| Summary: | We propose a type of hollow planar waveguide with corrugated walls, which can realize electrically tunable terahertz (THz) filtering by filling the slit with liquid crystals. When the THz signals propagate in a planar waveguide with periodic corrugations, the transmission spectrum always exhibits many pass and stop bands. Inserting a section of defects in the middle of the periodic corrugations can excite an extremely narrow transmission peak, which would be a very good THz filter for frequency division. To achieve tunability of this narrow linewidth THz filter, we also fill the slit between the two corrugated walls with a nematic liquid crystal. The effective refractive index of liquid crystals will change with the external electric field, thus tuning the frequency of the narrow peak. The simulated results show that the center frequency of the proposed filter can be tuned linearly in the frequency range of 0.984~1.023 THz by the external electric field. Moreover, the bandwidth of the filter can be adjusted from 3.2 GHz to 0.3 GHz by increasing the number of periods in the waveguide, and a maximum Q value of 2556 can be achieved when the number of periods at both sides of the defect is 12.
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