Generation of Bessel beams with tunable topological charge and polarization.

Bessel beams hold significant potential in optical communications, particle manipulation, and medicine due to their self-healing and nondiffracting properties. However, most existing Bessel beam generation devices are either static or capable of dynamically adjusting only a single characteristic. In this paper, we propose a tunable Bessel beam generation scheme based on a moiré meta-device. The device consists of two cascaded layers of all-dielectric metasurfaces. By adjusting the relative rotation between two layers, Bessel beams with varying topological charges can be generated. Moreover, the overall rotation of the cascaded metasurfaces modulates the polarization state of the Bessel beam by leveraging both the propagation phase and geometric phase. Experimental results confirmed the generation of Bessel beams with tunable uniform linear polarization and topological charge, as well as Bessel beams with tunable topological charge and controllable polarization variations along the propagation direction. This method offers a flexible design strategy for the continuous dynamic manipulation of both the transverse and longitudinal optical field properties of Bessel beams. In addition, it may also advance the development of related fields, including optical communications, particle manipulation, and super-resolution imaging.