Tunable graphene-based plasmonic multispectral and narrowband perfect metamaterial absorbers at the mid-infrared region.

We numerically investigate the optical performance of a periodically patterned H-shaped graphene array by the finite-difference time-domain (FDTD) in the mid-infrared region. The simulated results reveal that absorption spectra of the proposed structure consist of two dramatic narrowband perfect absorption peaks located at 6.3 μm (Mode 1) and 8.6 μm (Mode 2) with high absorption coefficients of 99.65% and 99.80%, respectively. Two impressive absorption bandwidths that are the full width at half-maximum (FWHM) of the resonant frequency of 90 nm and 188 nm are obtained. The dipole resonance mode is supported by graphene ribbon at a wavelength of 6.3 μm. While the other absorption, attributed to the hybridized mode, is a new resonance that is different from the dipole resonance. The spectral position of the absorption peaks can be dynamically tuned by controlling the refractive index of the dielectric and the Fermi energy of graphene. Furthermore, we can obtain multispectral absorption peaks by applying multilayer graphene arrays. These design approaches enable us to control the number of absorption spectra and such absorbers will benefit the easy-to-fabricate nanophotonic devices for optical filtering, thermal detectors, and electromagnetic wave energy storage.