Perfect vortex beam generation with high numerical aperture in broadband UV-Visible regime

The ultraviolet (UV) and visible regions of the electromagnetic spectrum incorporate many exciting applications, including high-resolution imaging, optical communication, lithography, sensing, and many more. The classic ways of manipulating electromagnetic waves through bulky, large, and expensive components stand between the new technologies like on-chip systems. The advancement of nanofabrication technologies enables the advent of optical metasurfaces that can manipulate approximately the whole electromagnetic spectrum. However, the availability of a suitable and lossless material for the UV and Visible region hinders the creation of metasurfaces and their integration for practical applications. Herein, we exploit the bandgap-engineered silicon nitride (Si3N4) material, which is transparent in most parts of the UV spectrum and can perform efficiently in both regimes. For proof of the concept, we design and numerically simulate different metasurfaces to generate the perfect vortex beam with different topological charges and a numerical aperture of 0.6. Each metasurface is functional for both UV and visible regions and efficiently manipulates the incident light. The independence of phase profile from topological charge helps perfect the vortex beam, to control the shortcomings of the optical vortex beam. The cross-polarization efficiency of the metasurface is also up to the mark. This work may find potential applications in different fields like on-chip communication, lithography, quantum processing, and optical communication.