Ultra-narrowband dielectric metamaterial absorber for sensing based on cavity-coupled phase resonance

Abstract

We propose an ultra-narrowband dielectric metamaterial absorber with dielectric-dielectric-metal (DDM) structure where a dielectric cavity layer is inserted between the top compound periodic dielectric microstructures and bottom metal substrate. The results show that this absorber has an ultra-narrowband absorption with a full width at half-maximum (FWHM) of 0.028 nm and quality factor larger than 50,000 in the near-infrared regime. The electric field distribution shows that the phase resonance excited in the microstructures slits is coupled with the cavity resonance occurring in the middle dielectric layer which can greatly narrow the absorption bandwidth. More importantly, the absorption bandwidth can be flexibly manipulated by adjusting the thickness of the dielectric cavity layer. Due to the ultra-narrow absorption bandwidths and electric field concentrated in the slits, we can get a huge figure of merit (FOM) of 6731 which is much larger than those of the reported absorbers in the near-infrared regime. In addition, the larger FOM of 20,366 can be attained with higher-order mode resonance in the dielectric cavity layer. The proposed metamaterials have the great potentials in sensing applications.