Numerical study on the tight focusing of radially polarized beams with polarization-insensitive metalenses

Radially polarized beam (RPB) could be focused to a tighter spot than a spatially homogeneous polarized beam with a high numerical aperture (NA) objective lens. However, the traditional objective lens suffers from high cost and bulky size. In this paper, polarization-insensitive nanopillar metalenses were designed to execute tight focusing without the requirement of the incident beams to be specific polarized states. It was found that the focal spot of RPB was potentially smaller than that of a linear polarized beam because of the longitudinal component. Diffraction-limited focusing of RPB was achieved by a high NA polarization-insensitive metalens through an annular aperture illumination. This study may contribute to high-resolution photonics and optoelectronic applications.