Propagation dynamics of the cosh-Airy vortex (CAiV) beams in a chiral medium is investigated analytically with Huygens–Fresnel diffraction integral formula. The results show that the CAiV beams are split into the left circularly polarized vortex (LCPV) beams and the right circularly polarized vortex (RCPV) beams with different propagation trajectories in the chiral medium. We mainly investigate the effect of the cosh parameter on the propagation process of the CAiV beams. The propagation characteristics, including intensity distribution, propagation trajectory, peak intensity, main lobe’s intensity, Poynting vector, and angular momentum are discussed in detail. We find that the cosh parameter affects the intensity distribution of the CAiV beams but not its propagation trajectory. As the cosh parameter increases, the distribution areas of the LCPV and RCPV beams become wider, and the side lobe’s intensity and peak intensity become larger. Besides, the main lobe’s intensity of the LCPV and RCPV beams increase with the increase of the cosh parameter at a farther propagation distance, which is confirmed by the variation trend of the Poynting vector. It is significant that we can vary the cosh parameter to control the intensity distribution, main lobe’s intensity, and peak intensity of the CAiV beams without changing the propagation trajectory. Our results may provide some support for applications of the CAiV beams in optical micromanipulation.

In this paper, theory concerning scattering of EM (electromagnetic) waves with orbital angular momentum (OAM) is presented, in which a metallic sphere illuminated by OAM waves is adopted to simplify the study. Based on the series expansion and the physical optics (PO) methods, expressions of incident and scattered OAM waves are obtained. To get the expansion coefficients of the scattered fields, boundary conditions and Debye potentials are applied to establish the relationship between incident and scattered fields. Besides, a full EM wave simulation of the scattered field has been accomplished by the computer simulation technology (CST), the measurement of scattered field is done in an anechoic chamber. The simulated results are in good consistency with numerical calculations, demonstrating the interaction between the OAM EM waves and the metallic target sphere effectively. This study also paves the way for researches on scattering of complex targets of OAM waves, and for future studies on target detection.

In this letter, a novel integrated physical optics (PO) method for calculating high-frequency scattering of nonplane wave is proposed, and the orbital angular momentum (OAM) wave scattering upon an electric-large metallic sphere is illustrated. A high-order Bessel wave expanded by a series of plane wave angular spectra is selected to irradiate a perfect electric conductor sphere. Combining the PO approximation, the scattered field from the facet element is calculated, and the total scattered effect is obtained by vector superposition of the scattering from all facets. The calculated results are verified by the EM simulated software FEKO and scattering measurement experiment. Numerical results show that the scattered field of the vortex wave passing through the standard target still has the OAM characteristics, retaining the same topological charge. It can be seen that the proposed combined PO method is feasible at high frequency and can be extended to solve the scattering of other beams and objects, which has a broad range of applications.

In an effort to address the problem of the insufficient accuracy of existing orbital angular momentum (OAM) detection systems for vortex optical communication, an OAM mode detection technology based on an attention pyramid convolution neural network (AP-CNN) is proposed. By introducing fine-grained image classification, the low-level detailed features of the similar light intensity distribution of vortex beam superposition and plane wave interferograms are fully utilized. Using ResNet18 as the backbone of AP-CNN, a dual path structure with an attention pyramid is adopted to detect subtle differences in the light intensity in images. Under different turbulence intensities and transmission distances, the detection accuracy and system bit error rate of basic CNN with three convolution layers and two full connection layers, i.e., ResNet18 and ResNet18, with a specified mapping relationship and AP-CNN, are numerically analyzed. Compared to ResNet18, AP-CNN achieves up to a 7% improvement of accuracy and a 3% reduction of incorrect mode identification in the confusion matrix of superimposed vortex modes. The accuracy of single OAM mode detection based on AP-CNN can be effectively improved by 5.5% compared with ResNet18 at a transmission distance of 2 km in strong atmospheric turbulence. The proposed OAM detection scheme may find important applications in optical communications and remote sensing.