Perfect vortex beam with all-dielectric terahertz metasurface using 3D printing

Abstract

Wavefront manipulation is essential for various optical applications requiring specific optical states generated by a combination of multiple bulky optical elements with precise alignment. Especially generating the perfect vortex (PV) beam, which can be applied to various fields including optical communications, super-resolution microscopy, optical tweezing, and advanced quantum optics based on its stable intensity profiles across various topological charges, requires a spiral optics, an axicon, and a lens, unlike a conventional vortex beam simply generated using an axicon. Metasurfaces enable the generation of a specific light state using a single optical element, while it is still challenging to integrate multiple optical functionalities into a single metasurface design. Here, we demonstrate a straightforward approach for terahertz PV beam generation using a singlet metasurface fabricated by additive 3D printing manufacturing. Recent advances in microfabrication, including highresolution 3D printing, now make it possible to engineer single metasurface elements with complex phase profiles, paving the way for compact optical systems that generate PV beams directly. The proposed unit cell operates as a micro-optical scatterer, providing a full-wave phase shift with effectively suppressing undesired higher-order diffraction. By elaborately arranging these unit cells, we constructed a single meta-optical element whose phase distribution simultaneously implements spiral, axicon, and lens functions. Also, we experimentally verify the orbital angular momentum (OAM) manipulation of the fabricated metasurface and its robustness against variations in the incident polarization.