Narrow-band and highly absorbing fano resonance in a cavity-coupled dielectric metasurface

Abstract

Metamaterial resonance offers a flexibility in engineering the frequency and bandwidth of light absorption for a variety of optoelectronic applications such as wavelength-selective photodetection, optical sensing and infrared camouflaging etc. In this paper, we demonstrate a class of metal-dielectric thin-film cavity-coupled dielectric metasurfaces, which feature Fano resonances with both narrow bandwidth and strong light absorption. Our fabricated metasurface consists of a Si cuboid array on top of a SiO2 film backed with a metallic Cu layer. The weak coupling between electric mie mode in Si cuboid and Fabry–Perot mode within the SiO2 spacer layer yields a Fano resonance at 4.19 μm wavelength, which exhibits a strong light absorption of 65.8% and a quality (Q) factor of 112. The strongly absorbing Fano resonance is tunable within the 3–5 μm band by varying geometric parameters of the metasurface. To reveal potential application of the metasurface, the Fano resonance is applied in refractive index sensing and exhibits a sensitivity of 518.75 nm RIU−1 and a figure-of-merit (FoM) of 14.82 RIU−1. These results suggest that cavity-coupling presents an effective way in reducing the resonance bandwidth and enhancing light absorption in dielectric metamaterials, which holds promise for expanding the properties and device functionalities of metamaterials.