Anapole Manipulation in Tailored Si Nanocubes for Near-Field Enhancement and High Q-Factor Resonance

Dielectric materials exhibit negligible dissipative losses and strong electromagnetic multipolar optical responses at operating wavelengths compared to metallic materials. In a high-refractive-index dielectric, the destructive interference of the radiation fields from electric and toroidal dipole moments results in the anapole, which has the optical properties of a dark state and cannot emit energy in the far-field region. This study uses periodic Si nanocubes (SN) to support anapole excitation with lattice resonance based on numerical simulation and manipulates the anapole by tailoring structures according to the electromagnetic field distribution characteristics of the anapole. Long slits are introduced in the center to regulate the electric dipole moments, and elliptical holes are opened on both sides to adjust the current distribution and thus influence the toroidal dipole moments. The reflection resonance peak of tailored Si nanocubes shows a narrow bandwidth of 0.11 nm and a large Q-factor of 8053. Also, their reflection resonance peak shows more than 237 times the electric field enhancement in the dielectric. The tailored Si nanocubes provide an alternative to plasmonic metal to support hot spots and achieve near-field enhancement, which can be applied to enhance photon emission, surface-enhanced Raman scattering (SERS), and photocatalysis.