Terahertz Extreme Skin-Depth Waveguides

All-silicon substrateless waveguides have become a leading contender for terahertz device integration owing to their broad operating bandwidth and exceptional efficiency. However, without metallic confinement, these unshielded waveguides are susceptible to evanescent coupling, requiring that waveguides be placed sparsely to resist unwanted interactions. This sparsity remains a critical obstacle to compact devices and integrated systems. To counter this, we demonstrate substrateless extreme skin-depth waveguides, utilizing a self-supporting anisotropic cladding that markedly reduces the evanescent field penetration into the surrounding cladding, and hence, suppresses cross coupling between waveguides. Here, we achieve 20-dB cross-talk suppression across the WR3.4 band, 220–330 GHz, a 40% fractional bandwidth, with less than 0.5 free-space wavelength separations and coupling lengths exceeding ten free-space wavelengths. In addition, we exploit the low bending loss of this waveguide to realize an efficient and simply designable power divider to realize arbitrary extinction ratios between 1:1 and 10:1. Integrable with existing all-silicon devices, we foresee these techniques enabling the dense integration of terahertz systems with substrateless silicon waveguides.