Radial phase shift spiral zone plate fabrication using direct laser writing for generating a perfect vortex beam

A vortex beam is a special light field that carries an orbital angular momentum (OAM). Different from a normal vortex beam, the vortex radius of a perfect vortex beam is independent of its topological charge. Due to this special property, perfect vortex beams have been widely used in fields such as optical communications, quantum optics and laser manufacturing. Traditional methods for generating perfect vortex beams are mainly based on liquid crystal spatial light modulators and digital micromirrors. These methods not only increase the system complexity but also the cost, making it hard for the system minimization and commercialization. In this paper, a radial phase shifting spiral zone plate (RSSZP) is fabricated to generate a perfect vortex beam using direct laser writing (DLW) with high fabrication speed and low cost. It is shown that the radius of a perfect vortex beam can be adjusted by tuning the radius phase shift of the RSSZP. Moreover, it is verified through interference experiment that the orbital angular momentum carried by the perfect vertex is consistent with the designed topological charge. Overall, this work demonstrated the potential of using DLW for the rapid fabrication of integrated photonic chips.