Broadband high-efficiency aperiodic metasurface for the vortex waves generation

Vortices have diverse applications in optics, such as ultrafast singular optics, quantum optics, microscopy as well as optical trapping. These applications require compact, easily integrated, and high-performance devices, so the development of highly efficient broadband single-layer structures for vortex generation and control is an extremely relevant research topic. Here, we propose an aperiodic transmissive all-dielectric metasurface, which controls the phase delay of the electromagnetic waves via Pancharatnam–Berry (PB) phase manipulation. The metasurface is constructed on the basis of TiO2 nanopillars in the form of an aperiodic golden angle (GA) Vogel spiral. Through numerical simulations, we demonstrate that the metasurface enables the generation of vortex waves with a desired topological charge l and high mode purity over a wide wavelength range from 470 to 580 nm, which indicates a relative bandwidth of 21%. The proposed metasurface platform, due to its simple structure and wide bandwidth, is a good candidate for manipulating ultrashort vortex pulses and for the developing optical devices with improved functionality and performance.