单光子轨道角动量的传输特性研究

描述了高阶椭圆厄米-高斯光束及其单光子平均轨道角动量,并分析了一些与其单光子轨道角动量变化的有关情况,通过计算机仿真简要进行了说明.最后分析了单光子轨道角动量在空间某范围的概率分布及其变化情况.研究结果表明,高阶椭圆厄米-高斯光束与物质相互作用时,其单光子平均轨道角动量的变化幅度随接触物质材料的不同而异.     

扭转对称光束的产生及其变换过程中的轨道角动量传递

研究了采用扭转柱面镜光学系统将厄米-高斯光束变换成为具有轨道角动量的拉盖尔-高斯扭转对称光束. 采用本征模式分解的方法分析了扭转柱面镜光学变换系统实现光束变换的原理.利用光束传输矩阵和二阶矩理论分析计算了光束经过扭转柱面透镜变换过程中的轨道角动量传递过程，证明光束与透镜系统的轨道角动量交换发生在第一个柱面透镜处，光束经过第一个柱面透镜后，具有的轨道角动量保持不变. 关键词： 轨道角动量 光束变换 扭转对称光束 轨道角动量传递     

复杂像散椭圆光束的轨道角动量的实验研究

提出一种直接测量光束的轨道角动量的方法，其原理是把具有轨道角动量的光束照射到一个金属靶上，使其在光束的角动量作用下发生转动. 通过测量靶转动的角度来计算光束的角动量值. 对几种不同参数的光束的轨道角动量进行了测量，获得了轨道角动量与光束参数之间的关系，实验结果与理论分析较好地符合. 关键词： 复杂像散椭圆光束 轨道角动量 测量     

具轨道角动量光束用于光通信编码及解码研究

无衍射光是在自由空间传播过程中一定范围内横向强度分布保持不变的光场,具有方向性好以及传输距离远等特点,某些类型的无衍射光具有轨道角动量.分析了具有轨道角动量光束以及无衍射光在空间中的传输特点,以计算全息图作为反射式相位调制的空间光调制器(SLM)实现光学变换,并通过由锥形透镜构成的模式转换器,将携带信息的拉盖尔-高斯(L-G)光束转换成为具有相同拓扑荷的高阶Bessel无衍射光束,提出了一种通过具有轨道角动量的高阶Bessel无衍射光束来进行空间光信息传输的编码解码方法,在保证激光大气通信的安全保密性的同时,提高了信息传输的密度和准确率.     

利用干涉光场的相位涡旋测量拉盖尔-高斯光束的轨道角动量

对拉盖尔-高斯光束经多圆孔衍射屏在远场平面上形成的干涉光场的相位和零值线进行了计算模拟.当入射光束的轨道角动量量子数为零时,实部零值线与虚部零值线在干涉光场中心点不相交,因而在该点上不能形成相位涡旋.当入射光束的轨道角动量量子数为+1和-1时,实部零值线与虚部零值线在干涉光场中心垂直并相交,干涉光场相应位置处的相位涡旋的符号相反.当入射光束的轨道角动量量子数为±2和±3时,有四条零值线相交于干涉光场的中心点上,并且实部零值线和虚部零值线交替分布,该交点处形成的相位涡旋的拓扑荷的值恰好与拉盖尔-高斯光束的轨道角动量量子数相等.这种结果可以用来测量涡旋光束的轨道角动量.     

大气湍流信道中聚焦涡旋光束轨道角动量串扰特性

携带轨道角动量的涡旋光束作为传输信息的载体能有效提高信息传输效率,然而在传输过程中受大气湍流影响轨道角动量会发生串扰.基于螺旋谱分析理论,推导得到了聚焦拉盖尔高斯光束在各向异性大气湍流中传输时的螺旋谱解析表达式,并对比分析不同湍流和光束参数对聚焦与非聚焦拉盖尔高斯光束接收功率的影响,最后利用多相位屏法进行模拟验证.结果表明:随着传输距离、湍流强度、拓扑荷数的增大以及湍流内尺度、光束波长的减小,接收功率减小,轨道角动量串扰增大;接收孔径到达一定值时对轨道角动量串扰的影响非常小;聚焦光束比非聚焦光束的轨道角动量串扰要小.这些结果将对提高自由空间光通信的质量有一定意义.     

