Optical Metasurfaces for Tunable Vortex Beams

Abstract The pursuit of device miniaturization and the generation of complex output responses has driven the development of optically tunable metasurfaces. Among these advancements, metasurface‐based vortex beams (VBs) have emerged as promising optically tunable knob technology due to their infinite output states through various orbital angular momentum (OAM) modes. In this study, the metasurface‐based VBs are successfully fabricated with exceptionally high OAM modes of 32 and 16, carefully examined using the Mach‐Zehnder interferometer. Throughout this study, these devices are referred to as infinite‐OAM meta‐knobs (IOMKs). The optical tunability of IOMKs is demonstrated by illuminating them with incident light possessing diverse degrees of freedom, including different polarizations and wavelengths. Furthermore, the interference nature of the IOMKs is experimentally explored by incorporating them into interference eraser measurements, providing an additional degree of freedom to the optical knob. In the interference eraser experiment, the broadband capability and the high reproducibility of the IOMKs with the OAM modes of 32 and 16 at three distinct wavelengths of 450, 530, and 610 nm is demonstrated. These findings represent a significant step toward understanding the potential applications of IOMKs in quantum optics and their promising role in the generation of complex output states.