Broadband Single-Mode Hybrid Photonic Crystal Waveguides for Terahertz Integration on a Chip

Broadband, low-loss, low-dispersion propagation of terahertz pulses in compact waveguide chips is indispensable for terahertz integration. Conventional 2D photonic crystals (PCs) based terahertz waveguides are either all-metallic or all-dielectric, having either high propagation losses due to the Ohmic loss of metal, or a narrow transmission bandwidth restricted by the range of single-mode operation in a frequency range defined by the PC bandgap, respectively. To address this problem, a hybrid (metal/dielectric) terahertz waveguide chip is developed, where the guided mode is completely confined by parallel gold plates and silicon PCs in vertical and lateral directions, respectively. A unique multiwafer silicon-based fabrication process, including gold–silicon eutectic bonding, micropatterning, and Bosch silicon etching, is employed to achieve the self-supporting hybrid structure. Theoretical and experimental investigations demonstrate that the hybrid waveguide supports a single-mode transmission covering 0.367–0.411 THz (bandwidth of 44 GHz, over twice wider than that of all-silicon PC waveguides) with low loss (below 0.05 dB mm−1) and low group velocity dispersion (from −8.4 to −0.8 ps THz−1 mm−1). This work enables more compact, wideband terahertz waveguides and auxiliary functional components that are integratable in chips toward ultra-high-density integrated terahertz devices in particular in the field of wireless communications.