Theoretical study of a widely tunable terahertz metafilter based on a simple double-layered subwavelength metallic rod architecture

Tunable bandpass terahertz filters are demanded in various key applications, such as hyperspectral imagers, miniaturized spectrometers, and high-speed wireless communication systems. Here, a mechanically reconfigurable double-layered subwavelength metallic structure is presented for frequency-agile terahertz transmission bandpass filtering. The theoretically demonstrated polarization-insensitive filter shows remarkable performance metrics. By varying the vertical interlayer spacing of the metallic layers from 20 µm to 4 µm, the operation frequency tunes from 0.81THz to 1.32THz, and the full width at half maximum bandwidth changes from 209 GHz to 135 GHz, with maximum transmission efficiency greater than 98% and quality factor ranging between 3.88 and 9.77. A larger variation range of the vertical interlayer spacing leads to an enhanced frequency tuning range of the filter. Furthermore, simultaneous vertical and lateral interlayer displacements can provide polarization-dependent behavior for the filter. The underlying physical mechanism governing the filter’s frequency response and tuning capability is analyzed by examining the electromagnetic field distributions within the double-layered subwavelength metallic structure and its Fabry–Pérot-like behavior. The presented scheme holds significant promise for many terahertz applications due to its large tuning range, easy tuning mechanism, simple structure, and compatibility with fabrication materials and processes.