Nanoscale TiO₂ dielectric resonator absorbers

We demonstrate a narrow-band plasmonic absorber based on a uniform array of nanoscale cylindrical dielectric resonators (DRs) on a metallic substrate at visible frequencies. Under a normally incident plane-wave excitation, the DRs resonate in their horizontal magnetic dipolar mode, which can be seen as localized plasmonic hot spots. Such a localized resonance also couples incident waves into surface plasmon polaritons (SPPs) bidirectionally, and perfect absorption is achieved by creating SPP standing waves. The simulation shows perfect absorption at 633 nm and 1.8% relative bandwidth with >90% absorption, while the measurement demonstrates maximum absorption of 90% at 636 nm. Both simulation and measurement results are analyzed with coupled mode theory. An additional numerical study elaborates on the dependence of absorption on the resonator size, period, and incidence angle.