Strong field enhancement and ultra-narrow linewidth based on the coupling of anapole/gap modes in silicon nanodimer-ring arrays

All-dielectric metamaterials have recently received significant attention in the field of nanophotonics, due to their negligible dissipative losses and strong polariton response compared with metallic metamaterials. However, simultaneously achieving an ultra-narrow resonance linewidth and a significant field enhancement in the all-dielectric metamaterials is still a great challenge, limiting their further practical application. In this work, a novel nanostructure composed of silicon ring and nanodimer arrays is theoretically proposed and numerically simulated. Through introducing the coupling between the anapole mode originating from the ring arrays and the gap mode deriving from the nanodimer arrays, the as-designed dielectric metamaterial manifests dual-band high-quality resonance characteristics with strong electric field enhancement reaching up to 300 times, an ultra-narrow linewidth as narrow as 0.35 nm, and a large Q-factor of 4223.43 synchronously. Benefiting from the exceptional optical spectral characteristics, the proposed dielectric nanodimer-ring metamaterial can work as a high-available refractive index sensor, whose sensitivity can reach 307.69 nm RIU−1 with its figure of merit attaining 879.11 RIU−1, efficiently distinguishing an index change of less than 0.01. This research opens up a promising path for achieving extremely narrow spectral linewidth and significant enhancement of the electric field, exhibiting immense possibilities in applications such as biochemical sensing, nonlinear optics, and surface enhanced spectroscopy.