Development of flat-surface nanostructured phase components for the formation of fractional optical vortex beams

Abstract We report the development and characterization of a fractional nanostructured gradient-index (GRIN) vortex phase component for generating fractional optical vortex (OV) beams in the near-infrared. The element was fabricated using a modified stack-and-draw method, yielding a proof-of-concept mask with a thickness of 38 μ m and a 30 μ m vortex core. The performance of the component was evaluated through both theoretical analysis and experiment. Optical measurements confirmed the formation of OV beams with integer and fractional topological charges between l = 3 and l = 4, exhibiting characteristic phase singularities and corresponding intensity structure, in good agreement with numerical simulations. The flat-surface geometry, broadband spectral response, and reproducible fabrication approach confirm the fractional nanostructured GRIN vortex phase component as a compact and versatile platform for controllable vortex generation, with potential applications in optical tweezers, biological particle manipulation, optical communication, optical imaging, and laser-based material processing.