical field obeys a saturable nonlinear Schr?dinger equation and we experimentally observe it; ②The robustness and existence of the defect localized states of vortex solitons in 2D optically induced photonic lattices with photorefractive effect and phase singularity of vortex beam is going also studied experimentally; ③ We will experimentally and theoretically study the flow of optical signals propagation in 2D optically induced photonic lattices using the beam propagation method, We is going to explore relationship of shape and size of defect localized state and deflection of optical signals, We want to discover how to control the optical signals by means of changing shape and size of defect localized state。Possible breakthrough：We predict there is controlled defect localized state of vortex soliton; We will realize that optical signals is controlled by defect localized state; The problem of harmonic wave inaccuracy will be solution on interference of multiple beam. The project open new field of research which vortex beam propagation in photonic lattice is dominated by discrete effect, nonlinearity and its angular momentum. Many new phenomana and effects are expected. These distinct features of discreteness can be exploited for potentially important application in all-optical signal and data processing, optical communication systems and switching networks.

光控光的全光路由、全光开关是实现全光通信网络之关键问题。光折变晶体的弱光非线性及其诱导光子晶格为实现光控光提供了有效手段，但项目组前期的研究发现光折变光子晶格对光信号的任意偏转调节控制问题尚待解决。结合课题组前期研究基础和涡旋光研究文献，我们推测：光折变非线性和涡旋光相位奇异性共同作用形成光子晶格中的缺陷局域态。本项目拟开展：①采用离散非线性薛定谔方程和实验研究涡旋光在光折变诱导的光子晶格中的传播行为；②研究涡旋光的相位奇异性在光子晶格中形成涡旋孤子的缺陷局域态的存在性和稳定性；③采用光束传播法研究光信号流在光子晶格中的传播，探索涡旋孤子缺陷局域态尺度、形状等对光信号流的控制。可能的突破：发现稳定、可控的涡旋孤子缺陷局域态；利用缺陷控制光信号流的路径；多光束干涉导致的谐波误差问题。本项目拓展了光子晶格在光控光方面的研究领域，为光子晶格在全光交换网络、全光信号处理等方面的应用奠定基础。

研究涡旋光束在自聚焦四方光子晶格中的传输特性。研究发现，不存在晶格时涡旋光束会分裂成基态孤子。存在晶格后，非格点激发和格点激发的一阶涡旋光束在合适的条件下能形成稳定传输的离散涡旋孤子，而二阶涡旋光束在传输过程中则会出现拓扑翻转现象，生成准稳态的涡旋孤子。研究了涡旋光束在自散焦四方晶格中的传输特性。研究发现，格点激发的一阶涡旋光束在合适的条件下可以形成稳定传输的离散涡旋孤子，但四瓣聚焦在格点之间。二阶涡旋光束传输过程中也存在拓扑翻转的现象。研究了一阶涡旋光束在贝塞尔晶格中传输的情况。由于贝塞尔晶格的径向对称性，当输入的涡旋光束恰好落在晶格的第一环道内并且晶格深度和外加电场强度都合适时可以形成稳定传输的环状涡旋孤子。研究了二阶涡旋光束在自聚焦0阶，1阶贝塞尔晶格中传输的情况。当输入光束强度，外偏压，晶格深度相互匹配时，不同横向尺度系数的贝塞尔晶格中，输入光束传输一段距离后可以演变成不同类型的环状涡旋孤子。光束在光学晶格中传输时，当晶格深度达到一定程度后，纵轴有调制变化的晶格使得孤子在势阱处呈现压缩的现象，增大外加电压强度有助于孤子压缩。当晶格深度与外加电压强度相匹配时，孤子保持原形能相对稳定传输；否则孤子在传输过程中会出现“脉动”现象。(2+1)维孤子较(1+1)维孤子复杂，其中(2+1)维孤子在特定情况下会出现涡旋孤子的现象。当光束宽度与晶格宽度可比拟的时候，从晶格能量峰值处入射的孤子容易局域在波导中稳定传输；而从晶格最低能量处入射的孤子就容易受相邻波导间的影响，分裂成两个或多个孤子振荡性的往前传输。当光束宽度远大于晶格宽度时，这时在一定晶格深度下，光学晶格中横向周期性折射率调制对光束所起的作用较大，会导致离散孤子形成，但需要材料、光学晶格、光束自身的参数严格匹配。本项目研究的为在光子晶格中实现光控光取得了一些成果，从而实现在光交换网络、光开关，光空分复用等方面的奠定了基础。