An ultra-wideband bandstop plasmonic filter in mid-infrared band based on metal-insulator-metal waveguide coupled with an hexagonal resonator

Abstract

An ultra-wideband band-stop plasmonic filter (UWB-BSF) in mid-infrared (MIR) range based on metal–insulator–metal (MIM) waveguide coupled with a hexagonal resonator is proposed in this work. Using RSoft CAD commercial software, the designed BSF is numerically and theoretically investigated by the 2D Finite-Difference Time-Domain method. To enhance the BSFs system in mid-infrared, obtaining ultra-wide bandgap width (UWB) with the maximum passband transmission at the left and right of the bandgap and a high value of the rectangular coefficient, we increase the number of hexagonal cavities. Hence, the number of hexagonal resonators controls the range of the filtered wavelength of the BSFs system. In the case of two hexagonal-shaped resonators, the Fano resonance appears on the left and right sides of the bandgap, forming a U-shaped transmission spectrum, which is very helpful for improving the performance of the band-stop filter. Furthermore, by changing the geometric parameters of the hexagonal cavities the filtered wavelength range is shifted toward the near-infrared (NIR) band. The center wavelength of the bandgap of the proposed nano-stop-band filter is adjustable by varying the geometric parameters of the structure. This device operates in the near-infrared (NIR) and mid-infrared (MIR) wavelength ranges. With a larger bandgap width and tunable performance, this proposed nanostructure provides an advantageous application for plasmonic integrated circuits and broadband transmissions.