Subwavelength focusing and experimental detection of large-scale metallic multi-annular metasurfaces

To realize a long working distance and high resolution focusing for diffraction optical element, the large-scale optical elements need to be employed. Based on the vectorial angular spectrum theory and genetic algorithm, a large-scale metallic multi-annular metasurface (MAM) was designed. The MAM realizes subwavelength focusing and has a main focal spot within the range of 0–140 μm. The focal length is 113.5 μm. Using electron beam lithography, the designed MAM was fabricated. The experimental setup was built. The intensity distribution of the main focal spot was experimentally obtained. The theoretical and experimental results have a good agreement, which show that the proposed method can be used to design the large-scale MAM.