Single polarization single mode THz hollow-core anti-resonant waveguide with multi-size semi-elliptical tubes and high-resistance silicon layer

We present the design of a Single Polarization Single Mode (SPSM) Terahertz Hollow-Core Anti-Resonant Waveguide (THz HC-ARW) by using multi-size semi-elliptical tubes (SETs) and high-resistance silicon layer. High single mode performance can be achieved by optimizing the structural parameters in the structure of the THz HC-ARW with multi-size SETs in the cladding. Numerical results indicate that the single mode bandwidth with High Order Mode Extinction Ratio (HOMER) above 100 reaches up to 420 GHz covering the frequency range from 0.82 THz to 1.24 THz, in which the loss of Fundamental Mode (FM) remains below 0.05 dB/m. To the best of our knowledge, this is the first instance of achieving low loss of FM under 0.05 dB/m and HOMER exceeding 100 within an exceptionally wide frequency bandwidth for a THz HC-ARW. On the basis of the above structure, a modified structure is proposed to further obtain single polarization characteristics by selectively coating a high-resistance silicon layer on the inner surface of one SET. When a high-resistance silicon layer with the thickness of 0.258 mm is coating on the inner surface of the biggest SET, a high polarization extinction ratio of 371 and a HOMER of 106 can be attained simultaneously at a frequency of 1 THz, thus only the X-polarization FM with low loss of 0.04 dB/m can propagate through the waveguide. This means SPSM can be achieved in the proposed modified structure.