Research On High-Efficiency Broadband Metasurface Devices Based On Catenary-like Structure

Metasurfaces,which are the two-dimensional electromagnetic metamaterial consisting of sub-wavelength antenna array,have the ability to flexibly control incident electromagnetic waves within sub-wavelength scale.Over the past decades,researches on metasurfaces have yielded fruitful results.To improve the efficiency and bandwidth performance of metasurface-based devices,there are three stages during the process of the metasurfaces: single-layer transmissive metal metasurface,metal-insulator-metal(MIM)structure reflective metasurface and all-dielectric transmission metasurface.For transmissive metasurface devices,the design of metal-based single-layer metasurfaces has limited efficiency(?25%)due to strong ohmic losses;while the all-dielectric metasurfaces based on discrete strategies have a narrower operating bandwidth.This article focuses on the difficulty of designing transmissive metasurface devices with both high efficiency and wide bandwidth.The main contents of the work are as follows:1.The PB phase has inherent bandwidth characteristics in physical properties due to its wavelength-independent.Catenary-like sub-wavelength structures have been designed by integrating the spatial phase distribution to alleviate the trap of the narrow bandwidth of the traditional PB phase metasurfaces based on the discrete strategy.The optimized catenary-like silicon dielectric pillar has nearly 100% diffraction efficiency in the 23.08 ~ 33.52 THz band.A deflector is designed and processed to experimentally verify the efficiency and bandwidth of the meta-device based on the catenary-like silicon dielectric column design.Furthermore,a two-dimension self-accelerated beam generator with a cubic phase distribution was designed to further verify the performance of catenary-like silicon dielectric pillars in designing complex meta-devices.The selfaccelerating beam trajectories,which are agree well with the theoretical curve,were measured under left-circularly polarized light at various frequencies.The polarization multiplexing characteristic of the self-accelerating beam generator is validated by different beam trajectories which are generated under different polarized light.2.Continuous PB phase manipulation can be achieved by nano-aperture which is complementary to the sub-wavelength pillar structure.Firstly,the catenary-like slit structure,which has both an absolute efficiency and a diffraction efficiency of about 50%,has been designed based on the dielectric material from 23.08 ~ 33.52 THz.Furthermore,a one-dimension metalens with ultra-long focal length was designed to verify the performances of the catenary-like slit structure.The results of electromagnetic simulation are basically consistent with the numerical calculation results.The imaging properties of the two-dimensional metalens with ultra-long focal length were further studied by numerical calculations,and its imaging range was 12.5 times the focal depth of the traditional lens.Additionally,the catenary-like slit structure optimized in the visible light band has a diffraction efficiency of 72.54% at the center wavelength,and an average diffraction efficiency of 67.66% in the 374THz~574THz band.A first-order Bessel beam generator is designed based on this sub-wavelength structure.The electromagnetic simulation results show that its diffraction-free distance meets with the theoretical result under 0.4% relative error.