Optical spin-symmetry breaking for high-efficiency directional helicity-multiplexed metaholograms

摘要

Helicity-multiplexed metasurfaces based on symmetric spin-orbit interactions(SOIs)have practical limits because they cannot provide central-symmetric holographic imaging.Asymmetric SOIs can effectively address such limitations,with several exciting applications in various fields ranging from asymmetric data inscription in communications to dual side displays in smart mobile devices.Low-loss dielectric materials provide an excellent platform for realizing such exotic phenomena efficiently.In this paper,we demonstrate an asymmetric SOI-dependent transmission-type metasurface in the visible domain using hydrogenated amorphous silicon(a-Si:H)nanoresonators.The proposed design approach is equipped with an additional degree of freedom in designing bi-directional helicity-multiplexed metasurfaces by breaking the conventional limit imposed by the symmetric SOI in half employment of metasurfaces for one circular handedness.Two on-axis,distinct wavefronts are produced with high transmission efficiencies,demonstrating the concept of asymmetric wavefront generation in two antiparallel directions.Additionally,the CMOS compatibility of a-Si:H makes it a cost-effective alternative to gallium nitride(GaN)and titanium dioxide(TiO2)for visible light.The cost-effective fabrication and simplicity of the proposed design technique provide an excellent candidate for high-efficiency,multifunctional,and chip-integrated demonstration of various phenomena.