Polarization-insensitive, high numerical aperture metalens with nanoholes and surface corrugations

Metalenses provide new solutions to the shortcomings of traditional lenses, such as bulky volume and low resolution. In this paper, an ultrathin planar metalens based on the nanohole structure in a gold film was designed, which had only one variable (the diameter of the nanohole) and showed the ability to focus at the designed wavelength of 980 nm. Then, further improvements were made by adding a finite array of circular surface corrugations, which could enhance the resolution and energy at the focal spot because of the excitation of surface plasmons (SPs). The central symmetry of the metalens makes it polarization insensitive. Besides, the metalens with surface corrugations had a relatively high numerical aperture (NA = 0.848). This method of adding surface corrugations could also be adopted for other metal surface plasmon metalens to enhance the focusing effect in the far-field.