Tunable extraordinary optical transmission spectrum properties of long-wavelength infrared metamaterials

Metamaterial filters represent an essential method for researching the miniaturization of infrared spectral detectors. To realize an 8-2 µm long-wave infrared tunable transmission spectral structure, an extraordinary optical transmission metamaterial model was designed based on the grating diffraction effect and surface plasmon polariton resonance theory. The model consisted of an Al grating array in the upper layer and a Ge substrate in the lower layer. We numerically simulated the effects of different structural parameters on the transmission spectra, such as grating height (h), grating width (w), grating distance (d), grating constant (p), and grating length (S ₁), by utilizing the finite-difference time-domain method. Finally, we obtained the maximum transmittance of 81.52% in the 8-12 µm band range, with the corresponding structural parameters set to h=50n m, w=300n m, d=300n m, and S ₁=48µm, respectively. After Lorentz fitting, a full width at half maximum of 0.94±0.01µm was achieved. In addition, the Ge substrate influence was taken into account for analyzing the model's extraordinary optical transmission performance. In particular, we first realized the continuous tuning performance at the transmission center wavelength (8-12 µm) of long-wave infrared within the substrate tuning thickness (D) range of 1.9-2.9 µm. The structure designed in this paper features tunability, broad spectral bandwidth, and miniaturization, which will provide a reference for the development of miniaturized long-wave infrared spectral filter devices.