Experimental observation of higher-order anapoles in individual silicon disks under in-plane illumination

Abstract

Anapole states—characterized by a strong suppression of far-field scattering—naturally arise in high-index nanoparticles as a result of the interference between certain multipolar moments. Recently, the first-order electric anapole, resulting from the interference between the electric and toroidal dipoles, was characterized under in-plane illumination as required in on-chip photonics. Here, we go a step further and report on the observation of higher-order (magnetic and second-order electric) anapole states in individual silicon disks under in-plane illumination. To do so, we increase the disk dimensions (radius and thickness) so that such anapoles occur at telecom wavelengths. Experiments show dips in the far-field scattering perpendicular to the disk plane at the expected wavelengths and the selected polarizations, which we interpret as a signature of high-order anapoles. Some differences between normal and in-plane excitation are discussed, in particular, the non-cancelation of the sum of the Cartesian electric and toroidal moments for in-plane incidence. Our results pave the way toward the use of different anapole states in photonic integrated circuits either on silicon or other high-index dielectric materials.