作为新型结构光束的一类，全庞加莱球光束因其横截面上自旋角动量和轨道角动量发生耦合，近年来在自由空间光通信领域内受到广泛关注。然而，传输信道中的大气湍流将产生诸如光束扩展、漂移、光强闪烁等严重影响，进而限制光通信系统性能。结合随机相位屏，对具有“C”型偏振奇点的全庞加莱球光束、“V”型偏振奇点的柱矢量光束和均匀偏振的标量涡旋光束在湍流大气中的传播进行大量的数值模拟。归一化光强相关系数和模式纯度被用于研究杂合庞加莱球表面不同位置处表征的全庞加莱球的稳定性。结果表明，相较于具有相似偏振拓扑荷和光强分布的柱矢量光束以及标量涡旋光束而言，坐标位于南半球的全庞加莱球光束在弱湍流和中湍流(r₀=0.5 m, 0.125 m)下具有较高稳定性。而在强湍流下(r₀=0.056 m)，优势区域缩小至2σ∈[−5π/32, 0](纬度坐标)。上述结果将为自由空间远距离通信中传输介质的选取提供重要依据并进一步促进通信质量的提升。

We experimentally demonstrated an approach to generate arbitrary total angular momentum (TAM) states by using two liquid crystal devices. Photons’ TAM, the sum of spin and orbital angular momenta (SAM and OAM) under paraxial approximation, has found many applications in optics and attracted increasing attention in recent years. Our approach is based on the orthogonality of two eigen SAM components, that arbitrary TAM states will be produced through encoding different holograms in one system. The comparison with theoretical predications yields an excellent agreement, including both the separable state and the non-separable state. The proposed scheme takes a step forward for generating complex structured fields and broadens its application to various fields like laser processing and large capacity data transmission.

Multi-ring optical vortices are a kind of structured beams that carry orbital angular momentum (OAM) and have concentrical doughnut intensity distributions. In this Letter, we present both theoretically and experimentally a scheme that employs the dimensions of both the OAM states and radial index of multi-ring optical vortices simultaneously to accomplish high-dimensional free-space data coding/decoding transmissions. Such a scheme can further improve the coding efficiency when limited OAM states are available. In the proof-of-concept experiment, 64-ary coding/decoding employing 16 OAM states and four radial indices are present. Also, the coding/decoding performance when facing various atmosphere turbulences is evaluated. Furthermore, a 64 × 64 gray image (totally, 32,768 bits) is also transmitted through multi-ring optical vortices coding in free-space successfully, showing good transmission performance.

A scheme for beam combination at any angles employing a specially designed multilayer grating is proposed. Such a grating is able to convert noncoaxial laser beams to coaxial ones, and the combined beams are able to output along the normal line of the grating. The intensity and the phase structure of combined beams can also be controlled. The experiments are carried out by loading an encoded grating on a liquid-crystal spatial light modulator. The results agree well with the simulations. This method of beam combination with a multilayer grating serves to simplify the complexity of beam combination.