A novel, highly efficient terahertz fully polarized transmission line is designed by two-dimensional tellurium photonic crystals consisting of square lattice rod arrays with a complete photonic bandgap. The TE and TM photonic bandgaps of the tellurium photonic crystals, which are computed by plane wave expansion, happen to coincide, and the complete photonic bandgap covers from 2.894 to 3.025 THz. The function of the designed waveguide is simulated by the finite element method, and the transmission characteristics are optimized by accurately adjusting its structural parameters. The transmission efficiency of the waveguide for TE mode achieves a peak value of −0.34 dB at a central frequency of 2.950 THz and keeps above −3 dB from 2.82 THz to 3.02 THz, obtaining a broad relative bandwidth of about 6.84 percent. The operating bandwidth of the tellurium photonic crystals’ waveguide for TM mode is narrower than that of TE mode, whose relative bandwidth is about 4.39 percent or around 2.936 THz above −5 dB. The designed terahertz photonic crystals’ waveguide can transmit both TE and TM waves, and not only can it be used as a high-efficiency transmission line, but it also provides a promising approach for implementing fully polarized THz devices for future 6G communication systems.

Future 6G communication systems will require wideband nonreciprocal devices in the terahertz frequency domain. A novel ultra-wideband terahertz circulator is implemented by inserting a Ni_xZn_1−xFe₂O₄ ferrite sphere into the Al₂O₃ dielectric rod-array. The operating bandwidth of the circulator is broadened to 40 GHz via the external matching method through two hexagonal aluminum sheets. The three-dimensional numerical simulation suggests that the designed circulator also has an excellent insertion loss and isolation of 49.37 dB and 0.56 dB, respectively, via the finite element method. The low loss, high isolation and ultra-wideband show that the proposed scheme provides an effective path for realizing high-performance THz devices.