具有轨道角动量光束入射下的单球粒子散射研究

根据广义Mie理论,研究了具有轨道角动量拉盖尔-高斯光束（LGB）的空间传输特性以及单粒子散射特性.在单体球粒子对高斯光束散射研究的基础上,分析了在自由空间不同传输距离LGB光束的光强分布情况,在不考虑散射和波束相移关系的情况下,将LGB作为入射高斯光束,通过对波束入射时的散射衰减截面求解得到波束因子,利用矢量球谐函数对入射高斯波束进行展开,从而研究了单球粒子在在轴条件下对具轨道角动量高斯波束入射的散射问题.通过数值计算,讨论了散射强度及角分布在不同波束宽度情况下对其散射特性的影响,并与平面波的情况做了对比.结果表明,当波束束腰半径较小时,束腰半径对衰减率的影响较大,而当束腰半径远大于粒子半径时,接近于平面波的情况. 关键词： 广义Mie理论 轨道角动量 Laguerre-Gauss光束 单球粒子     

基于机器学习检测相位畸变后的涡旋光束轨道角动量

针对涡旋光受大气湍流而产生的相位畸变问题,设计了卷积神经网络检测涡旋光束轨道角动量态.将相位畸变的拉盖尔高斯涡旋光光强图像作为样本数据输入,网络利用输入的数据集进行自主学习,经过多次迭代能够精确检测出光束高阶轨道角动量信息.仿真结果表明:在大气湍流强度不确定的情况下,模型对轨道角动量态范围为1～40、1～100、1～1...     

汉克-贝塞尔光束在海洋湍流信道中的螺旋相位谱分析

携带轨道角动量的汉克-贝塞尔(Hankel-Bessel,HB)光束具有无衍射和自聚焦特性,用来作为信息传输的载体有望增大信息传输容量.基于Rytov近似理论,推导得到了HB涡旋光束经过海洋水平弱湍流信道后的螺旋相位谱的解析表达式,并利用数值仿真方法研究了海洋湍流参数对轨道角动量模式探测概率的影响.结果表明,海洋湍流导致发射轨道角动量模式的探测概率下降,出现模式串扰和螺旋相位谱扩展.海洋湍流对HB涡旋光束的负面影响随着轨道角动量模式数、传输距离、温度方差耗散率的增加而增强,随湍流动能耗散率的增加而减弱.HB涡旋光束受以盐度波动驱动的海洋湍流的负面影响更大.另外,在弱湍流及几十米传输距离条件下,HB涡旋光束的传输性能要差于最佳束腰大小设置的拉盖尔-高斯涡旋光束.这些结果有望为海洋环境水下光通信链路的实现提供一定的参考价值.     

利用具有轨道角动量的光束实现微粒的旋转

采用扭转柱面镜光学系统将半导体激光抽运固体激光器产生的厄米高斯光束变换成为具有轨道角动量的扭转对称光束.利用该光束具有的轨道角动量特性研制成功了“光学扳手”， 利用“光学扳手”实现了对微米量级微粒的俘获和旋转. 关键词： 轨道角动量 扭转对称光束 光学扳手 光束变换     

Canonical momentum,angular momentum,and helicity of circularly polarized Airy beams

We report a study of the momentum, angular momentum, and helicity of circularly polarized Airy beams propagating in free space. By using the vector angular spectrum representation, the explicit analytical expressions for the electric and magnetic field components of circularly polarized Airy beams are derived in detail. To overcome the drawbacks of classical kinematics formulae when applied to structured light beams, a general canonical approach is introduced to describe the momentum, angular momentum and helicity of Airy beams. Numerical simulation results for the spatial distributions of the canonical momentum, spin and orbital angular momentum, as well as the helicity densities are presented and discussed. This study may provide useful insights into the dynamical properties of Airy beams that may be important in several applications, including the optical control, micromanipulation, and information processing.     

