Probing higher order optical modes in all-dielectric nanodisk, -square, and -triangle by aperture type scanning near-field optical microscopy

Abstract All-dielectric nanoantennas, consisting of high refractive index semiconductor material, are drawing a great deal attention in nanophotonics. Owing to their ability manipulate efficiently the flow light within sub-wavelength volumes, they have become building blocks wide range new photonic metamaterials and devices. The interaction antenna with is largely governed by its size, geometry, symmetry multitude optical cavity modes it supports. Already for simple shapes, unraveling full modal spectrum using conventional far-field techniques nearly impossible due spatial spectral overlap mismatch incident radiation fields. This limitation can be circumvented localized excitation antenna. Here, we report on experimental near-field probing higher order (CMs) whispering gallery (WGMs) amorphous silicon nanoantennas simple, but fundamental, geometrical shapes decreasing rotational symmetry: disk, square, triangle. Tapping into an aperture type scanning microscope (SNOM) opens window rich variety patterns resulting from local different even odd parity. Numerical analysis SNOM probe shows how reveal node positions – allows us distinguish between modes. As such, this study contributes richer deeper characterization structure confined nanosystems, impact structuring fields generate.