Design optimization of the single-mode hybrid photonic crystal terahertz waveguide chips

Broadband, low-loss and low-dispersion propagation of terahertz pulses in compact waveguide chips is indispensable for terahertz integration. We successfully fabricated and demonstrated an air-channel hybrid (gold parallel planes and silicon pillars) photonic crystal terahertz waveguide chip using silicon microfabrication techniques, which exhibits a better performance in terms of bandwidth compared to single-mode all-dielectric photonic crystal waveguide and lower loss compared to all-metallic photonic crystal waveguide. In our primary design, a row of photonic crystal pillars is removed to achieve the air-channel for guiding terahertz waves. Here, we investigate the effect of air-channel width and height on the overall performance of the hybrid waveguide. To ensure a strict single-mode propagation, we estimate the maximum height values using the cut-off frequency of the first high-order mode of a parallel metallic waveguide. Moreover, due to the different lateral confinement feature between the hybrid waveguide and the metallic rectangular waveguide, we determine the maximum channel width by numerical simulations. The simulation results confirm that the optimal waveguide with air-channel size of 335 μm × 550 μm provides single-mode, low-loss (below 0.05 dB/mm) propagation bandwidth up to 0.149 THz, which is 26.27% wider compared to that of the initial design (0.118 THz).