3D Dirac Semimetal Elliptical Fiber Supported THz Tunable Hybrid Plasmonic Waveguides

A novel tunable terahertz hybrid plasmonic waveguide based on a 3D Dirac semimetal (DSM) elliptical fiber separated from a silicon layer by a dielectric gap is explored. Interestingly, the results manifest that as the elliptical ratio increases, the real part of the effective mode index and the propagation length both monotonically increase. Importantly, the figure of merit strikingly reaches more than 1500. The propagation length shows a peak near the interface between the near filed and dissipation regions. The near field region is significantly affected by the Fermi level, in that the critical transition thickness is from 10.8 μm to 0.92 μm when the Fermi level varies in the range from 0.03 eV to 0.10 eV. The propagation properties of hybrid modes can be modulated in a wide scope via the Fermi level of the 3D DSM fiber, the propagation length can be modulated from 6.27 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> μm to 1.16 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> μm on the condition that the Fermi level changes in the range of 0.04 eV--0.15 eV, and the corresponding modulation depth is about 95%. The results are very useful to aid the design of novel plasmonic devices, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e.g.</i> , low threshold lasers, modulators and polarizer.