Multifunctional optical transverse vortex manipulation via cylindrical metasurfaces under cross-medium conditions.

Metasurfaces have provided a powerful platform for exploring the fundamental physics and advanced applications of optical vortices. However, most existing studies focus on the same background medium and largely overlook multifunctional vortex manipulation under cross-medium scenarios. In this work, we propose an innovative structure of two-dimensional (2D) cylindrical metasurfaces (CMs) with different interior and exterior media and investigate the multifunctional control of optical transverse vortex under two-way diffraction conditions. The underlying physical mechanism is jointly ensured by angular momentum conservation and spatially asymmetric transmission. The isofrequency diagram respectively exhibits a wavevector momentum gap and overlap under the dense-to-rarer transition and rarer-to-dense transition, which provides a theoretical foundation for the diversified manipulation of 2D vortex fields. This work enriches the theoretical framework of vortex beam manipulation and holds promise for applications in cross-medium multichannel optical communications.