An ultra-thin high-efficiency plasmonic metalens with symmetric split ring transmitarray metasurfaces

Metasurface lenses (or metalenses) have aroused great attentions and efforts in the community of metamaterials or metasurfaces due to its ultrathin device dimension and superior focusing performances. High-efficiency transmissive metalenses with an ultra-thin device thickness are an important aspect especially in the low fre-quency by using plasmonic transmitarray antennas. In this paper, an ultra-thin plasmonic metalens with only 0.1 lambda (lambda is working wavelength, the aperture size is 7 lambda) device thickness is designed by changing the radius of the proposed symmetric complementary split ring resonator antenna metasurfaces. Thanks to its high transmittance and large phase shift of the plasmonic meta-atoms, the designed metalens achieves both high transmissive ef-ficiency of 80% and high focusing efficiency of 50% on the focal plane of F = 4.6 lambda in the simulations. The designed ultra-thin plasmonic metalens has a moderate large numerical aperture of 0.67 (NA = 0.67). In order to verify its high working efficiency of the proposed plasmonic metalens, a sample is also fabricated and a much higher focusing efficiency of 65% is realized in the measurements. The influence of the open angles of the symmetric split ring transmitarray metasurface on the focusing performances such as working efficiency and NA of the designed metalens is also studied and analyzed finally, which can add new degree of freedoms to optimize its focusing performance. The presented studies can facilitate the development of high-efficiency metalenses in the low frequency and have significant potential applications in high-resolution microwave imaging, high-gain metalens antennas and others.

Automated summary

This paper presents an ultrathin plasmonic metalens with high transmissive efficiency and focusing efficiency, which can play a significant role in the low frequency range. By changing the cell size on the lens surface, an ultra-thin metalens with a thickness of only 0.1 times the working wavelength is designed. Experimental results show that the metalens achieves 80% transmissive efficiency and 50% focusing efficiency on the focal plane. The influence of the open angle of the symmetric split ring transmitarray metasurface on the focusing performance of the metalens is also studied and analyzed, providing new insights for optimizing its performance.