Near-perfect absorber with ultrawide bandwidth in infrared region using a periodically chirped structure

We propose a near-perfect absorber with ultrawide bandwidth in infrared region using a periodically chirped subwavelength structure implemented in both one-dimensional (1D) and two-dimensional (2D) schemes. The structure is composed of an array of chirped metal-insulator-metal resonators made of a metal/dielectric two-layer grating sitting on a uniform metal layer. Each resonator harvests the photon via the SPP localization at its own resonance wavelength which exhibits linear distribution due to the linearly chirped structure. A near-perfect absorption in wide bandwidth is realized with an appropriate design under the restriction of phase-matching and subwavelength dimension. A stop-band with a FWHM of 3 μm at central wavelength of ∼9 μm and a high absorption efficiency of up to 92% is achieved simultaneously. This provides a novel method in designing and implementing flexible thin-film devices with wide bandwidth and high absorption efficiency.