A terahertz polarization filter based on non-uniform thickness dielectric twin-tube

A simple-structured total internal reflection terahertz filter based on a microstructured optical fiber is proposed in this paper, consisting of two non-uniform thickness dielectric tubes symmetrically nested within an outer cladding. The investigation uses the finite element method and the simulation results show that the x-polarized fundamental mode (XPFM) is well confined within the fiber core, while the lowest-loss higher-order mode (LL-HOM) exhibits significant loss, and y-polarized fundamental mode (YPFM) exhibits even greater loss. Specifically, the loss difference between the XPFM and the LL-HOM is 15.39 dB/cm at 1 THz. After a 2 cm transmission length, the LL-HOM achieves an extinction ratio of 30 dB, while the insertion loss of the XPFM is only 0.67 dB. Furthermore, when the length of the filter is fixed at 4.1 cm, stable single-mode transmission of the XPFM is maintained over the frequency range from 0.755 THz to 1.075 THz, with the insertion loss of the XPFM remaining below 1.5 dB. The proposed filter demonstrates excellent fabrication tolerance and holds significant potential for applications in terahertz systems.