Toroidal multipole is a special current distribution that has many different characteristics from electric multipole and magnetic multipole distributions. Because of its special properties, the toroidal dipole is a research hotspot in the field of metamaterials and nanophotonics. However, the low scattering of the toroidal dipole moment makes its excitation a challenging task. At present, there are relatively few studies on its specific engineering applications. In this paper, by slotting in the rectangular cavity, the excitation of an equivalent toroidal dipole is successfully achieved over a wide frequency range of 53–58 GHz. Results indicate that under the action of the toroidal dipole, the TE10 mode electromagnetic waves transmitted in the rectangular waveguide are converted into vector beams and are radiated outwards. Further adjusting the spatial distribution of the magnetic dipoles in the toroidal dipoles yields results that indicate that the resonance mode in the slot is still dominated by the magnetic toroidal dipole moment, and the electromagnetic waves radiating outward are vortex beams carrying vector polarization. The scattered energy of each dipole moment inside the antenna is calculated. This calculation verifies that the mass of the vector beam and vector vortex beam is closely related to the toroidal dipole supported by this antenna. The proposed structure can be applied to explorations in vortex filtering, in photon entanglement, and in the photonic spin Hall effect.

为了实现高纯度脉冲柱矢量光的输出，提出并搭建基于对称双模耦合器的波长可切换的被动锁模柱矢量全光纤激光器。根据光纤传输原理得到基模向高阶模转换的折射率匹配直径，运用模式耦合模理论及光束传播法模拟分析了对称双模耦合器的结构参数对模式选择及耦合特性的影响，采用熔融拉锥法并免去传统的模式选择耦合器制作上的预拉锥工艺制作了对称双模耦合器，通过搭建一套被动锁模柱矢量全光纤激光器实现了中心波长1 039 nm和1 068 nm可切换、脉冲时间间隔为113.8 ns、重频为8.78 MHz、脉宽660 ps/656 ps、最大输出平均功率为5.25 mW/5.2 mW、模式纯度大于97%的柱矢量光输出。实验验证了对称双模耦合器的可行性，为后续高纯度柱矢量光的获得提供一种可行的方案。

We reporte and demonstrate a solid-state laser to achieve controlled generation of order-switchable cylindrical vector beams (CVBs). In the cavity, a group of vortex wave plates (VWPs) with two quarter-wave plates between the VWPs was utilized to achieve mode conversion and order-switch of CVBs. By utilizing two VWPs of first and third orders, the second and fourth order CVBs were obtained, with mode purities of 96.8% and 94.8%, and sloping efficiencies of 4.45% and 3.06%, respectively. Furthermore, by applying three VWPs of first, second, and third orders, the mode-switchable Gaussian beam, second, fourth, and sixth order CVBs were generated.

We introduce the Stokes scintillation indices and the corresponding overall Stokes scintillations for quantitatively studying the fluctuations of both the intensity and polarization of an optical vector beam transmitting through the atmospheric turbulence. With the aid of the multiple-phase-screen method, we examine the Stokes fluctuations of a radially polarized beam in Kolmogorov turbulence numerically. The results show that the overall scintillation for the intensity distribution is always larger than the overall scintillation for the polarization-dependent Stokes parameters, which indicates that the polarization state of a vector beam is stabler than its intensity distribution in the turbulence. We interpret the results with the depolarization effect of the vector beam in turbulence. The findings in this work may be useful in free-space optical communications utilizing vector beams.

Recently, structured light beams have attracted substantial attention in many applications, including optical communications, imaging, optical tweezers, and quantum optics. We propose and experimentally demonstrate a reconfigurable structured light beam generator in order to generate diverse structured light beams with adjustable beam types, beam orders, and beam sizes. By controlling the sizes of generated free-space structured light beams, free-space orbital angular momentum (OAM) beams and vector beams are coupled into an air–core fiber. To verify that our structured light generator enables generating structured light with high beam quality, polarization distributions and mode purity of generated OAM beams and vector beams in both free space and air–core fiber are characterized. Such a structured light generator may pave the way for future applications based on higher-order structured light beams.

We propose a chip-integratable cylindrical vector (CV) beam generator by integrating six plasmonic split ring resonators (SRRs) on a planar photonic crystal (PPC) cavity. The employed PPC cavity is formed by cutting six adjacent air holes in the PPC center, which could generate a CV beam with azimuthally symmetric polarizations. By further integrating six SRRs on the structure defects of the PPC cavity, the polarizations of the CV beam could be tailored by controlling the opening angles of the SRRs, e.g., from azimuthal to radial symmetry. The mechanism is governed by the coupling between the resonance modes in SRRs and PPC cavity, which modifies the far-field radiation of the resonance mode of the PPC cavity with the SRR as the nano-antenna. The integration of SRRs also increases the coupling of the generated CV beam with the free-space optics, such as an objective lens, promising its further applications in optical communication, optical tweezer, imaging, etc.