Ultra-broadband long-wave infrared metasurface absorber based on Peano fractal curve

Abstract

Fractals have emerged as a promising platform for realizing broadband absorption metasurfaces. In this paper, we propose an ultra-broadband absorber with high absorption operational in the long-wave infrared regime by means of a second-order Peano fractal curve (PFC) metasurface with a four-layer insulator–metal–insulator–metal (Ge/Cr/Ge/Cr) waveguide structure. The unique space-filling shape of the PFC enables the generation of multiple gap plasmon resonance modes, which expands the bandwidth of the absorber. In addition, the hybridization of these modes with cavity mode resonances and localized surface plasmon resonances enhances the average absorption of the device in the spectrum of operation, with an average absorption of 94.3% obtained for TM-polarized light with wavelengths between 12.3 µm and 32 µm in our simulations. A second-order quasi-PFC is designed for polarization-insensitive broadband absorption. Our findings establish general and systematic strategies for guiding the design of metamaterial absorbers with excellent broadband absorption.

Keywords

• Peano fractal
• Metasurface
• Long-wave infrared