On the optical field confinement at the anapole mode in nanohole silicon metasurfaces

TL;DR

This paper investigates optical field confinement at the anapole mode in silicon nanohole metasurfaces, demonstrating that certain nanostructures do not achieve desired confinement, but alternative designs can significantly improve it.

Contribution

It shows that replacing a grouped nanohole array with a square nanohole array enhances electric field confinement at the anapole mode.

Findings

Grouped nanohole array does not achieve valuable electric field confinement.

Square nanohole array with different meta-atom improves confinement.

Anapole mode can be exploited more effectively with optimized nanostructure design.

Abstract

Recently, researchers demonstrated numerous types of the metasurfaces with non-radiating states including the anapole ones. These metasurfaces have promising properties for various applications in optics which are mainly connected with the optical field confinement. But by itself, the existence of the anapole state does not make one available to exploit this feature. For example, Ospanova et al. [\textit{Laser \& Photonics Rev.}, 2018, vol. 12, p. 1800005] presented a grouped nanohole array in silicon slab possessing anapole mode in visible range. In this work, it is proved that despite of the existence of the anapole mode in the proposed nanostructure the valuable electric field confinement is not reached. Thus most expected uses of the anapole state cannot be gained through this nanostructure. As demonstrated here, the aforementioned nanostructure may be replaced by the square nanohole array having the anapole state with different meta-atom and much larger electric field confinement.