Effects of atmospheric turbulence on the orbital angular momentum of multi-Gaussian Schell model beams

The effects of multibeams and partially coherent source on the orbital angular momentum transmission of multi-Gaussian Schell model beams in an atmospheric turbulence channel are analyzed. An effective crosstalk probability model of the orbital angular momentum is derived which leads to crosstalk probability function for eigenmodes of different orbital angular momentum states and beamlets. The work shows that the evolution of the effective spatial coherence radius with growing the rms width of the correlation of the partially coherent source and the number of the beamlet in multi-Gaussian model beams. The crosstalk probability of the orbital angular momentum of an effective Gaussian-Schell model beam decreases as increasing of the degree of the spatial coherence of the partially coherent source and the beamlet number of the multi-Gaussian Schell model beams.     

Specular and vortical Airy beams

A new kind of truncated Airy beams is investigated and discussed. These beams are a superposition of shifted and truncated Airy functions and its specular counterparts, where zeroes or extremal points of the Airy function are chosen as a truncation point. The specular Airy beams are smooth at the truncation point and produce a diffraction pattern similar to Hermite-Gaussian modes. Under propagation in Fresnel zone, specular Airy beams demonstrate a symmetrical acceleration in opposite sides and the beam divergence is proportional to the traveled distance squared. The astigmatic mode converter transforms a two-dimensional specular Airy beam into a quasi-annular field with a nonzero orbital angular momentum. Vortical Airy beams based on truncated Airy functions are also discussed. These beams are similar to Laguerre-Gaussian modes, while their annular structure is changed during propagation.     

Study on holographic grating diffraction for Laguerre--Gaussian beam generation

Laguerre-Gaussian beams, as a special model with spiral phase structure, have been intensively investigated. Holographic grating method is a convenient method of generating Laguerre-Gaussian beams and measuring their orbital angular momenta. But due to some inevitable adverse factors such as lateral displacement, angular deflection and elliptical incident profile of incident beam, the practical effectiveness should be reevaluated. This paper is devoted to the study on the influences of the abovementioned three adverse factors on the holographic grating method. The characteristics of the mode decomposition of diffractive order and the relative powers of the orbital angular momentum eigen-states are also given.     

Entangled orbital angular momentum states of multi-Laguerre Gaussian Schell beams pumping in a Zernike tilt corrected turbulence

Based on the paraxial approximation of the beams propagation in communication system, the square approximation of the wave structure function, the Zernike polynomial expansion of the non-Kolmogorov atmospheric turbulence-aberration and the assumption of the signal photon propagation in slant Zernike tilt corrected turbulence-channel, we analyze the effect of the multi-beam on entangled orbital angular momentum states. The joint detection probability of orbital angular momentum state entangled photons is modeled. Our work shows that the correction of the Zernike tilt aberration by adaptive optics is a method to improve the joint detection probability of orbital angular momentum state entangled photons. The crosstalk probability of the entangled orbital angular momentum states decreases as increasing of the degree of the spatial coherence of the partially coherent source and the beamlet number of the multil-Laguerre Gaussian Schell model beams.     

A simple scheme for quantum networks based on orbital angular momentum states of photons

We propose a new quantum network scheme using orbital angular momentum states of photons to route the network and spin angular momentum states to encode the information. A four-user experimental scheme based on this efficient quantum network is analyzed in detail, which is particularly appealing for the free space quantum key distribution. Users can freely exchange quantum keys with each other.     

Sorting and detecting orbital angular momentum states by using a Dove prism embedded Mach-Zehnder interferometer and amplitude gratings

An experimental system consisting of a Dove prism embedded Mach-Zehnder (M-Z) interferometer and two gratings was built to sort and detect orbital angular momentum (OAM) states of light beams. The helical beams with different OAM states were generated by propagating the fundamental-mode Gaussian beam through a spatial light modulator. The Dove prism embedded M-Z interferometer was used to sort helical beams with odd or even OAM number and two binary amplitude gratings were used to measure the OAM states. Sorting of coaxially-superposed coherent and incoherent helical beams with odd and even OAM states was realized in the experiment.