Multi-band perfect vortex beam generation using all-dielectric metasurface

Vortex beams offer a novel avenue for advancing information transmission, storage, and processing within the optical domain. However, conventional optical apparatus and systems depend on the phase accumulation technique to create vortex beams. These methods frequently lead to the development of cumbersome and expensive configurations, hindering the integration with on-chip photonic systems. Metasurfaces, planar structures composed of nano-elements, hold immense promise for extensive adoption in optics and photonics. Their remarkable capacity to manipulate light at the nano-level has led to widespread utilization, particularly in generating optical vortices. In this work, we proposed an all-dielectric transmissive metasurface platform that generates a perfect vortex beam with a trigonometric function embedded in it to achieve an infinite topological charge. We selected silicon nitride (Si3N4) as the material of choice. It exhibits transparency in the ultraviolet (UV) region and across the visible spectrum. It also exhibits best-suited optical properties to ensure exceptional response in the targeted dual bands. We selected a numerical aperture of NA = 0.7 for verification of the concept, and two trigonometric functions are θ. cos(θ) and 1/2 sin(θ). The presented design technique and material may find potential applications in biomedicine, free-space optical data communications, and optical data modulation.