  Compact and low-loss photonic crystal waveguides are critical in integrated
terahertz (THz) applications. Compared with pure metal or dielectric photonic
crystal waveguides, hybrid (metal-dielectric) integrated waveguides provide a
simple way to further improve the field confinement and the propagation loss.
In this work, we investigate a hybrid waveguide consisting of metallic photonic
crystals and dielectric films in 0.1-1.0 THz. Photonic crystal waveguides based
on metal pillar arrays (MPAs) support two resonance modes including the
fundamental and high-order transverse magnetic (TM) modes and then form one
apparent bandgap in 0.45-0.55 THz. The high-order TM-mode shows higher
confinement than the fundamental mode and are thus sensitive to the dielectric
film on the MPAs. The propagation loss and field confinement can be optimized
by changing the dielectric film thickness and refractive index. The
investigation shows that the lowest loss occurs at 0.68 THz because the
high-order TM-mode THz waves are tightly confined inside the hybrid waveguide.
This work proves that such hybrid waveguides based on metallic photonic
crystals are promising to develop as a compact integrated terahertz device.
