High-index nanoparticles are known to support radiationless states called anapoles, where dipolar and toroidal moments interfere to inhibit scattering to the far field. In order to exploit the striking properties arising from these interference conditions in photonic integrated circuits, the particles must be driven in-plane via integrated waveguides. Here, we address the excitation of electric anapole states in silicon disks when excited on-chip at telecom wavelengths. In contrast to normal illumination, we find that the anapole condition—identified by a strong reduction of the scattering—does not overlap with the near-field energy maximum, an observation attributed to retardation effects. We experimentally verify the two distinct spectral regions in individual disks illuminated in-plane from closely placed waveguide terminations via far-field and near-field measurements. Our finding has important consequences concerning the use of anapole states and interference effects of other Mie-type resonances in high-index nanoparticles for building complex photonic integrated circuitry.

Anapole resonances in high-index dielectric nanoparticles arise from the destructive interference between electric and toroidal dipole moments. So far, this mode interference has been solely observed using normal incidence free-space radiation. Here we show that anapole resonances can also arise in silicon disks being excited by an in-plane oriented waveguide. We provide both far-field and near-field measurements at telecom wavelengths which, in good agreement with numerical simulations, show the expected signatures of an anapole resonance. This work paves the way towards the use of the anapole resonances in on-chip silicon photonics.