Broadband metamaterial absorber at mid-infrared using multiplexed cross resonators

In this paper, we theoretically and experimentally demonstrate broadband metamaterial absorbers that work in the mid-infrared regime. In the absorbers, two or four gold cross resonators with different sizes are multiplexed in a unit cell on SiO(2) spacing layer on top of gold ground plane. Compared with the single cross resonator absorbers with a Q factor of 6.39, the developed absorber with two cross resonators multiplexed reduces the Q factor to 3.78. When four different cross resonators are integrated, the Q factor drops to as low as 1.85, and the bandwidth almost covers the full mid-infrared regime from 3 μm to 5 μm with absorbance higher than 50%.