Variable vortex optical metasurface: synergistic control of topological charge and focal position

An optical field with orbital angular momentum has shown significant application value in the fields of particle manipulation, quantum optics, and optical communication. Meanwhile, a vortex beam in the ultraviolet band exhibits the characteristics of high photon energy, short wavelength, and orbital angular momentum. Most vortex generators composed of metasurfaces lack adjustability, which limits their applications. In this paper, tunable metasurfaces based on the moiré effect are proposed. By controlling the relative rotation angle between the two cascaded metasurfaces, dynamic control over the wavefront phase of the outgoing beam was realized at a wavelength of 365 nm. This metasurface possesses both dual-beam output and multi-dimensional control capabilities for vortex beams. The vortex beams exhibit the ability to simultaneously manipulate the characteristics of orbital angular momentum, focal position, and deflection angle. With continuous adjustability and flexible control, metasurfaces are widely used in super-resolution imaging, optical micro-nano manipulation, micro-nano processing, integrated optical systems, and so on.