Directionally Asymmetric in Orbital Angular Momentum Generation Using Single-Layer Dielectric Janus Metasurfaces

Janus metasurfaces, offering versatile light manipulation contingent on incident direction, are explored across microwave to mid-infrared spectra. Nonetheless, prior designs often resort to spatial multiplexing or vertical stacking, entailing complex fabrication. Metallic Janus metasurfaces, owing to material properties, suffer notable Ohmic losses in the visible spectrum. In this study, Single-layer TiO2-based Janus metasurfaces with arbitrary polarization control is experimentally demonstrated, exhibiting directionally asymmetric functionalities in spin and orbital angular momentum (OAM). A novel Jones matrix formulation tailored for Janus metasurfaces is presented, enabling efficient generation of two asymmetric, high-purity OAM states of vortex beams at wavelength of 532 nm, contingent on incidence direction. This innovation facilitates compact and versatile phase manipulation, encompassing applications such as lasers and optical combiners, thereby expanding its utility across diverse domains. The first Janus metasurfaces convert asymmetric orbital angular momentum directionally from arbitrary spin angular momentum. Titania-based meta-atoms enable operation in the visible range. These meta-atoms also offer local and global rotation, as well as width control, achieving multifunctionality in a single-layer design, surpassing previous approaches based on spatial multiplexing or vertical stacking. image