The effects of asymmetry atmospheric eddies on the beam spreading and wander of Bessel-Gaussian (BG) beams in anisotropic turbulence are studied. Results show that turbulence anisotropy leads to the declines in both beam spreading and wander of BG beams in the atmosphere. A BG beam with larger beam shape parameter η has a narrower spot size in a short-distance range and a wider spot size in a long-distance range. The effective Rayleigh ranges of BG beams for every turbulent situation decrease with the beam shape parameter η. When η is larger than 10, atmospheric turbulence has a negligible effect on effective Rayleigh range. The effective Rayleigh range and beam spreading increase and beam wander decreases as topological charge increase. Beam spreading is mainly affected by turbulence inner-scale, and outer-scale evidently affects beam wander in the atmosphere.

The probability densities of orbital angular momentum (OAM) modes of the autofocusing Airy beam (AAB) carrying power-exponent-phase vortex (PEPV) after passing through the weak anisotropic non-Kolmogorov turbulent atmosphere are theoretically formulated. It is found that the AAB carrying PEPV is the result of the weighted superposition of multiple OAM modes at differing positions within the beam cross-section, and the mutual crosstalk among different OAM modes will compensate the distortion of each OAM mode and be helpful for boosting the anti-jamming performance of the communication link. Based on numerical calculations, the role of the wavelength, waist width, topological charge and power order of PEPV in the probability density distribution variations of OAM modes of the AAB carrying PEPV is explored. Analysis shows that a relatively small beam waist and longer wavelength are good for separating the detection regions between signal OAM mode and crosstalk OAM modes. The probability density distribution of the signal OAM mode does not change obviously with the topological charge variation; but it will be greatly enhanced with the increase of power order. Furthermore, it is found that the detection region center position of crosstalk OAM mode is an emergent property resulting from power order and topological charge. Therefore, the power order can be introduced as an extra steering parameter to modulate the probability density distributions of OAM modes. These results provide guidelines for the design of an optimal detector, which has potential application in optical vortex communication systems.

The orbital angular momentum (OAM) of a Laguerre–Gaussian beam (LGB) is classified using the support vector machine (SVM) model. The scintillation index, beam width, and beam wander of the Gaussian beam and the LGB at the receiving site are taken as feature vectors, and the OAM number of a LGB is taken as the label in the training and test samples. The influences on the detection accuracy of the number of training samples, the transmission distance, and the different ways of grouping OAM values are analyzed, where the detection accuracy is defined as the percentage of correctly detected OAM. The results show that only a few training samples are needed up to a range of 4000 m to achieve saturation accuracy. When the transmission distance is within 2500 m, the detection accuracy of a single SVM model in four turbulent environments ( 10−14, 10−15, ) is close to 100%. When the distance increases, detection accuracy decreases gradually, and in the range of 4000 m the detection accuracy is more than 91%. Compared with the traditional spiral spectrum expansion method, the SVM model has obvious advantages. In addition, when the range of OAM to be detected is large, the OAM values may be grouped thereby improving the accuracy when using the multi-SVM models for joint detection.

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