Multiplexing of terahertz signals based on gold-coated polymer parallel-plate waveguides

We propose and experimentally realize a three-channel terahertz (THz) multiplexer based on a gold-coated polymer plate with periodical corrugations. The periodic undulating structure was designed on the polymer flat plate and fabricated with a CO2 laser marker. To confine THz wave propagation, a layer of gold film was coated on the corrugated polymer surface by using the ion sputtering. The perfect periodic structure can cause resonances between the guided wave modes, which always produce the frequency forbidden bands. In the forbidden bands, no THz signal can pass through the waveguide. Then, we introduce a protrusion in the middle of the periodic structure to form a defect, which can lead to the spectral band splitting and get a passband with a narrow bandwidth within the former forbidden band. The additional three corrugated structures with different middle protrusions were designed as a row with aligned defects to realize the three THz channels, which can be used as a multiplexer and the achieved narrowest linewidth is 1.0 GHz. The further numerical simulations show that the center frequency and bandwidth of the multiplexer can be easily selected by changing the design of waveguide parameters. The proposed multiplexer is easier to fabricate and has excellent performance, which would effectively improve THz band utilization and provide a way for frequency division multiplexing in THz communication systems.